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The Rate and Extent of Deforestation in Watersheds of the Southwestern Amazon BasinAuthor(s): Trent W. Biggs, Thomas Dunne, Dar A. Roberts and E. MatricardiSource: Ecological Applications, Vol. 18, No. 1 (Jan., 2008), pp. 31-48Published by: Ecological Society of AmericaStable URL: http://www.jstor.org/stable/40062109 .Accessed: 23/03/2014 23:29

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THE RATE AND EXTENTOF DEFORESTATION IN WATERSHEDSOF THE SOUTHWESTERNAMAZON BASIN

EcologicalApplications, 8(1),2008, pp. 31-48 2008 by the EcologicalSociety f America

Trent W. Biggs,1'5 Thomas Dunne,2 Dar A. Roberts,3 and E. Matricardi41Department f Geography, an DiegoState University, an Diego,California 2182 USA2Donald Bren chool of Environmentalcience nd Management, niversity f California, anta Barbara, California 3106USA3Department f Geography, niversity f California, anta Barbara, California 3106 USA4Secretaria o Estado do Desenvolvimento mbiental, strada do Santo Antonio, 00-VilaCujubim, airro Triangulo 8900-000

Porto Velho-RO, Brazil

Abstract. The rate and extent f deforestation etermine he timing nd magnitude fdisturbance o both terrestrial nd aquatic ecosystems. apid change can lead to transientimpacts o hydrology nd biogeochemistry, hile complete nd permanent onversion oother and uses can lead to chronic hanges.A large population f watershed oundaries N=4788)and a time eriesof Landsat TM imagery 1975-1999)in the southwestern mazonBasin showed hat ven small watersheds 2.5-15 km2)weredeforested elatively lowly ver7-21 years. ess than 1% of all small watersheds ere more han 50% cleared n a singleyear,

and clearing ates veraged 5.6%/yr uring ctive learing.A large proportion 26%)of thesmall watersheds ad a cumulative eforestation xtent f more than 75%. The cumulativedeforestation xtent was highly patially utocorrelated p to a 100-150 km ag due to thegeometry f the agricultural one and road network, o watersheds s large s -40 000 km2were more than 50% deforested y 1999. The rate of deforestation ad minimal patialautocorrelation eyond lag of -30 km, nd the mean rate decreased apidlywith ncreasingarea. Approximately 5% of the cleared area remained n pasture, o deforestation nwatersheds f Rondonia was a relatively low,permanent, nd complete ransition opasture,rather han a rapid, transient, nd partial utting with regrowth. iven the observed and-cover ransitions, heregional tream iogeochemicalesponses ikely o resemble he hronicchanges bserved n streams raining stablished astures, ather han temporary ulsefromslash-and-burn.

Keywords: AmazonBasin;deforestation; isturbance; and cover hange; asture; Rondonia, razil;scaling aws;tropical orest.

Introduction

Large areas of the humid ropicsare beingdeforestedfor ogging nd agriculture DeFries2002).The regionalimpact f the deforestation n hydrology, iogeochem-istry, nd aquatic ecosystems epends on the rate,extent, nd scalingbehavior f clearing nd subsequentland use. Within a region, and-use and land-coverchangeshavecharacteristic emporal nd spatial cales,and they herefore ccupynestedwatersheds f diversescale to varying egrees. n gauging the nature andintensity f various watershed-scalempacts, t s useful

to recognize nd quantify he probability istributionsof such effects.What s the proportion f watersheds fa given size that can be completely eforested n achosen time nterval? o what extent re intensivelytransformed atersheds ontiguous? t what geograph-ic scale is deforestation ikely o be diffuse ather hancontiguous? hesecharacteristics ffect heconnectivityof impacted watersheds, s well as the intensity fhydrologic nd biogeochemical hanges o stream low.

Deforestation auseschanges nhydrology nd streambiogeochemistry hat an be either ransient r chronicdepending n the rate of clearing, he final xtent fdeforestation, nd the subsequent land use. Rapidclearing nd burning f forest egetation roduces apulse of cations and nutrients n soil pore waters(Chorover et al. 1994, Williams et al. 1997) and instreamwaters raining mallwatersheds hat havebeenrapidly eforested Bormann nd Likens 1979,Swankand Vose 1997,Williams nd Melack1997, wank t al.2001).Thesepulsesmay persist or everal yearsbut are

generally attenuated less than a decade followingdisturbance. fter learing,more permanent hanges nvegetation nd and use can also cause chronic hanges nthe concentrations f nutrients n receiving treams,including ncreased itrogen nd/or hosphorus oncen-trations or watershedsmaintained n grass Swank andVose 1997)or pasture Biggs t al. 2004).Thechanges nthe nutrient nd light egime an leadto changes n algalproduction, issolved xygen, nd ecosystem roductiv-ity (Neill et al. 2001). Further hanges in land useincluding attle establishment, gricultural ntensifica-tion, ertilizer se, nd urbanization lso impact utrientconcentrations and biogeochemical functioning n

Manuscript eceived October 2006;revised 9 June 007;accepted 1 June 007. Corresponding ditor: M. Friedl.5E-mail: [email protected]

31

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32 TRENT W. BIGGS ET AL. Ecologica|Applicatk>ns

streams Matson et al. 1997, Downing et al. 1999,Martinelli t al. 1999,Biggs t al. 2004).

In the ontext f stream iogeochemistry, ecognitionof the spatial and temporal tructure f deforestationleadsto two central uestions:What proportions f thewatershed opulation n deforesting egions undergorapid clearing nd are likely o show transient treambiogeochemical erturbations f the kind documentedby the Hubbard Brook experiments Bormann andLikens 1979), the Coweeta experimental watersheds(Swankand Vose 1997), nd a small 2 ha) catchment nthe CentralAmazon Williams nd Melack 1997)?Whatproportion re slowly ut heavily eforested, onvertedto pasture, nd likely o show chronic tream biogeo-chemical erturbations f the kind documented y Neillet al. (2001)and Biggs t al. (2004)?

