Fire management plan ODMP - Draft Report Second Section June 2006

EnviroNET Solutions Pty Ltd

Okavango Delta Management Plan – June, 2006

98

quantity of plant materials like papyrus and Phragmites that are harvested by local communities for their personal needs. Conversely fires are viewed as a serious legitimate threat to tourist structures like lodges located in the Permanent Swamps and steps need to be taken to prevent fires in these instances. 5.2.3.4 Discussion and conclusions As mentioned in the introduction to section 5.2 one of the primary objectives of the project addressing fire in the Okavango Delta Ramsar Site was to determine the effects of fires on the major vegetation types and associated fauna. This could not be addressed directly because there are no long term burning experiments in Botswana that could provide data on the effects of the fire regime on the vegetation or the fauna i.e. the effects of type and intensity of fire and season and frequency of burning. However, Heinl (2005) initiated a research project in 2001 in the south eastern distal portion of the Delta and adjacent dryland areas of the Ramsar Site to address this question and concluded that the general response of the vegetation to fire in the drylands of the Okavango Delta is similar to the savannas elsewhere in southern Africa. On the basis of this conclusion an assessment of the condition of the grass sward was conducted in relation to fire in the vegetation types in the Ramsar Site that comprised the Acacia, Burkea and Mopane Woodlands and the Seasonal Swamps. The condition of the vegetation was assessed using the ecological criteria that have been developed in southern and east Africa based on the general response of grassland and savanna vegetation to season and frequency of burning and type and intensity of fire. As described in section 5.2.2.1 the condition of the grass sward was assessed according to its botanical composition, ecological status, basal cover and standing crop of herbaceous material. This procedure proved to be very successful in terms of being able to quantitatively determine whether fire will have a desirable or deleterious effect on the grass sward in terms of its productivity, sustainability and biodiversity for use as grazing for domestic livestock and wildlife. It is therefore strongly recommended that the procedure for assessing range condition described in section 5.2 be used in the Okavango Delta Ramsar Site as means of being able to determine quantitatively what effect fire will have on the vegetation and its associated fauna in the Acacia, Burkea and Mopane Woodlands and the Seasonal Swamps. It can therefore also be concluded that the primary objective of determining the effects of fires on the major vegetation types and associated fauna in the Ramsar Site has been successfully addressed in this section. Regarding the effect of fire in the Permanent Swamps no quantitative criteria exist or have been able to be developed in the time available to be able to assess the condition of the vegetation in the dominant plant communities in relation to fire. To meet this requirement an intensive research program is required and this will be dealt with in section 5.4.



97

fire. However, it would be expected that because of these plant species not always being inundated by water during the dry season and when the annual flood in the Delta subsides, then fires could have detrimental effects and cause mortalities in these plant communities if the exposed dry roots systems are subjected to fire. These conclusions are supported by views expressed by ecologically aware and qualified stakeholders from the safari and tourist industry. Addressing the other key questions regarding the effects of fire in the Permanent Swamps there are opposing views on the effect of fire in the papyrus communities and its effect on sititunga antelopes. During interviews with different stakeholders involved in tourism in the Delta some said that fires have a negative impact on sititunga numbers and that many animals get burnt. Conversely others pointed out that the new green shoots of recently burnt papyrus provides prime grazing for sititunga and that if fire had such a negative impact on these animals then there should be none left in the Delta. There was consensus though that wildfires during the breeding season would impact negatively on the survival of many sititunga young. No information could be found on the effect of high intensity fires on the survival of reptiles, Pythons in particular, and other small mammals inhabiting papyrus communities. In view of the high intensity of the fires and their ability to consume the major portion of the standing crop of vegetation during the burns, fires in the Permanent Swamps can and do have significant detrimental effects on birds nesting in these plant communities. The endangered slaty egret is one such example and care should be taken to protect nesting sites of these birds in the Delta to ensure their survival (Hancock, 2006). This also applies to situations where controlled burning is applied and the necessary step must be taken to safeguard the continued existence of habitat for wildlife that could be negatively affected by burning the vegetation. Again the lack of time and suitable opportunities were not available to personally investigate the effect of fire on the production and quality of reeds harvested from Phragmites communities. Suffice it to say that interviews with stakeholders from the tourist industry and rural communities in the Delta revealed the opinion that it was both necessary and desirable to periodically burn reed communities to remove the accumulation of old moribund reed material in order to stimulate the regrowth of more and better quality reeds for use as building material. Care should be taken though to avoid burning these stands of reeds under dry condition that would damage the rootstocks of the plants. Similar views were expressed by local communities in the Delta about burning papyrus as the quality of harvestable material for weaving purposes was improved by burning old moribund mature stands of papyrus to stimulate new regrowth that provided better quality weaving material. Therefore it can be concluded that generally burning does not have any direct detrimental effects on the vegetation in the Permanent Swamps, particularly if fires occur when the vegetation is standing in water or the soils in which it is growing are moist. However, fires can have both positive and negative effects on wildlife with the positive effects related to improving the quality of forage for grazing animals like sititunga and negative effects on bird species that nest in vegetation. Similarly fires can have positive effects on the quality and



96

Figure 34. From left to right: the high flammability of dry papyrus umbels burning intensely in contrast to the green, live papyrus umbel and finally the successful but less intense combustion of a combination of dry and green, live papyrus umbels.

This simple trial would suggest that papyrus does not contain phenolic or volatile compounds that enhance its flammability and that the high intensity fires associated with this vegetation are caused by the excessively high fuel loads that accumulate annually due to the extraordinarily high growth rate. Considering the quoted annual dry matter production rate of 48 – 143 tons, and that these plant communities are not utilized to any significant degree by grazing animals, the accumulated fuel loads must be enormous. If in a moribund condition and under extreme weather conditions of high air temperatures, low relative humidities and strong winds, the resultant fires must be extremely intense. This can be illustrated using estimates of the predicted fire intensity that would be generated by papyrus communities burning during September when conditions are very hot, dry and windy prior to the onset of the Spring rains using the fire intensity model available for African savannas presented in Chapter 3. Assuming the following fuel and weather conditions for September:

• a conservative fuel load of 50 000 kg/ha considering the annual production rate of 48 - 143 tons of dry matter;

• an estimated fuel moisture content of 30% for a moribund stand of papyrus comprising a majority of dry dead shoots;

• an air temperature of 380C at 14h00 and a wind speed of 25 kilometres per hour quoted by Tinley(1975) for Maun during September.

The predicted fire intensity would be 42 896 kJ/s/m. This is 14 times more intense than what is regarded as an extremely intense fire burning in African savannas and more in keeping with fire intensities that could be expected to be generated during wildfires burning in commercial pine plantations. It is therefore not surprising that high intensity fires associated with these extreme fuel loads are thought to have enhanced flammability. Fire intensities of this nature would explain the excessive flame heights and the accompanying noise of the fires that are illustrated in Figure 33. Unfortunately no examples of the effects of fire on communities of Phragmites australis and P. mauritianus were available for inspection but judging from the extensive communities of these two species occurring in the Delta and which were observed during the boat trips in the Seronga area and in the Boro River channel this species must also be well adapted to



95

Figure 33. Views of the high intensity fire that burnt the papyrus swamps opposite Drotsky Cabins at Shakawe on the 19th November, 2005 (Photos: P. Scheepers, 2005)

A simple trial was conducted where five live and five dead papyrus stems were harvested from a papyrus community at Shakawe and ignited separately and in combination over a camp fire. The flammability of the live and dead stems was subjectively assessed and it was abundantly clear that the green, live stems did not contain any phenolic type substance that enhanced their flammability and they would only burn when placed in combination with the dead stems in the flames of the fire. The spiky flower heads of papyrus, called “umbels” burnt vigorously and helped to ignite the green, live stems which would only burn if the dead papyrus stems constituted a majority of the papyrus fuel load. An interesting finding was that heat was conducted more effectively up the green papyrus stems than the dead stalks when the shoots were burnt in combination in the fire. A visual illustration of the trial is presented in Figure 34.



94

level by a fire during January, 2006 and in a period of approximately three months had regrown to a height of three metres which was almost back to its original height prior to the fire. This extraordinary growth rate of papyrus is referred to by Roggeri (1995) who reported that the annual dry matter production for this species ranges from 48 - 143 tons per annum. This extraordinary regrowth rate of papyrus after fire was confirmed by local inhabitants at Seronga and Shakawe and tourist lodge owners located on the banks of the Okavango River in the Panhandle section of the Delta. This observation leads to the conclusion that fire does not have any detrimental effect on papyrus and leads to the removal of excessive amounts of old dead material thereby reinvigorating the papyrus plants that have become moribund. This non-detrimental effect of fire on papyrus is not a surprising result in that the growing points of the papyrus plants are located on rhizomes below the level of the water and would therefore not be affected by the heat released during the high intensity fires that occur in these communities. These submerged rhizomes send up new shoots at regular intervals and within 90 days they have grown, matured and died (Ross, 1987). The non-detrimental effect of fire and the rapid accumulation of dead shoots in stands of papyrus is illustrated in Figure 32.

Figure 32. On the left a view of the papyrus community near Seronga that had regrown after three months to a height of approximately three metres after a fire in January, 2006. On the right a mature stand of unburnt papyrus located opposite the unburnt area showing the accumulation of dead shoots that grow, mature and die after 90 days.

There is a commonly held view amongst inhabitants of the Panhandle region of the Delta that papyrus contains phenolic type substances that cause it to be highly inflammable thereby contributing to the raging wildfires that occur frequently in this section of the Delta posing a serious threat to dwellings and tourist lodges located on the west bank of the Okavango River. Mr Pieter Scheepers from Drotsky Cabins at Shakawe has provided some unique photographs of the fires that burnt the papyrus swamps opposite Drotsky Cabins on the 19th November, 2005 – see Figure 33.



93

Figure 30. A view of the significant mortality of the large trees >10 m in the burnt area north east of Tsodilo and the negative impact of bark stripping by elephants and fire on a large Pterocarpus angolensis (Kiaat) tree in the burnt area.

5.2.3.3 Permanent swamps A striking feature of the Permanent Swamps are the water channels that dissect the papyrus communities which form dense stands of matted vegetation up to four to five metres in height.

Figure 31. Narrow water channels lined with dense stands of papyrus (Cyperus papyrus) four to five metres in height dissect the Permanent Swamps in the Panhandle region of the Okavango Delta.

Fires are a regular feature of the Permanent Swamps and a dense stand of papyrus growing along one of the main channels of the Okavango River located approximately 8 km west of Seronga was visited on the 7th April, 2006. This area had been burnt down to water



92

area then the mortality of large trees is very low for the woody vegetation as whole viz. mean density of large trees >10 m = 96 + 73/ 2 = 85 P/ha. With a mortality of large trees of 41% this yields a density of dead large trees >10 m = 35 P/ha. Therefore the mortality of large trees expressed as a percentage of the woody vegetation as a whole is 35/ 2189 P/ha = 1.6% which is similar to the mortality of trees and shrubs recorded after fire in the Kruger National Park (Trollope, et al, 1990). Therefore as fire research has shown in other savanna areas in southern and east Africa the main impact of burning on trees and shrubs is to change the height structure of the woody vegetation and not the density of the tree and shrub vegetation. The comparison of the effects of the fires on the total woody vegetation involving the unburnt area at Tsodilo and the burnt area 8km north east of Tsodilo is illustrated in Figure 29 where the reduction in phytomass of tree and shrub vegetation is clearly visible in the more open appearance of the vegetation in the burnt area.

Figure 29. On the left is the more dense woody vegetation in the unburnt area at Tsodilo and on the right is the more open vegetation in the burnt area 8 km north east of Tsodilo.

The high mortality of large trees >10 m in the burnt area north east of Tsodilo is illustrated in Figure 30. It must be borne in mind that this mortality of large trees is the product of frequent fires over years and should not be ascribed to fire alone. There was ample evidence that there was also an interaction of fire and elephants responsible for the demise of the trees as many of the stems had been damaged by elephants stripping the bark.



91

tree equivalents per hectare from 2 679 before the fire to 483 after the fire i.e. an 82% decrease in the phytomass of trees and shrubs. However, it is interesting to see how rapidly the trees and shrubs recovered after the fire by coppicing from the base of the plants and shooting from branches that had not suffered a complete topkill of the aerial portions of the trees and shrubs i.e. after six months the phytomass of the woody vegetation had increased from 483 to 2 014 tree equivalents per hectare. The results also showed that there had been no mortality in the trees and shrubs recorded in the surveys, as they had recovered after the fire by coppicing and shooting. This result was undoubtedly because the majority of the woody vegetation in the sample site comprised trees and shrubs that were less than 10 m in height (mean recorded height 7m) and this low mortality of woody vegetation after fires in this height class of trees and shrubs is a general response recorded elsewhere in the savannas of southern and east Africa (Trollope & Tainton, 1986; Trollope et al, 1990). Observations in the burnt area showed that there had been a significant mortality of large trees >10 m and as mentioned this aspect was investigated further and the results are presented in Table 11. Table 11. The impact of frequent high intensity fires on the mortality of large trees

>10m in height in the Tsodilo region of the Burkea Woodlands in the north western region of the Okavango Delta Ramsar Site.

