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Australian Savanna Eco System S J.J

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Australian Savanna Eco System S J.J AUSTRALIAN SAVANNA ECO SYSTEM S J.J. Mott*, John Williams**, M.H. Andrew*** and A.N. Gillisonf * CSIRO Division of Tiopical Crops and Pastures,Cmnirgh;; Laboratory, St. Lucia, Australia e. 4067, ** CSIRO Division of Soils,Davies Laboratory, Private Mail Bag,P.O. Aitkenvale, 4g14, Australia :F:t* CSIRO Division e. of TropicalCrops and Pastures, Darwin Labor-atories,private Bag No. 44, Winnellie, NT 5789,Australia. t cSIRo Division of Water and Land Resources,P.O. Box 1666, Canberra City, AcT Australia. 2601, SUMMARY within the Australiansavannas-six.major groupshave been recognisedon the basisof the graminoid understorey'I.n all groupsthere is a dominant stimm,ergrowing season ,rrltr, lttt. productivity in winter months. characterisationof the mainlimiting.factors to produciivityrf,o*, thut ttretropical Monsoon Tallgrass has the most scvereenvironment system with a winter'droughtani pred<rminaninutrient limitation subhumid svstems to grofih. In the the higher-soil fertility in the S"ubtropi;Ji;ii;;; compensates climaticenvironment' for a less favourable but in the inlandsemi-arid communities bottiincreasing aridity combineto limit plant production. and low nutrientsoils Throughoutthe subhumid,uuunnu" ii..,iither natural almostannual occurrence. or man-inducedis an In termsof functionaladaptations to the stressesof the savannaenvironment, plants show to thoseoccurring in manysimilarities speciesin othercontinental savaffia systems. In ecosystemfunctioning limitation of the severenutrient the northerngroups closely parallel those conditiorr .*lrtirg savannas. in west and central African vertebratebiomass is low on all savannatypes with p-roductivityof both nativeand introducedspecies being curtailedbv low herbagequality in the driei months.'Invertef;"1";,;;;;;i"lly termites,reach high biomass levelsand play a majorpart in tirefunctioning of the ecosystems,especially in termsof nutrientcycling. SCOPEAND DESCRIPTION Introduction Australian savannalands form wide a continentalarc that extendsacross the northerntropical landsdown to the sor'rth-easternsubtropical zones, and extendfrom the humid coastalareas inland until they abut the Ti'iodia spp'.hummockgrasslands arid and the wetterreaches of the arid,Acacla shrublands(Figure I Theselands have a graminoidunderstorey ). of variablefloristic compositir:n-a ,pi.Oo.inantly eucalyptupper stratum. d, DARW OWNSVILLE TROPICAL SAVANNAS OF AUSTRALIA ! *onsoo* TALLGRASsEl *,oo"o"" FFFFIM rnorrcAL TALLGRAsS FFffi ffi r,on"oss oil cLAysorls SUB-TROPICAL TALLGNA SS WZ ru""o"K GRAssLANDs - ARID/HUttD ZONELtt{E Figure l. Main vegetationtypes in the Australiansavanna zone. Australian savannas 5'1 'l'he:rsualdescriptionfbrsavannalikeformationsinAustraliaisthegenerictermwoodland'Ithasbeenused (e-'g'Carnahan' 1976)' ln this wav it both for systemsorrt.u.iu.ui".g.laiion whichmany authors (e'g' "tassifi"^tii"^""a-Limuppin"gar,tt. e*p'.nseorirt. giutiioidiltttnt hasemphasised ttre wood] ipp.i-sru,urn functionalelement' andWalker, iS83j asthe dominant a, Q. 4067, Bourliereand Hadley, 1970;Huntley "ontiaJt (calabv' 1980)' In thosein A;;;lt;;;;;ie*.natiu" herbivores In contrastwith African.savannas, over the rr*, d*;;;.ld;able variationin climate Quaternary [, Australia commonwith other *..ri"ruiurr"r,'tt.r. etal',1976 VanderHammen' 4,Winnellie, period,butithasu."nr.Iuiii.iy^;;;t[;;.tth^.1"r;ioooov""*(Bowler records(Kershaw' puit.ottfr.