· . _ Reports .

ing or gleaning) of bees on flowers ofMyrtaceae depends on the morphology,polIen quantity and floral display, andalso on the specific behavior ofbees .•

References and notes

1. Proença CEB, PE Gibbs 1994 Reproduc-tive biology of eight sympatric Myrtaceaefrom Central Brazil. Neli' Phytol 126: 3·D-354

2. Rodrigues RR, LP Morellato, CA Joly, HFLeitão-Filho 1989 Estudo florístico efitossociológico em um gradiente alritu-dinal de mata estacional mesófila serni-decídua na Serra do Japi, Jundiai, SP. ReliBras BOI 12: 71-84

3. Peixoto AL, A Gentry 1990 Diversidade ecomposição floristica da mata de tabuleirona Reserva Florestal de Linhares (EspíritoSanto, Brasil). ReI' Bras BoI 13: 19-25

4. Proença CEB 1992 Buzz-pollination-older and more widespread than we think?J Trop Ecol 8: 115-120

5. Buchmann SL 1983 Buzz pollination inAngiosperms. p 73-113. 111 Handbook 0/exp erim eu t a l pol linoti on bi ol ogv. CEJones, RJ Little cds, Va n NostrandReinhold Co. NY

6. Oliveira PE. M Sazima 1990 Pollina-tion biology of two spccics of Kielmeyera(Guttiferac) from Brazilian cerrado veg-etation. Plalll S,'S E\'(J/ 172: 35-49

7. Goodland R 1971 A physillllomic analy-sis of the cerrado vcgctation of centralBrazil. J Ecol 59: 411--119

8. Landrul11 LR 1982 Thc dcvcloprnent ofthe fruits and suds 01' C,IIIIWIIIOll(!sio(Myrtaceac). Britt o niu ~4: 120-224

9. Rotrnan AD 1976 Rcvision dei géneroCam po m an csi a cn Ia Argentina(Myrtaceac). Dorwiniu na 20: 327-340

10. Radford Ar:, WC DiL'kSllll . .I R Massey.CR Bell 1974 Va.\'(,II/"I' 1'/"111 systeniat-ics. Harper & Row, NY

I I. Ruiz TZ. MTK Arroyo 197X Rcproduc-tive ecology of a sCClllldary dcc iduousforest. Biotropica 10: 22 I-230

12. Faegri K. VI) Pijl 1979 Thc principles (4"polli nat ion ccologv. I'crgamon Press.Oxford

13. Sazirna I, M Sazima 1989 Mamangavase irapuás (Hyrnenopt er a, Apoidea):visitas, interações e consequências para apolinização do maracujá (Passifloracea).ReI' Bras Entomol 33: 109-118

14.Inouye DW 1980 The terminology offloral larceny. Ecology 61: 1251-1253

15. Roubik DW, lE Moreno. C Vergara, DWittmann 1986 Sporadic food compe-tition with the African honeybee: pro-jected impact on ncotropical social bees.J Tro/ Ecol 2: 97-1 I I

16.Acknoll'/edgemellls: We thank CEBProença for a stimulating discussion onbuzz pollination, and commenting on themanuscript; to R Marquis, PE Oliveira.B Triplehorn and three refcrees for sug-gestions on the paper; I Sazima and MSaz ima for initial stimulation, and thestaff of Fazenda Campininha for accessto the cerrado area. K Dei-Claro receivedfinancial support from the CNPq(352030/96-8)

Reccived O I February 1996Accepted 10 July 1997

Drought patterns in the Brazilian Amazon:Application to fire risk mappingt

r(

ELSON D. DA SILVA

Empresa Brasileira de Pesquisa Agropecuária, EMBR;//~·1. Núcleo de Monitoraniento Antbientale de Recursos Naturais por Satélite. NMA. Campinas, SP /3088-300. Brasil

The assessment of fire danger is critical to environmcntal management in the Amazon. Pre-cipitation data were assembled from 212 climate stations spread throughout the BrazilianAmazon. Using a GIS, maps were constructed showing the spatial patterns of precipitationand drought. Then, these maps were crossed-referenced with vegetation cover to create firerisk categories. Using this approach, 38.1 % of the Brazilian Amazon was classified in thelow fire-risk category, either because of a wet, low-seasonal climate (10.0%) and/or be-cause of the presence of closed-canopy evergreen forcst with the longest droughts less than75 continuous days (32.8%). Forty-one percent of thc Brazilian Amazon was placed in the

