13B I O D I V E R S I T Y 5 ( 4 ) 2 0 0 4

Kurt W. Cremer

PO Box 275, Cooma,NSW, 2630, Australiakcremer@snowy.net.au

Abstract. Fire is a widely used vegetat ionmanagement tool, particularly in Australia, whereresearch has generated a large amount of informationbut the patterns and principles apply extensively alsoto many other parts of the world. This paper is forworldwide readers, as well as for local fire ecologists.At present, much of the burning seems to be donemainly to satisfy public expectation concerningprotect ion of l i fe and property. Burning forenvironmental conservation may sometimes be impliedbut is still rarely mentioned by fire managers.

Australia’s vegetation has evolved with fire, and nowvariously copes with, and even depends on, a range offire regimes. Strategies for coping with fire vary withspecies and vegetation. In tall, moist forests fires tendto be rare but kil l nearly all plants and induceregeneration from seeds that are either stored on thecrown or in the soil, depending on the species. In dryforests, fires tend to be frequent but they rarely killthe trees or the undergrowth. The undergrowth andthe smaller trees tend to be killed back to the groundbut recover from subsoil buds. Although there is muchtolerance to fire, excessive frequency and severity ofburning are likely to change the vegetation to moreresistant species (e.g. from woody plants to ferns orgrasses) and to degrade soil fertility.

Since bush fires also threaten people and theirproperties, prescribed burning is used to reduce fuelsto safer levels. Unfortunately, such fuel reductions havelittle success in mitigating severe fires, and the ratesof fuel accumulation are mostly so fast that such burningneeds to be so frequent (mostly every 3-5 years) thatserious concerns arise about the conservation ofvegetation and fertility. There is ongoing research anddebate about this to clarify aims and resolve conflicts.Fire plays a major role in biodiversity protection all overthe world.

INTRODUCTIONThe aim of this article is to provide a better understandingof the importance of fire in maintaining vegetationbiodiversity in Australia and to improve the effectivenessof fire management. After agriculture, fire is the mostpowerful and widely used tool to manage vegetation andit is a major factor in biological diversity throughoutmuch of the world. It has become a major issue inAustralia. There is an opportunity to apply thisinformation to biodiversity protection elsewhere.

BACKGROUNDThe vast expanse of Australia has a wide range ofclimates and hence a wide range of vegetation and fireenvironments, depending mainly on rainfall (or, moreprecisely, on the ratio of rain to evaporation). Rainforests,confined to the wettest places, now cover less than 1%of the area. They occur extensively in Tasmania andpatchily near the east coast of the mainland. They tend

to burn only once in ~ 100-400 years. The other forestsare ‘open’, i.e. they have sparser canopies, and aredominated by just one genus, Eucalyptus, except in someof the driest types of forest. The open forests range fromthe relatively few, relatively rarely burnt (~ 50-100 years)‘tall-open’ or ‘wet sclerophyll’ forests in the moisterareas to the more common ‘open’ or ‘low–open’ forests,also called ‘dry sclerophyll’ forests ( burnt every ~ 5-50years), and to the most common, driest, most openand most frequently burnt ‘woodlands’. By far thegreatest part of the mainland is semi-arid or arid and iscovered by desert or variously sparse grass or shrubvegetation. The sparsest vegetation burns only whenenough fuel is built up by a (rare) wet season. In thetropical north (with very wet summers and very dry‘winters’), massive amounts of grass are produced everyyear and these are burnt extensively every ~ 1-3 years.There have been fires here for at least tens of millionsof years (generated by lightning) before the aboriginesarrived some 40,000 years ago and added their burning.Some 20 million years ago, much of the land was wetand covered by rainforests. With the drying of the climateand the increases in fire frequencies, the rainforests havealmost disappeared and been replaced by vegetationsbetter adapted to drought and fire. After rainfall and fire,the most important environmental influence is soilfertility. Declines to generally low soil fertility, due toleaching, erosion and probably due to burning of thesenow ancient land surfaces have boosted the trend to moreburning and to more flammable vegetation.

The total effects of fire depend on the “fire regime.”This covers fire types (surface, ground, and peat) andintensities (height, depth, and intensity), as well as firefrequencies, season of burning, spatial extent of the fire(ha), and spatial variabili ty (mosaic burns). Firebehaviour depends to a great extent upon the types andquantities of fuel available. The most important type isthe fine fuels: litter <6mm thick, plus grasses. Fine fuelsare the fastest to change in moisture content, and thusthe fastest to change in flammability with changes in fireweather. The aim of hazard reduction is typically to keeploads of fine fuels below ~ 10 tonnes/ha, because firesin heavier fuels are hard or impossible to control undersevere conditions. With some moisture, only some ofthe litter (and little of the humus/peat) may be able toburn. If abundant and continuous, the low undergrowthcan be even more important than the fine fuels indetermining the behaviour and effects of fire. Underextreme fire conditions, much of the taller undergrowthalso becomes available as fuel. Certain fibrous and ribbon

Biodiversity protection:Effects of fire regime on vegetation in Australia

ABOUT THE AUTHOR:Kurt W. Cremergraduated withforestry degrees fromthe universities ofSydney and Tasmania.He worked insilvicultural research,and retired in 1987 asPrincipal ResearchScientist with CSIRO(CommonwealthScientific andIndustrial ResearchOrganisation) inCanberra. Kurt’smajor interest in fireecology is fromstudies on theregeneration ofEucalyptus regnans inTasmania.