SAMPLE SITE OD15 OD18

VEGETATION UNIT Burkea Woodland Burkea Woodland LOCALITY Burnt area 8 km north

east of Tsodilo Burnt area 23 km north east of

Tsodilo

DATE 12/4/2006 13/4/2006 GPS S18.74817; E21.81224 S18.65992; E21.92740

ALTITUDE - m 1043 986 TREE DENSITY >10 m – P/ha 96 73

BOTANICAL COMPOSITION

LIVE

DEAD

MORTALITY

% LIVE

DEAD

MORTALITY

%

Acacia erioloba 1 0 0

Acacia luderitzii 1 0 0 Burkea africana 14 3 21 8 11 58

Erythrophleum africanum 6 0 0

Guibortia coleosperma 10 3 30

Philenoptera nelsii 1 0 0 Pterocarpus angolensis 14 9 39 Schinziophyton rautanenii 4 2 50

Unknown species 0 13 -

TOTAL 31 19 38 28 22 44

The results in Table 11 were recorded at two sample sites located 15.5 km apart in the burnt area north east of Tsodilo and therefore reflect the general impact of the fires on the large tree population in this area. The mortality of large trees was 38% and 44% respectively at the two sites giving a combined mean mortality for the two sites of 41%. While this appears to be a significantly high mortality of large trees in the overall burnt area it must be borne in mind that if the density of large trees is expressed as a proportion of the total density of trees and shrubs recorded at sample site OD 15 (2 189 P/ha) in the burnt



90

Table 10. A comparison of the botanical composition (%), density (plants per hectare), phytomass (tree equivalents per hectare) of an unburnt area and a frequently burnt area in the Tsodilo region of the Burkea Woodlands in the north western region of the Okavango Delta Ramsar Site.

SAMPLE SITE OD14 OD15

VEGETATION UNIT Burkea Woodland Burkea Woodland LOCALITY Tsodilo World Heritage

Site - unburnt area Burnt area 8 km north east

of Tsodilo

DATE 12/4/2006 12/4/2006 GPS S18.76014 E21.73615 S18.74817; E21.81224

Altitude - m 1014 1043


N 48 59

SPECIES % %

Acacia nigrescens - 18

Berchemia discolor - 2 Burkea africana 13 - Bauhinia petersiana 8 -

Combretum imberbe - 14 Combretum molle 2 -

Dichrostachys cinerea - 17

Euclea divinorum - 2

Grewia bicolor - 12 Grewia retinervis 2 5

Guibortia coleosperma 10 -

Gymnosporia senegalensis - 3

Philenoptera nelsii 55 - Pterocarpus angolensis 2 - Terminalia sericea 8 0

Terminalea pruinoides - 22

Ximenia americana - 3

Ziziphus mucronata - 2

TOTAL 100 100

Density - P/ha 1585 2189 - Before fire

Phytomass - TE/ha 4224 2679 - Before fire

Density - P/ha 2189 - After fire

Phytomass - TE/ha 483 - After fire

Density - P/ha 2189 - 6 months after fire

Phytomass - TE/ha 2014 - 6 months after fire

The results in Table 10 indicate that while the density of the trees at the unburnt Tsodilo sample site (OD14) was significantly less than at the burnt sample site (OD15) the phytomass of trees and shrubs expressed in tree equivalents was significantly greater at the unburnt site than at the burnt site i.e. 4 224 TE/ha versus 2 679 TE/ha. This is undoubtedly the result of frequent fires that have affected this area prior to the high intensity fire in 2005. The dramatic impact of the 2005 fire on the woody vegetation is illustrated by the decline in phytomass of woody vegetation immediately after the fire viz. a decrease in



89

The results in Table 9 provide a very general overview of the physiognomy and botanical composition of the tree and shrub vegetation that was subjectively recorded in the sample sites surveyed in the different vegetation units in the Ramsar site. Generally the Mopane Woodlands dominated by Colophospermum mopane were the densest and tallest of the different woodland communities with the Seasonal Swamps being the most open with shorter trees and shrubs. The Acacia and Burkea Woodlands were intermediate in structure and height with Acacia erioloba and Burkea africana being the most prominent tree species characterizing these two woodland communities respectively. The results of the intensive investigation of the impact of frequent high intensity fires on the tree and shrub vegetation in the Tsodilo region of the Ramsar Site are presented in Tables 10 and 11. In Table 10 a comparison is made of the density and phytomass of the total tree and shrub community in an unburnt area in the Tsodilo National Heritage Site (Sample Site OD14: S18.76014; E21.73615) with an area that had been frequently burnt in the past (OD15: S18.74817; E21.81224) including a high intensity fire during October 2005, located 8 km north east of Tsodilo on the road to Nxamasere. In Table 11 the impact of the fires on large trees is presented as the density of live and dead trees >10m in height recorded at the aforementioned sample site OD15 and sample site OD18 (S18.65992; E21.92740) located 23 km north east of Tsodilo.



88

of this project the prevention of wildfires in those vegetation units with a low resistance to accelerated soil erosion is a high priority and provides an additional ecological criteria to use in deciding what areas should be and not be considered for controlled burning in the Okavango Delta Ramsar Site. 5.2.3.2 Tree and shrub vegetation The mean canopy cover, height and prominent tree and shrub species recorded in the Seasonal Swamps and Acacia, Burkea and Mopane Woodlands in the Okavango Delta Ramsar Site are presented in Table 9. Table 9. The mean canopy cover, height and prominent tree and shrub species

recorded in the Seasonal Swamps and Acacia, Burkea and Mopane Woodlands in the Okavango Delta Ramsar Site.

VEGETATION CHARACTER

Acacia Woodlands

Burkea Woodlands

Mopane Woodlands

Seasonal Swamps

Canopy Cover - %:

0 – 10 +

11- 40 + +

41 – 70 +

71 - 100

Mean Height- m 7 8 10 4

Prominent Species: Acacia ataxacantha Acacia erioloba Colophospermum mopane Acacia erioloba

Acacia erioloba Acacia nigrescens Acacia erioloba Acacia harpoclada

Acacia fleckii Baikiaea plurijuga Grewia flava Acacia nigrescens

Acacia mellifera Baphia massaiensis Grewia flava Acacia tortilis

Acacia nigrescens Burkea africana Terminalea sericea Colophospermum mopane

Acacia tortilis Combretum hereroense Combretum hereroense

Albizia sp Combretum imberbe

Combretum imberbe

Boscia albitrunca Guibortia coleosperma

Croton megalobotrys

Combretum hereroense Philenoptera nelsii

Hyphaene petersiana

Combretum imberbe Pterocarpus angolensis

Terminalia sericea

Combretum mossambicense Terminalia pruinoides

Pechuel-loeschea leubnitziae

Croton megalobotrys Terminalia sericea

Diospryos lycioides

Grewia bicolor

Grewia flava

Grewia flavescens

Kigelia africana

Mundulia sericea

Pechuel-loeschea leubnitziae

Philenoptera nelsii

Terminalia pruinoides

Terminalia sericea

Ziziphus mucronata



87

shown that the mopane tree (Colophospermum mopane) has, in contrast to other tree and shrub species, a greater concentration of surface roots thereby providing greater competition for moisture with herbaceous species resulting generally in a sparse and pioneer dominated grass sward. Also all the fuel loads in these vegetation units were significantly less than 4 000 kg/ha indicating that generally the grass sward was not in a moribund condition thereby excluding them from being considered for controlled burning. The fact that these vegetation units are also dominated by pioneer Increaser II grass species would also exclude them from being considered for burning. These low grass fuel loads also provide support to the conclusion that emphasis is given to avoiding and preventing the occurrence of wildfires that threaten the inherently scarce forage resources available in these areas.

iv) Soil Erosion Potential The effects of basal cover (point to tuft distance), grass standing crop and the proportion of annual grass and non-grass species in the grass sward on the resistance of the grass sward to accelerated soil erosion in the Seasonal Swamps and Acacia, Burkea and Mopane Woodlands in the Okavango Delta Ramsar Site is presented in Table 8. Table 8. The effects of basal cover (point to tuft distance - cm), grass standing

crop (kg/ha) and the proportion of annual grass and non-grass species (%) on the resistance to accelerated soil erosion in the Seasonal Swamps and Acacia, Burkea and Mopane Woodlands in the Okavango Delta Ramsar Site.

VEGETATION UNIT POINT/ TUFT RESISTANCE GRASS STANDING RESISTANCE ANNUAL RESISTANCE OVERALL

RESISTANCE

DISTANCE TO EROSION CROP TO EROSION SPECIES TO EROSION RESISTANCE TO

cm kg/ha % SOIL EROSION

Acacia Woodland 5 High(<10cm) 2769 High

(>1500kg/ha) 89 Low Low

Burkea Woodland - Burnt 5 High(<10cm) 1766

High (>1500kg/ha) 33 High High

Burkea Woodland - Unburnt 6

High(<10cm) 1847

High (>1500kg/ha) 77

Low

Low

Mopane Woodland 7 High(<10cm) 738

Low (<1500kg/ha) 93

Low

Low

Seasonal Swamp - Intensively Grazed 4

High(<10cm) 1331

Low (<1500kg/ha) 73

Low

Low

Seasonal Swamp - Lightly Grazed 3

High(<10cm) 6004

High (>1500kg/ha) 12 High High

The results in Table 8 indicate that the Acacia Woodlands, unburnt Burkea Woodlands, Mopane Woodlands and the intensively grazed areas in the Seasonal Swamps have a significantly low resistance to accelerated soil erosion particularly as a result of the high proportion of annual, herbaceous species in the grass sward. The lightly grazed Seasonal Swamps had a high resistance to accelerated soil erosion because of the very low point to tuft distance (basal cover), high standing crop of grass covering the soil surface and the high proportion of perennial grass species. The burnt Burkea Woodland also had a high resistance to accelerated soil erosion because of the low point to tuft distance, an adequate standing crop of grass and the dominance of perennial grass species. While these data do not necessarily mean that accelerated soil erosion will occur in those vegetation units that have a low resistance to soil erosion because other factors like slope and intensity of rainfall also affect soil erosion, it does provide the means of applying management practices to the vegetation that will not exacerbate the soil erosion situation. In the context



86

2769

1825

738

1331

6467

0

1000

2000

3000

4000

5000

6000

7000

FU

EL

LO

AD

- k

g/h

a

Acacia

Woodlands

Burkea

Woodlands

Mopane

Woodlands

Seasonal

Swamps -

Intensively

Grazed

Seasonal

Swamps -

Lightly

Grazed

VEGETATION UNIT

b

ab

a

ab

c

Figure 28. The mean grass fuel loads expressed in kilograms per hectare recorded

in the Seasonal Swamps and the Acacia, Burkea and Mopane Woodlands in the Okavango Delta Ramsar Site. Note: Different alphabetical letters indicate significant differences between means at P<0.05. Data expressed as kilograms per hectare.

