Temporal variation in species composition, diversity and ...€¦ · mountains’ using a measuring...
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( Received 26 October 2019; Accepted 18 November 2019; Date of Publication 20 November 2019 )
WSN 138(2) (2019) 192-224 EISSN 2392-2192
Temporal variation in species composition, diversity and regeneration status along altitudinal gradient and slope: The case of Chilimo dry Afromontane
forest in the Central Highlands of Ethiopia
Mehari A. Tesfaye1,a, Oliver Gardi2,b, Jűrgen Blaser2,c
1Central Ethiopia Environment and Forest Research Centre, Box 30708, Addis Ababa, Ethiopia
2Bern University of Applied Sciences, School of Agriculture Forest and Food Sciences HAFL, CH - 3052, Zollikofen, Switzerland
a-cE-mail address: [email protected] , [email protected] , [email protected]
aCorresponding author: Mehari A. Tesfaye, Phone +251911356756, +251-0116-46044
ABSTRACT
This study is aimed towards investigating the temporal variation in species composition, diversity
and regeneration status of Chilimo dry Afromontane forest in the Central Highlands of Ethiopia. A total
of 35 permanent sample plots of 20 m × 20 m (400 m2) each were established in the natural forest, laid
out on transects of altitudinal gradients, with a distance of 100m between plots. The plots were measured
twice in 2012 and 2017. Three subplots, 5m × 5m, and 1 m2 were laid out inside the main plots for
sapling, shrub and seedling data collection. Species composition, diversity, important value index (IVI)
and regeneration data were analyzed using appropriate formulas. Data analysis was made using R -
studio software. A total of 31 trees and shrubs representing 25 families were recorded, 20 (64.52 %)
were trees and 11 (35.48 %) were shrubs. Thereof, 28, 23 and 26 species under highest, middle and
lowest altitudinal gradient were recorded. The most dominant tree species were: Juniperus procera,
Podocarpus falcatus, Olea europea, Scolopia theifolia and Allophyllus abyssinicus. The species
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composition, diversity, abundance, dominance and important value index significantly varied among
species, altitudinal gradient and slope. The diameter distribution was an inverted J - shaped distribution
pattern. The highest species richness and diversity index were found under middle altitudinal gradient,
while the lowest species richness and diversity index were found under the highest altitudinal gradient.
The mean annual volume increment ranged from 4.223 to 0.228 m3 ha-1 yr-1, while the basal area
increment varied from 0.85 to 0.020 m2 ha-1 yr-1. Among the sampled species, ten species had fair, 5 poor
and 14 species had no regeneration. In conclusion, the Chilimo dry Afromontane forest is suffering from
low recruitment and regeneration. Thus, appropriate forest management options should be implemented.
Keywords: Abundance, altitude gradient, Ethiopia, native species, population structure, saplings,
seedlings and shrubs
1. INTRODUCTION
The structure and function of the forest ecosystem are determined by the plant component
more than any other living component of the system [1]. The population structure is expressed
in terms of a number of individuals present in a particular diameter class and the distribution of
tree species. Understanding the growth status of forests is key for ecosystem stability [2].
Topography, soil, climate and geographical location influence the vegetation diversity of the
forest ecosystem [3].
Sustainable forest management requires forest inventories, in combination with modeling
tools, forest growth and sustainable harvesting or cutting plans [4]. Such systems are common
in many parts of the world [5]. However, they are scarce for Africa’s forest in general and
Ethiopian forests in particular.
The dry Afromontane forests are either mixed Juniperus - Podocarpus forests or
predominantly Podocarpus forests, both with an element of broad-leaved species. They occur
in both the northwestern and southeastern highlands, especially on the plateau of Oromia,
Tigray, Amhara and Southern Nations, Nationalities and Peoples Regional States (SNNP) at
altitudes from 1500 - 2700m [6].
Reports indicate that the deforestation rate amounts to 92,000 ha-1yr-1, while, new
plantation area change is about 18,000 ha-1yr-1 [7]. A majority of the high forests found in
Ethiopia are managed primarily for protection and conservation purpose, while, commercial
utilization is a secondary objective. The forestry administration at the Federal level has
classified 108 of the most important high forest areas totaling an estimated area of 2 million ha
as National Forest Priority Areas of the country. Over two thirds of these high forests are
heavily disturbed forest and need appropriate forest management. The estimated annual height
and diameter growth are very low [8].
Moreover, information on species diversity, population structure and regeneration are
scanty in the study area, except for a few studies by [9] and [10]. Sustainable forest management
is possible if adequate information is available in these regards [11] and [12].
Chilimo forest is one of the few remnants of dry afro-montane forest located in the Central
Highlands, Chilimo forest is composed of - Juniperus procera, Podocarpus falcatus, Olea
europaea, Scolopia theifolia, Rhus glutinosa, Olinia rochetiana and Allophylus abyssinicus [9],
[13] and [14]. In the last, [14] reported 33 different native species in 3 forest patches and [9]
reported 213 different plants species categorized into 83 families.
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Of these, 17 plant species are unique to the Chilimo forest. The forest is also found in the
nearby the capital city of Addis Ababa, easily accessible through all - weather road and having
old historical palaces inside it.
Due to continuous deforestation, the Chilimo forest cover has declined from 22,000 ha in
1982 to 6,000 ha in 1991 and 4,500 ha in 2016 [10] and [16]. As result, some plant species are
becoming endangered [9].
Thus, scientific knowledge on the regeneration of Chilimo forest is important for
conservation and restoration endeavors. However, this knowledge is scanty for most forests in
the country, except for a few works done for dry Afromontane forests, Acacia woodlands or
woodlands and exclosures in the country [16-20].
In the present study, the species composition, diversity, growth, yield and regeneration
status of Chilimo dry Afromontane forest is investigated. We hypothesized that there is
temporal variation in species composition, diversity, yield and regeneration status along
altitudinal gradient and slope. Growth and yield study were, therefore, done for the eleven most
common native species viz:- Allophyllus abyssinicus, Apodytes dimidiata, Juniperus procera,
Celtis africana, Ekebergia capensis,Olea europaea,Olinia rochetiana, Podocarpus falcatus,
Prunus africana, Rhus glutinosa and Scolopia theifolia, because these native tree species are
the most abundant and dominant tree species in the forest. Moreover, the study was socially
acceptable and economically important. Some of the species are under increased pressure due
to illegal cutting for fuelwood, construction wood, farm implements and charcoal [20].
Therefore, such studies had been conducted with the hypotheses that species composition,
diversity and the regeneration status of Chilimo dry Afromontane forest vary along altitudinal
gradient and slope factors. Thus, the intent of the study was: (i) To determine the relative
frequency, density, dominance and important value index of woody species in the study sites;
(ii) To investigate the growth and yield of 11 dominant and economically important native tree
species; (iii) To assess the natural regeneration status of seedlings, sapling and tree population
densities along altitudinal gradients, slope percent and forest patch.
2. MATERIALS AND METHODS
2. 1. Chilimo dry afro-montane forest
Chilimo dry afro - montane forest is geographically located at 38° 07′ E to 38° 10′ E
longitude and 9° 30′ to 9° 50’ N latitude at an altitude of 2,170 - 3,054 m asl (Figure 1) in Dendi
district, Western Shewa zone, Oromia Administrative Region, Central Highlands of Ethiopia.
The mean annual temperature of the area ranges between 15 – 20 ºC and receives mean annual
precipitation of 1000 - 1, 264 mm [10]. Köppen’s classification defines the climate of Chilimo
forest is classified as warm temperate climate I (CWB) type [21].
2. 2. Reconnaissance survey
A discussion forum held with Oromiya Wildlife and Forest Enterprise higher officials in
Addis Ababa for awareness creation and to get permission. Subsequently, a reconnaissance
survey was conducted through a field visit and physical observation across the Chilimo forest.
Then, 3 forest patches (Chilimo, Gaji and Gallessa) selected based on accessibility, species
composition and representativeness for further study. Inventory done starting from Chilimo
proceed to Gallessa and finally to Gaji forest patches.