Correspondence to: EIson Dias da Silva, Empresa Brasileira de Pesquisa Agrop~Cllúria. EMBRAPA, Núcleo de Monitorarnento Ambiental e deRecursos Naturais por Satélite, NMA, Av. Dr. Júlio Soares de Arrudu 803. Parque São Quirino, Campinas. SP 13088-300, BrasilE-mail: silva@nma.embrapa.br

284' Ciência e Cultura Journal of the Brazilian Association for the Advancement of Science

............. Reports ' .

moderate fire risk category, owing to their more open vegetation cover (intermediate be-tween closed-canopy evergreen forest and savanna) and association with .anthropogenic ac-tivities in the region. Maximum drought disclosed by weather stations with over 10 years ofdata collection showed that 41.7% of the Brazilian Amazon has suffered drought for morethan 75 days. Dense evergreen forest was classified as moderate risk in 13.50/0 of the area.The remaining 20.9% of the Brazilian Amazon was rated in the high fire-risk category. Thevegetation in the latter areas is savanna or droughts are long and frequento In the southernand northern borders of the basin rainfall may be as low as 1000 mm/year. An estimated35.8% of the Brazilian Amazon receives < 2000 mm of rainfall each year. The driest regionsreceive an average < 1 mm/day of rain during the driest quarter of the year. Approximately ,48% of the Brazllían Amazon falls into this category. In general, human presence increasesfire susceptibility in the Amazon because man frequently replaces closed forest formations(low fire risk ecosystems) with low, open vegetation (fire prone vegetation).Assessoramento ao risco de fogo é critico parao manejo ambiental da Amazônia, Dados deprecipitação de 212 estações meteorológicasda Amazônia brasileira foram usados nesteestudo. Mapas que mostram padrões espaci-ais de precipitação e de seca foramconstruidos usando técnicas de sistemas deinformações geográficas. Então, estes ma-pas foram cruzados referencialmente commapas de vegetação para criar categoriasde risco ao fogo. Usando este procedimento,foi classificado 38,1% da Amazônia brasi-leira na categoria de baixo risco ao fogopelo fato de ser úmida, ter clima poucoestacional (10,0%), e/ou pela presença de

Forestfires have been a constantconcern in the temperate zoneduring recorded history (1). Thehumid tropics, and the Amazon,

in particularly, have generally been re-garded as a rainforest immune to fire.However, the Amazon basin encom-passes an immense area with very vari-able rainfall patterns (from 1000 mm to4100 mm/year) and a rich order ofveg-etation types (from tall, dense, ever-green forest to open savanna). Fires arecommon in savanna regions in the Ama-zon but fire events decrease as canopycover thickens and rainfall increases.Thus, while humans reduce canopycover and provide ignition sources, oc-currence of fire is increasing through-out the Amazon (2,3).

A prerequisite for any fire is fuel.In general, Amazon ecosystems arerich in organic matter, fuel is rarely lim-iting. However, fuels will only burn ifthey are dry enough for combustion,and fuel drying depends on the micro-c1imate. Canopy height and canopydenseness are critical to the fuel dry-ing processo A high, closed canopy

Volume 50(4)' July/August 1998

floresta com copa fechada com períodosmáximos registra dos de seca menores de 75dias (32,8%). Cerca de 41,0% da Amazôniabrasileira foi classificada como tendo riscomoderado ao fogo, pela vegetação de copasmais abertas (vegetação intermediária entrefloresta densa e s av an a) e atividadesantropogênicas na região. Secas máximasocorridas nas estações com mais de 10 anosde coleta indicaram que 41,7% da Amazô-nia brasileira já teve secas com mais de 75dias. A floresta densa foi classificada comosendo de risco moderado ao fogo em 13,5%da área. O restante 20,9% da Amazônia bra-sileira foi classificada como sendo de alto

acts as a microc1imate buffer - radia-tion is received and processed highabove the ground and the fuel-rich for-est floor frequently remains humid andfire resistant. When canopies are openanellor low, radiation processing occursclose to the fuel layer. As the groundlayer warms, the drying power of theair increases (rise in vapor pressuredeficit) and with the fire risk (3).