The results in Figure 28 clearly indicate that the lightly grazed areas in the Seasonal Swamps had statistically significant greater grass fuel loads than in the other vegetation units. This result provides quantitative evidence of the observed moribund condition of the grass sward in this vegetation unit and lends support to the conclusion that the lightly grazed Seasonal Swamps have a high potential for initiating and sustaining high intensity wild fires. The combination of having grass species with a high genetic potential for producing large quantities of grass fuel plus a regular generous moisture supply in the form of the annual flood and a regular period of rest from grazing when the areas are seasonally flooded, guarantees a significant annual accumulation of grass fuel available for intentional and unintentional fires. This result also highlights the necessity for and the ecological desirability of applying a controlled burning program in this vegetation unit, in areas where it is practical to apply, as a means of restoring the vigour and palatability of the grass sward for grazing by wildlife species. Controlled burning under these conditions would also have the advantage of reducing excessive grass fuel loads and minimizing the occurrence of high intensity wildfires towards end of the dry season when the fire danger is at its worst. It also provides quantitative credibility to the ecological criteria of permitting controlled burning if the grass sward is not in a pioneer condition and the grass fuel load exceeds 4 000 kg/ha indicating that the grass sward is in a moribund condition. Finally there are no clear-cut differences in the grass fuel loads in the intensively grazed Seasonal Swamps, Acacia and Burkea Woodlands. The lowest fuel loads were in the Mopane Woodlands which is characteristic of this type of tree community. Research by Smit & Rethman (1998) has



85

the lightly grazed areas in the Seasonal Swamps have such a high fuel production potential. These areas were dominated by highly productive Increaser I grass species characterised by Oryza longistaminata, Imperata cylindrical, Pennisetum glaucocladum and Leersia hexandra. However these grass species are very unpalatable, particularly when they are in a moribund condition, and only make moderate contributions to the forage production potential of the grass sward if they are burnt and stimulated to provide palatable regrowth after the burn. This grazeable material is only available for a relatively short period of time before it becomes unpalatable again because of the inherent rapid regrowth rate of these species. Their grazing potential can only be exploited to a maximum if they are burnt and the regrowth maintained in a short palatable condition for as long as possible. While this practice can lead to overgrazing in rainfed, dryland grassland and savanna systems the seasonal flooding of these areas ensures that for a significant number of months they are protected from grazing and are able to recover and regrow when the flood recedes again. Finally the high frequency of Decreaser grass species in the burnt Burkea Woodland near Tsodilo explains both the high fuel production potential of this area and the significant forage production potential of the grass sward. The dominant grasses were Digitaria eriantha and the perennial variety of Panicum maximum. Both these species have a high fuel factor and together with a significant occurrence of Aristida stipitata, an Increaser I species, resulted in a high fuel production potential. Conversely this latter species is very unpalatable with a low forage factor resulting in the overall forage production potential of the area being only moderate. iii) Grass Fuel Load An analysis of variance showed that there were highly significant differences between the grass fuel loads in the different vegetation units (F = 23.04; DF = 50; P< = 0.01). These differences were investigated with a multiple range test and the results are presented in Figure 28. In this case there was no necessity to separate the grass fuel loads estimated with a disc pasture meter for the burnt and unburnt areas in the Burkea Woodlands because the burnt areas in the Tsodilo region had been recently burnt by a wildfire on the 2nd October, 2005.



84

for producing grazing for domestic livestock and wildlife species. Only the Tsodilo area in the Burkea Woodlands and the lightly grazed areas in the Seasonal Swamps had a moderate potential for producing grass forage for grazing animals. All the remaining areas in the vegetation units had very low potentials for producing grass forage emphasizing the necessity to avoid and prevent wildfires that threaten the inherently scarce forage resources available in these areas. ii) Botanical Composition – Grass Sward The botanical composition of the grass sward as represented by the proportion of Decreaser and Increaser grass species in the different vegetation units in the Okavango Delta Ramsar Site is presented in Figure 27.

8 2

90

47

7

46

10

21

69

5 2

93

2 1

97

17

52

31

0

10

20

30

40

50

60

70

80

90

100

FR

EQ

UE

NC

Y -

%

Acacia

Woodland

Burkea

Woodland -

Burnt

Burkea

Woodland -

Unburnt

Mopane

Woodland

Seasonal

Swamp -

Intensively

Grazed

Seasonal

Swamp -

Lightly

Grazed

VEGETATION UNITS

DECREASER

INCREASER I

INCREASER II

Figure 27. The mean frequency of Decreaser, Increaser I and Increaser II grass species in the Seasonal Swamps and the Acacia, Burkea and Mopane Woodlands in the Okavango Delta Ramsar Site. Data expressed as percentage frequency.

The striking feature of the results of the different categories of grass species presented in Figure 27 is the high frequency of Increaser II grass species in the Acacia Woodlands, the unburnt Burkea Woodlands, Mopane Woodlands and the intensively grazed areas in the Seasonal Swamps. This feature of the vegetation in these vegetation units explains why these areas have such a low fuel and forage production potential, the latter in particular as indicated in Figure 27. The dominant grass species in these three vegetation units were annual species characterised by Schmidtia kalihariensis, Urochloa tricophus, Pogonarthria fleckii, Dactyloctenium giganteum, Eragrostis viscosa, Digitaria velutina, Aristida congesta, Aristida stipoides and Echinochloa desvauxii. These results also indicate that these areas in the Ramsar Site are very heavily grazed suggesting that during below average rainfall years the stocking rate of grazing animals in the predominantly domestic livestock areas far exceeds the grazing capacity of the grass sward. The results in Figure 27 also explain why



83

i) Fuel and Forage Potential The potential of the vegetation to produce grass fuel to initiate and sustain fires and forage for domestic livestock and wildlife in the aforementioned vegetation units in the Ramsar Site is presented in Figure 26.

286

184

503

370

340

195257

163

216

157

685

381

0

100

200

300

400

500

600

700

FU

EL

/ F

OR

AG

E S

CO

RE

Acacia

Woodland

Burkea

Woodland

- Burnt

Burkea

Woodland

- Unburnt

Mopane

Woodland

Seasonal

Swamp -

Intensively

Grazed

Seasonal

Swamp -

Lightly

Grazed

VEGETATION UNITS

Fuel Score

Forage Score

Very High Potential

High Potential

Medium Potential

Low Potential

Very Low Potential

Figure 26. The potential of the vegetation to produce grass fuel to initiate and sustain fires and forage for domestic livestock and wildlife in the Seasonal Swamps and the Acacia, Burkea and Mopane Woodlands in the Okavango Delta Ramsar Site. Data expressed as fuel and forage scores.

The results in Figure 26 indicate that there were only two situations in the different vegetation units that had a high potential for producing grass fuel that could initiate and sustain wildfires. These were the lightly grazed Seasonal Swamps and the burnt area north east of Tsodilo in the Burkea Woodlands. The data also show that the major portion of the Burkea Woodlands only have a medium potential to produce grass fuel while as a whole the Acacia and Mopane Woodlands and the intensively grazed areas in the Seasonal Swamps generally have a low potential for producing grass fuel. An analysis of variance showed that there were statistically significant differences in the fuel scores reflected in Figure 26 (F = 18.76; DF = 47; P <0.01) and a multiple range test showed that the fuel scores for the Tsodilo area in the Burkea Woodlands and the lightly grazed areas in the Seasonal Swamps were statistically higher than in the other vegetation units (P <0.05). These results clearly indicate why there is a high frequency of fire in the Tsodilo area and the lightly grazed Seasonal Swamps as indicated by the Modis satellite images for the period 2000 to 2005. It can therefore be concluded that the Tsodilo area and the lightly grazed Seasonal Swamps are areas in the Okavango Delta Ramsar Site that have a high potential for wildfires because the grass sward has an inherently high genetic potential to produce large quantities of grass fuel capable of initiating and sustaining high intensity wildfires. Regarding the forage production potential of the different vegetation units the results in Figure 26 indicate that generally none of the areas that were assessed had a high potential



82

species contains phenolic type substances that make it highly flammable and prone to high intensity wildfires. These pose a serious fire threat to the tourist lodges situated on the banks of the Okavango River in the Delta and knowledge about the flammability of this major component of the vegetation is essential for formulating practical fire management measures to counter this threat. 5.2.3 Results 5.2.3.1 Grass sward Assessments of the condition of the vegetation in relation to fire were conducted in the Seasonal Swamps and Acacia, Burkea and Mopane Woodlands during the period 27th March to the 7th June, 2006. A total of 71 sample sites were surveyed of which the data from 54 sample sites have been used directly in assessing the condition of the grass sward in the aforementioned vegetation units. A total of 66 different grass species were identified to the species level and forage, fuel and thatch factors were allocated to each species reflecting their potential to produce grass forage, fuel and thatch material under optimum management conditions. As a result of the above average rainfall conditions that have occurred to date during 2006 the grass surveys were conducted under optimum growing conditions for identification purposes. This was a great advantage in that the grass surveys were able to capture possibly the widest range of grass species present in the different vegetation units thereby reflecting the full biological potential of this important component of the vegetation in the Ramsar Site. As described in the procedure the condition of the grass sward in relation to fire in the Ramsar Site will be presented in functional terms that indicate:

• the potential of the vegetation to produce grass fuel to initiate and sustain fires and forage for domestic livestock and wildlife;

• the current overall botanical composition of the grass sward;

• the potential for accelerated soil erosion;

• the grass fuel loads reflecting the current potential for wildfires and the current need for controlled burning.

During the analysis of the data it became evident that the condition of the vegetation was not uniform in all of the vegetation units and it was necessary to subdivide the results accordingly. This applied to the Burkea Woodlands where the area 5 to 20 kilometres north east of Tsodilo had been, according to satellite data, frequently and recently burnt and was significantly different in appearance from the other areas in this vegetation unit. Therefore the results for the Burkea Woodlands have been separated into “burnt” and “unburnt” areas. Similarly in the Seasonal Swamps there were areas that were and had been intensively grazed by either wildlife or domestic livestock in contrast to other areas that were being either lightly grazed or avoided by grazing animals. Therefore in these cases the results for the Seasonal Swamps were separated into lightly and intensively grazed areas.



81

5.2.2.3 Permanent swamps No botanically based technique was available for assessing the condition of the aquatic vegetation in the permanent swamps. This vegetation is characterized by dense stands of generally floating plant communities dominated and characterised by papyrus (Cyperus papyrus) often with a fringe of floating grasses dominated either by Vossia cuspidata or Echinochloa stagnina. Dense reed communities anchored in soil but standing in water also occur dominated by Phragmites mauritianus in the Panhandle and P. australis in the fan of the Delta.

Figure 25. On the left a typical stand of papyrus (Cyperus papyrus) growing in the Panhandle region of the Okavango Delta with a fringe of floating Vossia cuspidata grass at the base of the tall growing papyrus community. On the right a well developed reed community of Phragmites australis growing in the Permanent Swamps of the Boro River in the fan region of the Okavango Delta.

A more detailed description of the vegetation in the Permanent Swamps is presented in Chapter 4 section 4.4.1. These aquatic plant communities perform various biological and social functions in the Delta. These range from providing habitat and a forage source for a great diversity of wildlife like hippopotami, sititunga, crocodiles, pythons, fishes, insects and birds to being harvested by local communities for use as building materials (reeds) and constructing household commodities (papyrus). It was with these biological functions and social uses in mind that five expeditions were undertaken into the Permanent Swamps by motorboat to view at first hand the different plant communities occurring in the Delta. Two boat trips were undertaken from Seronga and a third excursion by boat from Shakawe in the Panhandle region of the Delta and two boat trips were undertaken up the Boro River to the field research site of the Harry Oppenheimer Okavango Research Centre in the fan region of the Delta. The key question to be answered regarding fire in the Permanent Swamps is whether burning is detrimental to the vegetation and what effect does it have on habitat and forage resources for wildlife. Also what effect does fire have on the production of reeds and papyrus for use by local communities living in close proximity to the Permanent Swamps particularly in the Panhandle region of the Delta. Finally while at Shakawe the flammability of papyrus was investigated to test the hypothesis that this plant



80

Nxamasere. The total density and phytomass of the tree and shrub vegetation was estimated using the Point Centered Quarter Method developed by Cotam & Curtis (1956) and adapted for use in the arid savannas of the Eastern Cape Province of South Africa by Trollope et al (2005). The procedure followed for surveying the tree and shrub vegetation comprised:

• Located 12 and 6 recording points at 10 metre intervals in a straight line transect at sample sites OD14 and D15 respectively;

• Recorded the following parameters of the nearest rooted tree or shrub in each of the four quarters surrounding the recording point viz. distance and overall height from the different recording points expressed in metres;

• In the case of height: i) In the first two quarters recorded the nearest tree or shrub <2m in height from

the recording point; ii) In the third and fourth quarter recorded the nearest tree or shrub that was >2m

in height from the recording point; iii) In the fourth quarter recorded the tallest tree or shrub that was within 10m of

the recording point.

The density of trees and shrubs expressed in plants per hectare, was calculated by dividing 10 000 m2 i.e. one hectare, by the square of the mean distance expressed in metres of the trees and shrubs from the recording points in the different sample sites. The phytomass of trees and shrubs was expressed as the number of tree equivalents per hectare. A tree equivalent is defined as a tree or shrub that is 1.5m in height (Trollope et al, 1990) and serves as an index of the phytomass of woody vegetation. This parameter is calculated by multiplying the density of trees and shrubs in the sample site with the mean height of the trees and shrubs in the two height classes <2m and >2m. The total height of trees and shrubs in these two height categories is then divided by 1.5 m and expressed as the number of tree equivalents per hectare. For example assume that the density of woody vegetation in the two height classes, <2m and >2m, is 1 000 and 500 plants per hectare respectively. Also assume that the mean height of woody vegetation in the two height classes, <2m and >2m, is 1 and 3 metres respectively. Then the tree equivalents per hectare = ((1 000 x 1m) + (500 x 3m)) / 1.5m = 1 667. The other assessment of the impact of fire on the woody vegetation in the Tsodilo area comprised estimating the density of live and dead trees >10m in height. These assessments were conducted at the aforementioned sample site OD15 and sample site OD18 (S18.65992; E 21.92740) located 23 km north east of Tsodilo on the road to Nxamasere. The survey procedure comprised estimating the mean distance between 50 live and dead trees >10m in height. This was achieved by selecting an initial tree >10m in height and then recording the species and distance of the nearest tree >10m while always proceeding in a forward direction. The density of trees was then calculated by dividing the mean distance between the trees in half and assuming this length to be the radius of a circle around a tree in which there were no other trees >10m. The mean area around a tree was then calculated using the formula for the area of a circle i.e. πr2, and divided into 10 000m2 to express the density in trees per hectare.