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Figure 1. Sampling plots of Chilimo dry afromontane forest.
2. 3. Scheme of sample plot
A systematic sampling approach was implemented to conduct inventory. A total of thirty
- five, 20 × 20 m (20 in Chilimo, 11 in Gallessa and 4 in Gaji) squared sampled plots were
marked, based on Neyman optimal allocation formula in the natural forest [22]. The plots were
laid out along 100m ground distance, starting from the highest to the lowest ridges of the
mountains’ using a measuring tape, GPS and compass. The boundaries of the main plots were
pegged and marked, then altitude, slope, latitude and longitude data were recorded from the
center of each main plot. A total of ten transect lines (4 in Chilimo, 4 in Gallessa and 2 in Gaji)
were used along with an altitudinal gradient from top to bottom ridges of the mountain. The
distance between two consecutive transect lines was 300m to 1 km, depending on the
accessibility of the next transect. Sampling and data collection were done in the measured plots
of the mixed natural forest and plantation. Data collection was taken from October to
November 2012 and June to July 2017, respectively.
2. 4. Field data collection and sampling
Individual species were categorized into trees (≥ 5 cm diameter at breast height), shrubs
(dbh 5 to 2.5 cm), saplings (height ≥ 1.3 m and dbh 2.5 - 5 cm) and seedlings (height 0.30 - 1.3
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m and dbh ≤ 2.5 cm) following, Lamprecht classification [23]. Before actual measurements, all
bordering trees and shrubs were marked using red paints and numbered. Tree diameter (cm)
was measured using a metallic caliper for smaller and medium - sized trees, while, diameter
tape was used for bigger trees.
Total height (meter) was measured to the nearest two digits using Vertex III digital
electronics tree height measurement instruments. In cases, where trees branched at or below the
breast height, the diameter was measured separately for each branch and quadrado. Diameter at
each stem was measured separately for trees with multiple stems connecting near to the ground.
For irregularities and or buttresses on large trunks, measurement was taken at the nearest lower
point. In a similar way, each marked individual trees in 2012 was remeasured in 2017. Saplings
and shrubs were sampled inside each main plot on 3 subplots, 5m × 5m laid out diagonally.
Height and diameter were a measurement for saplings done using graduated wooden bars
and metallic caliper. While seedlings were sampled in 3 subplots, 1m x 1m, one at the center
and 2 in the edge of the diagonal, counting an average height measurement made using a
wooden ruler.
To study the growth and yield 11 trees species viz: - Allophyllus abyssinicus, Apodytes
dimidiata, Juniperus procera, Celtis africana, Ekebergia capensis, Olea europaea, Olinia
rochetiana, Podocarpus falcatus, Prunus africana, Rhus glutinosa and Scolopia theifolia were
selected based on their relative (frequency, density and dominance) and IVI. Moreover, visual
observation was done for some of the tree species based on their social acceptability and
economic importance.
2. 5. For growth and yield data
Basal area (BA) (m2 ha-1) and volume (Vt) (m3 ha-1) was calculated using inventoried data.
Total volume was calculated using the conventional volume equation because local volume
equations not available for these species:
V = 𝜋 (𝐷𝐵𝐻
4) 2 ∗ ℎ ∗ 𝑓 [24] ……………….. (eq.1)
where V: tree volume, DBH: diameter at breast height, h: total height, 𝑓: form factor (0.42) [24]
BA (Basal area) calculated using the formula:
BA = 𝜋𝐷𝐵𝐻2
4……………………………… (eq.2)
where BA: Basal area, DBH : Diameter at breast height, 𝜋: 3.142
Basal area and volume increment calculated as:
VtI = Vt2017- Vt2012…………………… (eq.3)
BAI = BA2017- BA2012……………… (eq.4)
where VtI: volume increment (m3 ha-1 yr-1 and BAI basal area increment (m2 ha-1 yr-1)
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3. DATA ANALYSIS
3. 1. Aboveground biomass
Aboveground biomass was calculated using [25] (eq. 5) because this equation is the most
recent and important predictive variables for estimation using diameter at breast height (DBH),
total height (H), basic wood density (ρ) and forest type.
AGBest = 0.0673(ρHD2)0.976…………………..… (eq.5)
where AGBest = above ground biomass (kg), D = DBH (cm), H = height (m), and ρ = basic
wood density (g·cm-3).
Accumulated above ground and below ground carbon density was calculated following
eq.6 and eq.7:
ACD = AGB ∗ 0.47 ……………………………… (eq.6) [26]
BCD = ACD ∗ 0.24 …………………………… (eq.7) [27, 28]
where ACD = Aboveground carbon density, BCD = Below ground carbon density.
The aboveground and below biomass for each tree was calculated separately in each plot,
then, the biomass of each tree was summed up to give plot biomass and converted into ha.
3. 2. Woody Speciesdiversity and structure analysis
The Species diversity was analyzed using the Shannon diversity index (H') [29] (eq.8):
Shannon-Wiener diversity index was calculated as
H'= - ∑ pi
s
i=1
lnpi ………………………........ (eq.8)
where; H' = Shannon - Wiener index of species diversity, pi = proportion of individual found
in the ith species and evenness were calculated using the following formula:
Equitablity (evennes) Equitability (evenness) J =H′
H′max
…….. (eq.9)
where H'max is ln (natural logarithm) of S (number of species).
Simpson's index of diversity was calculated as follow:
D = 1 − ∑ (pi)2si=1 …………………….. (eq.10)
where, D = Simpson's diversity index; pi=as described in equation 1
Simpson diversity index gives relatively little weight to the rare species and more weight
to the most abundant species [30]. The value ranges from 0 (low diversity) to a maximum of
(1-1/s), where S is the number of species. It is predominantly affected by sample size [30]:
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Simpson or dominance index (D) =-∑s [(Ni(Ni−1)]
i=1 N(N−1) ……………. (eq.11)
where, Ni is the number of individuals of speciesi; N is the total number of individuals of all
species. As index values increase, diversity decreases
3. 3. Important value index (IVI)
The importance value index (IVI) was calculated as follows to rank species contribution
to the forest community composition [29]:
IVI = RD + RF + RDO ……………………………………… (eq.12)
where, RD is relative dominance, RF s relative frequency, and RA is relative abundance.
RD = 𝑁𝑢𝑚𝑏𝑒𝑟𝑜𝑓𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑙𝑎𝑜𝑓𝑎𝑆𝑝𝑝
𝑇𝑜𝑡𝑎𝑙𝑛𝑢𝑚𝑏𝑒𝑟𝑜𝑓𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑜𝑓𝑆𝑝𝑝× 100 ……………………… (eq.13)
RF = 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦𝑜𝑓𝑎𝑆𝑝𝑝
𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦𝑜𝑓𝑎𝑙𝑙𝑆𝑝𝑝× 100 …………………………………… (eq.14)
RDO = 𝐷𝑜𝑚𝑖𝑛𝑎𝑛𝑐𝑒𝑜𝑓𝑎𝑆𝑝𝑝
𝐷𝑜𝑚𝑖𝑛𝑎𝑛𝑐𝑒𝑜𝑓𝑎𝑙𝑙𝑆𝑝𝑝× 100 …………………………….… (eq.15)
Basal area (BA) (m2 ha-1) and volume (Vt) (m3 ha-1) for the natural forest was calculated
using inventoried data. Total volume was calculated using the conventional volume equation
because local volume equations not available for these species:
V =𝜋 (𝐷𝐵𝐻
4) 2 ∗ ℎ ∗ 𝑓 [24] ………………………………….….. (eq.17)
where V = tree volume, DBH= diameter at breast height, h = total height, 𝑓 = form factor (0.42)
[24].