14 T R O P I C A L C O N S E R V A N C Y

barks can greatly accelerate the spread of fire bygenerating fire brands carried by strong winds tostart spot fires, 10s or 1000s of metres ahead of themain fire. Heavier branches and logs contribute littleto fire behaviour, but can be important for locallyheating the soil or by causing fire scars if they burnnext to a tree trunk.

SUCCESSION IN A TALLMOIST EUCALYPT FORESTA look at the moistest, densest, tallest, and mostrarely burnt of Australian forests illustrates the mostdramatic effects of fire and a recovery that dependsalmost entirely on seeds, not on resprouting. A hotfire tends to kill and replace such a stand entirely(based on Cremer 1960, Cremer & Mount 1965).(See Figs. 1 & 2)

Consider a s tand of Eucalyptus regnans, theMountain Ash, at up to ~100 m high, the world’stallest flowering plant. This example stand is now70 m tall and all the eucalypts in it are 300 yearsold, having germinated after a fire 300 years ago.As the site is fertile, the ‘undergrowth’ is a simple,dense, temperate rainforest dominated by just twowoody species: Nothofagus cunninghami (AntarcticBeech) and Atherosperma moschata (SouthernSassafras). These are up to 30 m tall and of variousages, mostly close to 300 years old. There is alsoa profusion of mosses, liverworts, and ferns onthe ground and on the tree trunks. Since theeucalypts began seeding, about 280 years ago,eucalypt seeds have germinated here almost everymonth, but no new tree was able to establish,because light intensities near the ground are toolow: ~2% of full daylight. If not burnt during theirl ifetime (~450 years), the eucalypts will die,without regeneration and without a store of seedin the soil. The rainforest species, being moreshade tolerant, may continue to regenerate: a self-perpetuating vegetation climax is then reached.Eucalyptus regnans is thus both fire sensitive anddependent on fire for its regeneration.

Now consider that a fire occurs, burns deep layersof humus and thus girdles all the trees. As these oldeucalypt cannot coppice, they all die. Only some 2%of the Nothofagus and Atherosperma manage tosprout. Tree ferns survive as do ferns that hadrhizomes within the mineral soil below the burnthumus. The ground is now virtually bare of all livevegetation.

The ground is then colonized rapidly. Mosses(mainly Funaria hygrometrica and Ceratodonpurpurea) and the liverwort Marchantia polymorphacover ~ 90% of the ground in 1 year and ~99% halfa year later. These ancient, highly mobile bryophytes

Figure 1 (top). A one-aged, wet, old eucalypt forest overtopping a rainforest understorey, notburnt since the fire ~300 years ago that gave rise to both.

Figure 2 (bottom). A one-aged, wet, young eucalypt forest resulting from a fire 39 years agothat had killed nearly all of the previous forest and its undergrowth. The skeletons of someof the old killed eucalypts are still standing.

(All images in this article credit to the author).

15B I O D I V E R S I T Y 5 ( 4 ) 2 0 0 4

occur worldwide in similar situations. They depend onhigh supplies of nutrients and moisture. As the nutrientsupply diminishes with time, they are replaced by theless nutrient-demanding moss Polytrichum juniperinumat 3-5 years after burning. Another mobile fireweed,Senecio minimus, a herb of the daisy family, also takesadvantage of the cleared and fertile ground. It reachespeak abundance ~2 years after burning and then dies.The ferns resurge more slowly but continue indefinitely.Regeneration of the woody plants is mainly by seedfrom two sources. The eucalypts grow only from seedpresent on the crowns on the burnt site at the time ofburning. They germinate within ~ 1 year. Should anyseed fall from a surviving old tree at more than 2 yearsafter burning, it will find the seedbed occupied and nolonger receptive. Regeneration from the two rainforesttrees is mainly of similar origin, but so modest at firstthat it is hardly seen in the early years. The initiallymost abundant regeneration of woody plants is fromimmobile seed stored in the soil for more than 100years, mainly Acacia dealbata and Pomaderris apetala.The plants that had produced these seeds had died ofold age in that ra inforest more than 100 yearspreviously. Had the forest been younger, the abundanceof seeds still surviving in the soil would have beengreater. The fire boosted the germination of these seeds.Any germination at other times is ineffective, as thesespecies also do not tolerate shade.

Succession after fire can also follow other paths,depending on fire intensities and frequencies, and on theage and composition of the forest. Should the above forestremain unburnt till the eucalypts have died, it will becomea pure rainforest. Should the young eucalypt forest beburnt and killed before the new eucalyptsproduce their first seed, at 15-20 years, theeucalypts will not be replaced. A couple ofmore fires soon after that could exhaust thesupply of ground-stored seeds as well, andleave the site occupied by dense bracken. Firecould thus eliminate the fire sensitive speciesand produce a highly fire prone but highlyfire tolerant vegetation. This brackenvegetation is of low value and of lowbiodiversity, and it is not rare in Tasmania.Fire of sufficiently high frequency is thuslikely to eliminate the ‘obligate seeders’ andreplace them with the more fire tolerant‘sprouters’.