Studies of the effect f deforestation n streamchemistry nd aquatic ecosystems ften amplea smallnumber f streams nd, even n regional urveys, nlysmall fraction f the watershed population can besampled.Understanding he regional mpact of defor-estation n the stream network equires eterminationof the probability istributions f the rate of clearingand extent f pasture stablishment. egional analysesof deforestation ave often used the pixel or adminis-trative oundaries Dale et al. 1993,Flamm nd Turner1994,Verburg t al. 1999,Chomitz nd Thomas 2001,Weng 2002)but have not used watershed oundaries oanswer hequestions osed above.

The scaling behavior of land cover controls itscumulative ffects n watersheds f different izes Kinget al. 2005).Land cover s often patially utocorrelated(Qi and Wu 1996) due to patterns n soil type,settlements Wear and Bolstad1998),road construction(Chomitz nd Gray 1996,Qi and Wu 1996), nd zoning.Spatial autocorrelation onserves he moments f theprobability istributions f a random variable nd willcorrespond ohigher eforestation ates r extents verlarger reas than expected nder patial ndependence.For example, if small watersheds hat are heavilydeforested 75-100%of the watershed rea) tend to beclustered, he probability s increased that a largerwatershed ill lso be heavily eforested. onversely, fheavily eforested, mallwatersheds re equally ikely obenext o a forested r deforested atershed, hen argerwatersheds ill have a lower robability f beingheavilydeforested. utocorrelation herefore ncreases he sizeof watersheds hat re heavily eforested nd likely oexperience isturbed tream biogeochemistry. n em-pirical understanding f the scalingbehavior f defor-estation s necessary o assess how regional and usetransformations ay ffect egional iogeochemicalndhydrological ycles cross a range f scales.

The goals of this paper were to quantify he rate,extent, nd scalingbehavior f deforestation n water-shedsof the outhwestern razilianAmazon Basin andto identify he ypes f mpacts ikely o result n streambiogeochemistry iven heobserved attern f defores-

tation. The frequency istribution f clearing izes andthe patial rrangement f clearing is a vis administra-tive zoning boundaries were quantified sing a timeseries f Landsat ThematicMapper TM) images 1975-1999) over the Brazilian state of Rondonia in thesouthwestern mazon Basin Fig. 1).A large opulationof watershed oundaries n = 4788)was overlaid n thetime eries maps, nd a simplemathematical odel wasfit o the deforestation ime eries or ach watershed oquantify hedeforestation ate Table 1).The probabil-ity density unctions f the extent nd rate of clearingwere then determined or the observed watersheds.Geostatistical nalysiswas used to quantify hespatialautocorrelation f the rate and extent f deforestationand was used to quantitatively xplain the observedscalingbehavior. Literature n the effects f rapid orextensive eforestation n stream iogeochemistry assummarized o identify he ikely ypes f perturbationsexpected iven hedeforestation atterns bserved n the

watershed nalysis.The specific questions addressed by the researchincluded these questions: What was the rate ofdeforestation n watersheds f different izes n Rondo-nia during periods of active vegetation onversion?What was the final, stable deforestation xtent nwatershedswhere the clearing ate had slowed? Werethe learing ate nd extent utocorrelated, nd howdidthis ffect heir calingbehavior nd the ize of heavilydeforested watersheds? inally, s deforestation etterconceptualized s a rapid transformation f vegetationcausing transient ulses of stream nutrients r as agradual nd permanent ne leading o chronic hanges

in stream iogeochemistry?Study Area and Methods

Study reaThe Brazilian State of Rondonia lies in the south-

western mazon Basin on the border with Bolivia 7.5-14 S, 59-66 W; Fig. 1). Closed- and open-canopytropical rainforest ominate the original vegetationcover (RADAMBRASIL 1978).Large-scale oloniza-tion of Rondonia began with the construction f theBR-364highway n the late 1960s (Goza 1994).Thepopulation eached1.3 million eopleby the year 2000,and -53000 km2 25%) of the forest was cleared forcropping nd pasture y 1993 Pedlowski t al. 1997).

Land in Rondonia has been zoned for different ses,including griculture 51% of the State's area), extrac-tion of forest roducts uch as nuts, rubber, ruit, ndlimited elective ogging 14%),and protection f forestfor ndigenous eoples, parks, and biologicalreserves(35%;Fig. 1).The main gricultural orridor markedAin Fig. 1) accounted for 99% of the area zoned foragriculture n Rondonia in 1999. The corridor onsistsof one contiguous block of land that encompasses117940km2, nd extends 600 km along the highwayBR-364and extends 1 -300km wide,perpendicular othe highway Fig. 1).The 35 protected reas n the State



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34 TRENT W. BIGGS ET AL. Ecologica|AppHcatk>ns

Table 1 Summary f criteria sed to identify hedeforestation tageof a givenwatershed nd variables sed to describe herateand extent f deforestation sing he ogistic quation.

Variable Description Stage Stage I Stage II

Identification f watershed tage/1999 cumulative eforestation xtent n 1999 0.15 >0.15

(fraction f watershed rea)A:1999 deforestation ate n 1999 >0.01


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January 008 DEFORESTATION WATERSHEDS AMAZONBASIN 35

Table 2. Landsat TM time eries mages.

Scene Mapname code Years available

Porto Velho PV 1986, 1988, 1992, 1993,1996^1998Ariquemes AR 1975, 1984, 1988-1999Jiparana JI 1978, 1986, 1988-1990, 993, 1996-1999Santa Luzia SL 1986, 1988-1990, 992, 1995-1997, 999Cacoal CA 1988, 1989, 1992, 1994, 1996, 1998, 1999

The deforested rea ncluded ll pixels hat lassified spasture or secondary growth using spectral mixtureanalysis. his represents heterogeneous ixof pasturein different onditions and secondary vegetation nvarying tages f regrowth. he remote ensing efinitionof deforestation id not include other anthropogenicprocesses, ncluding ubcanopy fires or disturbancessmaller than 30 X 30 m which may impact tropicalforests Nepstadet al. 1999).