79

The conclusions that can be drawn from the results of the range condition technique presented in Table 7 are based on the following ecological criteria that have been developed through research experience gained in the East Caprivi Region of Namibia (Trollope et al, 2000). Controlled Burning: All the grass species that were identified as having a significant potential for producing thatching material are Increaser I species indicating a high ecological status in terms of the development of the grass sward and are therefore well adapted to fire. Consequently it is recommended that if the grass sward is dominated by these grass species (>50%) then it can be considered for burning to remove old moribund grass material that is unsuitable for thatching purposes. Field observations in the Caprivi Region areas dominated by these grass species indicated that the grass sward becomes moribund when the standing crop of grass material >4 000 kg/ha. Therefore under these conditions it needs to be defoliated by burning or some other means to restore the vigour, productivity and quality of thatching material produced by the grass sward (Trollope et al, 2000). Thatch Potential: There are currently no empirical guidelines for assessing the potential of the grass sward for producing thatching material. Consequently the descriptions related to the different Thatch Scores are tentative estimations for this functional characteristic of the grass sward and must be refined through adaptive management based on field experience (Trollope et al, 2000). Soil Erosion Potential: The same procedure and criteria were used for assessing the potential of the grass sward to resist soil erosion as applied to assessing the condition of the rangeland for the production of grass forage and fuel. 5.2.2.2 Tree and shrub vegetation As indicated earlier the emphasis in the assessment of the condition of the vegetation in relation to fire was focused on the grass sward and not the tree and shrub vegetation. Nevertheless a general description of the woody vegetation was included for each sample site. On the advice of Mr C.J.H. Hines, the professional botanist on the consulting team, the canopy cover, mean height and a list of the prominent trees and shrubs were recorded for each sample site. The different classes used for estimating the canopy cover for the tree and shrub vegetation were 0 - 10 % (open), 11 - 40 % (moderate), 41 - 70 % (dense) and 71 - 100 % (very dense). This procedure proved very successful and effective in capturing the physiognomy of the woody vegetation in the different vegetation units. However, a detailed quantitative description of the density and phytomass of the tree and shrub vegetation was necessary in the Tsodilo region of the Burkea Woodlands where fire had severely impacted the tree and shrub vegetation, particularly trees equal to and greater than 10m in height. Two procedures were followed in this case. Firstly a comparison was made of the density and phytomass of the total tree and shrub community in an unburnt area in the Tsodilo National Heritage Site (Sample Site OD14: S18.76014; E21.73615) with an area that had been frequently burnt in the past (OD15: S18.74817; E21.81224) including a high intensity fire during August 2005, located 8 km north east of Tsodilo on the road to



78

Table 7. Technique for assessing the potential of the grass sward to produce thatching material and the necessity for controlled burning in the Okavango Delta Ramsar Site.

ASSESSMENT RANGE CONDITION - GRASS THATCH

Okavango Delta Ramsar Site

Vegetation Unit:............................................. Sample Site:.................................Date:……...........

Soil Type:............................................... GPS: S:..........................E:.......................... Altitude:…………

CATEGORY SPECIES FREQUENCY

% THATCH FACTOR

THATCH SCORE

THATCH GRASS SPECIES Andropogon gayanus 10 Andropogon schirensis 10 Aristida pilgeri 8 Aristida stipitata 8 Cymbopogon excavatus 10 Eragrostis pallens 10 Eragrostis rotifer 8 Hyparrhenia rufa 10 Hyperthelia dissoluta 10 Schizachyrium jeffreysii 8 Tristachya lualabaensis 6 Tristachya nodiglumis 10 Tristachya superba 10 Vetivera nigritana 10 THATCH GRASS SPECIES TOTAL OTHER GRASS & HERBACEOUS SPECIES

0

Bare Ground 0 OTHER GRASS SPECIES TOTAL

TOTAL 100 THATCH SCORE CONCLUSIONS THATCH POTENTIAL CONTROLLED BURNING

POTENTIAL THATCH SCORE Tick BOTANICAL COMPOSITION % BURN

Very High >800 Yes No

High 701 - 800 Grass Thatch Species

Medium 601 - 700 Other Grass and

Low 500 - 600 Herbaceous Species

Very Low <500 FUEL LOAD - kg/ha

OVERALL DECISION TO BURN

SOIL EROSION FACTOR POTENTIAL FOR EROSION

TUFT DISTANCE LOW MOD HIGH

<10 cm 10-20 cm >20 cm

Distance = cm

GRASS STD CROP LOW HIGH

>500 kg/ha <500 kg/ha

kg/ha =

OVERALL SOIL EROSION POTENTIAL



77

excellent index of the canopy cover of the grass sward and is readily measured in the field with a disc pasture meter. Field experience has shown that with a standing crop of grass of greater than approximately 1 500 kg/ha the grass sward has a closed canopy of grass capable of significantly intercepting rain drops during a rainfall event thereby preventing “puddling” of the soil surface and reducing runoff and accelerated soil erosion. Finally an additional factor has been introduced to assess the effect of the condition of the vegetation on the resistance of the grass sward to accelerated soil erosion, namely, the proportion of annual herbaceous species making up the grass sward. Field experience in Botswana indicates that once the annual grass and non-grass species die-off in the winter the basal cover of the grass sward declines very rapidly resulting in the development of large areas of bare soil. These areas can become very prone to wind erosion during the late winter season with the occurrence of hot windy conditions during September and October. Such areas can also be prone to water erosion caused by heavy spring downpours prior to the germination and development of an annual plant cover during the initial onset of the growing season. Unfortunately there are no research data available to set threshold values above which soil erosion will increase significantly with an increase in annual grass and non-grass species. A threshold value of >50 % annual herbaceous species is being intuitively set to indicate the negative effect of this factor on the resistance of the grass sward to accelerated soil erosion. It is recommended that an adaptive management approach be used to test in the future whether this value of >50 % is appropriate or not and adjustments made when and if necessary. During the investigation into the fire ecology of the Okavango Delta Ramsar Site there was very limited opportunity to assess and obtain information on the effect of fire on grass communities that are used for harvesting thatch material in the Ramsar Site. Consequently use was made of information that was obtained during an investigation into the effects of and use of fire in the management of similar grass thatch communities in the East Caprivi Region of Namibia (Trollope et al, 2000). A technique was developed for assessing the potential of the grass sward to produce thatch material and the necessity for controlled burning in the Caprivi Region and this has been adapted for use in the Okavango Delta Ramsar Site in view of the close proximity and similarity in the vegetation in the Caprivi Region of Namibia. Details of the adapted technique are presented in Table 7.



76

Controlled Burning: The necessity for rangeland to be burnt or not depends upon its ecological status and physical condition. In order to maintain the potential of the grass sward to produce forage burning should not be applied if it is in a pioneer condition dominated by Increaser II grass species caused by overgrazing. Burning should not be applied when the grass sward is in this condition in order to allow it to develop to a more productive stage dominated by Decreaser grass species. Also burning herbaceous vegetation when in a pioneer condition, particular when it is dominated by annual grasses and forbs, will effectively reduce its biodiversity by negatively affecting its seed reserves and basal cover. Conversely when the grass sward is in an under grazed condition dominated by Increaser I species, it needs to be burnt to increase the better fire adapted and more productive Decreaser grass species. Finally controlled burning is also necessary when the grass sward has become overgrown and moribund as a result of excessive self-shading. When in this condition it is necessary to remove this old unpalatable grass material to restore the vigour of the grass sward and allow new nutritious regrowth to occur. Field experience indicates that when the standing crop of grass >4 000 kg/ha in African grasslands and savannas then the grass sward has become moribund and needs to be defoliated by burning or any other means (Trollope et al, 1995). Forage & Fuel Potentials: The range in the forage and fuel scores from very high (>500) to very low (<200) reflect the potential of the grass sward to produce forage for grazing wild ungulates and to produce grass fuel to support a high intensity grass fire. These categories have proven to be ecologically meaningful with highly applicable practical management implications. Grazing Intensity: This refers to whether the rangeland is being moderately grazed, under grazed, selectively grazed or over grazed. The criteria used for deciding the intensity of grazing is that if the veld is dominated by Decreaser grass species then it is being moderately grazed. If it is dominated by Increaser I grass species then it is being under grazed. If it is dominated by Increaser II grass species then it is being over grazed. Finally, if it is dominated by both Increaser I and Increaser II grass species, it is being selectively grazed (Trollope, 1986). Soil Erosion: The effect of the herbaceous vegetation on soil erosion depends upon the basal and canopy cover of the grass sward. If the basal and canopy covers are high then the potential for soil erosion is low and vice versa. Simple indices have been identified for these two parameters. Basal cover is satisfactorily described by recording the distance from a measuring point to the edge of the nearest grass tuft and is easily measured in the field. The different categories of point to tuft distance reflecting low (<10cm), moderate (10 - 20cm) and high (>20cm) potentials for soil erosion were formulated during the development of simplified techniques for assessing range condition in the East Caprivi Region of Namibia (Trollope et al, 2000). The use of the point to tuft distance as an index of the basal cover of the grass sward and its resistance to soil erosion was objectively tested by Vetter (2003) in the Herschel district in the Eastern Cape Province of South Africa. She found a highly significant relationship between the point to tuft distance and the degree of soil erosion in the landscape. It was therefore concluded that the point to tuft distance measure could be used as an index of the basal cover of the grass sward. The standing crop of grass is an



75

Eragrostis pseudosclerantha 1 1

Eragrostis viscose 0 1

Eragrostis sp. 2 2

Eragrostis superba 2 2

Eragrostis trichophora 1 2

Dactyloctenium giganteum 4 5

Digitaria velutina 1 1

Melenis repens 1 2

Microchloa indica 0 0

Perotis patens 1 1

Pogonarthria fleckii 1 3

Schmidtia kalihariensis 2 4

Setaria verticilliata 2 2

Sporobolus africanus 2 4

Sporobolus panicoides 1 1

Sporobolus spicatus 1 1

Stipagrostis uniplumis 5 5

Tragus berteronianus 1 1

Tricholeana monachne 1 2

Urochloa panicoides 1 1

Urochloa trichopus 1 2

INCREASER II TOTAL

TOTAL 100 FORAGE SCORE

FUEL SCORE

CONCLUSIONS: FORAGE/ FUEL POTENTIAL GRAZING INTENSITY

POTENTIAL SCORE FORAGE FUEL CATEGORY % GRAZING Tick

Tick Decreaser spp. Moderate

Very High > 500 Increaser I spp. Under

High 401 - 500 Increaser II spp. Selective

Medium 301 - 400 Increaser II spp. Over

Low 200 - 300

Very Low < 200

CONTROLLED BURNING

SOIL EROSION


%

BURN

FACTOR POTENTIAL FOR EROSION YES NO

TUFT DISTANCE LOW MOD HIGH Decreaser spp.

<3 cm 3-5 cm >5 cm Increaser I spp.

Distance = cm Increaser II spp.

GRASS STD CROP LOW HIGH FUEL LOAD - kg/ha

>1500 kg/ha <1500 kg/ha OVERALL DECISION TO BURN

kg/ha = ANNUAL HERBACEOUS SPECIES

LOW <50 % HIGH >50 %

OVERALL SOIL EROSION POTENTIAL

The conclusions that can be drawn from the results of the range condition technique presented in Table 6. are based on the following ecological criteria that have been developed through field experience gained with the use of this procedure of assessing range condition in the Eastern Cape Province and Kruger National Park in South Africa (Trollope, 1989; Trollope et al, 1986), the Ngorongoro Crater in Tanzania (Trollope, 1995), in the central highlands of Kenya (Trollope & Trollope, 1999b) and the Caprivi Region in Namibia (Trollope, Hines & Trollope, 2000).



74

Table 6. Technique for assessing the grazing potential of the grass sward and the necessity for controlled burning in the Acacia, Burkea and Mopane Woodlands and Seasonal Swamps in the Okavango Delta Ramsar Site.

ASSESSMENT RANGE CONDITION - GRASS SWARD Okavango Delta Ramsar Site

Vegetation Unit:............................................. Sample Site:.................................Date:……...........