Time is necessary for the dryingprocesso Therefore, the presence ofrain-free periods (e.g., more than 10days) (3) is a key determinant ir. the cre-ation offire conditions in the Amazon,as in temperate regions.

Data on climate, vegetation, and fu-eIs have been used in the developmentoffire warning systems (4,5,6). This re-search from the temperate zone suggeststhat the length and characteristics ofdrought periods are much more impor-tant than absolute annual rainfall in pre-dicting fire occurrence because of thedry season patterns (7).

Our study was undertaken to de-velop techniques to analyze droughtdistribution and duration in Amazon

risco ao fogo. Isto ocorre pelo fato do tipo devegetação ser savana e/ou secas prolonga-das serem muito freqüentes. Nos extremos sul-e norte da bacia, as chuvas se reduzem a até1000 mm/ano. Foi estimado que 35,8% daAmazônia brasileira recebe < 2000 mm/ano.As regiões de estiagem mais intensas rece-bem menos de 1 mm/dia durante o trimestremais seco do ano. Cerca de 48% da Amazô-nia brasileira foi classificada nesta catego-ria. Em geral, a presença humana aumentaa suscetibilidade ao fogo na Amazônia pelafreqüente transformação da floresta densavirgem para vegetação aberta e baixa (ve-getação suscetível ao fogo).

and to join this information with veg-etation data to construct a fire risk mapfor the Brazilian Amazon.

The Amazon hydrologic basincovers around 6.1 million km- with theBrazilian ~ortion occupying about 4.9million km . This area inc1udes the wholeof the states of Acre, Amapá, Amazo-nas, Pará, Rondônia and Roraima; andpart of Goiás, Maranhão, Mato Grossoand Tocantins states. We used datafrom 212 weather stations spreadthroughout the Brazilian portion of thebasin: 135 of these weather stationswere operated by DNAEE (Departamen-to Nacional de Águas e EnergiaElétrica); 56 by INEMET (InstitutoNacional de Meteorologia); 8 by IDESP(Instituto de Desenvolvimento Econô-mico e Social do Pará); 6 by ELETRO-NORTE (Centrais Elétricas do Norte doBrasil); 5 by EMBRAPA (EmpresaBrasileira de Pesquisa Agropecuária)and 2 by DEPV (Diretoria de Eletrônicae Proteção ao Vôo do Ministério daAeronáutica).

Obtaining reliable estimates is par-ticularly difficult when the areal cover-

Ciência e Cultura Journa/ of lhe Brazillan Assoc/atlon for lhe Advancemenl of Sc/ence' 285

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age provided by the surrounding sta-tions is sparse or when precipitationcharacteristics vary greatly with loca-tion. Hevesi et aI (8) anaIyzed rainfalldistribution in southem Nevada andsoutheastem Califomia, USA, and hadto use the length ofrecord ranging from2 to 53 years of 62 gaging stations. Inanother study by Hevesi etaI (9) in thesame are a, the Iength of record variedfrom 8 to 53 years for 42 precipitationstations.

Most of the Amazonian weatherstations are in developed regions in theeastem and southern part of the basin.ln the central portion of the basin, theweather stations are usually near theriver margins, where hurnan communi-ties have developed because ofthe rivertransportation systems. The selectionof the weather stations for this studywas aimed at gaining even coverage ofthe Brazilian Amazon (Fig. 1). Someweather stations outside the basinwereused to reduce error related to extrapo-lation. lnitially, it was decided to onlyuse stations with at least eight years ofcomplete data (not necessarily in con-secutive years). However, in the finalphase ofthis study this requirement wasrelaxed to a minimum of four years toinclude data from underrepresented ar-eas. Fifty-four ofthe 212 weather sta-tions used had less than 8 years of data.Of these, 19 provided 7 years of data

(stations with only 4-6 years of data arenoted in Figure I). The average numberof years of data per station, consider-ingall212 stations, was 10.3 (sd= 6.3).Most ofthe data (87%) were from theperiod 1970-1987. All databases weremeticulously checked for possible col-lection errors and any suspected differ-ent value was compared with results inthe same year in the neighborhood sta-tions. Abrupt changes in climate param-eters are supported by more than oneweather station in the neighborhood.

