RESEARCH, VOL. 101, NO. D19, PAGES 23,531-23,539, OCTOBER 30, 1996
of biomass and fire behavior
in
the small experimental burns in the Kruger National Park W.S.W. TrollopeandL.A. Trollope Department of LivestockandPastureScience, Facultyof Agriculture, UniversityFort Hare, Alice, SouthAfrica
Abstract. As oneof thegroundcomponent projects in the SouthAfricanFire-Atmosphere Research Initiative(SAFARI-92)theherbaceous fuelloads,comprising mainlyfine grassfuels,were characterized beforeandaltertheapplication of controlled burnsto smallexperimental plots, approximately 7 ha in size,situated in moistsavanna in thePretoriuskop section of theKrugerNational Park.Thegrassfuelloadswereestimated beforeandapterthecontrolled fireswith a diskpasturemeter (DPM) whichcomprises a circularaluminiumdiskfittedwith a measuring rodandwhichrelatesthe settlingheightof thediskto thequantityof grassmaterialholdingit off theground.Onehundred readings wererecorded in eachplotbeforeandaptertheburns,andthesedatawereusedto estimatethe quantityof fine fuel constuned duringthefires.Surveyswereconducted to describethebotanical composition andstructure of the grassswardandtreeandshrubvegetation in theplotspriorto burning.The fuel moisture,air temperature, relativehumidity,andwind speedanddirectionwere recorded for eachfire.Fire behaviorparameters comprising rateof spread,fire intensity,andflame heightwereestimated for theheadandbackfiresoccurring duringeachbum.The resultsshowed that
thefinefuelloads ontheplots varied greatly ranging from323to4495kgha4. Generally, thebehavior of theheadfireswasmorevariablethanthebackfireswith fire intensities varyingfrom 93 to 3644 kJ s4 m4 fortheformerand20 to 160kJ s4 m4 for thelatter. Introduction
the biomass and fire behavior associatedwith the controlled burns.
Oneof themajordevelopments in fire ecology in Aft/caoccurred in 1992 when the SouthernAffi• Fire-Atmosphere Research Initiative(SAFARI)waslaunched to investigate theeffectof biomass bumragonthechemical content of theatmosphere. Thediscovery of significantly elevated concentrations of ozone(03) overlargepartsof the tropics,particularly overthe southern tropicalAtlanticOcean betweenAfhca and SouthAmericaduringthe periodAugustto Octoberevery year providedthe originalstimulusfor a major research investigation in the formof the Southern TropicalAtlantic Regional Experiment (STARE).The STAREresearch programwas designed to investigate the chemicalcharacteristics of the ozoneenriched air masses overthe southern tropicalAtlanticandto study thesources of thetracegases of theseairmasses. STAREconsists of two majorintegrated research components, namely,Tramportand
Eightofthetencontrolled bumswereappliedto smallexperimental plotsofapproximately 7 hain sizeandthecontents of thispaperwill belimitedtoandfocused ontheseeightsmallexperimental bums. Procedure
Sevenof theaforementioned smallplotsformpartof a long-term burningexperiment thatwasinitiatedin 1954to determine theeffect
of season andfrequency of bumragon the grassandtreesavanna vegetation ofthePretoriuskop areaof thesouthwestem portionof the KrogerNationalPark(25 deg10min S, 31 deg16minE). Theplots hadbeensubjected to biennialburningtreatments for 38 yearsand thecontrolled bumsappliedduringthe SAFARI-92projectformed partof thenormalexperimental treatments. The eighthplot,which wasapproximately of equalsize,waslocatedin the sameareaand Atmospheric Chemistry neartheEquator-Atlantic (TRACEA) which hadnotbeenburntfor38 years. addresses the sourceregionsin Brazil andthe long-range transport The application of the experimental bumswas dividedinto two andlarge-scale distribution of pyrogenic