BA (Basal area) calculated using the formula (eq.18):
BA = 𝜋𝐷𝐵𝐻2
4 …………………………………………… (eq.18)
where BA = Basal area, DBH = Diameter at breast height, 𝜋 = 3.142
3. 4. Regeneration status
Regeneration was analyzed based on the density of the seedlings, saplings, and stems
(matured individuals) ha-1 and categorized as :- (a), Good regeneration (GR) if the ratio of:-
“seedlings : saplings” and “saplings : stems‟ > 1 or seedlings >> saplings > mature individuals
(for shrub species if the ratio of seedlings : saplings (small trees)” > 1 or seedlings >> saplings)
: (b), Fair regeneration (FR) if the ratio of “seedling : sapling” ≥ 1 and/or “saplings: stem” ≥ or
≤ 1 or seedlings ≥ saplings ≥ or ≤ stem : (c), Poor regeneration (PR) if the ratio of “seedling :
sapling” < 1 and “sapling : stem” ≥ 1 or ≤ 1 or seedling < sapling ≥ or ≤ stem” : (d), No
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regeneration (NR) if a species is represented only by stem individuals and (e) New (N) if the
Species is represented only by seedling stage [31] and [10]. Further analysis of the regeneration
status of the species, forest patches, altitudinal gradient, and slope percent was made based on
these categories.
4. RESULTS
4. 1. Species composition and abundance of Chilimo forest
A total of 31 species of trees and shrubs, representing 25 families were recorded in all
study plots. Out of these, 20 (64.52 %) were trees and 11 (35.48 %) were shrubs. Sixteen
(51.61%) species were encountered in all forest patches, 6 (19.36 %) in two forest patches and
9 (29.03 %) in one forest patch. Thereof, 28, 23 and 26 species under highest, middle and lowest
altitudinal gradient were recorded. Moreover, 27, 29 and 25 species were recorded under gentle,
middle and steep slopes, respectively.
The total number of individuals in Chilimo forest patch was ranged from 2479.84 to19.05
N ha-1 for Podocarpus falcatus and Ilex mitis and 1919.55 to 19.05 N ha-1 for Maytenus
gracilipes and Rosa abyssinicus, in 2012 and 2017, respectively. The total number of
individuals in 2017 was ranged from 802.75 to 3.81 N ha-1 for Olea europea and Ilex mitis for
trees and 1854.6 to 3.81 N ha-1 for shrubs under the same forest patch. The number of
individuals trees sampled under Gallessa forest patch was ranged from 565.65 to28.31 N ha-1
for Juniperus procera and Ekebergia capensis and 263.49 to 29.85 N ha-1 for Juniperus procera
and Scolopia theifolia in 2012 and 2017, respectively and for Gaji forest patch in 2012 ranged
333.42 to 15.24 N ha-1 for Podocarpus falcatus and Buddleja polystacha and 297.47 to 3.81 for
Olea europea and the same species in 2012 and 2017, respectively. The number of individuals
for shrubs was also ranged from 1860.42 for Dovyalis abyssinicus to 50 N ha-1 for Osyris
quadripartita.
The 5 most abundant tree species under Chilimo forest patch was :- Podocarpus falcatus,
Olea europea, Allophyllus abyssinicus, Juniperus procera and Bersama abyssinicus, in
Gallessa were Juniperus procera, Allophyllus abyssinicus, Podocarpus falcatus, Bersama
abyssinicus and Scolopia theifolia and in Gaji:- Podocarpus falcatus, Olea europea, Allophyllus
abyssinicus, Juniperus procera and Scolopia theifolia. Moreover, the most abundant shrub
species under Chilimo forest patch were Maytenus gracilipes, Myrsine africana, Rhamnus
prenoides, Dovyalis abyssinicus and Carissa spinorrum in Gallessa Dovyalis abyssinicus,
Maytenus gracilipes and Maytenus addat and in Gaji were Dovyalis abyssinicus, Maytenus
gracilipes and Rhamnus prenoides.
4. 2. Species richness and diversity
Dendrometry and tree data measurements of diameter at breast height, diameter at stump
height and height were made for 2,379 trees. The most dominant tree species were: - Juniperus
procera, Podocarpus falcatus, Olea europea, Scolopia theifolia and Allophylus abyssinicus. In
contrast, Cassiopourea malosana, Carissa spinorram, Osyris quadripartita, Sideroxylon
oxycanthum and Erica arborea are rare species. The diameter at breast height (DBH) and
diameter at stump height (DSH) of the sampled species were ranged from 5 to 121.82 and 5 to
126.67 cm, respectively. Total height of the sampled trees was also ranged from 0.5 to 39.00m.
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The species richness was ranged from one to eleven, while, the Shannon Weiner diversity
index was ranged from 1 to 2.21 (Table 1). The highest species richness and diversity index
were found under middle altitudinal gradient, while, the lowest species richness and diversity
index were found under the highest altitudinal gradient.
Table 1. Shannon wiener and richness index of the sampled plots of Chilimo natural forest.
Plo
t
No
Pat
ch
Tra
nse
ct
Ric
hn
ess
20
17
Sh
ann
on
20
17
Plo
t N
o
Tra
nse
ct
Fo
rest
pat
ch
Ric
hn
ess
20
17
Sh
ann
on
20
17
01 Chilimo T1 4 0.59 18 T4 Chilimo 2 0.33
02 Chilimo T1 5 1.27 19 T4 Chilimo 8 1.99
03 Chilimo T1 8 1.70 20 T4 Chilimo 5 1.31
04 Chilimo T1 7 1.11 23 T2 Gallessa 1 0.00
05 Chilimo T1 8 1.43 24 T2 Gallessa 1 0.00
06 Chilimo T2 8 1.91 25 T2 Gallessa 9 1.99
07 Chilimo T2 8 1.79 26 T2 Gallessa 2 0.38
08 Chilimo T2 5 1.15 27 T3 Gallessa 0 0.00
09 Chilimo T2 7 1.74 28 T3 Gallessa 7 1.43
10 Chilimo T2 6 1.62 29 T3 Gallessa 5 1.44
11 Chilimo T2 7 1.75 30 T4 Gallessa 5 1.18
12 Chilimo T2 11 2.210 31 T4 Gallessa 8 1.53
13 Chilimo T2 5 1.14 32 T1 Gaji 9 1.86
14 Chilimo T3 1 0.00 33 T1 Gaji 10 1.92
15 Chilimo T3 4 1.27 34 T1 Gaji 9 1.91
16 Chilimo T3 6 1.54 35 T2 Gaji 7 1.53
17 Chilimo T3 7 1.47
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Table 2. Diameter distribution of most sampled tree and shrubs for the overall forest
in 2012 (area = 1.4 ha)
Patch Year
Sppdiameter distribution in Chilimo dryafro montane forest
No Local name Scientific
name
Diameter distribution (cm)
Sum
≤ 1
0
10
-20
20
-30
30
-40
40
-50
50
-60
60
-70
≥ 7
0
Overall 2012 1 Gatira habessha Juniperus
procera 54 52 36 32 11 10 10 4 209
Overall 2012 2 Berbersa Podocarpus
falcatus 129 24 4 4 - - 1 2 164
Overall 2012 3 Dalecho Olinia
rochetiana 41 54 16 5 2 2 1 - 121
Overall 2012 4 Ejerssa Olea
european 23 20 18 8 3 2 - 2 76
Overall 2012 5 Sarara Allophylus
abyssinicus 22 19 6 3 1 - - - 51
Overall 2012 6 Gaallee/Amotta Scolopia
theifolia 28 16 4 - - - - - 48
Overall 2012 7 Kertame Maytenus
gracilipes 32 2 - - 1 - - - 35
Overall 2012 8 Anfar Buddleja
polystacha 14 8 4 - - - - - 26
Overall 2012 9 Tatessa Rhus
glutinosa 3 12 6 - - 1 - - 22
Overall 2012 10 Kombolcha Maytenus
addat 9 9 - - - - - - 18
Overall 2012 11 Algae Celtis
africana 2 8 2 5 - - - - 17
Overall 2012 12 Gaachanfullaa Cassipourea
malosana 1 10 4 - - - - - 15
Overall 2012 13 Mieessa Ilex mitis 1 3 2 - - 1 1 2 10
Overall 2012 14 Sombo Ekebergia
capensis 5 1 - - 1 - - 1 8
Overall 2012 15 Watto Osyris
quadripartita 6 2 - - - - - - 8
Overall 2012 16 Tikure inchet Prunus
africana 2 4 1 - - - - 1 8
Overall 2012 17 Cheleleka Apodytes
dimidiata 3 3 - 1 - - - - 7
Overall 2012 18 Azamire Bersama
abyssinicus 3 2 - - - - - - 5
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Overall 2012 19 Asta Erica arborea 2 2 1 - - - - - 5
Overall 2012 20 Biitee Sideroxylon
oxycanthum 1 3 - - - - - - 4
Overall 2012 21 Ceeka Calpurina
aurea 3 - - - - - - - 3
Overall 2012 22 Barooddoo Myrica
salicifolia - 2 - 1 - - - - 3
Overall 2012 23 Kosso Hagenia
abyssinica - - - 1 - - - 1 2
Overall 2012 24 Cheleleka Apodytes
dimidiata 1 - - - - - - - 1
Overall 2012 25 Agam Carissa edulis 1 - - - - - - - 1
Total 386 256 104 60 19 16 13 13 867
4. 3. Population structure of Chilimo forest
The diameter distribution of the sampled trees under Chilimo forest in 2012 and 2017 is
presented in Table 3. The number of stems for Juniperus procera, Podocarpus falcatus, Olinia
rochetiana, Olea europea and Allophyllus abyssinicus was highest in 2012. However, Carissa
spinorrum followed by Apodytes dimidiate was the lowest (Table 2). Similarly, in 2017, the
highest number of stems were measured for Juniperus procera, Podocarpus falcatus, Olea
europea, Olinia rochetiana and Allophyllus abyssinicus (Table 3). The lowest number of
diameter measurement was made for Dovyalis abyssinicus, Carissa spinorrum and Hagenia
abyssinicus (Table 3). Graphical representation is presented for the most frequent tree species
in Figure 2a - 2n. Juniperus procera and Podocarpus falcatus had an inverted J shaped
distribution. Olea europea followed a normal distribution pattern, Allophyllus abyssinicus and
Scolopia theifolia were followed a similar fashion and showed a normal population pattern.