For the local maintenance of E. regnans as aspecies, fires should thus occur at least every~ 400 years (before it dies) and at most every20 years (after it starts seeding). Keepingimpressive stands requires that intervalsbetween stand-replacement fires be more than100-200 years.

SUCCESSION IN A LOW DRY EUCALYPT FORESTThis example illustrates Australia’s more common drierforests, and fire effects that are quite different from, andfar more widespread, than the above. Most plantindividuals, although injured to various degrees, survivethe fire and the forest structure remains largely intact.The forest is usually dominated by eucalypts, but the treesare of many ages. Mount (1979) enumerates evidencesuggesting that eucalypts not only are adapted to copewith fire, and even need fire, but also produce fuels thatpositively attract and promote fire. This gives theeucalypts a competitive advantage over the more firesensitive rainforest species. The eucalypts shed abundantfoliage, bark, and branchlets and these decompose slowly,accumulating as highly flammable fuel. During fires,bark on many trees produces floating embers that spreadthe fire. Even the live leaves are relatively flammable,because they contain oils and waxes, but relatively littleminerals and water.

Fire can occur every 3-6 years, but may be absent formore than 50 years. The larger trees usually survivefire with their trunks and at least their major limbsintact, but the undergrowth tends to be killed back toground level, together with the smallest trees. If thefoliage of the eucalypt trees is scorched or consumed,the surviving branches and trunks sprout shoots. Theburnt down vegetation sprouts from underground buds(Table 1). Even though the aboveground portions ofthe grasses and o ther herbs a re the most eas i lycombusted parts of the whole vegetation, these plantsare the first to recover fully. After one year withnormal rain, they tend to look better than before thefire (see Figure 5).

Figure 3 (left).A low open eucalyptforest 1 year after firehad killed all itsfoliage. Sprouting ofnew shoots wasconfined to those partsof the tree where budshad survived due tothicker bark: mainlythe trunks of the largertrees.

Figure 4 (right).A smooth-barkedeucalypt shedding theouter bark that hadbeen killed by fire ayear earlier. As all theinnermost bark hadsurvived, no butt scarwas formed.

16 T R O P I C A L C O N S E R V A N C Y

The undergrowth in low, dry forests varies from almostabsent (on the poorest, driest sites) to a wide range indensities and heights of grasses or shrubs or both. Fertilesites tend to promote grasses, especially after frequentburning, and infertile sites shrubs (Watson 2002). Whilefire accelerates seed shed, and stimulates the germinationof soil-stored seeds, the establishment of new plants from

seed tends to be much lessprominent than sprouting.Indeed, on harsher sites withlow and erratic rainfall ,establishment from seed tendsto depend on wet spells thatmay not occur till many yearsafter burning. Recruitment inthe dry forests tends to belimited not by light, but bycompetit ion for water andnutrients, and by weather.

In the drier forests, most newgrowth after burning is fromthe recovery of plants thathave been partly or entirelykilled back to the ground, butnot below the ground. Wherethe recovery is from rhizomes

or by sprouting from roots, the number of new plantsmay actually be considerably larger than before the fire.Such vegetative spread occurs also without fire. Abilityto resprout from underground may vary with the species,vigour and age of the plant burnt, and with intensity,season and high frequency of burning (Gill 1981). Abilityto sprout from underground may be much reduced if thefire was hot (e.g. Stoneman 1994). Plants whose budsare just above or just below the soil are far more likelyto die after a hot burn on dry soil than after a cool burn.Depletion of food reserves, especially when the newsprouts are grazed intensively, may explain many deaths.

Purdie (1977) studied effects of controlled burns ofmoderate intensity (~1000 – 4000 kW/m) in a dry forestat Canberra (ave. rain 626 mm/yr). Of the 64 specieswhose mode of recovery she observed, 11 were annualsand grew from soil stored seeds. Of the 53 perennialherb and woody species, 49 (i .e. 92%) recoveredvegetatively (11 by sprouting from bulbs, 19 fromcoppice, 12 from root suckers or suckers plus coppice,and 4 from rhizomes). All species, except those withbulbs or rhizomes, produced seedlings, most from soil-stored seed. In contrast to the very low mortality ofsprouts , the mortal i ty of seedl ings was high, asexpected. But, because rainfall in the two years afterburning was high (~1000 mm/yr), many seedlings did

1 sidubehtnehw,)0P(,orezsinoitcetorPrettebsinoitcetorP.erifehtotesolcroni

erifehtevobahgihsidubehtnehw

fosdubyramirp.g.e(sdubdekaN1.1 sutpylacuE ).g.e(sdubderevoC2.1 sugafohtoN )

krab)mm2<(nihtnihtiwsdubcimrocipE3.1

1-0P1-0P2-1P

2 -0(dnuorgehtotesolcdetacolsdubhtiWdedivorp,noitcetorpemossiereht,)mc1

eromnevedna,tsiom~siliosehttahtleufelttilylnosierehtfinoitcetorp

)sessargemos.g.e(snolots/srennuR1.2sbrehettesordnasessargniatrecfosdublasaB2.2

liosehtevobarebutongilfonoitroP3.2nehtdnatoorkoot,dnuorgehtdehcuottahtsmets.e.i:sreyaL4.2

.g.e(retemaidnihcumwerg aeruprupxilaS )