Soil Type:............................................... GPS: S:..........................E:.......................... Altitude:…………

CATEGORY SPECIES FREQUENCY %

FORAGE FACTOR

FORAGE SCORE

FUEL FACTOR

FUEL SCORE

DECREASER Anthephora pubescens 8 8

SPECIES Brachiaria nigropedata 8 8

Brachiaria dura 5 5

Bulbostylis sp 4 4

Cenchrus ciliaris 8 8

Digitaria eriantha 8 8

Echinochloa pyramidalis 7 8

Panicum maximum - perennial 8 8

Panicum maximum - annual 4 6

Panicum repens 8 8

Schmiditia pappophoroides 6 6

Setaria sphacelata 8 8

Sporobolus fimbriatus 7 7

Sporobolus iocladus 3 3

DECREASER TOTAL

INCREASER I Aristida stipitata 2 6

SPECIES Aristida meridionalis 1 4

Cyperus sp. (Medium) 3 4

Cyperus sp. (Tall) 5 6

Eragrostis cimicima 4 4

Eragrostis pallens 2 8

Hermarthria altisima 10 10

Imperata cylindrical 1 10

Leersia hexandra 5 5

Miscanthus junceus 2 10

Oryza longistaminata 4 10

Pennisetum glaucocladum 2 10

INCREASER I TOTAL

INCREASER II Arisitida congesta 2 2

SPECIES Aristida stipoides 1 2

Bare Ground 0 0

Forbs 1 2

Brachiaria deflexa 2 2

Chloris virgata 1 2

Cenchrus incertus 1 1

Cynodon dactylon 5 6

Enneapogon desvauxii 2 2

Eragrostis aspera 1 2

Eragrostis echinochloidea 2 2

Eragrostis inamoena 2 3

Eragrostis lehmanniana 3 3

Eragrostis rigdior 3 6



73

the grass sward. This comprised recording the disc height at approximately two meter intervals in each of two 50 metre transects arranged 25 metres apart i.e. recorded 50 disc heights per sample site. The 50 disc height readings were used to calculate the mean disc height and the grass fuel load was estimated with the following calibration equation and expressed in kilograms per hectare.

y = -3019 + 2260 √x Where: x = mean disc height of 50 readings – cm;

y = mean fuel load - kg/ha.

Normally the mean disc height is estimated using 100 disc height readings but test data involving 25, 50, 100, 150 and 200 disc height readings showed that there were no significant differences between the estimated mean disc heights using the different numbers of disc heights in an analysis of variance (F=0.74; DF=520; NS). Therefore it was decided to use 50 disc height readings per sample site as a means of significantly reducing the time required for assessing the standing crop of herbaceous material of the grass sward in the different vegetation units. Initially a minimum of 10 sample sites were surveyed in each vegetation unit in localities that were subjectively chosen to be representative of the condition of the vegetation in the different vegetation units as whole. With greater familiarity of the vegetation in the Ramsar Site these were increased to a total of 54 sample sites and the subsequent analysis of the data indicated that they provide a credible quantitative description of the condition of the grass sward in the Ramsar Site. The procedure used for interpreting the range condition data recorded in the different vegetation units involved developing a range condition assessment technique in which the different grass species were classified into Decreaser and Increaser species together with their respective forage, fuel and thatch factors. Separate assessment techniques were developed for situations where the vegetation was being used as grazing for domestic livestock and wild ungulates and where the grass sward was used for harvesting thatching material. Besides providing an assessment of the potential of the grass sward for producing forage, fuel and thatching material the technique also provides indications of whether the vegetations needs to be considered for controlled burning or not, the potential for accelerated soil erosion and trends in the vegetation in response to different grazing intensities. The technique used for assessing the grazing potential of the vegetation and the necessity for controlled burning in the Okavango Ramsar Site is presented in Table 6.



72

The assessment of the condition of the vegetation in relation to burning involved conducting grass surveys in the aforementioned vegetation units and involved determining the botanical composition and basal cover of the grass sward with a point quadrat survey according to the procedure described by Trollope et al (2005). This comprised recording the species and distance of the nearest rooted herbaceous plant at approximately two meter intervals in each of two 50 metre transects arranged 25 metres apart i.e. 50 recording points per sample site. Normally the botanical composition of the grass sward is determined using 100 points per sample site for estimating fuel and forage scores but test data involving 25, 50, 100 and 150 points showed that there were no significant differences between the mean forage and fuel scores using the different numbers of points in an analysis of variance (Fuels Score: F=1.37; DF=18; NS) and (Forage Score: F=1.00; DF=18; NS). It was therefore decided to use a sampling intensity of 50 points per sample site as a means of significantly reducing the time required for assessing the condition of the grass sward in the different vegetation units. The grasses were recorded and identified to species level but non-grass species were classified and recorded in a general category as forbs. This is an accepted procedure used for assessing the condition of the grass sward in African rangelands because grass plants produce the majority of the herbaceous material in the grass sward, with non–grasses generally contributing a minor portion of the standing crop. A third category of recordings was included in the grass surveys, namely, “bare ground”. This was necessary because in certain sample sites, particularly in situations where the grass sward was extremely overgrown and moribund or in sparsely covered annual grassland, the basal cover of herbaceous plants was very low. This resulted in the procedure of recording the nearest rooted plant to the point quadrat yielding unrealistic proportions of the different herbaceous species in the grass sward. This problem was overcome by recording “bare ground” when there was no rooted herbaceous plant within a radius of 25 centimetres from the point quadrat. This procedure has been successfully used in the assessment of the condition of the grass sward in similar arid grasslands and savannas in the Kruger National Park and has the added advantage of also providing a quantitative indication of the density of the grass sward and its potential resistance to accelerated soil erosion.

The second procedure used in the assessment of the condition of the grass sward was estimating the standing crop of herbaceous plant material with a Disc Pasture Meter. This information is necessary for identifying areas where the grass sward has become moribund and unpalatable to grazing animals and where controlled burning can be considered as a means of restoring the palatability, nutritive value and vigour of the grass sward. Estimates of the grass fuel load are also necessary for assessing whether there is an adequate fuel load to use fire for controlling bush encroachment. The Disc Pasture Meter was developed by Bransby & Tainton (1977) and involves relating the settling height of an aluminium disc dropped onto a grass sward to the standing crop of grass holding up the disc, expressed in kilograms per hectare. The technique was calibrated for use in the savanna areas of the Kruger National Park in South Africa by Trollope & Potgieter (1986) and the calibration procedure has subsequently been successfully tested in the central highlands of Kenya, the Ngorongoro Crater in Tanzania and the Caprivi region in Namibia and shown to be the most reliable and practical means of estimating the standing crop of grass in savanna vegetation. (Trollope & Trollope, 2002). The estimation of the grass fuel loads was conducted on the same sample sites as used for determining the botanical composition and basal cover of



71

burning on the forage production potential of the herbaceous vegetation was of primary consideration. The technique used for assessing the condition of the grass sward was that developed by Trollope (1990) which is based on the following definition of range condition viz. range condition is the condition of the vegetation in relation to some functional characteristic (Trollope, Trollope & Bosch, 1990). The functional characteristics of the grass sward in the aforementioned vegetation units were identified as being the production of forage for grazing animals, grass fuel to support a fire to maintain the optimum balance between grass and woody vegetation and to resist soil erosion. The potential of the grass sward to produce thatching material was also considered in the northern areas of the Ramsar Site in the Shakawe region where this component of the herbaceous vegetation has become a very lucrative source of cash income to some of the communities. Generally grasses are well adapted to defoliation by grazing, burning or cutting but over-utilization or under-utilization of the grass sward can lead to a decrease in range condition. Therefore range condition is most desirable when the rangeland is neither over- nor under-utilized. In general there is a relationship between the grazing value of different grass species and their ecological status (Bothma, 1996). For example, species of low grazing value usually withstand conditions of overgrazing because they are not grazed as often as more palatable species and many of these unpalatable species increase under conditions of overgrazing. Conversely, palatable species, of high grazing value, are selectively utilized and tend to decrease under heavy grazing pressure. Arising from these concepts grasses have been classified according to their reaction to a grazing gradient which serves as a very meaningful and practical description of their ecological status. Arising from botanical surveys conducted in the Okavango Delta Ramsar Site during the fire management project (see appendix 4), the different grass species encountered were subjectively classified into the following categories based on field observations and consultations with local range scientists and land-users:

DECREASER SPECIES (D) - Grass & herbaceous species that decrease when rangeland is under or over grazed;

INCREASER I SPECIES (I) - Grass & herbaceous species that increase when rangeland is under or selectively grazed;

INCREASER II SPECIES (II) - Grass & herbaceous species that increase when rangeland is over grazed.

In addition to this classification the relative potential of each of the grass species for producing forage, fuel and/or thatch material was assessed. Through a process of experience, observation in the field and consultation with local range scientists and land-users forage, fuel and thatch factors were allocated to each grass species on a scale of 0 - 10 according to the potential of the different species to produce forage for bulk grazers, fuel for supporting a surface fire and good quality thatching material – see Table 7. In the case of grass species well suited for producing thatch material a limited number of different species were encountered during the field surveys so the majority of the species with a high potential for producing thatch material in this geographical region have been included according to information obtained from the Caprivi region of Namibia. These factors were used to assess the potential of the grass sward to perform functions relevant to the form of land use for which the rangeland is being used.



70

low producing annual grass species like Urochloa trichopus, Digitaria velutina and Aristida species. The significantly lower number of fires recorded in the Seasonal Swamps is surprising because again it will be shown in section 5.2 that this vegetation unit has both a high potential for producing grass fuel and a high grass fuel load. A possible reason for less fires having been recorded in this vegetation unit is that it is seasonally flooded with water for a major portion of the year and because this plant community remains green for longer it would be less flammable than the grassland communities in the dryland areas of the Ramsar Site.

5.2 Assessment of the Condition of the Vegetation Relative to Burning in the Major

Vegetation Types in the Ramsar Site 5.2.1 Introduction

One of the primary objectives of the project for developing a fire management plan for the Okavango Delta Ramsar Site was to determine the effects of fires on the major landscapes/vegetation types and the associated fauna. This objective was addressed by conducting an assessment of the condition of the vegetation (i.e. range condition) in relation to fire in the major dryland vegetation types in the Ramsar Site that comprised the Acacia, Burkea and Mopane Woodlands. After investigations in the field these assessments were also extended to the Seasonal Swamps in the Okavango Delta region in areas that were not currently inundated with water (see Figure 8 – Vegetation Map of the Ramsar Site). Botanical surveys were not conducted in the Permanent Swamps as the survey techniques used in the dryland vegetation units were not suitable for these permanently inundated plant communities characterized by dense stands of Cyperus papyrus and Phragmites mauritianus in the Panhandle region and P. australis in the fan portion of the Delta. The procedure used for assessing the condition of the vegetation comprised determining the botanical composition, basal cover and standing crop of the grass sward. Attention was focused on the herbaceous grass sward because this component of the vegetation provides the major portion of the plant fuels that support and carry fires in the aforementioned plant communities. Therefore in the majority of cases no detailed quantitative botanical surveys were conducted of the shrub and tree vegetation. Using these survey data of the grass sward simple and practical quantitative ecological criteria developed and tested in southern and east African grasslands and savannas, were used to differentiate between areas that could be considered for controlled burning and areas where fire should be excluded where possible to safeguard the productivity, sustainability and biodiversity of the ecosystem. This section will focus on the procedures used for assessing the condition of the vegetation and the interpretation of the botanical survey data in terms of the fire potential of the different vegetation units and recommendations on controlled burning based on range condition. 5.2.2 Procedure for assessing range condition 5.2.2.1 Grass Sward The primary use of the vegetation in the woodland and Seasonal Swamp vegetation units in the Ramsar Site is to provide grazing for domestic livestock and wild ungulates. Therefore when assessing the condition of the vegetation in relation to the effects of fire, the effect of



69

the dryland areas burn later in the year immediately before the start of the rainy season in October. The results in Figures 16 to 21 also tend to suggest that the Permanent Swamps were where the fires occurred during the lower number of fires recorded between March and May which again accords with Heinl (2005) who found that the Permanent Swamps tend to burn earlier peaking in June immediately before the arrival of the floodwaters in July and is closely associated with burning applied with the preparation of fields and fishing grounds. Finally an interesting point is that fires were recorded in the Ramsar Site throughout the year indicating the high potential for fire that exists in the different Ramsar Site as a whole. The total number of fires recorded in the different vegetation units in the Ramsar Site during the period 2000 to 2005 is presented in Figure 24.

407

3277

549

3265

1228

0

500

1000

1500

2000

2500

3000

3500

TO

TA

L N

UM

BE

R O

F F

IRE

S

Acacia

Woodland

Burkea

Woodland

Mopane

Woodland

Permanent

Swamps

Seasonal

Swamps

VEGETATION UNITS

a

b

a

b

a

Figure 24. Total number of fires recorded per vegetation unit by satellite for the period 2000 to 2005 in the Okavango Delta Ramsar Site. Note: Different alphabetical letters indicate significant differences between means at P<0.05.