The size of clearings made in a single year wasdetermined sing two years 1996 and 1997)that hadimagery n all five andsat TM scenes.The boundariesof the learings efined he umulative rea cleared s afunction f clearing ize,or the umulative rea function(CAF). The CAF is different rom a cumulativedistribution unction cdf),whichwould be the frequen-cy of clearings s a function f clearing ize. The CAF,by contrast, s the area or number f pixels in eachclearing ize and not the number of clearings. Thederivative f the CAF gives heprobability hat givenclearedpixel ieswithin clearing f size x.

Watershed oundariesA 90-m resolution igital elevation model (DEM)

from NASA's Shuttle Radar Topography Mission wasused to delineatewatershed oundaries. he final dataset had 8994watersheds f seven Strahler rders withdrainage areas ranging from 2.5 to 64127 km2 Ji-Parana basin; Table 3). An eight-direction low-accu-mulation lgorithm elineated he stream network ndwatershed oundaries, s coded in ARC/INFO (Jensonand Dominique 1988).The minimum watershed rea

was set to 2.5 km2,whichyielded stream etwork hatmost closelymatched he stream network f 1:100000topographicmaps.A digital levationmodelwith igherresolution nd accuracy may yield slightly ifferentwatershed boundaries, particularly n relatively latareas,which an generate rtifacts uch s long, traightwatersheds Tribe 1992). Most of the Rondonia studyarea had sufficient elief o yield hannelnetworks hatcloselymatched the blue lines of the 1:100000topo-graphic maps. The seven Strahler rders did not havemutually xclusive rea bins; .g., the argestwatershedsof order 2 were arger han the smallestwatersheds forder 3. Watersheds ess than 90% covered by theLandsat TM data were xcluded rom he nalysis.

The watershed oundaries wereoverlain n the timeseriesof deforestation aps in order to determine hecumulative eforestation xtent n 1999 all five cenes,8994watersheds) nd the full ime eries f deforestationback to 1975-1978 AR and JI scenes, 788watersheds).The analysiswas performed y binning hewatershedsby order nstead f by area to prevent ncluding estedwatersheds n a single in.

Mathematical escription f deforestationClearing f a givenwatershedmay be modeled s a

processwith hree tagesdefined y the rate nd extentof deforestation Fig. 3): (I) predisturbance, herecumulative deforestation xtent nd annual rates ofconversion re low; (II) active learing,where umula-tive eforestation xtent s ntermediate nd annual ratesof conversion are highest; and (III) stable, whereclearing f primary oresthas slowed and cumulativedeforestation xtent has begun to stabilize. The stabledeforestation xtent f Stage III may be controlled yseveral characteristics f the watershed nd regionaleconomy, ncluding the road network, oil quality,topography, ocationwithin he ransportation etwork,farmers' ccess to capital nd labor, population ensity,and market alue of agricultural roducts Chomitz ndGray 1996,Kaimowitz nd Angelsen 998).

The cumulative xtent f deforestation /(/)] s simplythe umulative raction f an area classified s deforest-

Table 3. Watershed ttributes.

Watershed rea (km2)Streamorder Mean Minimum Q05 Q95 Maximum N, Nts

~\ 5^5 2 2/7 15/3 64 6824 376?2 26 5.5 9.5 67 246 1710 7673 113 16.7 42 304 559 347 2174 534 107 174 1696 3137 85 355 2544 577 667 5964 6097 23 106 18792 7281 39465 4 07 46760 29392 64127 2 0Total 8994 4788

Notes: Nt is the number f watersheds n all five Landsat TM scenes used to determine hecumulative eforestation xtent n 1999, nd Nts s the number f watersheds n the cenes with ulltime eries hatwereused to determine herate of deforestation AR and JI scenes).Q05and Q95represent he5th nd 95th percentiles.



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36 TRENT W. BIGGS ET AL. Ecologica|AppUcatmns

Fig. 3. (A) Logisticmodelof deforestation n watersheds. B, C) Observed eforestation ime eries rom 975 o 1999for wofirst-order atersheds n Stages I (for B)and III (for C) with he ogisticmodelfits. ariables re as follows: "d, uration f activeclearing yr);k, annual rate f clearing yr"1); o, ear f the nset f active learing; e, ear f the nd of active learing; r, ear fmost recent atellite mage; s, umulative raction leared n stage-Ill watersheds.

ed up to a given year. Consistent definition ndinterpretation f the rate of deforestation s not asstraightforward. he deforestation ate,k, is

k=f^ (1)h-hwhere/ s the umulative raction f an area deforestedby time , and /, s the year at time /. The value of kdepends ritically n t\ nd t2. n practice, \ nd t2 reoften hosen based on the available satellite magery.This would tend o underestimate herate during ctivevegetation learing f onversion tarted much fter \ rended much before 2.Consistent efinition f the rate

of deforestation equiresunambiguous nd preferablyautomated dentification f the beginning nd end ofclearing.

Identification f the beginning /o) and end (/e) ofclearing may be accomplished y fitting n observeddeforestation ime series to a mathematical unction.Transitions nvegetation henology ave been dentifiedusing the ogistic unction Fischer 1994,Zhang et al.2003),which s adapted here to describe he deforesta-tion time eries,

'=(dU) (2)

where (/) is the cumulative raction f the watershedclearedby time ,fs s the tabledeforestation xtent, isthe base of the natural ogarithm, nd A and B are fittedparameters. minimum eforestation hreshold 0.15)separates forested Stage I) watersheds rom Stage IIand III watersheds. he value 0.15 was used becauseregional urveys howed minimal mpact of deforesta-tion on stream biogeochemistry elow a cumulativedeforestation xtent of 0.15 (Biggs et al. 2004) andbecausethe ogistic quation often id not converge ostablevaluesfor watersheds essthan .15cleared. tageII and III watersheds may then be separated by themagnitude f the first erivative f Eq. 2, which s the

rate of deforestation n 1999 (Fig. 3). Stage IIIwatersheds ere defined s those having deforestationrate less than 0.01 (1%) yr"1 in 1999. The stabledeforestation xtent /s) is known only for watershedsin Stage II, and is the deforestation xtent n the mostrecent vailable mage Table 2).