1P1P1P2P

3 ,hgihyrevotetaredomsinoitcetorPgnipolevnefossenkcihtnognidneped

erifevobathgiehdnaeussit

tsom.g.e(krabkciht~nihtiwsdubcimrocipE1.3 sutpylacuE )fael)elbammalfnon~(dekcapylesnednihtiwdetcetorpsduB2.3

,nrefeert,eertssarg.g.e(sesab areidraillibalaoP )ssargkcossut

5-3P5-3P

4 gnidneped,hgihyrevothgihsinoitcetorPnoitarudnodnalioslarenimnihtiwhtpedno

eriffo

srebutongilfosnoitropdeirubehT1.4smetsthgirpufosnoitropdeiruB2.4

sessargynamfosdubnaenarretbuS3.4.ge(stoorelitcartnocybliosehtotnidellupsduB4.4 ,aeohrrohtnaX

aigrebnelhaW sblubhtiwesohtyllaicepse,.ppsrehtoynamdna,,sessargniatrec,nekcarb.g.e(srebut,smroc,semozihrnisduB5.4

allenaiD ))saicacaemos.g.e(stoornosdubsuoititnevdalaitnetoP6.4

5-4P5P5P5P5P5P5P5P

Ways in which buds are protected from fire

P0 = no protection, P5 = greatest protection. Values depend on proximity and duration of fire, etc. Notapplicable to peat fires (which are likely to kill everything within the combusted zone.

Ways in which seeds are protected from fire

P0-1 if within combusted litter or in thin fruits adjacent to scorched or to combusted foliage.P2-3 if in a (moister, lower) litter layer that remains partly unburnt, or in fruit of medium size.P3-5 if protected within larger fleshy or woody fruits (e.g. Banksia, some Eucalypts), especiallywhen high above the fire.P4-5 if deep within soil, or in large fruit, e.g. Banksia, certain Eucalyptus (even when adjacentcrown is scorched).Figure 5.

A low, dry eucalyptforest, with very

sparse undergrowthand trees and shrubs of

many ages. Althoughno fire damage is seen

here, the older treeshave probably

experienced several(cool) fires. Note the

contrasting smoothand stringy bark types.

Table 1.

17B I O D I V E R S I T Y 5 ( 4 ) 2 0 0 4

manage to survive: those established on burnt plotswere seven times as numerous as those on unburnt plots.Apparently, not all the seed in the litter was killed whenthe plots were burnt: 63 viable seeds were found in theburnt litter (compared with 609 seeds in the unburntlitter).

Amongst the mechanisms by which fire affects plantsand the mechanisms by which plants can recover fromfire, the responses of buds and seeds are crucial (seeTable 1). Except for trees, most plants recover after fireby sprouting from underground buds.

HERBACEOUS UNDERGROWTHAND GRASSLANDSIn fire prone environments, herbaceous plants areoutstanding in their ability to recover after fire. Theyattain maturity in just one growing season. Most or allof the native perennial species have subterranean budsthat survive fire and sprout readily after burning. Andthe annuals (if any) tend to have ground-stored seeds.Grasses are usually particularly well adapted to fire,mostly by having their survival buds at or below the soilsurface. Adaptations of grasses to cope with fire (andgrazing, and frost) are outlined by Lunt & Morgan (2002)for SE Australia, and by Linder & Ellis (1990) for theFynbos type of vegetation in South Africa. The mainadaptations are (a) soil-stored seeds, mainly in certainannual species, and (b) the ability of perennial speciesto sprout after fire due to protected buds arising fromrhizomes, runners (stolons), bulbs, corms, and the notabletufted (caespitose) habit.

The tufted grasses (‘tussocks’) typically form densebunches of leaves and flowering stalks arising from atight mass of buds at 1-3 cm below the soil surface. Thefour dominant native grasses of SE Australia are of this

type. This habit makes them highly resistant to fire. Butit is not clear how these buds manage to becomesubterranean. In grasses, any seeds that germinate withinthe soil do keep the basal buds underground. However, itis more likely that the seeds (especially of species withshort-lived seeds) germinate at the soil surface andproduce a basal bud at the surface. The indications (atleast for Poa sieberiana and Austrostipa scabra) are that,while the first bud produced after germination may be atthe soil surface, new buds (tillers) budding off from thebase of a previous bud are deeper in the soil, and thissequence of deepening continues till a suitable depth isreached. A further factor in the resistance of tuftedgrasses to fire is that the leaf and stem bases emergingfrom the soil are resistant to combustion because of theirdense packing and because they hold much soil betweenthem (and thus starve the fire of oxygen). The presenceof much of this entrapped soil is due to being pushedthere as new tillers emerge from below the ground at theperiphery of the tuft. Some tufted species develop a deadcore as they age and spread peripherally, but even thedead core remains remarkably resistant to decay and tocombustion.

Writing mainly about America, Daubenmire (1968)concluded that frequent fire tends to change woodyvegetation to grassland (and conversely, rarity of firestends to allow woody vegetation to invade grass lands),that fire is often mainly beneficial to grasses (and makesthem more palatable and nutritious), that grass fires areusually much cooler than forest fires (especially at groundlevel) and that seeds lying right on the ground maysurvive fire, while those on the plants or on the litter donot. These conclusions also apply in Australia, with theadditional comment that survival of seeds on the groundprobably depend on how hot the fire is.