pollutants overthesouthern phases. FourplotswereburntduringAugust1992,andtheemissions Atlantic;SAFARI which investigates the emissions from savanna from thesefires were monitoredby the researchteam from the firesin southem Africaandtheirtransport across iheAfrican UnitedStatesForestService.The remaining fourplotswereburnt continent [Andreae etal., 1992].The SAFARIprojectcommenced in duringSeptember 1992,andthefire emissions weremonitored by August1992,and oneof the majorelementsof the projectwas a thefull compliment of researchers thatparticipated in the SAFARIgroundcomponent whichmonitored 10 controlled firesin theKruger 92 projectin theKrugerNationalPark. National Park in South Africa and involved the characterization of As partof thegroundcomponent projects in SAFARI-92the fine fuel loads(diameter< 6mm), comprising mainlystanding grass materialbut alsoincludingforbs,seedlings, and grasslitter, were Copyright1996by the AmericanGeophysical Union. characterised by estimating the amountof fine fuel beforeand after theapplication of the experimental fireson the smallplots.These Papernumber96JD00691. 0148-0227/96/96JD-00691
$09.00
datawereusedto calculatethe fuel loads,the bum efficiencies, and 23,531
23,532
TROLLOPE ET AL.: BIOMASS/FIRE BEHAVIOR IN SMALL BURNS
the fire intensities for the differentsnmllexperimental burns.Two methods were used to characterize the fine fuels. The first method
60cm heightstop
involvedtheuseof an apparatus calleda diskpasturemeter(DPM), andthesecond methodcomprised harvesting thefinefuelin clipped quadrats [seeSheaetal., thisissue].Two separate teamsof scientists wereinvolvedwiththesetwomethods butin thispaperattention will be limitedto describing the use of the DPM for characterizing the biomass of finefuelsexceptfora briefcomparison of theprecision of
Central rod
L,evelof mclcr reading
Rubberhandgrip
the two methods.
The ignition proc•ure for the applicationof the small experimental burnsis illustrated in Figure1. Sleeve Briefly,the proc•ure comprised ignitinga backfire alongthe leewardsideof theplotin relationto thedirection of thewind.Once thebackfirehadspreadadequately to forma wideenough firebreak, a headfirewasignitedsimultaneously alongthetwowindwardsides of theplot.Thisignitionproc•ure wasusedbothforcontaining the firetotheprescribed areabeingburntandtoprovidetheopportunity Threaded socket forrecording thebehavior of theheadandbackfiresin relationto the Base-plate typesof smokeemittedbythesetypesof fires. D•sc The atmospheric conditions pertainingat the time of the burns andthe behaviorof the firesappliedto the smallplotswere also Herbaceous grassmaterial recordedas oneof the main objectives of this component project. Finally, grassand bush surveyswere conducted in the small experimental plotsto serveas a generaldescription of the savanna vegetation in whichthesmallexperimental bumswereappliedin the Figure2. The diskpasturemeter(DPM) usedfor estimating f'mefuelloadsin theSAFARI-92project. KrugerNationalPark. Fine Fuels
TROLLOPE ET AL.: BIOMASS/FIRE BEHAVIOR IN SMALL BURNS
Table 8. The Recoveryof the GrassSwardDuring the First GrowingSeasonAfter the Small ExperimentalBums in the SAFARI-92 Project. Plot
Kambeai
PrebttmStanding Crop,
PostGrowing Seas• Crop,
kgha4
kgha-1
Recovery, percent
3
5130
3373
66
3453
3373
98
5
3524
3087
88
Shabeai 1
2135
1444
68
Nttmbi 4
2135
2471
116
Shabeai 5
Kambeai
Faai 4
1387
2471
178
Faai 1
1057
3531
334
Mean
2689
2 821
105
Data expressed m kilogramsperhectareandasa percentage.
deforestation and accelerated slashand burn agriculture which revolve a netrelease of gaseous chemical compounds, particularly C02,intotheatmosphere.