This model assumes that cleared areas remain npasture or secondary orest nd are not permanentlyabandonedto forest. n 1999, leared rea in Rondoniawas mostly 79%)pasture, with omesecondary rowth(21%;Roberts t al. 2002).In any given pair of yearsfrom 1986-1999, ransitions rom econdary rowth oforest ccurred n 1 1% of the econdgrowth rea 2.3%



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January 008 DEFORESTATIONWATERSHEDSAMAZONBASIN 37

of the otal deforested rea), but most econdary rowtheither emained s secondgrowth -65%), or reverted opasture 24%).Only 16% of pasture pixelstransitionedto secondary growth n the next year, and 84% ofpastures emained s pastures Roberts t al. 2002).Thissuggests hat cleared areas become a dynamic mosaicdominated ypastureswith ome econdary rowth ndlittle permanent bandonment o forest. The stabledeforestation xtent f Stage HI (/s) therefore eflectsdecrease n the rate of clearing f primary orest, atherthan state wheredeforestation ateequals the rate ofafforestation.

The rate of deforestation k) during ctive learing sdefined ifferently or watersheds n Stage II and IIIbecause he nd of active eforestation /e) s not definedfor tage I watersheds:

*_ J[/('e)-/('o)]/['e->o], Stagem watersheds (.WU/M-/('o)]/['r-'o], Stagen watersheds

.W

where oand te are the years of the onset and end ofactive deforestation, defined as when the secondderivative f f(t) is at its maximum nd minimum,respectivelyTable 1). f(te) and /(/) re the deforesta-tion xtents t the beginning nd end of Stage I, and tTis the year of the most recent vailable satellite mage.The duration Td) of active learing s defined nly forStage II watersheds ecause the end of activedefores-tation tc) s not defined or Stage I watersheds:

Td= te t0. (4)Time eries f deforestation xtent ywatershed Fig. 3)

were generated y overlaying atershed oundaries nthe ime eries f deforestation aps Fig. 1). Eq. 2 wasthen it o the observed ime eries using multidimen-sional,unconstrained onlinear minimization lgorithm(Nelder-Mead simplex direct search method). Timeserieswith low deforestation xtent ntil 1997 and arapid ump in 1998 or 1999 did not converge to asolution of Eq. 2. For those watersheds 5% of allwatersheds), was defined s the difference n defores-tation extent etween 1999and 1997,divided by twoyears.

Scalingbehavior, eostatisticsand spatial configuration

We hypothesize hat the probability istributions fdeforestation xtent (/) and the rate of deforestationduring ctive clearing k), and therefore he hydrolog-ical,biogeochemical,nd other umulative nvironmen-tal mpacts, houlddependon watershed ize due to thespatial and temporal tructure f clearing ctivities.smallwatershed ould be entirely orested r deforested,but s watershed rea ncreases, hewatershed oundaryintercepts combination f protected nd agriculturalzones, thereby ecreasing he maximum ossible andincreasing he minimum ossibledeforestation xtent.Likewise, clearing rates may be high in a smallwatershed f a single armer r group of farmers lears

a large fraction f their property n a singleyear. Aswatershed ize ncreases, heprobability f simultaneousclearings lso decreases, hereby ecreasing he aggre-gate deforestation ate. Colonists in the Amazontypically lear ess than 5-10% of their roperty n anygivenyear due to restricted ccess to labor and capital,though nitial learing atesmay be up to 50% n a singleyear Fujisaka et al. 1996).These imits n clearing atesshould cause annual deforestation ates o be relativelylow, evenon single lots nd lower n argerwatersheds.

The extent nd rate of clearing re random variablesthat have different means, variance, and scalingbehavior. The clearing ate or extent n a watershed fa givenorder n is the mean of the rate or extent n Mwatersheds f order n - 1. The variance f the samplemean for M independent andomvariables s

where on is the variance f the deforestation xtent nth-order watersheds, nd M is the number f water-shedsof order - 1contained n a watershed f order .Eq. 5 assumes hat watersheds f order n - 1completelyfill he rea of the watershed f order . Departures romEq. 5 can occur if the random variables re spatiallyautocorrelated.

Geostatisticalmethods were used to identify patialautocorrelation n deforestation ates and extents.Semivariograms, which identify how the variancechangeswith distance rom ll points n the tudy rea,wereconstructed or first-order atersheds. emivario-grams identify he small-scale variance nugget), herange over which variable s autocorrelated range),and the regional ariance sill).The range s the distancewhere he semivariance s -95% of the sill. Empiricalsemivariograms ere constructed sing the classical(Matheron) estimator, nd exponential emivariogrammodelswerefit o the empirical emivariograms.

The spatial configuration f deforestation ithinwatershed may also affect the impact on streams.Riparian zones often exert strong controls on thedelivery f sediment nd nutrients rom upslope andhave been demonstrated o influence he transport fnitrogen n forested atchments f the Amazon Brandeset al. 1996).The spatial configuration f deforestation

vis a vis the stream network was quantified or theRondonia watersheds sing buffers round the streamnetwork. he deforestation xtent n buffers f 90, 180,270, and 540 m around the stream network wascalculated from the deforestation map of 1999. Thedeforestation xtent n thesebuffers ascomparedwiththe deforestation xtent n the area as a whole toestablish f deforestation ad a spatial pattern is a visthe tream etwork.