Figure 6.Sketch of the base ofa young grass bunch,showing how basalbuds can becomesubterranean.

18 T R O P I C A L C O N S E R V A N C Y

HEALTH AND REJUVENATION OF PLANTSMany woody species of the undergrowth have short lifespans and their vigour declines after some 20-50 years.They may be rejuvenated by fire, either by sproutingor by growing new from seed. Such fire needs to occurbefore the seeds in the soil have all died. Also, just aslopping off decadent crowns sometimes rejuvenates atree, so fire may occasionally increase a tree’s vigour.A ~6m tall stand of coppiced Eucalyptus dives, havinglost a l l of i ts branches through a f i re in spr ing,recovered all its former leaf area in just half a year(Gill 1978).

F i re may boos t v igour and f lower ing in manyherbaceous perennials (Lunt & Morgan 2002). Fromhis and other studies Watson (2002) concluded thatgrassland species not only survive frequent burning,but species diversity in grasslands is dependent onfire.

Fire sometimes boosts tree health. It has been suggestedthat the nitrogen fixed by wattles arising after burningmay inhibit the jarrah’s root pathogen Phytopthoracinamomi (Shea & Kitt 1976). Ellis et al. (1980) foundthat the crowns of Eucalyptus delegatensis in parts ofTasmania tend to die back prematurely unless theundergrowth is burnt occasionally. Jurskis & Turner(2002) argue that most of the eucalypt diebacks seen insome of Australia’s forests and much of the rural areasare attributable to lack of cool fires to modify theundergrowth.

VEGETATION TRENDS WITH REPEATED BURNINGFire frequency can profoundly affect vegetation bothwhen frequency is too high or too low. Fires tend toeliminate the more fire sensitive species and thus favourthe more resistant species. Frequent fires favour speciesthat recover by sprouting, not those that depend on seed(Wilkinson et al. 1993). Conversely, lack of fires tendsto favour the more sensitive species. Fire in an 86-year-old stand of mixed eucalypt species killed 41% of the E.regnans, 17 % of the E. obliqua, and only 9% of the E.cypellocarpa, and boosted the bracken over the moresensitive understorey species (Ashton & Martin 1996).This related to differences in both bark thickness andability to produce shoots from epicormic buds, ie.strandsof bud-producing tissue located within live stem bark(Cremer 1972).

Bowman et al. (1981) present observations and argue thatin much of Tasmania, perhaps only on poorer sites,frequent burning reduces soil fertility, and that thevegetation tends to change from rarely burnt rainforestthrough eucalypt forest to frequently burnt sedgeland. Ingeneral, frequent fires tend to change woody vegetation tograssy or ferny vegetation, especially in the moister forests(as mentioned). Some vegetation, however, is highlytolerant of frequent fires, especially the drier forests (e.g.Christenson & Abbott 1989), provided they do not havespecies that rely on seeding, or that these can seed in theshort interfire periods. Some vegetation probably benefitsfrom frequent burning, e.g. the temperate grasslands, whenthey are not grazed or mowed (Watson 2002).

Figure 7.A 15 years old pine

plantation (Pinusradiata introduced

from California) killedby hot fire one year

earlier. As this pine hasno protected buds

above or below theground, it was unable

to sprout once all itsfoliage-and-bud-

bearing twigs had beenkilled. Seed stored inwell-insulated woody

cones on the trees shedafter the fire and

produced seedlings thatare now hidden by the

prominent dry grass, anintroduced annual

species grown fromsoil-stored seed.

19B I O D I V E R S I T Y 5 ( 4 ) 2 0 0 4

LOSS OF LITTER AND NUTRIENTSBurning lowers fuel hazards by reducing the quantitiesof litter, low vegetation and tree bark. This can amountto a serious loss of mulching effects: conservation ofsoil moisture, protection from erosion, and exposureof the ground to wider fluctuations in temperature. Ittakes some 10-20t/ha of litter to protect slopes of 16-30o (Good 1996). There have been reports (perhapsrelevant only to certain soil types) of extreme erosionafter hot fires followed by heavy rain: e.g. 148, 204,306, 550 tonnes/ha.Repeated burning of surface litter (and humus) mayeventually degrade the physical qualities of the soil,chiefly by reducing the organic content of the soil itselfand thus reducing water and nutrient holding capacities,soil crumbliness, aeration and drainage. There is alsoserious concern that repeated burning reduces long-termfertility through loss of nutrients. The nutrients are lostby volatilization, with ash blown away, by acceleratederosion, and by leaching. However, despite many studiesdemonstrating losses of nutrients, uncertainty remainsabout the significance of the observed losses, becauseof scales and difficulties of measurement, complexitiesabout: inputs and outputs of nitrogen, inputs from rainand from weathering of parent rock, and the total nutrientbudget (p 34, Williams & Gill 1995). Foresters of theSW are the strongest proponents of prescribed burning,where the evidence suggests that fertility is neitherdramatically nor permanently affected by low intensityfire (Christensen & Abbott 1989).The case for conservation of organic matter has, however,been sufficient to lead to the widespread cessation ofburning of logging debris between crops of planted Pinusradiata (e.g. Flinn et al. 1979). Conservation of organicmatter (mulch, compost) is now widely practiced ingardening and organic farming. The removal by farmersof litter from forests of central Europe over past centurieshas been recognized as a major degrading influence onfertility and has been stopped.