Table 3. Diameter distribution of most sampled tree and shrubs for the overall forest
in 2017 (area = 1.4 ha).
Patch Year No Local name Scientific name
Diameter class distribution (cm)
Sum
≤ 1
0
10
_20
20
-30
30
-40
40
-50
50
-60
60
-70
≥ 7
0
Overall 2017 1 Gatira habessha Juniperus
procera 50 58 22 31 12 12 9 4 198
Overall 2017 2 Berbersa Podocarpus
falcatus 144 38 2 2 1 - 2 1 190
Overall 2017 3 Ejerssa Olea european 23 19 19 8 3 2 - 2 76
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Overall 2017 4 Dalecho Olinia
rochetiana 21 34 10 5 1 1 3 - 75
Overall 2017 5 Sarara Allophylus
abyssinicus 20 19 6 3 1 - - - 49
Overall 2017 6 Gaallee/Amotta Scolopia
theifolia 23 18 3 - - - - - 44
Overall 2017 7 Kertame Maytenus
gracilipes 31 6 1 - 1 - - - 39
Overall 2017 8 Anfar Buddleja
polystacha 14 8 3 - - - - - 25
Overall 2017 9 Tatessa Rhus glutinosa 4 13 5 - - 1 - - 23
Overall 2017 10 Algae Celtis africana 2 6 6 3 - - - - 17
Overall 2017 11 Kombolcha Maytenus addat 10 7 - - - - - - 17
Overall 2017 12 Sombo Ekebergia
capensis 9 1 3 - - 1 - 1 15
Overall 2017 13 Gaachan fullaa Cassipourea
malosana 1 9 4 - - - - - 14
Overall 2017 14 Miessa Ilex mitis 1 2 2 1 2 1 1 2 12
Overall 2017 15 Watto Osyris
quadripartita 9 2 - - - - - - 11
Overall 2017 16 Tikure inchet Prunus africana 2 4 1 - - - - 1 8
Overall 2017 17 Cheleleka Apodytes
dimidiata 1 5 - 1 - - - - 7
Overall 2017 18 Azamire Bersama
abyssinicus 4 2 - - - - - - 6
Overall 2017 19 Biitee Sideroxylon
oxycanthum 2 3 - - - - - - 5
Overall 2017 20 Asta Erica arborea 2 1 1 - - - - - 4
Overall 2017 21 Barooddoo Myrica
salicifolia 0 4 - - - - - - 4
Overall 2017 22 Ceeka Calpurina aurea 3 0 - - - - - - 3
Overall 2017 23 Hetto Hagenia
abyssinica 0 0 - - - - - 1 1
Overall 2017 24 Agam Carissa edulis 1 0 - - - - - - 1
Overall 2017 25 Koshim Dovyalis
abyssinica 1 - - - - - - 1
Sum 377 260 88 54 21 18 15 12 845
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Figure 2a. Diameter distribution 2012 J. procera Figure 2b. Diameter distribution 2017 J. procera
Figure 2c. Diameter distribution 2012 P. falcatus Figure 2d. Diameter distribution 2017 P. falcatus
Figure 2e. Diameter distribution 2012 O. rochetiana Figure 2f. Diameter distribution 2017 O. rochetiana
54 52
3632
11 10 10
4
0
10
20
30
40
50
60
≤ 10 10_20 20 - 30 30 - 4040 - 50 50 - 60 60 - 70 ≥ 70
Nu
mb
er
of
ste
ms
Diameter class (cm)
Juniperus procera, 2012
50
58
22
31
12 12 94
0
10
20
30
40
50
60
70
≤ 10 10_20 20 -30
30 -40
40 -50
50 -60
60 -70
≥ 70
Nu
mb
er
of
ste
ms
Diameter class (cm)
Juniperus procera, 2017
129
24
4 4 0 0 1 20
20
40
60
80
100
120
140
≤ 10 10_20 20 -30
30 -40
40 -50
50 -60
60 -70
≥ 70
Nu
mb
er
of
ste
ms
Diameter class (cm)
Podocarpus falcatus, 2012
144
38
2 2 1 0 2 10
20
40
60
80
100
120
140
160N
um
be
r o
f st
em
s
Diameter class (cm)
Podocarpus falcatus, 2017
41
54
16
52 2 1 0
0
10
20
30
40
50
60
≤ 10 10_20 20 -30
30 -40
40 -50
50 -60
60 -70
≥ 70
Nu
mb
er
of
ste
ms
Diameter class (cm)
Olinia rochetiana, 2012
21
34
10
51 1
30
0
5
10
15
20
25
30
35
40
Nu
mb
er
of
ste
ms
Diameter class (cm)
Olinia rochetiana, 2017
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Figure 2g: Diameter distribution 2012 A. abyssinicus Figure 2h. DBH distribution 2017 A. abyssinicus
Figure 2i. Diameter distribution 2012 O. europea Figure 2j. Diameter distribution 2017 O. europea
Figure 2k. Diameter distribution 2012 S. theifolia Figure 2l. Diameter distribution 2017 S .theifolia
22
19
6
31 0 0 0
0
5
10
15
20
25
Nu
mb
er
of
ste
ms
Diameter class (cm)
Allophyllus abyssinicus, 2012
20 19
6
31 0 0 0
0
5
10
15
20
25
Nu
mb
er
of
ste
ms
Diameter class (cm)
Allophyllus abyssinicus, 2017
2320
18
8
3 20
2
0
5
10
15
20
25
Nu
mb
er
of
ste
ms
Diameter class (cm)
Olea europea, 2012
23
19 19
8
3 20
2
0
5
10
15
20
25
Nu
mb
er
of
ste
ms
Diameter class (cm)
Olea europea, 2017
28
16
4
0 0 0 0 00
5
10
15
20
25
30
Nu
mb
er
of
ste
ms
Diameter class (cm)
Scolopia theifolia, 2012
28
18
3
0 0 0 0 00
5
10
15
20
25
30
≤ 10 10_20 20 -30
30 -40
40 -50
50 -60
60 -70
≥ 70
Nu
mb
er
of
ste
ms
Diameter class (cm)
Scolopia theifolia, 2017
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Figure 2m. Diameter distribution 2012 R. glutinosa Figure 2n. Diameter distribution 2017 R. glutinosa
4. 4. Frequency, density, dominance and important values index of Chilimo dry
Afromontane forest
The relative (frequency, density, dominance and IVI) for 2012 and 2017 of the studied
natural forest is presented in Table 4. In 2012, the relative frequency was ranged from 18.01
(Juniperus procera) to 0.25 (Allophyllus abyssinicus). Juniperus procera, Podocarpus falcatus,
Olinia rochetiana, Rhus glutinosa and Maytenus gracilipes were most frequent tree species, on
the contrary, Carissa spinorrum and Calpuria aurea were less frequent species. The relative
density in 2012 also ranged from 17.65 for Juniperus procera to 0.31 N ha-1 for Carissa
spinorrum. The relative dominance ranged from 45.55 to 0.01 G ha-1 for Juniperus procera and
Carissa spinorram. The IVI in 2012 ranged from 27.14 (Juniperus procera) to 0.22 (Carissa
spinorrum). The relative frequency in 2017 ranged from 13.24 for Juniperus procera to 0.46
for Sideroxylon oxycanthum. The relative density also ranged from 23.55 to 0.12 % for Carissa
spinorrum and Hagenia abyssinica (Table 4). The relative dominance also ranged from 44.98
for Juniperus procera to 0.01 G m2 ha-1 for Carissa spinorrum.