Stream iogeochemistrynd the ffects f deforestationThe probability istributions f the rate nd extent f

deforestation ere used to estimate the fraction f



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38 TRENT W. BIGGS ET AL. Ecologica|AppHca^o

Fig. 4. (A)Cumulative raction leared s.clearing ize logscale)between 996 and 1997 n the main gricultural orridorof Rondonia. The data include ll pixels learedbetween 996and 1997 and define he cumulative rea function CAF). (B)Derivative f the CAF vs. clearing ize (log scale).See Studyarea and methods orfurther etails.

watersheds ikely oexperience ither apidor extensiveclearing. iterature alues wereused to characterize hetype nd magnitude f changes n stream iogeochem-istry ssociated with ither apid or extensive efores-tation. An intensive tudy f a small 2-ha)watershed nthe CentralAmazon Williams t al. 1997)quantified heeffect f slashing nd burning f forest egetation nstream nutrient luxes nd concentrations. ore than80% of the watershed was cut and burned n a singleyear, o those resultswere used to characterize hangesin stream biogeochemistry aused by rapid clearingwithout attle populations.The soil type nd depth ofthe catchment n the Central Amazon differ rom oils

commonly ncountered n Rondonia, o actual changesin stream iogeochemistryn Rondoniamay differ romthose observed by Williams et al. (1997). The mainobjective s not to predict precise values for streamnutrient oncentrations n all rapidly eforested ater-sheds in Rondonia, but rather to place data fromsampledwatersheds n a regional ontext nd to placesome values on the likely probability istribution fmagnitudes f changes ausedby cutting nd burning ftropical ainforest.

A regional urvey f stream utrient oncentrations nRondonia was carried ut by Biggset al. (2004).Thewatersheds ncluded a range of drainage areas (1.8-

33000 km2),orders, nd deforestation xtents. efor-ested watershedswere predominantly n pasture, ndheavily deforested watersheds >80% deforested) adlowclearing ates n the 1-3 years rior osampling ndresembled tage III watersheds n the logisticmodel.The results howed an increase n stream Cl, total

dissolvednitrogen TDN), and total dissolved hospho-rus TDP) in the dry easonand a smaller ut detectableincrease n Cl and TDP in the wet season,but only forwatersheds more than -60-80% in pasture. Theobserved tream biogeochemistry as used to charac-terize he changes expected from xtensive umulativedeforestation nd pasture stablishment.

Results

Clearing izes

Clearingsmade in a singleyear 1996-1997)rangedfrom .09 ha (1 pixel)to 490 ha (Fig. 4A). Single-pixelclearings ccounted for 10% of the total area cleared,and the modalclearing izewas 5 ha (Fig.4B).Clearingsof fewer han 22 ha accounted for 90% of the clearedarea, and less than 2.4% of the cleared area was inclearings arger han 100 ha. Some of the single-pixelclearings ikely represent noise" or misclassificationsdue to topographic hading, anopy ffects, nterannualvariability n plant phenology, r natural ree-fall aps,which may be as large as 0.07 ha (Myerset al. 2000).Other small clearings may be due to anthropogenicvegetation onversion ssociated with elective oggingand clearing along forest edges. The single-pixelclearings epresent nly 10% of the total cleared areaand do not significantly mpact the results at thewatershed cale.

Zoningboundaries nd deforestationAreas zoned for agriculture ranching) n the 1997

zoning map had a higher deforestation xtent 50%)than protected reas (7%)and extractive eserves6%;Fig. 5). This large difference n deforestation xtent yzonealso held for he 1988 oningmap:areasdesignatedfor protection, xtraction, r agriculture n the 1988zoning map were 7%, 17%,and 50% cleared by 1999,respectively. gricultural ones had a higher ercentageof fertile lfisol soils (15%) comparedwith protectedareas (3%) or extractive eserves 1.5%), partly ue tothe nclusion f soiltype n the nitial lanning tages fthe development rojects n Rondonia. The high ateofclearing n agricultural ones and low clearing ates nprotected areas resulted n a contiguous block ofdeforestation n the entral gricultural orridor, lankedby contiguous locksof forest.

Watershed oundaries nd deforestationThe center f the gricultural orridor long Highway

BR-364spans the Jam and Ji-Parana watersheds ndwas largely eforested y 1999(Figs. 1 and 6). Mostfirst-order atersheds n the center f the agriculturalcorridor were 76-100% clearedby 1999 Fig. 6).



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January 008 DEFORESTATION WATERSHEDS AMAZON BASIN 39

Fig. 5. (A) Deforestation xtent n 1999,measured s the umulative raction f the rea that s deforested, y zone,and (B)distribution

f soil types, y zone.

Fig. 6. Map of the cumulative eforestation xtent, y 1999, n first-order atersheds 2.5-15 km2). Each dot represents newatershed.



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40 TRENT W. BIGGS ET AL. Ecologica^AppHcat^ons

Table 4. Mean deforestation xtent n 1999 /1999), eforestation ateduring ctive learing k), and duration f active learing(r


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Fig. 7. Maps of A) the rate nd (B) the year of onset of clearing n first-order atersheds 2.5-10 km2).Each dot representsone watershed.

of the otal variance omes from arger-scale atterns pto 200 km. Bycontrast, 1%of the total variance n kwas due to small-scale ariability.

Due to spatial utocorrelation, hevariance n/1999 idnot decrease with watershed rea as predicted y Eq. 5(Table 6). The standard eviation redicted y ssumingspatial ndependence t the next order aind)was lowerthan the observed standard deviation. The standard

deviation n k, by contrast, ecreasedwith watershedorder for econd- o fourth-order atersheds Table 6).Values of aindpredicted ssuming patial ndependencewere maller han bserved or econd-order atersheds,reflecting ome autocorrelation or hort ags (Fig. 11).


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42 TRENT W. BIGGS ET AL. Ecologica|AppHcatk>ns

Fig. 8. Probability istributions f the umulative eforestation xtent n first- o fifth-order atersheds n 1999,/i999/1999sthe fraction f the watershed rea that was deforested p to 1999).Data include ll watersheds nd all three tages f deforestation(Nt n Table 3).

km. The analysis uggests hat he rate of deforestationwas a spatially independent random variable forwatersheds f second order nd larger.