FUEL ACCUMULATION AND FLAMMABILITYThere have been many studies on fuel dynamics ineucalypt forests, mainly on the fine fuels, < 6mm thick,(Raison et al.1983, Good 1996). Depending on site andvegetation, fine fuels are produced typically at 1-5 t/ha/yr. Fuel accumulation is fastest in the first 5-7 years aftera fire, about 1-4 t/ha/yr. Accumulation then slows asdecomposition becomes more prominent, till productionand decomposition often balance to produce a ‘steady’state after some 10 to 20 years, with equilibrium fuellevels ranging from ~10 t/ha in some dry forests to ~40t/ha in certain moist forests. Within each year, fuel levelsvary modestly (e.g 1-2 t) rising during summers inresponse to accelerated leaf shed (especially afterdrought), and declining in winters when decaypredominates. The above pattern is probably the most

widespread in Australia, but may not apply in cool moistforests where humus/peat may well accumulateindefinitely.

Generally, fine fuels tend to regain hazardous levels (10t/ha) in just 2-5 years after a fuel reduction burn, withrecovery being faster after spring burns than after autumnburns. In a dry forest, with an equilibrium fuel level ofsome 12 t/ha, fuel levels may be reduced to ~5 t/ha byburning but fully recover in 2-4 years (Tolhurst 1996).Dangerous levels of fuel will be exceeded in just 2-3years after fuel reduction burn in most eucalypt forests.There is increasing recognition that shrubs and bark areimportant in promoting severe wild fires, and it issuggested that the benefit of fuel reduction burning ismore lasting if these are reduced. A hot wild fire causesmuch greater fuel reduction and is followed by muchslower fuel accumulation.

Eucalypts attract fire. Mount (1979) enumerates evidencesuggesting that eucalypts not only are adapted to copewith fire, and even need fire, but also produce fuels thatpositively attract and promote fire. This gives theeucalypts a competitive advantage over the more firesensitive rainforest species. The eucalypts shed abundantfoliage, bark, and branchlets and these decompose slowly,accumulating as highly flammable fuel. During fires,bark on many trees produces floating embers that spreadthe fire. Even the live leaves are relatively flammable,because they contain oils and waxes, but relatively littleminerals and water.

This high flammability contrasts with certain othertypes of vegetation that not only tend to be moister, buthave far less flammable foliage and accumulate far lesslitter: e.g. rainforests and thickets of willows. WhereSalix purpurea has come to dominate a stream inAustralia, it tends to exclude even severe bush fires.Its moister live foliage is harder to ignite; its denseshade excludes nearly all other plants (and hence theirlitter) and its own litter decays so fast that very littleaccumulates.

In certain vegetation types, burning greatly increasesfire hazard: e.g. when rainforest is changed to brackenor grass, or when sub-alpine, grassy, open woodland ischanged to dense, shrubby, forest with Bossiaea foliosa(R. Good, pers. comm.). Bracken tends to accumulateenough dry fuel to burn readily almost every three yearsand it is similar for many grasses. It is important toidentify any vegetation that is made more flammableby burning.

PROBLEMS IN RECONCILINGTHE AIMS OF FIRE MANAGEMENTProblems in managing fire include:

Lack of sufficient knowledge, despite more than athousand scientific papers on Australian fire ecology.

20 T R O P I C A L C O N S E R V A N C Y

Conflict between the needs of public safety andenvironmental conservation.Rapid accumulation of fuel to dangerous levels (~2-4 years).The probable ecological damage done by too frequentburning (every ~ 2-5 years).The need to make sensible choices.After agriculture, fire is the most powerful andwidely used tool to manage vegetation.

The aims need to be objectively identified, understood,and accepted. The ‘philosophies’ commonly espoused(e.g. ‘suppress all fires’, ‘let them burn, it’s good forthe bush’, ‘imitate aboriginal burning’, ‘aim for “natural”fires/vegetation’) are of little objective value. ‘Blizzardsof ecological detail’ are also of little help, unless theycan be disti l led into broader guidance, within anunderstanding that we inevitably have to live with fire.At present, much of the burning seems to be done mainlyto satisfy public expectation concerning protection of lifeand property. Burning for environmental conservationmay sometimes be implied but is still rarely mentionedby fire managers.

Bush fires are terrifying and destructive, but, if the aimis to save life and property, we should note the relativelylow importance of bush fires. The annual deaths on roadsand annual losses of houses from other fires are eachhundreds of times greater than losses due to bush fires.Lives can probably be saved more efficiently elsewhere.There are other ways of addressing fuel hazards. Fuelscan sometimes be reduced by mowing or grazing. Therisk to buildings has begun to be reduced through betterbuilding and landscape designs, driven by education andbuilding regulations, especially in bushland settings.Regular fuel reduction burning is now tending to beconfined to zones where it is most urgent and mostworthwhile: where people and property are mostthreatened.

PROBLEMS WITH BURNINGTO REDUCE FIRE HAZARDIt is widely understood that fine fuels should be keptbelow ~10 ton/ha. This fuel load occurs when the litterforms a continuous, 2 cm deep layer. The level abovewhich fire control becomes impossible varies, of course,with fire weather, availabili ty of manpower andequipment, terrain and access. It may be higher or lowerthan 10 t/ha in some situations: this should be defined.Gill et al. (1987) estimated that for the Melbourneclimate, and on level ground, fires would be justcontrollable on almost all days if fuel weights were lessthan 8 ton/ha.