The following were determined foreach station: I) Mean of annual pre-cipitation; 2) mean of percentage ofdays of each year that were part ofdroughts with a duration ~ 10 days; 3)mean of rainfaIl in the driest quarteryearIy and 4) the longest drought reg-istered in the weather stations with atIeast 10 years of data (only 94 stationswere used for this variable). Climatemaps were produced using the inversedistance weighted interpolation routine(10). The map projection used wasUTM.

Using data from ProjetoRADAMBRASIL (1973-1984) it waspossible to develop a simplified vegeta-tion map with six main vegetation types.These six groupings were further re-duced to the following three classesthat have an important significance forfire mapping: I) Dense, closed-canopy

..;z,·~;7~,~";~,;~~i.;~~~~{~8~~~~i2~';;~;'J.%Y-',,~~~:,;:;j3;~~;;~.,,~?:'t'. 6::ttt'W:::~.a~:;:~:,,5à·1t:~~"·:~;?:::"2',,·: 44~~t'~~:~;"/:~1:-//~',:'~~" ..;.;",./ ..

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4':~.;;:.;~~:!::..:tJ~+i"7~j-'~:7.'--tf.;::-:t::;::,-~7.7t~~H*~~;::;'+'·â~i}~i.;,~r:~.\f.:.

~.ol .; .•.•••••(,.0.1.

,'Úg...o, ~':";":::";'::";'''''':''''+~~JfciiíclôJ:iJã''':T-t:::-r~~~~~~~~'Ú!;'~~''

Figure 1.' Location o/lhe 212 climate stations in lhe Brazilian Amazon used in this study.

286· Ciência e Cultura Journal of the Brazilian Association for the Advancement of Science

evergreen forest; 2) "intermediate" in-cluding open-canopy vegetation, de-ciduous and semi-deciduous forest,secondary forest, capinarana (humidscrub forest), ecological tension and an-thropogenic areas and 3) savanna (char-acterized by sparsely scattered trees ina grass matrix). Areas of savanna alteredby man were not reported as anthropo-genic areas by Projeto RADAMBRASIL.Vegetation maps were overIapped withclimate maps using ldrisi (10) to demar-cate areas showing its potential fire risk,

Rainfall and drought patterns

The vegetation cover types of Amazonare varied. Based on our grouping ofProjeto RADAMBRASIL (11) vegeta-tion data, it was estimated that 37.9% ofthe Brazilian Amazon is covered byclosed-canopy forest, 41.2% is coveredby "intermediate", open-canopy vegeta-tion types, and 20.9% has savanna cover(Fig. 2). Closed canopy forest is mostabundant in the central portion of thebasin; open canopy forest, consistingof a variety of forest formations, is com-mon to the south and north ofthis cen-tral core, and savanna is concentratedin the southem and eastem portions ofthe basin.

There are also great differences inthe spatial distribution ofrainfall in theBrazilian Amazon. ln the wettest regions(e.g. Upper Rio Negro and mouth oftheAmazon river) rainfall can approach4000 mm/year. Nevertheless, in thesouthern and northern borders of thebasin rainfall may be as low as 1000 mmIyear. An estimated 35.8% ofthe Brazil-ian Amazon receíves s2000 mm of rain-fall year1y (Fig. 3) and 2.4% receives s,1500 mm yearly.

Essential to fire mapping is a knowl-edge of spatial pattems of dryness. Anaverage rainfall/day during the driestquarter of the year was used as a firstmeasure of dryness (Fig. 4). The driestregions ofthe Brazilian Amazon receive< 1 mmlday ofrainfall, and/or <20% oftotal rainfall, during the driest quarterofthe year. Some 48% ofthe BrazilianAmazon fits in this category. By con-trast, in the wetter are as of the basin,average daily rainfall during the driestquarter ofthe year is > 3 mm. These re-

Volume 50(4). July/August 1998

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. . . . . . . . . . . . . . . . . . . . . . . . . ,Reports

021.0

0NJ 6.0

mJ 5.0

Anthropogen. 11I 7.4

.21.5100 km

• Evergreen Forest• Humid Sorub Forest

• Biomass decore ases downwardin lhe legend above.