*.tti.."-.nt, aithoughpalvnological 19g3).Fire tu. uppo..nil;'iffi il;; yearsago' iJl*itg of abJrieinalman some 30'000 ACT 2601, indicateit may have'incre'aseCin importance been 1984) ;an,"tival ttre majoritv-of the subhumidlands have the past 150 ioi'l'JJ"glrt.-arrival E;;;;;; andburn over v.u.r, "*ii"r "f aboriginalman was not involvedin the slash years.prioi to the of .urop.un'f pastoral burntin most p"artsof the world' More recenteuropean is u tu"t- it ,utanna formatiot;;th* agriculturewhich p*r qualitvof dry seasonforage (Mott e/ a/' t u, ,.-uinlJ at a low t"u.t, .onrtrui;;;y';;; usec,f savannu, much slo*er aciumulationof fuel (Walker' le graminoid frequentin the arid:Tli;;;;",1t. of lggl). Fires are less forageresource' intermonths. pJricvorn." preventionto protectthe valuable lggl) anda deliberat; the presentecosyste.ms might be lgtasssystem and possible,"."nt ,nlr*res in fire frequencyl Given increasingaridity of th"s" changesis illustratedbv rowth.In the bf rapibecological consideredto be in a state "h"r;;.tl;p*.ntiui*"gnit,ide a largepart of the subhumidsavanna ls favourable of theunderstoreyof thechange in thefloristic australis dominatedsystem to nutrientsoils ""d;ililiEompo.itiJnThe understorey from a Themeda of south-easternQueensland. "^ft*gta periodin the late nineteenth 'inducedis an rru"ri.*'l"iri;;; a fortv-vear nredominantlyu nrtrroi;in loiiortrr ";.r of burning'However' resultoi tttt"p g'"ting and.incre.attd f"qutn"y ientury (Shawand Bisset,i955;, asthe sectionsof the 'ot'iniJniiut uititufture.it appearithat large ry similarities apart from completeclearing of-some. u..u, andfunctional properties. gverenutrient ffi;;;il i.iuin tt.i. o.iiinal physiognomic ntral African t" as tropicaldistribu,i:l savannas'However' speciesbeing ttft{rlf i{.f|ir has hishlishtedthe widespread :11"*tulian which are Africa, thereare areasof extra-tropicalvegetation highbiomass alsodescribed by Huntre! f r!g3.; for southern review'within r";;;;;.,u"a *" in"rudethese tesions in this cycling. structurallyand functionJi'#ti";;;;i;"i in a wide r"i;';rd;li;tic characteristicsw:hich are reflected thesavanna areas there are major variations i" ';;rx:t";:;x:;':;:;:"ll,lT* savannarandscapes andpedorogical characteristics of Australian ryg q:gloc1.ul of theselandscapes are zi '1., 1963t,;;i.ates that the soilsof manv (cole, 1983;Beckmann, i'9-83'-nr?ur. low nutrientstatus processes^ri'irt"i iltir is probablyresponsible for the weatheredrelics of earlierpedological morerecent landsdown to with thedeeply weathered planation surfaces are of manysoils on theseland surfac-es. lnterspersed weathered abut the arid drainagepuitt'n' that extendwest from Tertiary alluvial depositsin Uroui-f-, oi un"oo.dinuted formedthe ). Theselands t.dl;;;:; iog"trttt with basalticintrusions' have surfacesin centralQueensland. Argillaceous per shatum. nutrientstatus clay soilsin the savannazone' basisfor the originof tirefaige areas of better zV WNSVILLE SOILS OF NORTHERN AUSTRALIA so''" N s*ererrr sotrs ffi "r"ou,o,,ot" [\'s]lJ rexrunscolrnesr EEI-III oEEP ffi li::riiiliil sANDs c"^c*trcc.e"s - ABIO/HUMIO ZONE LINE ffi zone' Figure2. Major soil typesof the Australiansavanna 58 Ecology and Management of the World's Savannas Soilsof the savannaregions of Australiafall into fivegeneral groups (Hubble et a|.,1983) (Figure2). Tables