The results in Figure 24 clearly indicate that the majority of the fires recorded in the Ramsar Site during the period 2000 to 2005 were in the Burkea Woodlands and the Permanent Swamps indicating that these two vegetation units had statistically the highest potential for fires in the study area. This result is clearly illustrated in the satellite fire maps presented in Figures 16 to 21. The high occurrence of fires in the Permanent Swamps is understandable because of the vegetation being dominated by highly productive and flammable plant communities like Cyperus papyrus, Phragmites spp. and Miscanthus junceus. This is also to be expected in the Burkea Woodlands where it will be shown in section 5.2 that the grass sward in areas like Tsodilo has a high potential for producing grass fuel available for fires. Similarly the low occurrence of fires in the Acacia Woodlands and Mopane Woodlands is to be expected because again in section 5.2 it will be shown that the grass sward in these two vegetation units has a very low potential for producing grass fuel because it is dominated by



68

Permanent Swamps but the amount of inflow of water into the Okavango River at Mohembo is the main factor determining the levels of water in the Delta and therefore the amount of plant fuel produced and exposed for burning in this vegetation type. The results in Figure 22 and Appendix 2 illustrate the high variability in the annual rainfall for Maun and Shakawe in the Ramsar Site and the results in Figure 7 illustrate the significant variation that occurs annually in the inflow of water into the Delta at Mohembo. Other factors like variations in the ignition sources of fires and the degree to which the different vegetation types had burnt and the intensity of grazing will also influence the amount of grass fuel available for supporting fires. The results also show that rainfall tends to have a delayed effect on the occurrence of fires with the previous years rainfall determining the grass fuel loads the following year. This effect is illustrated for the number of fires that occurred during 2000, 2001 and 2004.

The mean number of fires recorded per month in the Okavango Delta Ramsar Site is presented in Fig23.

45

18

84

171158

56 62

226

322

177

105

31

0

50

100

150

200

250

300

350

ME

AN

NU

MB

ER

OF

FIR

ES

JAN FEB MARCH APRIL MAY JUNE JULY AUG SEP OCT NOV DEC

MONTH

abc

a

abc

abcabc

cd bcd

de

e

cd

abcd

ab

Figure 23. Mean number of fires recorded per month by satellite in the Okavango Delta Ramsar Site for the period 2000 to 2005. Note: Different alphabetical letters indicate significant differences between means at P<0.05.

The results in Figure 23 show that there were two peak periods in the year when greater numbers of fires were recorded during the period 2000 to 2005 in the Ramsar Site. The main fire season occurred during the late winter between August and October with September having the statistically highest number of fires occurring during the five-year period. A significant but lower peak of fires occurred during March to May with March having the highest number of fires recorded during this period. The lowest incidence of fires occurred during the summer period between December and February and mid-winter during June and July. The explanations for these variations in the number of fires recorded during the different periods of the year can be related to fires burning in the different vegetation units. The results presented in the satellite maps in Figures 16 to 21 for the dryland areas in the Ramsar Site indicate that the high incidence of fires in the Burkea Woodlands and the lower number of fires in the Acacia and Mopane Woodlands tended to occur mainly during the August to October period. The results in the satellite maps also indicate that a significant proportion of the Seasonal Swamps also burn in the latter part of the year from August to October. This result accords with Heinl (2005) who concluded that



67

The results in Figure 21 for 2005 shows that there was again a resurgence in the number of fires (1 950 fires) recorded during this year to levels similar to those recorded during 2002 and 2003. Generally similar numbers of fires occurred in the Burkea Woodlands and Permanent and Seasonal Swamps. In the case of the Burkea Woodlands there was a high concentration of fires in the Tsodilo area that occurred in October with the remainder of the fires in this vegetation unit occurring in the area northwest and north east of Seronga mainly during the August to October. The fires in the Permanent Swamps occurred mainly in the fan portion of the Delta during April and in adjacent areas in the Seasonal Swamps during October. The data presented in Figures 16 to 21 were analyzed statistically as means of summarizing this information in order to provide an overall description of the number of fires that were recorded annual, monthly and in the different vegetation units in the Okavango Delta Ramsar Site. The total number of fires recorded annually in the Ramsar Site for the period 2000 to 2005 are presented in Figure 22. The mean total rainfall for Maun and Shakawe is also included in Figure 22 as a means of illustrating the effect of the previous years rainfall on the production of plant fuel available for burning during the following year.

195

1014

2312

2097

1158

1950

355

662

480

282

223

526

461

0

500

1000

1500

2000

2500

1999 2000 2001 2002 2003 2004 2005

YEARS

NU

MB

ER

OF

FIR

ES

0

100

200

300

400

500

600

700

AN

NU

AL

RA

INF

AL

L

NUMBER FIRES

ANNUAL RAINFALL

a

ab

b

b

ab

ab

Figure 22. Total number of fires recorded per year by satellite and the mean annual rainfall for Maun and Shakawe in the Okavango Delta Ramsar Site for the period 2000 to 2005. Note: Different alphabetical letters indicate significant differences between means at P<0.05.

The results in Figure 22 indicate that there was a high variability in the total number of fires recorded in the Ramsar Site during the period 2000 to 2005. This is not a surprising result considering that rainfall is one of the main factors determining the amount of grass fuel available for burning in the Burkea, Acacia and Mopane Woodlands and also to a certain extent in the Seasonal Swamps. Rainfall will also influence the occurrence of fires in the



66

Figure 21. Total number and distribution of fires in the different vegetation units recorded in the Okavango Ramsar Site during the year 2005.



65

The results in Figure 20 show a dramatic decline in the number of fires (1 158 fires) recorded in the Ramsar Site during 2004 undoubtedly due to there being very low fuel loads remaining after the high incidence of fires over the Ramsar Site during 2003. The majority of the fires were recorded in the Burkea Woodlands in the area north west of Seronga during August to October in 2004, significantly less fires occurring in the Burkea Woodlands west of the Panhandle during this year. Relatively few fires occurred in the Permanent Swamps during 2004 and virtually no fires in the Seasonal Swamps and Acacia and Mopane Woodlands again probably due to the low rainfall conditions and widespread fires during the previous two years. The total number and distribution of fires in the different vegetation units recorded in the Okavango Ramsar Site during the year 2005 is presented in Figure 21.



64




63

concentrated in the Permanent Swamps in the Panhandle and the distal portions of the fan of the Delta. The results show that the majority of these fires occurred during the period November 2002 to March 2003. A high incidence of fires also occurred in the Burkea Woodlands during August to October but in contrast to 2002 there was an increase in the number of fires north east of Tsodilo. A relatively low number of fires occurred in the Seasonal Swamps in the distal portion of the fan of the Delta in October north west of Maun and virtually no fires were recorded in the Acacia and Mopane Woodlands during 2003. As in 2002 the high incidence of fires recorded in 2003 cannot be ascribed to the occurrence of high rainfall the previous season, as 2002 was a drought year. The year 2003 was also a drought year and this would suggest that the exceptionally dry conditions would have resulted in a very significant drying out of the residual grass fuel loads that had accumulated during the previous above average rainfall years. Also the results in Figure 7 show that in both 2002 and 2003 the inflow of water into the Delta at Mohembo was below average which would have resulted in the water level in the Delta being lower and the exposure of more dry flammable vegetation particularly in the normally in the Permanent Swamp areas. The total number and distribution of fires in the different vegetation units recorded in the Okavango Ramsar Site during the year 2004 is presented in Figure 20.



62


In 2003 the results in Figure 19 show that the incidence of fire was gain exceptionally high in the Ramsar Site (2 097 fires) and in contrast to 2002 a high proportion of the fires were



61

The results in Figure 18 show that in 2002 there was a high incidence of fires in the Ramsar Site (2 312 fires) the majority being recorded again in the Burkea Woodlands during the period August and September and in the Permanent Swamps in the fan portion of the Delta during April. Significant numbers of fires also occurred in the Seasonal Swamps during August to October and a sprinkling of fires again occurred in the Acacia Woodlands during September in an apparent “hotspot” south west of Sehithwa and a few during October east of Maun and north of Khwai. Fires also occurred in a restricted area in the Mopane Woodlands near Shorobe in September. The high incidence of fires during 2002 cannot be ascribed to high fuel loads caused by above average rainfall during the previous season because the annual rainfall both at Maun and Shakawe was not exceptionally high during 2001 suggesting that other factors such as variations in ignition sources also influence the number of fires occurring in the Ramsar Site. The total number and distribution of fires in the different vegetation units recorded in the Okavango Ramsar Site during the year 2003 is presented in Figure 19.



60

Figure 18. Total number and distribution of fires in the different vegetation units

recorded in the Okavango Ramsar Site during the year 2002.



59

The results in Figure 17 show that there was a dramatic increase in the number of fires recorded during 2001 in the Ramsar Site, the majority occurring in the Burkea Woodlands on either side of the Panhandle of the Delta. Significant numbers of fires (1 014 fires) also occurred in the Mopane Woodlands but were restricted to the area west of the Linyanti floodplains in the adjacent Caprivi region of Namibia. These fires probably could have originated from the extensive grasslands in the adjacent Linyanti floodplains because investigations by Trollope & Trollope (1999) showed that the Linyanti region is traditionally burnt very frequently on the Namibian side. Such fires driven by the predominantly easterly winds that dominate this region of southern Africa could easily “jump” the Kwando River which acts as a firebreak along this remote and inaccessible region of the border between Botswana and Namibia. The results also show that there were significant numbers of fires in the Permanent Swamps in the Panhandle and extended down into the fan of the delta and the adjacent Seasonal Swamps. Interestingly there were also a sprinkling of fires recorded in the Acacia Woodlands south west of Sehithwa. This significant increase in the number of fires recorded in 2001 was undoubtedly in response to the above average rainfall conditions that occurred during the growing season over the Ramsar Site during 2000 resulting in abundant grass fuel loads that year (refer to rainfall records for Maun and Shakawe in Appendix 2). The results in Figure 17 also indicate that in the Burkea and Mopane Woodlands the majority of the fires occurred during the period August to October while in the Permanent Swamps the majority of the fires occurred during January and in the Season Swamps in August. The total number and distribution of fires in the different vegetation units recorded in the Okavango Ramsar Site during the year 2002 is presented in Figure 18.



58




57

The results in Figure 16 indicate that very few fires (195 fires) were recorded during November and December in the Ramsar Site during 2000 and that they occurred mainly in the Panhandle portion of the Permanent Swamps between Ikoga and Mohembo. The distribution of the fires also indicate that there was a “hotspot “ of fires in the Seasonal Swamps near Tubu in the western portion of the Delta. Unfortunately, as mentioned there were no Modis fire data for the whole year but it is probable that there was a low frequency of fire events during 2000 because the total rainfall during the two preceding years was below average resulting in the overall occurrence of low grass fuel loads in the Ramsar Site, particularly in the dryland woodland vegetation units (refer to rainfall records for Maun and Shakawe in Appendix 2).

The total number and distribution of fires in the different vegetation units recorded in the Okavango Ramsar Site during the year 2001 is presented in Figure 17.



56

Figure 16. Total number and distribution of fire in the different vegetation units recorded in the Okavango Ramsar Site during the year 2000.



55

Causes of Wildfires in the Okavango Delta Causes of Wildfires in the Okavango Delta

Ramsar SiteRamsar Site

LightningAnthropogenicSourceSource

Unintentional

IntentionalMotivationMotivation

Carelessness

LandManagementArsonCauseCause

Land Use Conflict Communities

Wild firesWild fires

ConcessionHolders

Infrastructure security

Photographic Safaris

Hunting

HuntingCollecting Thatching

Reed & Papyrus CollectingFishing

AgricultureCollecting Wild Bees Honey

can cause

un

co

ntr

oll

ed

Figure 15. The interrelationships between the causes of fires in the Okavango Delta Ramsar Site and the activities related to different systems of land use that may result in the development of wildfires.

5.1.3 Satellite data related to the fire ecology of the Okavango Delta Ramsar Site Use was made of point data derived from Modis satellite imagery provided by Modis Maryland, USA to determine the number of fire events recorded in the Okavango Delta Ramsar Site during the period 2000 to 2005. Modis data records a fire event in a square kilometer pixel size and this could cover a single or multiple fire event within the pixel. Note that Modis is not able to penetrate cloud cover so the data are representative of the situation on the ground in the absence of cloud cover. These data were analyzed to determine a frequency profile of the number of fire events that occurred per year during this period and the mean number of fire events that occurred per month as an indication of the overall season of burning in the Ramsar Site. Finally the total number of fire events recorded in the different vegetation units was determined for the aforementioned period as a means of indicating which type of vegetation was most prone to burning in the Ramsar Site. The satellite data, which were available only from November 2000, were analyzed and prepared in map form by Anthony Emery of EMROSS Consulting (Pty) Ltd., P.O. Box 507, White River, 1240, South Africa. 5.1.3.1 Annual occurrence and distribution of fires The total number and distribution of fires in the different vegetation units recorded in the Okavango Ramsar Site during the year 2000 is presented in Figure 16.