Figure 2. Vegetation types and distribution in the Brazilian Amazon.

Rainfallmm/year

1000 - 1500 O1500 - 2000 O2000 - 2500 6'32500 - 3000 ~3000 - 3500 ~3500 - 4000 •

Figure 3. Distribution of annual rainfall in the Brazilian Amazol/.

mm/d

0.0 - 0.1 D1.0 - 2,0 D2.0 - 3.0 D3.0 - 4.0 [2]...4,0 - 5.0 ~5.0 - 6.0 tml6.0 - 7.0 11I7.0 - 7,5 •

Figure 4. Average daily rainfall during the driest quartel' of lhe year in the Brazilian Amazon.

Ciência e Cultura Journal of lhe Brazilian Association for lhe Advancemenl of Science· 287Volume 50(4) • July/August 1998

gions of re1ative1y even rainfall distri-bution throughout the year represent14% ofthe Brazi1ian Amazon.

The second measure of drynessused is the percentage of days in theyears that are part of droughts exceed-ing 10 days in 1ength. Using this mea-sure, it was found that weather stationsvaried from having 1,2 to 58.0% oftheirdays assigned to drought periods (Fig.5), On an aeria1 basis it was calcu1atedthat 66,7% ofthe Brazilian Amazon hasat 1east 20% ofthe days (73 days) beingpart of drought periods yearly (:2: 10 con-secutive rain1ess days) and 61.2% ofthis portion has a1ready experienced asing1e drought period of more than 75days,

The third measure of dryness thathe1ped in the screening process was themaximum drought experienced by theweather stations reporting at 1east 10years of data, The range ofthe data var-ied from 13 days to 242 days. It was cal-cu1ated that 41,7% ofthe Brazilian Ama-zon has undergone > 75 days of droughtand on1y 2.4% ofthis area did not havemore than 20% of the days (73 days)yearly totalling rain1ess periods > 10days. In addition there was some voidof weather stations, therefore the sur-face interpo1ation used the 8 neareststations to cover these areas (Fig. 6) .This happened because sorneweatherstations did not have data enough tofu1fill the requirements in this ana1ysis .

. It is expected that the accuracy of firepotentia1 is higher in the more deve 1-oped regions that a1so have moreweather stations collecting data. Analy-sis of corre1ation between maximumdroughts and the percentage of days inthe year that are part of droughts ex-ceeding 10 days in 1ength showed a cor-re1ation coefficient ofr= 0.84 (t= 468.9),maximum drought and rainfall in the dri-est quarter yearly showed a corre1ationcoefficient ofr= -0.82 (t = -431.2).

Fire map

Of the Brazi1ian Amazon 38,1% wasclassified in the 10w tire risk category,41.0% in the moderate fire risk category,and the remaining 20.9% in the hightire risk category (Fig. 7). Regions inthe 10w risk category initially met one .

.1

/-----------------------zilian Amazon can be classified in thelow fire risk category at present (Fig. 8).

The remainder of the BrazilianArnazon (61.9%) was placed at moder-ate or high fire risk (Fig. 8). Areas thatwere not protected by climatic condi-tions and have a vegetation intermedi-ate between dense forest and savanna(41.2% ofthe Brazilian Amazon) wereplaced in the moderate fire risk category,41.0% and 12.4% of this area havingclosed canopy forest. Areas with sa-vanna, 20.9%, were classified as highfire risk. This map should stress firesusceptibility of existing vegetation. Alow fire risk area can become a moder-ate or high fire risk area through con-version to pasture or agriculture.

. . . . . . . . . . . . . . . . . . . . _Reports .

% 01 days indrought periods

~10days

00 - 10 •10 - 20 111II20 - 30 ml30 - 40 82140 - 50 [J50 - 60 D100 km

Figure 5. Percentage of the days of the yeal" that are part of drought periods é: 10 days in theBrazilian Amazoll.