The spatial autocorrelation tructure ffected he

scaling behavior of extensive nd rapid clearing Fig.12). The probability hat a watershed was heavilydeforested y 1999 P(fl999> 0.75))decreased lightlyfrom irst- o second-order atersheds, ut was constantfrom econd- through ourth-order atersheds range:9.5-1696km2).P(f\999 0.75)then decreased or fifth-order watersheds, eflecting he ack of spatial autocor-relation t large ag distances.The probability hat awatershedwas rapidly leared P(k > 0.10))decreasedmore rapidly hanP(f\999 0.75)due to the ow spatialautocorrelation f clearing ates nd to spatial variabil-ity n the onset of clearing Figs. 6, 7, and 11).

The semivariogram nalysis suggests that clearing

events n small watersheds eganwithin few years ofeach other, but cumulative clearing proceeded todifferent xtents. Beyond a 30-km lag, the rate ofdeforestation etter esembled n independent andomvariable, uggesting hat the rate of deforestation asrelatively niform ver the region. The net effect wasthat ome large watersheds ere extensively eforesteddue to autocorrelation, ut the rate of clearing waslower han learing ates n small watersheds.

The deforestation xtent n buffers round the treamnetwork f 90, 180, 270, and 540 m in the AR and JIscenes (0.513, 0.517, 0.521, and 0.524) was notsignificantly ifferent rom he deforestation xtent ver

the mages s a whole 0.524).Thissuggests hat learingdependedmore n the road network hanon the treamnetwork, nd the deforestation xtent n the watershedwas equivalent o the deforestation xtent n the near-

stream one. Some smallriparian onesnot detected ythe Landsat TM imagery may still nfluence utrienttransport, nd higher esolution igital levationmodels(DEMs) could yield more precise estimates of thelocation of the stream network is a vis the riparian

Fig. 9. Probability istribution f the cumulative efores-tation xtent /1999),measured s a proportion f the rea thatis deforested, n first-order atersheds 2.5-15 km2) n 1978,1989,and 1999. Data include ll first-order atersheds n allstagesof clearing. requencies or 1978 and 1989 at the owerdeforestation xtent wereoff he cale 0.52and 0.89).



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Fig. 10. Frequency istribution f deforestation ates k) by watershed rder. he solid black ines re ognormal istributionsusing heobservedmean and variance.

vegetation. he broad pattern ocumented ere uggeststhat clearing or pasture s largely ndependent f thestream etwork.

Stream iogeochemicalffects: ransient nd chronicThe land cover nalysis uggests hat apid learing f

forests was uncommon, while slow but extensive ndnearly omplete learing ccurred requently n water-

sheds of Rondonia. The potential hanges n streambiogeochemistry aused by rapid or extensive learing

Table 5. Parameters f the semivariograms f first-orderwatersheds.

RangeParameter Nugget Sill Nugget: ill (km)

Deforestation xtent, 0.02 0.115 0.17 140/l999

Clearing ate,A: 0.005 0.0062 0.81 30Onsetof clearing, o 17 44 0.39 210

Note: Nugget s the small-scale emivariance, nd sill s theregional emivariance.

were characterized using literature alues. Table 7summarizes hanges in stream biogeochemistry b-served n a small (2-ha) watershed ndergoing apiddeforestation Williams et al. 1997;Central Amazon)and in a regional urvey f established asture ystemsin Rondonia Biggs t al. 2004).In the CentralAmazonBasin, Williamset al. (1997)monitored tream waterchemistry efore nd after 0% of the watershed was

slashed and burned, nd they documented ncreasedfluxes f total dissolvednitrogen TDN), total dissolvedphosphorus TDP), and small ncreases n fluxes f Clcompared with he pre-disturbance ackground.Whilethe changes n stream biogeochemistry ere relativelylarge, very few watersheds n Rondonia showed rapidclearing:no watersheds .5-15 km2 had the deforesta-tion rate of 0.80 (80%)yr"1 bserved n the Williams tal. (1997) study, nd only % had a deforestation ate f0.2 (20%)yr"1. A clearing rate lower than 0.2 wouldshow less than 25% of the response documented byWilliams t al. 1997 and is not considered o be "rapiddeforestation."



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44 TRENTW.BIGGST AL. "^mK

Fig. 11. Semivariance of (A) cumulative deforestationextent n 1999, B) clearing ateduring tage I, and (C) yearof the onset of active clearing. Shown are the small-scalesemivariances nugget), he range over which a variable isautocorrelated, nd the regional emivariance sill).The rangeis the distance where he emivariance s 95% of the ill.

A regional urvey f streams n Rondoniaby Biggs tal. (2004)showed that streams raining astures hadincreased l, TDN, and TDP concentrations n the dryseasoncomparedwith treams raining orests, ut only

Fig. 12. The probability hat watershed ad a cumulativedeforestation xtent reater han 75% [/V1999) 0.75]or aclearing ate k) greater han 10%/yr P(k > 0.1)]vs. watershedarea note the og scale).The numeral ear ach point ndicatesthe order of the watershed first hrough ixth rder) n eacharea bin.

for watershedsmore than -75% deforested. n the wet

season, streams raining astures had higher oncen-trations f CI and TDP than streams raining orests.The regional eforestation nalysis resented ere howsthat 26% of the population of small watersheds nRondonia were heavily >75%) deforested y 1999andsusceptible othe types f stream utrient erturbationsfound n pasture ystems. he magnitude f the treamnutrient isturbance ue to extensive eforestation ndpasture establishment, s measured by the regionalsurvey, was comparable to the disturbance aused byrapid clearing eported y Williams t al. (1997)in theCentralAmazon. Streams n Rondonia are not ikely oexperience temporary erturbation n stream utrients

from learing, ut rather howchronic isturbance ueto permanent hanges n land cover and conversion opasture.