54

• In many instances there is misinterpretation of the Herbage Preservation Act to the extent that some consider it illegal to burn and that it is punishable by law to do so under any circumstances;

• Maun is the only office where burning permits are issued and that since it takes several days for people living in remote areas to get to Maun, because of lack of transport, plus the subsistence and traveling expenses incurred on the journey, and the fact that it may take several more days to get a permit, the majority of rural dwellers ignore this compliance requirement to use fire as a management practice;

• It is the Government’s responsibility i.e. the Department of Forestry and Range Resources, to fight fires. This attitude often persists even if wildfires are threatening community livelihoods. Many rural communities are of the opinion that if the Government employees receive a per diem or “night allowance” while fighting wildfires, then they should also receive remuneration and not just get food and water;

• There is a major concern about lack of fire fighting equipment, many respondents said that they only used branches for fighting wildfires;

• That it is impossible to control wildfires because either firebreaks are lacking or there is low maintenance on firebreaks that have been constructed;

• Rural communities, certain Government staff and NGO’s are concerned about the lack of protective clothing, radios for communication in case of emergencies in particular, and medical attention should there be injuries to the teams fighting the wildfires.

• All stakeholders agree that decentralized pools of fire fighting equipment situated possibly at several Agricultural Offices in the districts surrounding the Okavango Delta would definitely be a good idea.

• That there is an urgent need for a clear policy on fire that includes fire management guidelines and criteria for deciding objectively when and when not to burn;

• There is an urgent need for training controlled burning for the construction of firebreaks, fire suppression and fire management practices;

• That criteria specifying why, when and how to burn should be added to permits issued for burning under the Herbage Preservation Act.

The information gathered during the interviews is summarized in Figure 15 and clearly illustrates the interrelationships between the causes of fires in the Okavango Delta Ramsar Site and the activities related to different systems of land use that may result in the occurrence of wildfires.



53

• There is a widespread tendency to blame mostly the hunters and/or poachers for causing wildfires often ignoring other causes.

• Although no definitive data could be collected because either no culprits were identified, or people were afraid of retribution if they identified anyone responsible for causing wildfires, there was general consensus that the many causes of wildfires in the Ramsar Site were at least 80% anthropogenic in origin and were related to the requirements of the different systems of land use. Wildfires were said to be initiated by:

- hunters and/or poachers; - fishermen; - thatching grass collectors; - reed cutters; - photographic safari operators; - mokoro safaris polers for visibility and to attract game; - game trackers; - slash and burn agriculture for clearing new lands; - clearing crop lands for planting; - burning to reduce the tick population affecting domestic livestock; - collecting wild honey; - campers; - carelessly discarded cigarettes; - opening channels in the swamps; - protection from predators; - felling large trees for preparing new mokoros - burning off moribund grass to improve grazing for livestock; - trans-boundary fires from Namibia and Zimbabwe; - arson related to jealousy.

• The incidence of wildfires depends on whether it has been a dry season and the annual flood level. During dry seasons the fires may start as early as mid April and burn through to the end of October or the commencement of the rains in early November. Stakeholders’ perceptions are that the peak fire season is from the end of July to the end of September or early October and it is claimed that “the whole Delta burns”;

• Although there are concerns about habitats for rare and endangered species several stakeholders said that fire per se is not damaging to Papyrus or Phragmites as both have amazing abilities to regenerate within a short period of time. They did highlight that fire in dry reedbeds is destructive, as are elephants and the swarms of nesting Quelia birds and all could affect Slaty Egret habitat;

• There are opposing views on the effect of fire in the papyrus in the permanent swamps and its effect on sititunga, some say there is a negative impact on the sititunga numbers and that many animals get burnt whereas others point out that the new green shoots of recently burnt papyrus is prime grazing for sititunga and that if fire had such a negative impact on these animals there would be none in the Delta. They do agree though that wildfires during the breeding season would impact negatively on the survival of many sititunga young;

• Several stakeholders agree that water, elephants and fire drive the Delta ecosystem and that fire is not the primary cause of declining biodiversity;



52

In all cases the interviews were confidential and conducted in private on the understanding that the views and opinions expressed by the different stakeholders would not be presented on an individual basis but rather as the views and opinions of the different categories of stakeholders active in the Ramsar Site. In cases where an interpreter was required this service was provided by members of the Department of Forestry and Range Resources in Maun. The detailed results of the interviews have been analysed and are presented in Appendix 3. The conclusions that were drawn from the results in Appendix 3 revealed that:

• People are generally well informed about the seriousness of the fire problem and expressed concern about the occurrence of wildfires in the Ramsar Site;

• Many stakeholders though, recognize that fire is a natural factor of the environment and that in the correct context of season and frequency it has an important and essential ecological role to play in the functioning of the ecosystems in the Okavango Delta;

• The perceptions of many people who have negative views on fire, including many tourists visiting the Delta, particularly international tourists, is that fire is damaging to both fauna and flora and impacts negatively on biodiversity. Their perceptions are generally, that anthropogenic fires are destructive whereas lightning or “natural” fires do not have negative effects on the ecosystem. They are more than likely influenced by rhetoric based on Eurocentric attitudes that have influenced thinking on a worldwide basis, namely that fire is bad and should be avoided. This concept originates from the European forestry industry because anthropogenic induced wildfires have and are having serious deleterious effects on the forests in Europe and therefore are viewed by the general public as being damaging to the ecosystem both locally and globally (Viegas, 1997). As a protectionist measure the view that “all fire is bad” originated without taking into consideration the fact that certain ecosystems, notably African savanna ecosystems, have evolved with fire over millennia. Personal experience during visits abroad indicates that this Euro centric attitude to fire has been the agent of major vegetation changes in many countries and paradigm shifts in the lifestyles of native peoples. For example, in the North West Territory of Canada the Inuit and Native American peoples were threatened with legal retribution if they burned the native rangelands, as was their custom. It is now hypothesized that the demise of the Wood Bison in North America is not solely due to extermination through excessive hunting but may be also due to loss of habitat caused by the prevention and suppression of all fires resulting in the loss of open grassy glades and meadows in the forests, and the extensive grasslands that became forests due to lack of fire. In North America the very successful “Smokey the Bear” campaign denigrating fire led to the catastrophic Yellowstone Fire of 1988. Subsequent to the Yellowstone Fire where hundreds of thousands of hectares of wilderness were devastated by an extreme wildfire which burnt for months, the policy of the National Parks and Wildlife Service has been reviewed and fire is now included as a management practice. Furthermore, the withdrawal of the use of fire as a management option in Norway has led to a shift in the landscape dynamics from scattered woodlands and open herbaceous communities to a densely afforested landscape. This has resulted in a serious urban/wildland fire interface problem where fire needs to be re-introduced to reverse the shift in the composition and structure of the overall plant communities;



51

about the aims and objectives of the research and the possible outcomes that would benefit the community. Time did not permit this process to happen in this investigation into the fire ecology of the Ramsar Site. Also to obtain constructive input from rural communities takes several visits and interactions that enable one to build up an inventory of the different practices and technologies being applied in the different systems of land use in the area. Again this was not possible in the short time available for developing a fire management plan for the Ramsar Site. It would also have been beneficial to have had the opportunity to interview communities across the board to develop seasonal calendars which would focus on the different seasonal changes in specific wetland activities among the rural communities living throughout the Ramsar Site. This would have provided a more in depth basis for the analysis of the fire ecology of the Ramsar Site. It must also be realized that participatory methods are not an infallible means of collecting information. At the simplest and most obvious level, they are prone to bias on the part of the facilitator and misunderstanding by both parties, especially where translators are used to convey questions, activities and responses. In many incidences it is difficult to establish if the respondents were deliberately misleading the group facilitator or interpreter, but in this series of interviews rephrasing some questions at different times during the interviews it became evident that the responses were such that the community leaders, understandably, were presenting the best case scenario in order not to disadvantage either the village leadership, both within the community and in the eyes of the Government employees. It is interesting to note that with interviews focused on the causes of fires in the Okavango Delta in the AquaRap Report (Alonso & Nordin, 2003) reported that accusations or perceptions were often based on incomplete or incorrect information and on emotional rhetoric and in several instances during the interviewing process there was a widespread tendency to blame mostly the hunters and/or poachers for causing fires thereby often ignoring other causes. Since Cassidy (2003) and Tlotlego (2004) both conducted surveys using the participatory rural appraisal technique over longer periods of time and therefore probably developed greater levels of trust with the people they were interviewing, the EnviroNET consultants were of the opinion that more reliable data on the fire ecology of the Ramsar Site could be obtained from these investigations and consequently this information has been dealt with in detail in the review of literature presented in the previous section i.e. 5.1.1. For the same reason use was also made of the responses that were listed from the rural communities at the ODMP information meetings held with the Kgotlas throughout the Ramsar Site during 2003 and 2004. The report prepared for the ODMP by Benson (2004) was used to identify burning “Hot Spots” in the Ramsar Site to ensure that field visits and interviews with rural communities were conducted in these areas. Bearing in mind the aforementioned factors influencing the validity and reliability of information obtained from participatory rural appraisal programs, interviews were conducted with 41 stakeholders comprising representatives from the following categories active in the Okavango Delta Ramsar Site:

• Rural Communities;

• Government Departments;

• Commercial Stakeholders;

• Non-Government Organizations;

• Private Individuals.



50

The papyrus (Cyperus papyrus) community also grows in luxuriant stands in the Permanent Swamps and can reach heights of 4 – 5 metres. It typically comprises an entangled mass of horizontal rhizomes that float during periods of high flow and subsides during low flows but even during periods of low flows the rhizomes are not aerially exposed. The Cyperus papyrus community is restricted to areas where rhizomes are permanently submerged such that they are not destroyed by fires. Cassidy (2003) reported from interviews with local communities in the Panhandle region of the Ramsar Site that that fire does not affect water lilies because they grow in water. Also fire removes the dense hippo grass (Vossia cuspidata) that floats on top of the water and closes over open pools resulting in the water lilies getting more sunlight and less competition from the hippo grass for space to grow. Fire also had no adverse effects on papyrus (Cyperus papyrus) as stated by Ellery (2003) resulting in an improvement in its edibility for human consumption and quality for weaving mats. Cassidy (2003) also reported that from the Panhandle region that households involved in fishing believed that fish populations had increased because the fires stimulated the growth of new shoots that were palatable for fish. In addition, fire removed vegetation leaving the sand clear for the tilapia to make their nests once the flood filled the flood plains. Not only did fishermen themselves state that fire was important for stimulating new shoots to attract fish closer, and to create space for their nets, but government fisheries officers confirmed that fire was increasingly being used. Generally the communities in the Panhandle believed that the overall effects of fire in this region were positive and that fire improved both the quality and quantity of the wetland resources they use, and in some instances, the absence of fire decreases the availability of some resources. Regarding the study on the effects of fire on micro-organisms in the Seasonal Swamps of the Ramsar Site Banda (2004) found that although micro-organisms are sensitive to the changes in their micro-environment caused by fire, the changes were not statistically significant. A non-significant increase in fungal biomass, population and dehydrogenase activity was detected after a fire event. He showed that burning causes a temporal disturbance after which the microbial decomposers returned to similar levels to those found in unburnt plots. These results would suggest that for all practical purposes fires do not have any long terms effects on the populations of microorganisms in the soils of the Okavango Delta ecosystem. 5.1.2 Interviews related to the fire ecology of the Okavango Delta Ramsar Site As another means of obtaining information on the fire ecology of the Okavango Delta Ramsar Site interviews were conducted with rural communities, commercial stakeholders, non-government organizations and relevant government departments. It must be recognized though that sociological studies cannot give facts but tendencies in people’s attitudes. One cannot expect to get into peoples minds and find images of beliefs and generalized opinions. Therefore the objectives of such studies cannot be to discover information, but rather what the people say about the information (Vélez, 1997). Also in order to carry out a successful participatory rural appraisal (PRA) program in a community, it is important that an atmosphere of mutual respect and trust is created (Dixon, 2003). Prior to the onset of a research program, each community should be visited and discussions held