Droughtdays

000 - 050 D050 - 075 @Sl075 - 100 gJ100 - 150 1'&1I

100 km 150 - 200 •O Climate Stations 200 - 250 •

Figure 6. The maximum drought registered in the weather stations having 10 :? years of data.

or more ofthe following conditions: 1)An average daily rainfall in the driestquarter of the year greater than 4 mm!day (the evaporation rate is around 4mm!day) (12); 2) less than 10% ofthedays of the year being part of droughtsthat exceed 10 days (approximate timenecessary for fuels to dry to combus-tion leveI in open canopy ecosystemsof Amazon) (3). Regions oflow fire risk,based exclusively on these climaticconsiderations, occupy 10.0% of theBrazilian Amazon (4.9% in closed-canopy forest and 5.1 % in are as of"in-termediate", more open canopy veg-etation).

Areas of closed canopy, ever-green forest (37.9%) were consideredto be almost immune to fire (low firerisk) because closed canopies maintaina moist microclimate in the understorypreventing fuel drying (3). Even forclosed canopy under long drought, theunderground water reservo ir can belimiting in supplying water, so thisclosed canopy forest under more than75 days of drought was considered asmoderate risk. It was found that 13.5%ofthis are a of dense forest has experi-enced more than 75 days of drought.The joining of climate and vegetationcriteria suggests that 38.1 % ofthe Bra-

288. Ciência e Cultura Journal ofthe Brazilian Assoclatlon for the A5fvancement of Scienca

lncharacterizations ofthe Amazonianclimate, the spatial arrangement of

dryness in the region is emphasized. Itmight be the first study of the Amazo-nian climate that specifically focuses onspatial patterns of dryness and distri-bution ofrain-free periods. Droughts often days or more are common: 90% ofthe Brazilian Amazon experiences atleast two such droughts, on the aver-age, each year. And 41.7% ofthe Brazil-ian Amazon has already registered atleast one drought exceeding 50 days.Even prolonged droughts, more than 100days, are likely to occur in 14.7% ofthearea considering as the maximum occur-rence of each weather station reportingmore than 10 years of data. Droughtevents of long duration are most com-mon in the eastern and southern por-tions ofthe Brazilian Amazon and, there-fore, coincide with the regions wheredevelopment pressure is the greatest(see Fig. 6).

The vegetation of the Amazon re-sponds to these drought events by re-ducing leaf surfaces: Litter fall fre-quently increases during drier periodsofthe year in the Amazonian evergreenrainforest (13). A second response toprolonged dry periods is to extend rootsystems deep into the soil. Working atParagominas in the eastern Amazon,Nepstad et al (13) have found that theforest root system extends beyond 10m. Then, at this soil depth water wouldbe available to plants year round.Paragominas in our data reports the an-

Volume 50(4)· July/August 1998

=

CSAMEi.D --lih ; 'e-H2S+!,'CC •.§!" + as CiW44J1jwsw!p'm;:&i@i(4lijIl9!JJIlUliSit8!iitJWi'J'fbl&!&!ttB!4

............................ Reports .....

• Low Fire Risk 38.1 %

o Moderate Fire Risk 41.0%

ml High Fire Risk 20.9%

Figure 7. A fire map of lhe Brazilian Amazon showing areas that are at low, moderate or highfire risk.

.t -v-, • " O'"

Yes _Low tire risk 7.6 %(7.6%)

<10%otdays ot yearpar!01draughts

>10days." Iong

. YesLow tire risk 10.0 %(9.6%)

(37.9%)32.8%

(58.3%)

Yes

'.

Yes(20.9%)

,.';,..• t';

..",

Figure 8. The model used 10 develop lhe fire rating map for lhe Brazilian Amazon.

nual rainfall of 1802 mm/year, 0.84 mm/day in the driest quarter, and has alreadyexperienced maximum droughts > 75days.

While the Amazon flora of ever-green forest is effective in avoidingdrought, it is not resistant to fire.Through an examination ofbark tissuesand the application of simulated tires,Uhl and Kauffman (3) estimated that98% ofall stems 1 em dbh (diameter atbreast height) would be killed in sur-face tires in the eastem Amazon. Thickbark insulation for tire resistance wasnot developed genetically. Mortality isprojected to be high because most Ama-zonian tree species have only a' thinlayer ofbark protecting their cambial tis-sues.