Table 4. Relative (frequency, density,dominance) and IVI for Chilimo dry afromontane
forest DBH ≥ 5 cm
Species Habit
2012 2017
RF
(%) RD (%)
RDO
(%)
IVI
(%) RF %
RD
(%)
RDO
(%)
IVI
(%)
Juniperus procera Tree 18.01 24.61 45.55 27.14 13.24 23.55 44.98 26.51
Olinia rochetiana Tree 11.41 10.38 8.57 10.17 11.41 9.46 8.51 9.90
2
8
2
5
0 0 0 00
1
2
3
4
5
6
7
8
9
≤ 10 10_20 20 - 3030 - 4040 - 5050 - 6060 - 70 ≥ 70
Nu
mb
er
of
ste
ms
Diameter class (cm)
Rhus glutinosa, 2012
4
13
5
0 01
0 00
2
4
6
8
10
12
14
Nu
mb
er
of
ste
ms
Diameter class (cm)
Rhus glutinosa, 2017
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Podocarpus falcatus Tree 11.41 19.54 8.01 12.62 11.41 22.36 8.42 13.77
Olea europea Tree 10.05 9.16 12.36 10.56 10.05 9.11 12.68 10.61
Maytenus gracilipes Shrub 8.22 4.10 0.80 4.60 8.22 4.14 0.95 4.66
Buddleja polystacha Tree 5.94 3.14 1.13 3.55 5.94 3.19 1.13 3.56
Rhus glutinosa Tree 5.02 2.78 1.99 3.38 5.02 2.76 1.98 3.35
Scolopia theifolia Tree 5.02 5.79 1.65 4.14 5.02 5.21 1.51 3.95
Maytenus addat Shrub 3.20 2.18 0.61 2.05 3.20 2.25 0.55 2.06
Osyris quadripartita Shrub 3.20 0.96 0.15 1.55 3.20 1.30 0.20 1.66
Ekebergia capensis Tree 3.65 0.96 2.27 2.42 3.65 1.42 2.32 2.55
Cassiopourea
malosana Tree 2.28 1.69 0.96 1.68 2.28 1.65 1.00 1.69
Apodytes dimidiata Tree 1.82 0.85 0.39 1.07 1.82 0.83 0.45 1.09
Bersama abyssinicus Tree 1.82 0.60 0.09 0.90 1.82 0.59 0.10 0.90
Erica arborea Tree 1.37 0.60 0.19 0.76 1.37 0.47 0.16 0.71
Ilex mitis Tree 1.37 1.45 5.33 2.70 1.37 1.42 5.37 2.67
Myrica salicifolia Tree 1.37 0.49 0.18 0.73 1.37 0.47 0.22 0.73
Prunus africana Tree 1.37 0.96 2.16 1.51 1.37 0.95 2.22 1.52
Calpuria aurea Shrub 0.92 0.36 0.04 0.47 0.92 0.35 0.05 0.46
Celtis africana Tree 0.92 2.41 2.41 1.84 0.92 2.13 2.45 1.77
Carissa spinorram Shrub 0.46 0.13 0.01 0.22 0.46 0.12 0.01 0.21
Hagenia abyssinica Tree 0.46 0.24 1.57 0.76 0.46 0.12 1.31 0.63
Sideroxylon
oxycanthum Tree 0.46 0.49 0.17 0.37 0.46 0.47 0.18 0.39
Allophylus abyssinicus Tree 0.25 6.15 3.41 4.82 5.02 5.68 3.25 4.65
Sum 100 100 100 100 100 100 100 100
where: RF; Relative frequency: relative Density, RDO: relative dominance: IVI; Important
value index
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4. 5. Above-ground carbon, basal area, and number of stems
Figure 3a-d. Basal area (m2 ha-1) and number of stems (N ha-1) 2012 vs 2017 along alt
gradient, slope, forest patch and land use type
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Figure 3e-h. Number of stems (N ha-1) 2012 vs 2017 along alt gradient, slope, forest patch
and land use type
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The aboveground biomass for the sampled species in 2012 was ranged from 184.62 to
0.23 t C ha-1 for Juniperus procera and Carissa spinnorrum, respectively (Table 4). The basal
area was ranged from 16.15 to 0.06 m2 ha-1 in 2017 (Table 4). The number of stems was ranged
from 250 to 25. The highest number of stems was recorded for Juniperus procera followed by
Celtis africana. While, the lowest number of stems 25 N ha-1 was recorded for Ekebergia
capensis (Table 4).
The basal area and number of stems in the studied forest was significantly varied among
species, forest type and time of measurements. The basal area increased along with an increase
in time and ranged from 25 to 0.36 m2 ha-1 and 29.52 to 0.29 m2 ha-1 in 2012 and 2017,
respectively (Table 4). The 5 thickest trees were: - Juniperus procera, Ilex mitis, Olea europea,
Podocarpus falcatus, Olinia rochetiana and Rhus glutinosa. However, the thinnest trees were:
- Ekebergia capensis, Bersama abyssinicus, Osyris quadripartita and Mayrica salicifolia
(Table, 3). The basal area of Allophyllus abyssinicus, Celtis africana, Ekebergia capensis,
Juniperus procera, Maytenus addat, Olinia rochetiana and Rhus glutinosa decreased along
with increasing in time. On the contrary, the basal area of Apodytes dimidiata, Cassiopourea
malosana, Ilex mitis, Osyris quadripartita, Prunus Africana and Scolopia theifolia also
increased along with increasing in time. More trees belonging to a lower diameter class (Table
3). In addition, larger diameter class at breast height (DBH), low species diversity and density
recorded under higher altitudinal gradients (Figures 4(A,B), 5(A,B). The number of stems
ranged from 475 to 25. The highest number of stems recorded for Juniperus procera followed
by Celtis africana. While, the lowest number of stems 25 N ha-1 recorded for Ekebergia
capensis, Erica arborea and Myrica salicifolia.
4. 6. Growth and yield of eleven selected tree species of Chilimo natural forest
The height, diameter, basal area and volume of the sampled trees is presented in Table 5.