I a11d2 presentsummarised data for the moisture regimesof major subsurfacesoil types a1{ th9 nutrient contentofthe upperl0 cm in all soil typesapart from shallowstony soils [see also Butler and Hubble (1977) andWilliams (1983)1. Thble l. Estimated water holding capacities(WHC) for subsurfacesoils of different textural classesfrom savannaregions of Australia. Soil type Clay * silt Water-holding capacity Available meancontent mm/cm depth WHC (A)o7o wt. o/o, oven dry Non-available Available Total WHC hne earth (NA) (A) (NA+A) Deepsands l0 0.3 1.4 8l Massive sesquioxidicsoils 5t 1.0 1.9 64 Crackingclays (a) Surfacesealing IJ 2.7 l.l 29 (b) Selfmulching 86 3.r 2.2 42 Data from Staceet al. 1968and Stirk 1972. Table 2. Some chemical properties for surface horizons of several major soil groups of the Australian Savanna. Massive o/o o/o Available Total CEC* Exch Ca sesquioxidic pH organic PfP meqo/o meqo/o soils: C N ppm ppm No. of samples 16 16 81615 16 16 Mean 6.10 l.0l 0.08 4.5 20s 8.70 3.09 Standard error of mean 0.14 0.17 0.01 0.5 32 1.30 0.05 Max. 6.90 2.30 0.l4 10.0 570 2r.oo 7.70 Min. 5.00 0.06 0.04 1.0 60 3.13 0.81 Texturecontrast soils: No. of samples 29 29 29 29 29 29 29 Mean 6.17 1.59 0.19 25.2 314 14.70 4.48 Standarderror of mean 0.t2 0.17 0.04 5.2 4r r.66 0.63 Max. 8.10 4.90 0.76 130.0 ll50 46.3 14.00 Min. 5.10 0.29 0.02 3.0 50 t.6 0.18 Crackingclay soils: No. of samples 30 30 28 30 29 29 29 Mean 7.46 r.57 0.14 58.8 486 45.00 29.9 Standarderror of mean 0.l5 0.25 o.02 r7.2 168 2.70 2.2 Max. 8.80 6.50 0.61 480.0 4960 74.0 sz.O Min. 5.70 0.2s o.o2 2.2 50 23.0 8.0 Deepsands Mean r.20 0.07 10 200 Data for Deep Sandsis from Westonet al. (1981). All other data was suppliedby Mr G.D. Hubble, CSIRO, Division of Soils. Brisbane.The data refersto the 0.10 cm depth interval. f Available phosphoruswas that extractedwith 0.5M sodiumbicarbonate adjusted to pH 8.5 and shakenfor l6 hoursat2O"C. * Cation exchangecapacity was determined at pH 7.0 using ammonium chloride and the ammonium absorbedin the extractionofthe exchangeablecations. Australiansavannas 59 2).Tables Thesesoils groups, with the relatedsoil taxonomy(Soil SurveyStaff, 1975) orders in parenthesesare: ,enutrient l. Shallow Stony Soils(Entisols and Inceptisols).These soils are characterisedby a shallowstony solum, ie (1977) generallyless than 30-50 cm deep.Sandy to loamymaterials - oftenearthy in character- predominate.They arevery low in organicmatter and essential plant nutrients and support only a sparsevegetation, but occupya largearea of northernAustralia (see Figure 2). ssesfrom 2. DeepSands (Entisols). These sands have minimal profile development and are generallymore than I m deep.Water storagecapacity is very low, leachinglosses lrom healryrains are high and grossdeficiencies of manynutrient elements are typical. There are large areas in thewestern and central deserts of Australia,where hazardfollowingdisturbance ofthe surface.There are also extensive areas ofthis dlable winderosion can be a serious zoneofcentral north J (A)yo soiltype in the savanna Queensland. 3. CrackingC/ays (Vertisols). A divrrsegroup of finetextured soils that swelland shrink seasonally resulting metre.They areoften self mulching,although some form thin surfaceseals IWHC in cracks,often to a depthof one {+A) duringrainfall. P contentvaries widely, but in generalthe soils are potentially the most fertile of thesavanna zone.
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