DiscussionThe central arguments f this paper are that (1)

deforestation as a temporal nd spatial structure hatdetermines he rate and spatial density of biomassdisturbance n watersheds f different izes and (2) therate nd extent f and cover hange hen etermines hetype of stream biogeochemical isturbance xpectedduring regional vegetation onversion. Rapid cuttingand burning f vegetation, hichwas uncommon venin small watersheds, s expected o cause a transient

Table 6. Statistics f the xtent nd rate of clearing y watershed tream rder.

Deforestation xtent, i999 Clearing ate,k

Order u a Gm& Maximum u a


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Table 7. Perturbations n stream iogeochemistry ocumented or rapidly eforested atershed nd slowly, ut extensively,deforested atersheds, s well as watershed requency y deforestation ate nd extent.

o ,. . , Frequency f small 2.5-10 km2)Streambwgeochemical. . ,

watersheds n Rondoniaperturbation C0.8 >0.5 >0.2 >0.90 >0.75 >0.60Rapid 1.4 5.2 1.1 0 0 0.04Extensive 0.09 0.26 0.40

Dry season 1.7 0.1 2.3 1.5 12.5 6.4Wet season 1.1 0.2 1.9 1.1 3.4 1.4

f Values shown are the means of the ratio of the concentration n streams raining eforested atersheds CdefOr)o theconcentration n streams raining orestedwatersheds Cfor).Williams t al. (1997)reported nnual volume-weighted eanconcentrations nder rapid deforestation 80% cleared n a single year: k - 0.8 yr"1), nd data (means SD) for extensivedeforestation cumulative eforestation xtent > 0.75)are from iggs t al. (2004).

pulse of stream nutrients, hile slow but permanentconversion o pasture, which was relatively ommon,caused chronic isturbance o the stream iogeochem-ical regime. he main conclusions f the analysis resummarized s follows: 1) Deforestation f more than75% of a watershed was a relatively low process thattook more han7-21 years ven n small watersheds, othe pulse-and-recovery ype signal anticipated forrapidly onverted reas is not likely o be common nthe Amazon. (2) Zoning had important mpacts ondeforestation atterns nd their realization n water-shedsof different izes. Protected reas had much owerdeforestation xtents than agricultural ones, whichcreated arge blocks of forest on either size of thedeforested gricultural orridor. 3) Deforestation ro-ceededto >75% in most 26%)of watersheds ocated n

agricultural ones. (4) The cumulative xtent f defor-estation was highly patially utocorrelated, o water-sheds as large as 2889 km2 were heavily deforested(>75%), and watersheds s large as 39466 km2 had adeforestation xtent more than 50%. (5) The slow butcomplete learing nd conversion o pasture of water-sheds likely results n chronic nutrient isturbancecontrolled y pasture cosystems, ather han transientdisturbance ontrolled y forest learing.

Deforestation ynamicsn watershedsThe Landsat TM time eries howed that deforesta-

tion for pasture t the watershed cale did not happenrapidly 1-3 years),but was rather relatively radualbut permanent and-use ransition hat ook more handecade, even in small watersheds 2.5-10 km2).Whilesome smallwatersheds xperienced apid deforestation(


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46 TRENT W. BIGGS ET AL. EcologicalApplicationsVol. 18,No. 1

ascribing ll of the ow deforestation ates n reserves othe ffectiveness f zoning.The boundaries f protectedareasmay hange ver ime; f the 93 800km2 rotectedin 1988,15%was converted o agricultural ones and15% to extractive eserves y 1998. Such changes nprotection tatus will change the projected tate-wideprobability distributions f deforestation xtent inwatersheds.

By contrast with the low deforestation xtent nprotected ones, clearing veraged 50% in the agricul-tural one and proceeded oward mean of more than80%in the most ntensively ccupiedwatersheds. hishigh mean value contrasts with he 20% clearing imitstipulated y Brazilian olicy Nepstad et al. 2002)andsuggests hatwhile oninghas been relatively uccessfulat limiting learing at the regional scale, mandateslimiting learing on individual properties have beendifficult o enforce.

The high concentration of deforestation n theagricultural one coincided with high patial utocorre-lation of deforestation mong small watersheds. heautocorrelation ffected calingbehavior: arge water-sheds were more heavily deforested han expected fclearing were spatially random; some watersheds slarge as 39466 km2 were more than 50% cleared by1999.Autocorrelation t small eparation istancesmaybegoverned y rocky errain, oiltype, ocation f roads(Chomitz nd Gray 1996), r demographics. he rate ofconversion, y contrast, howed little utocorrelationand scaled as a random variable, esulting n relativelylow conversion rates in large watersheds (mean2.7%/yr). The homogeneity of clearing rate over

Rondonia suggests hat the technological nd socialfactors hat ontrol learing ates Fujisaka et al. 1996,Perz 2001, Moran and McCracken 2004) have beenconsistent or he duration f colonization.

Due to the ow extent f clearing n protected reasand high xtent f clearing n agricultural ones, he izeand spatial arrangement f administrative ones deter-mined the fraction f small watersheds hat remainedforested r wereheavily eforested, nd also controlledthe cumulative eforestation xtent n large watershedsand the largest watershed with a high deforestationextent. n Rondonia,deforestation as largely onfinedto the main agricultural orridor Figs. 1, 2). The

geometry f this block and its intersection ith thewatershed network ontrolled the largest watershedheavily eforested. n other egionswith ifferent patialarrangements f protected reas and infertile oils, thelargest eforested rea and watershed may be larger rsmaller han observed n Rondonia, but the patternswould be quantifiable y the watershed-based pproachused here.

Implicationsor stream iogeochemistryWatersheds n Rondonia were cleared slowly and

completely n ways that affected tream iogeochemis-try. nly % of the watersheds ere apidly leared k >

0.2 yr ), but a large percentage 26%)were lowly utextensively deforested to pasture and were likelysusceptible o the types f biogeochemical erturbationdocumented n Biggs t al. (2004)and Neill et al. (2001).The chronic erturbations ere haracterized y a largechloride signal, ncreased phosphorus oncentrations,slightly ncreased nitrogen oncentrations, nd lowoxygen oncentrations.