The ANOVA revealed that diameter, height, basal area and volume was significantly varied
among the species at P ≤ 0.05 (Table 6). The total height of the sampled trees varied among the
species. Juniperus procera had the highest height growth followed by Prunus africana.
However, Scolopia theifolia had the lowest height growth. The highest diameter growth
recorded for Juniperus procera followed by Olea europea. The mean annual volume and basal
area increment ranged from 0.330 to 2.338 m3 ha-1yr-1 and 0.007 to 0.47 m2 ha-1 yr-1. The mean
annual volume increment was highest for Podocarpus falcatus and lowest for Ekebergia
capensis. The mean annual diameter increment was highest for Juniperus procera and lowest
for Ruth glutinosa. In addition, the mean annual volume and basal area increment was highest
for Juniperus procera followed by Olea europea. However, the lowest mean annual, volume
and basal area increment observed for Ruth glutinosa followed by Scolopia theifolia.
Table 5. Analysis of variance for growth parameters.
Parameters Factor DF SS MS F - Value Pr> F
Volume 2012
Volume 2017
BA2012
BA2017
Species
Species
Species
Species
10
10
10
10
67.2
81
0.483
0.531
6.720
8.101
0.048
0.053
3.93
6.352
5.47
5.80
3.31e-05***
6.47e-06***
8.2e-08***
2.2e-08***
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Ht2012
Ht2017
Dbh2012
Dbh2017
HtI
DbhI
VtI
BAI
Annual DBHI
Annual HtI
Annual VtI
Annual BAI
Species
Species
Species
Species
Species
Species
Species
Species
Species
Species
Species
Species
10
10
10
10
10
10
10
10
10
10
10
10
7514
6830
26484
25614
95.8
102.5
0.710
0.0014
4.10
3.83
0.028
0.00006
751.4
683.0
2648.4
2561.4
9.581
10.249
0.07
1.42e-04
0.41
0.383
0.003
5.67e-06
14.73
14.67
11.54
11.45
3.35
7.458
7.70
7.77
7.46
3.35
7.70
7.77
2e-16***
<2e-16***
<2e-16***
<2e-16***
0.000288***
2.89e-11***
1.1e-11***
8.43e - 12***
2.89e - 11***
0.000288***
1.1e - 11***
8.43e - 12***
where: Ht: total height, Dbh: diameter at breast height, Vt; volume increment, BA; basal area
and I; increment, *** ; Highly significant at P < 0.01
Table 6. Mean ± standard deviation of the different growth parameters for eleven native
tree species.
Species
Mean Dbh
(cm)
Mean height
(m)
No
(N ha-1)
Basal area
(m2 ha-1)
Volume
(m3 ha-1)
2012 2017 2012 2017 2012 2017 2012 2017 2012 2017
Allophyllus abyssinicus 13.88 14.99 12.11 13.70 106.82 106.82 2.50 2.57 16.85 19.97
Apodytes dimidiata 13.44 15.47 12.48 15.11 43.75 43.75 0.839 0.997 5.761 7.199
Celtis africana 21.6 22.79 15.66 16.90 105 105 9.804 10.715 70.47 82.16
Ekebergia capensis 22.79 23.93 10.5 12.02 40 40 3.899 4.010 34.90 36.55
Juniperus procera 24.59 26.23 16.71 18.69 179.81 179.81 14.06 15.10 157.85 178.02
Olea europea 21.35 22.21 15.44 16.76 88.10 88.10 4.80 5.27 50.22 54.50
Olinia rochetiana 16.77 17.84 14.76 16.1 82.29 82.29 2.89 3.10 28.87 31.87
Prunus africana 26.50 27.98 18.72 20.82 43.75 43.75 0.662 0.695 9.031 9.688
Podocarpus falcatus 8.74 10.68 8.38 10.54 167.39 167.39 2.68 3.10 30.192 34.22
Rhus glutinosa 16.82 17.51 12.77 13.89 50 50 1.48 1.58 9.53 10.61
Scolopia theifolia 9.72 11.05 9.05 11.42 110 110 1.108 1.321 6.377 8.396
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Table 6(continue). Mean ± standard deviation of the different growth parameters
for eleven native tree species.
Species
Average
Diameter
increment
(cm)/yr-1
Average
Height
(m)/ yr-1
Vincrement
(m3ha-1yr-1)
G increment
(m2ha-1yr-1)
Vincrement
(m3tree yr)
BA increment
(m2 tree year)
Allophyllus abyssinicus 0.22 0.32 0.624 0.014 0.0058 0.0005
Apodytes dimidiata 0.405 0.525 0.288 0.0316 0.0066 0.00072
Celtis africana 0.238 0.248 2.338 0.182 0.0104 0.00081
Ekebergia capensis 0.228 0.3045 0.330 0.0222 0.0083 0.0006
Juniperus procera 0.33 0.40 4.034 0.21 0.02 0.0012
Olea europea 0.172 0.264 0.856 0.47 0.0092 0.0006
Olinia rochetiana 0.22 0.27 0.60 0.042 0.0073 0.0005
Prunus africana 0.296 0.418 0.131 0.0066 0.0209 0.0011
Podocarpus falcatus 0.38 0.43 0.81 0.084 0.0048 0.0005
Rhus glutinosa 0.138 0.224 0.216 0.02 0.0043 0.00037
Scolopia theifolia 0.266 0.474 0.404 0.043 0.0037 0.00039
where: Dbh; Diameter at breast height, N: number of stems, ha; hectare,
4. 7. Growth and yield along an altitudinal gradient
Diameter growth of the sampled trees under 3 altitudinal gradient ranged from 5 to 121.5
cm and non significant. Highest diameter growth recorded among the highest altitudinal
gradient, however, the lowest recorded under middle altitudinal gradients. The highest mean
weighted height increment also observed in the highest altitudinal gradient, however, the lowest
was observed in the middle altitudinal gradients.
The weighted mean diameter increment also showed a decreasing trend along with
increasing in altitudinal gradient. The mean annual diameter and height increment also highest
in the lower altitudinal gradient. The mean annual volume increment was showed a decreasing
trend along with increasing in altitudinal gradients.
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(A)
(B)
Figure 5(A,B). Diameter and height growth for the sampled trees along altitudinal
gradient in 2017
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(A)
(B)
Figure 6(A,B). Basal area and volume increment per tree per year along altitudinal gradient
World Scientific News 138(2) (2019) 192-224
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4. 8. The status of saplings, seedlings and shrubs synopsis
The shrubs, saplings and seedlings distribution under Chilimo dry Afromontane forest is
presented in Table 6. The 5 most commonly recorded shrub species were: - Myrsine africana,
Maytenus gracilipes, Dovyalis abyssinica, Carissa spinorrum and Osyris quadripartita. The
number of shrubs ranged from 1150.5 to 3.81 N ha-1 for Myrsine africana and Calpurea aurea,
respectively. The number of stems for Maytenus gracilipes, Dovyalis abyssinicus and Osyris
quadripartite decreased in 2017, while, Myrisen africana, Carissa spinorrum, Rosa abyssinicus
and Gnidia glauca remained constant. The number of stems for saplings ranged from 1230.48
for Podocarpus falcatus to 3.8 N ha-1 for Erica arborea. Podocarpus falcatus, Juniperus
procera, Scolopia theifolia, Bersama abyssinicus and Olea europea had good number of
saplings. While, Allophyllus abyssinicus and Olinia rochetiana had lower number of saplings
(Table 6). A total of 20 species of seedlings recorded into 2 measurement periods. Their number
ranged from 4059.70 to 119.40 N ha-1. In 2012, 3 species had good, 2 fair, 16 poor and 12 no
regeneration. Similarly, in 2012 10 had fair, 5 poor and 14 no regeneration. In 2017, 2 had good,
5 fair, 2 poor, 4new and 16 no regeneration. Allophyllus abyssinicus, Buddleja polystacha,
Cassiopourea malosana, Celtis africana had good regeneration.