49

the vegetation and the species composition and structure was principally determined by the frequency of flooding rather than by fire. Fires have little effect on the vegetation in the active floodplains because they occur when the vegetation is dormant. In addition most of the plants present are usually tall perennial sedges or grasses like Cyprus articulatus, Schoenoplectus corymbosus, Oryza longistaminata and Panicum repens which spread and grow by rhizomes which are protected by a thick organic layer of dead leaves and stems that remain moist long after the rains in February/March and are therefore well protected from fire (Heinl, 2005). In areas of the Seasonal Swamps that had not been inundated for extended periods approximately up to 10 years, the vegetation comprised both herbaceous and woody vegetation, the latter being due to the extended period without inundation. The study showed that with a high frequency of burning (6 - 10 burns during the 15 year study period) there were fewer large trees and a broader growth of small woody species compared to areas less frequently burnt (0 - 2 burns during the 15 year study period). The frequent burning resulted in a regular topkill and coppicing of the woody plants and together with small individuals, were prevented from escaping the “fire trap” in the grass layer affected by the fires. The frequent burning was not responsible for the mortality of large trees but rather for suppressing the recruitment of small individuals to the woody canopy layer (Heinl, 2005). By implication herbaceous grass vegetation was favoured in the Seasonal Swamps subjected to less flooding by increasing frequencies of burning as reflected by high cover values. However, with increasing time since burning the study showed that the relatively high cover values of annual herbaceous species declined after the fire and semi-perennial and later perennial species became more abundant. The most dominant plant species after burning were the stoloniferous perennial grass species Urochloa mosambicensis (signal grass) and the shrub Pechuel-loeschea leubnitziae (wild sage) which had a negative relationship to one another. Maximum cover values for U. mosambicensis occurred approximately eight years after burning but declined thereafter with rising cover values for P. leubnitziae and increasing competition from this woody species (Heinl, 2005). It was concluded that the general response of the vegetation to fire in the dryland areas covered by woodlands in the Okavango Delta Ramsar Site is similar to the savannas elsewhere in southern Africa but that the models on post-fire succession could only be partially supported, as succession was shown to be not only dependent on the life-history of the occurring species, but also by competition and niche differentiation (Heinl, 2005). Ellery (2003) reports that fires are widespread in the Okavango Delta, but that both the widespread species Phragmites (reeds) and Pennisetum glaucocladum are stoloniferous plants with their meristems occurring below the soil surface and therefore protected from fire. The extensive Phragmites reedbed community occurs in the channel margins of the Permanent Swamps in the upper reaches of the Panhandle where the soils have a high inorganic matter content and are seasonally flooded for months. It also occurs at a few sites along the Nqoga River. This is the most widespread plant community in the Panhandle and is flooded seasonally to a greater depth and for longer duration than the Pennisetum glaucocladum reedbed community.



48

swamps, thus trap large amounts of carbon. It has been estimated that the quantity of carbon stored in the organic soils of the Earth is 500 times more than the quantity of CO2 so far released into the atmosphere by burning of fossil fuels. Therefore burning of peat soils lead to the destruction of natural carbon reservoirs that could have moderated the increase in atmospheric CO2 contributing to the greenhouse effect and global warming. This, if confirmed could give a special significance to this function performed by some wetlands. Relating this overview of the formation and accumulation of organic peat material to the occurrence of peat fires in the Okavango Delta Ramsar Site Alonso & Nordin (2003) refer to the occurrence of peat fires in the drainage channels of the Thaoge River. It is estimated that the blockage of the Thaoge River has gradually occurred since the 1870’s. Quoting Ellery et al (1989) the drying of the peat deposits flanking the channel has resulted in the occurrence of peat fires, which have destroyed the original plant communities and peat deposits. This has resulted in the release of nutrients into the soil which improves forage quality and in the case of the Thaoge River has increased the utilization of the forage resources by cattle. In addition more recently there has been the cultivation of crops such as tropical fruit and sugar cane in this area because of the elevated soil fertility associated with the former burning of the peat deposits in this area. Thus a conflicting set of circumstances exists regarding the occurrence of peat fires in the Ramsar Site. On the one hand these fires are releasing CO2 into the atmosphere thereby contributing to the greenhouse effect and global warming. On the other hand the peat fires have and are raising the nutrient levels of highly infertile soils resulting in the production of grass forage with significantly improved quality for grazing animals. Therefore these fires are playing a significant role in the normal nutrient cycle occurring in the Okavango Delta ecosystem. It should also be considered that these fires are probably not a recent occurrence but have been occurring since time immemorial and are therefore a part of the normal cycle of the release and absorption of CO2 into and from the atmosphere associated with fires in African ecosystems. However, this conclusion does not necessarily apply to areas where peat fires have improved the soil fertility but which are now being used for the production of crops. In this case unless the nutrient status of the soil is maintained by either applying fertilizers or manure these soils will gradually decrease in fertility resulting in an impoverished ecosystem. Therefore this would not be part of the normal cycle of events associated with peat fires resulting in improved grasslands where moderate levels of grazing would maintain the fertility of the soil and the sustainability of the ecosystem. However, if these areas produced by peat fires are overgrazed and the grasslands destroyed then this would be no different to the harmful effects of exploitive crop production and the resultant deterioration in the condition of the ecosystems in these areas. Another perspective is that the area affected by peat fires in the Ramsar Site is limited and besides active peat fires being potentially dangerous and harmful to humans, livestock and large wild ungulates and considering their beneficial effects on soil fertility they are of limited ecological concern in the Ramsar Site. 5.1.1.6 Effects of fire In the Seasonal Swamps that are inundated regularly at least every second year, fires usually occur during the dry period after the rains in February/March and before the arrival of the floodwaters in July. However, studies involving single fire events showed that flooding was the major ecological factor responsible for most of the observed differences in



47

the floodwaters in July and is closely associated with burning applied with the preparation of fields and fishing grounds. The dryland areas burn later with the start of the rainy season in October (Heinl, 2005). Cassidy (2003) reported that in 2001 the majority of fires in the Seasonal Swamps in the Panhandle region of the Ramsar Site were in August and September with no fires being reported from February to July during that year.

5.1.1.4 Frequency of burning The floodplains in the Seasonal Swamps in the Okavango Delta are more frequently burnt than the dryland areas because of greater grass fuel loads due to their higher production potential and lower grazing pressure caused by the occurrence of less palatable grasses. The mean fire return period for these floodplains during the 14 year period between 1989 - 2003 was 6.6 years and for the drylands 22.2 years. The highest fire frequency occurred in the floodplains that are inundated approximately every second year resulting in a mean fire return period of 5 years. Generally the dryland areas rarely burn and for approximately 60% of all dryland areas no fires were recorded during the study period. Nevertheless the frequency of burning varied greatly in the different habitat types in the drylands with some areas being burnt more frequently than biennially particularly with fires spreading into the drylands from adjacent more frequently burnt floodplains. Heinl (2005) concluded that the high frequency of anthropogenic fires in the Okavango Delta is associated with fires being used intentionally and frequently to provide fresh grazing for wildlife and cattle, improved viewing for safari-tourism and safeguarding property. However, the affected areas are very limited (<5 % in the floodplains) and the overall frequency of burning in the Delta is highly variable indicating no large regulating and homogenizing effect on the vegetation at this stage. Arising from interviews with local communities in the Panhandle region of the Ramsar Site Cassidy (2003) reported that the frequency of fires in this region had decreased but this had resulted in the significant accumulation of greater fuel loads causing less frequently but more extensive and intense fires. The lower frequency of fires was also associated with protecting areas that were harvested for thatching material. 5.1.1.5 Type and intensity of fires No information was available in the scientific literature on the types and intensities of fires occurring in the Okavango Delta Ramsar Site except for ground fires burning accumulations of organic peat material (peat fires) in areas where the channels have dried out as part of the normal dynamic variations in the water flow through the fan of the Delta. A general description of the formation and accumulation of organic peat material in wetlands like the Okavango Delta is provided by Roggeri (1995) who states that during photosynthesis plants use carbon dioxide (CO2) available in the atmosphere. The CO2 consumed is partly transformed into organic carbon and accumulated in plant tissue. Under certain conditions (increased acidity, lack of oxygen, lack of nutrients or low temperatures) the organic matter is only partially decomposed and accumulates in the soil. The peat formed in this way forms a reservoir of organic carbon. Once stored in this form, carbon can only be returned to the atmosphere by oxidation or by combustion of the peat. Swamps, and in particular peat



46

Site in the vicinity of Shakawe and focused on the Temacane Community Trust where wild fires adversely effect the production and harvesting of thatching grass. This project investigated the possible use of satellite remote sensing and geographical information systems as a means of providing information for formulating management strategies to control wildfires (Tlotlego, 2004). Finally a research project was conducted by Banda (2004) between 2000 and 2003 in the Seasonal Swamps along the Boro route in the distal fan portion of the Okavango Delta near Maun. The objectives were to determine the effects of burning on soil microbial activity, fungal/bacterial carbon biomass, fungal populations and diversity and some soil physical and chemical properties.

5.1.1.1 Ignition sources of fires The main ignition source of fires in the Okavango Delta is anthropogenic because fires ignited by lightning are extremely rare during the dry season (Heinl, 2005; Tacheba, 2002). This high frequency of anthropogenic-ignited fires is of concern because of its perceived negative ecological impact being caused by increasing human populations in certain localized areas (Heinl, 2005).

5.1.1.2 Reasons for burning

The different reasons identified, cited or implied by the aforementioned researchers for using fire as a management practice in the Okavango Delta Ramsar Site were:

• to improve the quality of grazing for domestic livestock and wildlife (Cassidy, 2003, Heinl, 2005; Tacheba, 2002 and Tlotlego, 2004);

• to attract wildlife to green grazing for improved viewing by tourists (Heinl, 2005);

• to attract wildlife to green grazing for improved hunting (Cassidy, 2003; Tlotlego, 2004);

• to increase fish populations in the Permanent and Seasonal Swamps by stimulating new shoots palatable to fish and promote better nesting conditions for fish when the flood arrives (Cassidy, 2003);

• to improve access to the Permanent and Seasonal Swamps for fishing and setting of nets (Cassidy, 2003; Tlotlego, 2004);

• to clear land in preparation for establishment of crops (Tlotlego, 2004);

• to improve the quality of thatch grass and reeds by removing plant debris after harvesting (Cassidy, 2003);

• to improve the quality of papyrus for weaving of mats by removing old dead shoots and stimulating new growth (Cassidy, 2003);

• to improve access in the Seasonal Swamps for harvesting bulbs of water lilies (Cassidy, 2003; Tlotlego, 2004);

• to construct burnt firebreaks to safeguard property (Heinl, 2005).

5.1.1.3 Season of burning The main season of burning for both the Woodlands and the Permanent and Seasonal Swamps is the dry period of the year approximately between May and October. However, the Seasonal Swamps tend to burn earlier peaking in June immediately before the arrival of



45

CHAPTER 5 5. FIRE ECOLOGY OF THE OKAVANGO DELTA RAMSAR SITE 5.1 Collection, Assimilation, Analysis and Evaluation of Information Pertinent to

the Fire Ecology of the Ramsar Site In accordance with the Terms of Reference a review of all available information pertaining to the fire ecology of the Okavango Delta Ramsar Site was conducted. This comprised reviewing the available scientific literature, interviewing different stakeholders and analyzing satellite data of recorded fires in the Ramsar Site for the period 2000 to 2005. This review had as its main objective determining:

• ignition sources of fires;

• reasons for burning;

• season of burning;

• frequency of burning;

• type and intensities of fires;

• effects of fires. 5.1.1 Review of literature on the fire ecology of the Okavango Delta Ramsar Site Despite fires being common and widespread in and around the Okavango Delta and being recognized as an integral ecological process and historical land-use practice, the fire ecology of the Okavango Delta Ramsar Site had never been intensively investigated in both a scientific and political context (Heinl, 2005). Recently several research projects have been specifically conducted to investigate the occurrence and effects of fire in the Ramsar Site and these will be used in addition to other scientific sources to develop a description of the fire ecology of the study areas as a whole. Firstly in 2001 a fire research project was initiated in the south eastern distal portion of the Delta and adjacent dryland areas of the Ramsar Site covering an area of 6 141 km2. The objectives of the investigation were:

• to study fire and its effects on vegetation

• to gain insight into the spatial and temporal distribution of vegetation fires, and;

• to assess the response of the vegetation to burning regimes (Heinl, 2005). A similar study was conducted during the same period by Tacheba (2002) in an area located immediately south west of the aforementioned area and included portions of the Permanent and Seasonal Swamps in the Boro River valley and areas of Mopane and Acacia Woodlands extending to immediately east of the Makgadikgadi Pans. The objectives of this study were to determine the extent and season during which fires occurred during September 2000 and 2001 and the effects of these fires on the structure and biodiversity of plant communities in the wetlands of the Okavango Delta. In addition to these projects another intensive study on fire was initiated in 2001 to examine how illegal anthropogenic wildland fires affect people’s access to and use of resources in the Permanent and Seasonal Swamps of the Panhandle region of the Delta (Cassidy, 2003). Subsequent to this study a project was conducted in 2003 in the northern western portion of the Ramsar

Fire management plan ODMP - Draft Report Second Section June 2006

Documents

Transcript of Fire management plan ODMP - Draft Report Second Section June 2006