Whatever the likely hazard level is, the rate at whichfuels accumulate is mostly so fast that burning to keepbelow the hazard levels would need to be so frequent(typically every 3-5 years) that there is risk of serious

damage to soil and vegetation in the long run. Asindicated above, it takes only 2-3 years after a fuelreduction burn to rebuild fuel loads to 8-10 t/ha in mosteucalypt forests. Although it may not yet be clearlyproven, ecologists believe that burning indefinitely at2-5 yearly intervals is probably environmental lyunsustainable, in most situations (e.g. Morrison et al.1996).

So far, there is lit t le evidence that fuel reductionburning has been effective in mitigating major bushfires. There is no doubt that hazard is minimal rightafter a hot burn, but there is need to determine underwhat range of conditions fuel reduction burning isworthwhile in reducing hazards. Some observationsindicate that at more than two years after a fuelreduction burn, wildfire behaviour was not affectedwhile weather conditions remained extreme, but wasmade more manageab le once condi t ions hadmoderated ((McCaw et al. 1992, Buckley 1992). Thereis also need to determine to what extent (if any) fuelreduction burning can prevent the environmentaldamage done by severe wild fires.

PROBLEMS WITH BURNING FOR BIODIVERSITYIf we knew enough about the growth habits of each species,what it needs to regenerate and thrive, its reaction to firesof various sorts, its dependence on seed or sprouting, whenit seeds and when it dies, etc, and if we knew and haddecided which are the most sensitive species/communitieswe want to preserve, we could devise fire regimes to suitthem. Thus the desirable interval between burning mightbe at least 2 and at most 8 years for certain grasslands,10-30 years for certain shrublands, 50-400 years for someof the taller eucalypt forests, and 300-1000 years forrainforests. The National Parks Service of NSW aims toidentify the highest and lowest fire frequency needed toavoid local extinctions of species.

More specifically, we should identify vegetation typesthat should never be burnt deliberately: e.g. rainforests,areas above the alpine tree line, swamps and bogs whenthese are dry, stands of young eucalypt timber cropswhile these are vulnerable, the number of extensive areasthat only rarely accumulate fuels to dangerous levels.

In the past decade, laws have been introduced to balancethe needs for protection of humans and the environment.Nevertheless, the law requires landholders ‘to take anypractical steps to prevent the occurrence of bush fireson, and to minimize the danger of spread of bush fireson or from, that land’ (NSW Rural Fires Act 1997).What is ‘practical’? Only near complete and permanentclearing will stop an extreme fire. Fire managementhas to be an ever-shifting compromise between therequirements of laws, public safety, ecology, and publicexpectations.

21B I O D I V E R S I T Y 5 ( 4 ) 2 0 0 4

Cool fires are probably generally preferable to hot fires,as they do much less obvious harm to plants, seeds, andsites. But there are also arguments for some hotter fires,mainly to promote the hard-seeded species. Fromextensive laboratory studies on seeds of 35 species ofacacias and other Fabaceae, Auld & O’Connel (1991)predict that soil temperatures under cool fires are nothigh enough to stimulate germination of these species.That conclusion may be questioned. Some soft seedsoccur in most seed lots, and others develop with time inthe ground, so that some germination also occurs withoutfire. From his studies and extensive review, Catling(1991) suggests that frequent (at least every 5 years)burns tend to greatly reduce the height and amount ofundergrowth and litter and thus disadvantage the nativemammals in SE Australia, while rarer burns do theopposite. To maintain biodiversity it seems generallydesirable for burns to be patchy. For hazard reduction,however, at least 50% of an area should be burnt.

Intervals between fires should vary. Forest zones thatmay need frequent burning for fuel reduction also needoccasional fire-free spells of some 10-30 years to allowrecruitment to the tree stratum, instead of the young treesbeing killed back to the ground after each burn. In theabsence of sufficient information, it seems wise to aimfor variability and to avoid extremes. Cool fires withoccasional hot ones (some are inevitable) are preferable.Fire intervals should be varied and suited to thevegetation. Burning too frequently is to be avoided andburning in different seasons may be appropriate. It isparticularly important to monitor and learn from theresults. Whatever the ideal burning regime, it is hard toachieve because optimum conditions for prescribedburning occur only rarely: e.g. on 11-14 days/year; orless, if weekends and the fire season are excluded (Gillet al. 1987).

CONCLUSIONSThe debate on what burning is desirable is likely tocontinue indefinitely, even as we learn more, becausethe issues are many and complex (Gill & Bradstock1994). Fire is needed for both hazard reduction and forenvironmental conservation. Further study of effects onrare plant species, monitoring of overall fire managementresults and caution will help to improve the science offire management.

ACKNOWLEDGMENTSThanks to A.B. Mount and R.C. Ellis for valuablecomments on a draft of this article.

REFERENCESAshton, D.H. & D.G. Martin 1996. Changes in a spar-stage ecotonal

forest of Eucalyptus renans, E. obliqua and E. cypellocarpafollowing wild fire. Aust. For. 59: 32-41.

Auld, T.D. & M.A. O’Connell 1991. Predicting patterns of post-firegermination in 35 eastern Australian Fabaceae. Aust. J. Ecol. 16:53-69.