4. 9. Seedlings, saplings, and shrubs of native tree species along altitudinal gradient and
slope
The ANOVA for saplings, seedlings and shrubs significantly varied among altitudinal
gradient and slope at P < 0.05. In 2012, the number of saplings for Podocarpus falcatus,
Bersama abyssinicus and Scolopia theifolia were better than others. Podocarpus falcatus and
Juniperus procera under lower and middle altitude, Ekebergia capensis under lower altitude
and Scolopia theifolia and Bersama abyssinicus under middle altitude had good number of
saplings. On the contrary, Rhus glutinosa, Prunus africana and Buddleja polystacha had very
poor number of saplings.
Among the 26 species under lower altitude, 1had fair, 10 poor, 6 new and 9 no
regeneration. In middle altitude, 1 good, 3 fair, 6 poor, 5 new - and 7 no regeneration and in
highest altitude, 5 fair, seven poor, 7 new and 9 no regeneration. Podocarpus falcatus under
lower and upper altitude had good regeneration, Allophyllus abyssinicus, Olea europea and
Scolopia theifolia under lower, middle and higher altitude had fair regeneration. Cassiopourea
malosana, Ekebergia capensis, Olinia rochetiana, Rhus glutinosa and Scolopia theifolia had
poor regeneration. Olea europea under lower, Allophyllus abyssinicus middle and Prunus
africana, Dombeya torrida and Sideroxylon oxycanthum highest altitudes had new
regeneration. On the contrary, Apodytes dimidiata, Buddleja polystacha, Prunus africana under
lower, Juniperus procera (2017), Erica arborea, Hagenia abyssinica highest altitude had no
regeneratiuon.
5. DISCUSSION
5. 1. Species composition, structure and regeneration status of the forest
The present study is investigated the species composition, diversity, growth and
regeneration status of Chilimo dry Afromontane forest along an altitudinal gradient, slope and
species. The total number of tree and shrub species (31) recorded in this study are more or less
World Scientific News 138(2) (2019) 192-224
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in line with the reports of [32] and [10]. However, the number of species recorded under
Chilimo dry afromontane forest is lower than (Kumto dry afromontane forest [33]; Berbere
forest [34] , (170 species), Denkoro forest (174 plant species [35], Dodola forest (113 plant
species [36], Belete forest (157 plant species) [37] and Kimphelafa forest (130 plant species)
[38], Mana Angeto forest (211 plant species [39], Bale mountain national park forest (230 plant
species) [40] and Nechisar national park forest (208 plant species [41], Achera forest (48 woody
species) [42]and Boda dry afromontane forest (95 species) [43], Kumuli dry afromontane forest
(133 woody species) [44] and Tara Gedam dry afromontane forest (143 woody species) [45].
The most dominant trees under Chilimo dry Afromontane forest are: - Juniperus procera,
Podocarpus falcatus, Olea europea, Scolopia theifolia and Allophyllus abyssinicus. In contrast,
Cassiopourea malosana, Carissa spinorrum, Osyris quadripartita, Sideroxylon oxycanthum
and Erica arborea are rare species. Podocarpus falcatus in Chilimo, Juniperus procera in
Gallessa and Gaji are dominant species. Similarly, [10] reported Juniperus procera in Gallessa
and Chilimo and Olea europea in Gaji as dominant species. Hagenia abyssinica and Dombeya
torrida in Gallessa; Ilex mitis in Chilimo are rare species [32]. In the current study, Hagenia
abyssinica is found to be rare and no regeneration, but, Buddleja polystacha and Ilex mitis are
showed some improvements.
The higher tree species diversity and richness in the middle elevation gradients might be
due to better microclimate condition and favorable temperature. The lower biomass, diversity
and dominance in the lower and higher altitudinal gradient is also related to anthropogenic
disturbance. In line with, similar reports is also reported by [10, 15, 46] and [47]. In addition,
[33] found high species diversity in the middle altitudinal gradient in Kumto dry Afromontane
moist forest of Eastern Wellega zone, West Ethiopia. The differences in species richness arises
from altitudinal differences, climatic conditions and anthropogenic effect. But, the diversity
index of Chilimo forest is higher than Boda forest with the overall, diversity and evenessof 1.79
and 0.09 [43].
The tree density and basal area of Chilimo forest is lower than other tropical forests (685
- 820 tree ha-1) and (18.9 to 19.58 m2 ha-1), tropical semi - evergreen forest (34 to 610
individuals ha-1) and (7.81 to 98.58 m2 ha-1) tropical wet evergreen forest [48]. The Shannon
diversity index of this study is 0.5 to 2.21 in line with 1.5 to 3.5 recommended by [49] but lower
than tropical semi evergeen forest of Mizoran [50] Achera forest ( H’ was 3.37) [42].
The diameter distribution of Chilimo forest is found to be an inverted J shaped
distribution. This is might be due to a big number of stems shrubs, small sized tree species and
younger individuals of big sized tree species, too. Regarding the forest profiles few tree species
in the tree layer has contributed to most of the total dbh of Chilimo forest. These are Juniperus
procera, Olinia rochetiana, Podocarpus falcatus, Olea europea and Maytenus gracilipes
(65.45 %). Similar results are also reported by Shambel Bantiwalo (51). According
toLamprecht [23] the normal basal area of virgin tropical forest in Africa is 23 - 37 m2 ha-1.
Tree height value is also higher in the lower class and decreased in the higher class.This is also
true for other forests too [42].
This revealed that the forest is also suffered from selective cutting, this result smaller to
medium sized individuals attributed to high rate of regeneration but low recruitment. Similar,
results are also reported in Koto forest [33]. The DBH distribution of Chilimo forest is in line
with Tara Gedam dry Afromontane forest [45], Kumli forest [44], Indian forest [52], forest of
North East India [53] and [54]. The reverse J - shaped population curve of trees suggests an
evolving or expanding population, climax or stable type of population in forest ecosystems
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indicating that the forest harbors a growing and healthy population [58], [56] and [59]
(Parthasarathy and Karthikeyan 1997; Mishra et al. 2005; Sahu et al. 2012). Among the most
dominant tree, species Juniperus procera and Podocapus falcatus showed an inverted J shaped
distribution, Juniperus procera represented in all the diameter class, while, Podocarpus
falcatus, in lower diameter class. Similar results are also reported by [43] for Boda forest of
western Shewa, but Chilimo forest has lower basal area than Boda forest 114.64 m2·ha-1
reported by [43]. The lower value of IVI of the Chilimo forest indicating that majority of species
are rare species. This attributed to different density dependent and density independent factors
such as competition for nutrients, poor seed dispersal and germination.
The regeneration potential of the species under Chilimo dry Afromontane forest varied
along altitudinal gradient, slope and species. This is might be due to differences in climatic
condition and disturbance level. Podocarpus falcatus had good regeneration potential under
lower altitude, while, Juniperus procera under highest altitude. Hagenia abyssinica and
Apodytes dimidiata represented by few individuals. In addition, among the endemic species
Rhus glutinosa is a threatened and vulnerable species as mentioned by [9] and [10]. Rhus
glutinosa showed a U shaped distribution pattern due to lack of trees in the upper and lower
diameter classes.
Podocarpus is represented by more number of seedlings an indicative of excellent
recruitment which also reflects the prevailing environmental conditions. This entails high biotic
potential of the species which may be supported by existing environmental conditions. Similar
trends are also reported for Gedho dry Afromontane forest of West Shewa zone [57] and Tara
Gedam forest at South Gondar Zone, NW Ethiopia [45]. Trees and saplings densities varied
significantly among species, Podocarpus, showed the highest tree and sapling density.
Podocarpus is also the dominant tree species in dry Afromontane forest in Ethiopia [6]. The
population density of Podocapus falcatus in Chilimo is higher than Herenna forest [58] and
Dindin [59] Wef - Washa [60] and Menagesha - Suba state forest [61].