The area considered as generallyimmune to fire (low fire risk) in this studyrepresents 1.9 million km2 or 38.1 % ofthe Brazilian Amazon. The remainder ofthe Amazon is susceptible to tire. It islikely that tire will become more com-mon in the Amazon as human occupa-tions both transform fire-resistant veg-etation (closed forest) to fire-prone veg-etation (open fields) and provide moreignition sources. Indeed, if the Brazil-ian Amazon were totally deforested andthe distribution of rainfall did notchange, only around 10.0% of this re-gion would continue immune to tire(based just on climatic considerations)(Fig. 8). Since it is likely that the defor-estation ofthe Amazon rainforest wouldproduce more intense dry seasons be-cause water from evapotranspiration isdiverted to streams (14,15,16,17), theare a immune to tire would probably beeven smaller than 10.0%.

This is a very modest first step inbeginning to think about the climaticand vegetation components necessaryto develop tire risk maps for Amazon.The tire map (Fig. 8) is based on at leasttwo untested assumptions. First, basedon the work ofUhl and Kauffman (3) inthe eastem Amazon, it is assumed thatall closed forest areas will be immune totire. But, their work was done on deepsoils with good water holding proper-ties, allowing the stands under studyto maintain dense canopy cover duringthe occasional (ten-year maximum) se-vere drought event. Further studies mayreveal that such closed forest areas are,

c.

Volume 50(4) • July/August 1998 Ciência e Cultura Journal of the Brazilian Association for the Advancement of Science· 289

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.Reports.

in fact, at tire risk. Second, it is assumedthat open canopy (intermediate) forestsare more tire prone than closed forests.While this seems reasonable, there areno studies evaluating the tire sensitiv-ity of open canopy forests in the Ama-zon. I hope that others will use this workas a starting point to understand thecomplexity oftire potential in the Ama-zon basin, mainly because ofhigh con-cem for climate change related to defor-estation.

Disclaim notice: The views expressedin this artic1e are the author's and do not nec-essarily represent the official policy or inter-

pretations of the Brazilian Enterprise for

Agricultural Research (EMBRAPA). •

References and notes

I.Pyne SJ 1984 Introduction 10 wildlandfire: fire management in lhe United States.John Wiley and Sons, NY

2. Uhl C, R Buschbacher 1985 A disturbingsynergism between cattle ranches burn-ing practices and selective tree harvest-ing in the eastern Arnazon. Biotropica17: 265-268

3. Uhl C, JB Kauffman 1990 Deforesta-tion effects on fire susceptibility and the

potential response of tree species to firein the rainforest of the eastern Amazon.Ecology 71: 437-449

4. Burgan RE, MB Shasby 1984 Mappingbroad-area fire potential from digital fuel,terrain, and weather data. J Forestry 82:228-231

5. Burgan RE, RA Hartford 1988 Com-puter mapping of fire danger and fire 10-cations in the continental United States.J ForeSI1)' 86: 25-30

6. Fisher WC, AH Wright 1987 Firesys:Using artificial intelligence techniques tobuild a fire effects information systems.Compiler 5: 28-35

7. Harrington J, M Flannigan 1987 Droughtpersistence at forested Canadian stations,p 204-206. ln Ninth Conference 011 Fireand Fores/ Meteorology, San Diego, Cal i-fomia. American Meteorology Society,Boston, MA

8. Hevesi JA, JD Istok, AL Flint 1992 Pre-cipitation estimation in mountainous ter-rain using multivariate geostatistics. PartI. Structural analysis. J Appl Meteorol 31:661-676

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18.Acknowledgemenls: 1 thank the WorldWildlife Fund for financial support forthis study. I also thank the EmpresaBrasileira de Pesquisa Agropecuária forproviding infrastructural assistance;Christopher Uhl, Therezinha XavierBastos and Tatiane DAS Diniz for helpand encouragement during the study;Lígia M Hoshino for help with data col-lection; Foster Brown for assistancewith Idrisi; and Dan Nepstad for review-ing the manuscript.

Received 13 March 1996Accepted 26 March 1997

Volume 50(4). July/August 1998