Conclusions
One of the phmaryaimsof the SAFARI-92projectwasto characterize the emissions frombiomass burningin the savanna areasof southernAfrica and to determinetheir effecton the chemical
content of the atmosphere. It is therefore pertinent to determine whether thebehavior ofthefiresapplied duringthecontrolled bums
intheKroger National Parkwererepresentative offiresocctahng in thesavanna areas. Unfortunately, it is notpossible tomakea direct comparison with field scalebumsoccumng in the affected areas
because suchfiresare not characterized or monitored in any quantitative wayeitherm theKrugerNationalParkor elsewhere in Africa. Nevertheless,fire behaviorstudieshave been conductedin
thesavanna areas ofSouth Africa,primarily in theEastern Capeand theKroger National Park,andreported uponbyTrollope [1978]and One of the unique opportunities providedby the small Trollope andPotgieter [1985].Whilethese restfits donotprovide an experimental bumswastotestthehypothesis thatcontrolled burning overalldescription ofthebehavior of firesin thisregionorelsewhere as a range managementpracticem savannaareasresultsin a in thesavanna areasof Africa,thedata do indicate therangeof temporary releaseof gaseous emissions to the atmosphere. These conditions underwhichfirescanand do occurin thistypeof Recoveryof VegetationAfter Fire
emissions areprimarilyin theformof CO2whichis thenreabsorbed vegetation in southern Africa.
bythevegetation viaphotosynthesis whentheplants regrowdubrig Asfiresin thesavanna areasoccur during thedrywinterperiod thefollowing growing season. Thisphenomenon wasinvestigated by whenthe herbaceous vegetation is highlyinflammable, the most estimating thestanding cropof freefuelwitha diskpasture meter important factorinfluencing fire behaviorand in particular fire thathadaccumulated m sevenof theeightsmallplotsat theendof intensity, is theamountof freegrassfuelavailable for combustion. the first growingseasonafter the applicationof the small Consequently, thefiresappliedduringtheSAFARI-92projectwill experimental bumsin the KrugerNationalPark. The resultsare be compared with fire data collected from experimental bums presented in Table8. appliedin the EasternCapeand the KrogerNationalPark for Theresultsin Table8 indicate a meanrecovery of 105%in the comparative purposes. Theresults arepresented in Table9. standing cropoffinefuelsin relationto prebumlevels.Of course the It is clearfromthe resultspresented in Table9 thatthe small recovery rate variedfromplot to plot and the true recovery is experimental bumsappliedduringthe SAFARI-92projectwere confounded by theeffectsof grazingungulates like whiterhinoceros, conducted withintherangeof fuelloadsandfire intensities thatcan wildebeest, zebra,and sableantelopewhichwere attracted to the and do occurin the savannaareasof southemAfrica. The minirotan youngnutritious grazingon the plotsafterthe bums.Nevertheless, fuelloadsandfire intensities wereslightlylowerthanin theother thesedatalendsupport to the viewthatthe majoremissions from datasets,but takenin the contextof the relativeimprecision firesin theformof CO2associated withthenormalburning of the involved in themeasurements of thesetwovariables, thedatacanbe Afri• savannas sincetimeimmemorial, areof a cyclicnature,and assumed to be within the generalrangeof thesetwo variables.
are not from the formsof biomass burningthat are havinga Thereforeit can be concludedthat the researchdata collectedon significant effecton the changes thatareoccumng in the chemical emissions fromfiresmonitored in theKrugerNationalParkcanbe contentof the atmosphere. The more probablesources for these usedfor extrapolating to firesburningundersimilarconditions in emissions are thosetypesof biomassburningassociated with savanna vegetation in thesubcontinent.
Table9. Comparison oftheGrassFuelLoadsandFireIntensities Recorded DuringControlled Bumsin the Savanna Areasof the EasternCapeandthe KrugerNationalPark in SouthAfrica. Data
EasternCape
FuelLoad,
Mean Maximum M•imum Numberoff•es Coeffi•ent Vari•itm, Percent
KrugerNationalPark
FireIntensity, FuelLoad,
SAFARI-92
FireIntensity, FuelLoad,
kgha4
kgha4
kgha4
kgha4
kgha4
4233 10500 1477 132 39.8
2607 12912 213 132 85.8
3552 6850 1152 121 37
2351 8960 136 121 70.5
2092 2295 323 8 60.9
FireIntensity,
kgha-1 1309 3644 93 8 85
Tablealsoisa cox•arismwiththegrass fuelloadsandfireintensifies recorded during thesmallexperimental bumserinducted inthe KrugerNationalParkaspartofthe SAFARI-92project.
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(e-mail:AndreP(•_•Parks-SA.CO.ZA) W. S. W. TrollopeandL. A. Trollope,Department of Livestock andPasture Science, Facultyof Agriculture, University of Fort Hare,Alice,5700, South