The interpretation f deforestation s "rapid" or"slow but extensive" epends n the rate or extent hatis sufficient o impact stream biogeochemistry. hecumulative xtent f deforestation /1999) ufficient oimpact stream chemistry was determined sing theregional urvey f Biggset al. (2004),which uggestedthat more than 60-75% of a watershed needs to becleared to pasture before ignificant mpacts n streambiogeochemistryre observed. etermination f the rate(k) sufficient o impact stream chemistry nd theduration f the pulse n stream utrients rom learingof vegetation in Rondonia was more difficult oestablish.Multiyear ime eries of stream hemistry fthe type vailable at the Hubbard Brook watershed nthe northeastern nited States Bormann and Likens1979)and the Coweeta watershed n the southeasternUnited States Swank and Vose 1997)are not availablein the Amazon Basin. The study by Williams et al.(1997)in the Central Amazoncovers nly the first earfollowing eforestation, o it s not possible o determinethe magnitude r duration of a pulse of nutrients nstream waters. Multiyear time series suggest thatmaximum mpacts f forest learing n stream iogeo-chemistry ay be observed p to three years followingdisturbance Swank et al. 2001), so the values fromWilliams t al. (1997;Table 7) may underestimate hemagnitude f the mpact rom apidforest learing. hecatchment ampled by Williams t al. (1997)was alsosignificantly maller 2 ha) than the smallest watersheddelineated n Rondonia, and occurred n different oiltypes han those found n Rondonia. Future researchcould more precisely determine he magnitude ndduration f any transient ulse n stream iogeochem-istry aused by rapid forest learing n Rondonia. Theresults rom he Central Amazon establish reliminaryestimates f the type and magnitude f changes instream iogeochemistry ossible uring apid learing f

forest n the Amazon. In addition, the analysis ofdeforestation ates suggests hat relatively ew water-sheds were cleared as rapidly s the Williams et al.(1997)catchment, nd regional tream iogeochemistryis more ikely o be controlled y the extensive asturesystems hat dominate and use.

Permanent onversion f forest o grassland an havea larger nd more lasting mpact on stream biogeo-chemistry han cutting nd regrowth f forest Swankand Vose 1997). n Rondonia,pastures leared or morethan 20 years produce overland flow that transportsnutrients, speciallyphosphorus, o receiving treams(Biggset al. 2006),and established asture ystems an



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January 008 DEFORESTATION WATERSHEDS AMAZONBASIN 47

havechronically owoxygen oncentrations, articularlyin the dry season (Neill et al. 2001). Given the lowclearing rates, high cumulative learing extent, ndestablishment f pasture bserved n the watersheds fRondonia, we expect he regional mpact of deforesta-tion on stream biogeochemistry o be controlled bypasture systems. Other and-cover hanges, ncludingurbanization nd agricultural ntensification, lso im-pact stream biogeochemistry nd could result n agradual deterioration f water quality n the Amazon(Downing et al. 1999), rather than a "shock-and-recovery" ype esponse bserved n smallexperimentalwatersheds.

ConclusionTherate nd extent f deforestation ere uantified or

a large opulation f watersheds n a region xperiencingrapid deforestation n the Amazon Basin. The conclu-sions about clearing nd its implications or streambiogeochemistryn Rondonia ncluded he following:

1) Deforestation n areas larger han a few squarekilometers as a relatively radual process, esulting nmean clearing ates of 4.5-9.5% of the watershed eryear. Annual clearingswere mall relative o watershedareas.Only small raction f ll watersheds ere learedrapidly, overy ew treams re ikely o show transientpulse of nutrients n streams s observed n watershedexperiments here atural evegetation as allowed.

2) Thirty-one ercent f all small watersheds wereheavily deforested >75%) and subject to chronicdisturbance f stream iogeochemistry. hronic distur-bance includes elevated chloride, phosphorus, andnitrogen, ncreased light availability, nd decreasedoxygen oncentrations.

3)Zoning, articularly rotection f argeforest ractsthat prevented arge-scale ettlement nd infrastructuredevelopment, ffected he spatial probability istribu-tions of deforestation n watersheds. he cumulativedeforestation xtent between 1975 and 1999 exceeded50% in agricultural ones, but was lower than 7% inprotected reas.The zones were arge nd contiguous, osmall watersheds ended to fall in either griculturalzones and be heavilydeforested r in protected reasand be mostly forested. arge watersheds ntersectedboth agricultural ones and protected reas and hadintermediate eforestation xtents. he geometry f theintersection f agricultural ones, protected reas, andwatershed oundaries ontrols he deforestation xtentin large watersheds.

4)Thecumulative learing xtent howedhigh egreesof spatial autocorrelation, which resulted in highcumulative eforestation xtents >50%) in watershedsas large as 39466 km2. This suggests hat even largewatershedsmay be heavily deforested nd experiencestream iogeochemicalmpacts. he rate f clearingwasnot autocorrelated eyond 30 km, suggesting hat theclearing process was relatively omogenous over thestudy area, but the final deforestation xtent was a

function f local factors, he timing f the onset ofclearing, nd zoningboundaries.

5)Thepattern f deforestation nwatersheds ndicatesthat streams n Rondonia are not likely o experiencelarge, transient pulses in stream nutrients duringdeforestation, ut rather re more usceptible ogradualbut chronic hanges ulminating n a pasture-dominatedbiogeochemical egime.

AcknowledgmentsThis research was funded with grant from NASA Earth

Observing System project (NAG5-6120), logistical supportfrom the Large-scale Biosphere Atmosphere roject n theAmazon project NAG5-8396, and a NASA Earth SystemScienceFellowship o T. W. Biggs.Thanks to Karen Holmesfor providing hewatershed oundaries.

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