In 2017, the number of saplings for Podocarpus falcatus, Juniperus procera, Scolopia
theifolia, Bersama abyssinicus, Olea africana, Allophyllus abyssinicus and Olinia rochetiana
decreased, due to higher disturbance. While, the number of saplings for Ilex mitis, Cassiopourea
malosana, Prunus africana, Sideroxylon oxycanthum and Erica arborea remained constant.
Among the thirty - one sampled species in 2012 (38.70 %) 45.11 % in 2012 no regeneration, so
these species either they produce non - viable seeds or there might be some problems of
regeneration.
The differences in density of seedlings and saplings among the three forest patches might
be due to difference in biotic and abiotic factors [62], i.e. variation in site conditions,
disturbance level, species colonization and ecological properties [63] and [31]. Maytenus
gracilipes, Olea europaea, Podocarpus falcatus, Scolopia theifolia, Allophyllus abyssinicus
and Bersama abyssinica are among shade - tolerant species [32] and [9]. Seventeen % of the
tree species had no regeneration, this is might be due to high anthropogenic disturbance, animal
trampling and poor biotic potential of tree species.
Moreover, 7 species contributing 22.58 % of tree species where new arrivals are very
poor and have been felled by locals but seed remains as seed - bank and germinate during the
favorable season. The ratio of the seedling to mature individuals is 2.85 : 1, the ratio of the
seedling to saplings is 16.04 : 1 and saplings to mature individuals is 0.35 : 1. Juniperus procera,
Olinia rochetiana, Podocarpus falcatus, Olea europea and Maytenus gracilipes (65.45 %) have
contributed to major portion of the total dbh of Chilimo forest. Juniperus had individuals almost
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in most dbh classes indicating both good regeneration and good recruitments. While, Apodytes
dimidiata, Juniperus procera and Olinia rochetiana had poor regeneration and good
recruitment. Prunus africana indicating both poor regeneration and poor recruitments.
The data analysis revealed that the density value for seedling and saplings of the
population structure of the forest are high compared to the structure of individuals and agrees
with the normal patterns of the population. This implies the need to develop and implement
forest management regimes in the area in order to promote healthy regeneration. The less
number of sapling individuals as compared to seedlings implying the death of most of the
seedlings before reaching the sapling stage due to human intervention, browsers, grazers and
nature of the seeds. [64] reported that seedling recruitment is a block in the population dynamics
of many species of trees.
It is one of the most important factors in determining the local abundance of adult trees
and this calls for an urgent conservation strategy. Hence, those species that don’t have seedling
and sapling and species represented by only seedlings are grouped under priority class I. Others
whose seedling density is between 1 and 10 are categorized under class II and the remaining
species under class III. The species under priority class I should get the first priority due to lack
of seedlings and then followed by class II that are represented by a few seedling individuals.
Subsequently, for the sake of conservation endeavors, the third group is also recommended to
be given the appropriate conservation priority.
5. 2. Growth and yield of the most common native tree species
The mean annual volume increment of Chilimo forest is better than reported for dry
evergreen Afromontane forest for lowland and dry forest estimated to 1m3 ha-1 yr-1 and volume
of about 100 m3 ha-1 [65] and [66]. Moreover, mean annual increment of Chilimo forest is also
higher than Acacia- Commiphora woodland (0.0015 m3ha-1yr-1) with the standing volume of
about 6.5 m3·ha-1 and desert and semi-desert scrub and evergeen scrubs [66]. The number of
stems for Chilimo forest reduced due to selective cutting is also true for other evergreen
Afromontane forests too [66-68]. The mean annual increment of Celtis africana and Olea
europea in the present study is 2.34 and 1.013 m3 ha-1 yr-1 is in line with the mean annual volume
increment of the native tree species under natural forest [69], [70] and [71]. The mean annual
volume increment of Chilimo forest is in line with other dry Afromontane forests found in
Ethiopia in different locations [72] and [73].
The low MAI for the other species is might be due to lower number of stocks as a result
of illegal logging [23] and [74]. Our results are also in line with the reports of other dry
Afromontane forest of North Western Ethiopia by Sisay et al.( 73) reported a volume increment
rate of 3.5 m3 ha-1 (Gelawdiwos dry Afromontane forest), 3.6 m3 ha-1 (Katassi dry Afromontane
forest) and 1.0 m3 ha-1 (Taragedam dry Afromontane forest) with volume growth.
Thus, the research finding is very important for sustainable management of the species.
Consider as a remediation measure to reduce illegal cutting and pressure on Chilimo dry
Afromontane forest, the mean annual increment of Juniperus procera in Chilimo area is also
found to be 4.223 m3 ha-1 yr-1 in line with the reports 0.5 to 5.65 m3ha-1 yr-1 for high forests
[70]. In general, the number of forest growth models for tropical rain forests is few due to the
complexity of these forests. While, such systems are common in many parts of the world [5].
Moreover, Ethiopia has no standardized forest inventory system in place and increment
rates of the limited remaining system areas available. This makes sustainable forest
management and harvesting difficult or even impossible.
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6. CONCLUSIONS
A total of 31 trees and shrubs representing 25 families were recorded, 20 (64.52 %) were
trees and 11 (35.48 %) were shrubs. There of 28, 23 and 26 species under highest, middle and
lowest altitudinal gradient were recorded.The most dominant tree species were: - Juniperus
procera, Podocarpus falcatus, Olea europea, Scolopia theifolia and Allophyllus abyssinicus.
The species composition, diversity, abundance, dominance and important value index
significantly varied among species, altitudinal gradient and slope. The diameter distribution
was an inverted J - shaped distribution pattern. The highest species richness and diversity index
were found under middle altitudinal gradient, while, the lowest species richness and diversity
index were found under the highest altitudinal gradient. Juniperus procera and Podocarpus
falcatus had an inverted J shaped distribution while Allophyllus abyssinicus and Scolopia
theifolia had U shaped population distribution pattern. The aboveground biomass was ranged
from184.62 to 0.23 t C ha-1 while the basal area was ranged from 16.15 to 0.06 m2 ha-1 and the
number of stems was ranged from 250 to 25. The structure and regeneration status of Chilimo
forest was deteriorated within the last 9 years. The MAI of the forest was ranged from 4.22 to
0.23 m3 ha-1yr-1 and the basal area increment was ranged from 0.85 to 0.020 m2 ha-1yr-1. In 2012,
3 had good, 2 fair, 16 poor and 12 no regeneration, while, in 2017, 10 species had fair, 5 poor
and 14 no regeneration. Allophyllus abyssinicus, Buddleja polystacha, Cassiopourea malosana,
Celtis africana had good regeneration, while, Hagenia abyssinica had no regeneration. There
is no forest management in the study forest either to increase productivity or yield, thus,
attention should be given in these regards. Awareness creation and training should be also given
for local people and integration of their indigenous knowledge to manage the forest. I suggest
implementation of sustainable forest management practices.
ACKNOWLEDGEMENTS
The authors' thanks Genene Tesfaye, Central Ethiopia Environment and Forest Research Centre, for assisting us
in field data collection and preparation of plant and soil samples, Mossissa Kebede from Oromiya Forest and
Wildlife Enterprise. The Swiss Government Excellent Scholarship programme is also highly acknowledged for
funding Mehari A. Tesfaye's fellowship and the Ethiopian Environment and Forest Research Institute (EEFRI),
headquarter, for covering the cost of fieldwork and laboratory analysis.
BIOGRAPHY
Mehari Alebachew Tesfaye born on 14 March 1978, Gojjam (Dangila), Ethiopia working as a senior researcher in
Ethiopian Environment and Forest Research Institute, Addis Ababa from 2002 to present. He awarded his Post
Doc International Forestry and Climate Change Bern University of Applided, Switzerlands (2018), PhD degree in
Sustainable Utilization and Conservation of Forest system, University of Valladolid, Spain (2015), MSC degree
in Environmnetal science, Addis Ababa University (2006), BSC degree in Forestry from Alemaya University
(1997). He published more 30 articles in local, regional and international peer reviwed journals.
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