Bowman, D.M. J.S. & W.D. Jackson 1981. Vegetation succession insouthwest Tasmania. Search, 12 (10): 358-362.

Buckley, A.J. 1992 Fire behaviour and fuel reduction burning: BemmRiver wildfire, October 1988. Aust. For. 55: 135-147.

Catling, P.C. 1991. Ecological effects of prescribed burning practiceson the mammals of southeastern Australia. Pp 353-63 in‘Conservation of Australia’s Forest Fauna’, ed D. Lunney, Publ.Roy. Soc. NSW, Mosman.

Christensen, P. & I. Abbott 1989. Impact of fire in the eucalypt forestecosystem of southern Western Australia: a critical review. Aust.For. 52: 103-121.

Cremer, K.W. 1960. Eucalypts in rainforest. Aust. For. 24: 120-126.Cremer, K.W. 1972. Morphology and development of the primary and

accessory buds of Eucalyptus regnans. Aust. J. Bot. 20, 175-195.Cremer, K.W. & A.B. Mount 1965. Early stages of plant succession

following the complete felling and burning of Eucalyptus regnansforest in the Florentine Valley, Tasmania. Aust.J.Bot. 13: 303-322.

Daubenmire, R. 1968. Ecology of fire in grasslands. Advances inEcological Research. 5: 209- 260.

Ellis, R.C., A.B. Mount, & J.P. Mattay 1980. Recovery of Eucalyptusdelegatensis from high altitude dieback after felling and burningthe understorey. Aust. For. 43: 29-35.

Gill, A.M. 1978. Crown recovery of Eucalyptus dives following wildfire.Aust. For. 41: 207-14.

Gill, A.M. 1981. Coping with fire. Chapter 3 in “The Biology ofAustralian Plants,” ed. J. S. Pate & A. J. McComb. Univ. of WesternAustralia Press, pp.65-87.

Gill, A.M. & R.A. Bradstock 1994. The prescribed burning debate intemperate Australian forests: Towards a resolution. Proc. 2nd Int.Conf. Forest Fire Research. Pp 703-712. Coimbra.

Gill, A.M., K.R. Christian, P.H.R. Moore & R.I. Forrester 1987.Bushfire incidence, fire hazard and fuel reduction burning. Aust. J.Ecol. 12: 299-306.

Good, R.B. 1996. Fuel dynamics, preplan and future research needs. Pp253-261 in ‘Fire and Biodiversity’. Proc. of Confer. in 1994 atMelbourne. Publ. in 1996 by C/W Dept Environment, Sport andTerritories. 278pp.

Jurskis, V. & J. Turner 2002. Eucalypt dieback in eastern Australia: asimple model. Aust. For. 65: 87-98.

Linder, H.P. & R.P. Ellis 1990. Vegetative morphology and interfiresurvival strategies in the Cape Fynbos grasses. Bothalia, 20: 91-103.

Lunt, I.D. & J.W. Morgan 2002. The role of fire regimes in temperategrasslands of southeastern Australia. Pp 177-197 of ‘FlammableAusralia’ ed by R. A. Bradstock, J. E. Williams & A. M. Gill.Cambridge University Press. Melbourne.

McCaw, L., G. Simpson, & G. Mair 1992. Extreme wildfire behaviourin Western Australian Eucalyptus forest. Aust. For. 55: 107-17.

Mount, A.B. 1979. Natural Regeneration Processes in Tasmanian Forests.Search 10 (5): 180-186.

Morrison, D.A., R.T. Buckney, B.J. Bewick, & G.J. Carey 1996.Conservation conflicts over burning bush in SE Australia. BiologicalConservation 76: 167-175.

Purdie, R.W. 1977. Early stages of regeneration after burning in drysclerophyll vegetation. Aust. J. Bot. 25: 21-46.

Raison, R.J., P.V. Woods & P. K. Khanna 1983. Dynamics of finefuels in recurrently burnt eucalypt forests. Aust. For. 46: 294-302.

Shea, S.R. & R.J. Kitt 1976. The capacity of jarrah forest native legumesto fix nitrogen. Forests Dept., Western Australia, Res. Paper 21.

Stoneman, G.L. 1994. Ecology and physiology of establishment ofeucalypt seedlings from seed: A review. Aust. For. 57: 11-30.

Tolhurst, K. 1996. Effects of fuel reduction burning on fuel loads in adry sclerophyll forest. pp 17-20 in ‘Fire and Biodiversity’, Proc. ofConfer. in 1994 at Melbourne. Publ. in 1996 by C/W DeptEnvironment, Sport and Territories. 278pp.

Watson, P. 2002. Different strokes for different vegetation types. Pp 66-77 in ‘Proceedings of a Conference on ecologically sustainableBushfire Management’, Nature Conservation Council of NSW,Sydney.

Wilkinson, G., M. Battaglia, & A.B. Mount 1993. Silvicultural useand effects of fire. Forestry Commission of Tasmania, Tech. Bull.11, 56 pp.

Williams, J.E. & Gill, A.M. 1995. The impact of fire regimes on forestsin eastern New South Wales. NPWS, Environmental HeritageMonograph Series No 2, 69pp

.

Received: 11 Sept. 2004; Accepted: 2 Nov. 2004