online special issue: prescribed burning prescribed burning in … · 2013-09-04 · fall amounts...

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© The Ecological Society of America www.frontiersinecology.org

Fire management in biodiverse and densely populatedsouthern Australia is a highly contested issue, sharing

many features with scientific and public debates in otherfire-prone regions of the world (Keeley et al. 2012;Fernandes et al. 2013; Ryan et al. 2013). In southernAustralia, fire is an inevitable, natural, and vital elementof the environment (Pyne 1998, 2006), and thus firemanagement is integral to sustainable ecosystem manage-ment (Burrows 2008; Bradstock et al. 2012). ManyAustralians choose to live in fire-prone, temperateregions, leading to conflict between public safety andecological management objectives, and requiring politi-cians and land managers to strike a balance between eco-logical, economic, and social values.

Recent major wildfire events and subsequent parlia-mentary, judicial, or coroner’s inquiries in the states ofVictoria (Teague et al. 2010) and Western Australia(Keelty 2011) have highlighted community protection as

the primary goal of fire management in populated agricul-tural and forested landscapes of southern Australia. Firemanagers are continually faced with the challenge ofmeeting expectations for community protection whilesimultaneously conserving biodiversity and preservingthe natural environment. The relative importance placedon these conflicting objectives by the community and byfire managers varies somewhat with time since the previ-ous bushfire disaster, so that fire regimes appropriate formeeting multiple objectives continue to be debated(Pyne 1998, 2006; Bradstock et al. 2012; Attiwill andAdams 2013).

Here, we explore these complex issues through adetailed study of the management of fire in the forests ofsouthwestern Australia, which form part of one of theworld’s biodiversity hotpots and are also home to morethan 90% of the human population of the state ofWestern Australia. A relatively long history of prescribedburning to achieve multiple objectives, supported byapplied research into fire behavior and ecology (Abbottand Burrows 2003; Burrows 2008), makes fire manage-ment in the southwest an exemplar for fire managementin southern Australia. The Western Australian experi-ence is also relevant to fire-prone, forested landscapes intemperate environments around the world.

n Biophysical environment of southwesternAustralian forests

Forested lands and associated ecosystems between thecities of Perth and Albany (latitude 32–35˚S) extendover an area of about 2.5 million ha; these are predomi-nantly public lands that are managed for conservation,sustainable timber production, and water catchment pro-tection by agencies of the Western Australian govern-

ONLINE SPECIAL ISSUE: Prescribed burning

Prescribed burning in southwesternAustralian forests Neil Burrows* and Lachlan McCaw

Prescribed burning is an important but often controversial fire-management tool in fire-prone regions of the world.Here, we explore the complex challenges of prescribing fire for multiple objectives in the eucalypt forests of south-western Australia, which could be regarded as a model for temperate landscapes elsewhere. Prescribed fire has beenused in a coordinated manner to manage fuels in Australia’s eucalypt forests since the 1950s and continues to be animportant tool for mitigating the impacts of unplanned wildfires on human society and on a broad range of ecosys-tem services. Prescribed fire is increasingly being used to manage fire regimes at the local and landscape scales toachieve biodiversity outcomes through maintenance of spatial and temporal patterns of post-fire seral stages. Theprescribed burning program in southwestern eucalypt forests has been informed by a long-term program of appliedresearch into fire behavior and fire ecology. To remain successful in the future, the prescribed burning program inthis region will need to adapt to changing expectations of government and the community, emerging land-useissues, resource limitations, and a drying climate.

Front Ecol Environ 2013; 11 (Online Issue 1): e25–e34, doi:10.1890/120356

In a nutshell:• Forest landscapes in southwestern Australia are prone to wild-

fires• It is important to manage fire to meet multiple objectives,

including the protection of human society and the conserva-tion of biodiversity

• Prescribed fire is an effective tool for managing fuels to reducethe impact of unplanned fires on human communities as wellas on vegetation, soils, and ecosystem services

• Management of prescribed fire for multiple objectives requiressuccessful integration of scientific knowledge and practicalexperience, underpinned by an organizational commitment toadaptive management

Science Division, Department of Parks and Wildlife, Kensington,Australia *([email protected])

Prescribed burning in southwestern Australian forests N Burrows and L McCaw

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www.frontiersinecology.org © The Ecological Society of America

ment. Forest ecosystems occur primarily on undulating landsurfaces and nutrient-poor soils derived from Precambriangranite and gneiss (coarse-grained rock, typically consistingof feldspar, quartz, and mica) substrates that have under-gone prolonged leaching, erosion, and deposition (Wardell-Johnson and Horwitz 1996). Dry sclerophyll forests onuplands are dominated by jarrah (Eucalyptus marginata) andmarri (Corymbia calophylla), averaging around 20–30 m inheight (Figure 1). Wet sclerophyll forests dominated bykarri (Eucalyptus diversicolor) may reach heights of up to85 m at maturity on more fertile sites. Forest ecosystems area major element of the Southwest Australian FloristicRegion, which includes approximately 8000 plant taxa andexhibits a very high level of endemism (> 75%) (Yates et al.2003; Hopper and Gioia 2004).

Southwestern Australia has a Mediterranean-type cli-mate with cool moist winters and warm dry summers(Gentilli 1989). Western parts of the jarrah forest alongthe Darling Range escarpment receive mean annual rain-fall amounts in excess of 1200 mm; this is due to oro-graphic uplift of moist air masses associated with winterstorms arising in the Indian Ocean. Areas within about50 km of the south coast also receive more than 1000 mmof rainfall annually, but rainfall declines rapidly withincreasing distance from the coast. The eastern margin ofthe forest corresponds broadly with the 600-mm rainfallisohyet, although this boundary is now defined artificiallyby the interface with cleared agricultural lands. Typical ofMediterranean-type environments, rainfall in this regionis strongly seasonal, with more than 80% of annual rain-fall recorded during the six consecutive wettest months

(May–October), while mean monthly rainfall averagesless than 25 mm during the three driest months(December–February). Consequently, vegetation is dryenough to burn for 6–8 months of the year. Maximumtemperatures regularly exceed 35˚C during the summer,while winter maximum temperatures are cool (<18˚C)and nights may be frosty, occasionally dropping to –5˚C.For much of the year, prevailing winds are generally east-erly and of moderate strength (20–30 km h–1) withsoutherly sea breezes extending up to 50 km inland(McCaw and Hanstrum 2003). Destructive gale forcewinds and widespread bushfires have resulted from peri-odic incursion of decaying tropical cyclones below lati-tude 30˚S, notably in 1937 and 1978. Lightning stormsprovide a potential source of ignition for bushfiresthroughout the southwestern forests between Octoberand March in most years.

The climate of southwestern Australia has been in a per-sistent drying phase since the mid-1970s, with annual rain-fall reduced by as much as 20%, primarily due to a declinein autumn and early winter rainfall (Bates et al. 2008). Thistrend has intensified and expanded over an increasing areasince 2000 and is expected to continue in the future (IndianOcean Climate Initiative 2012), with potentially severeconsequences for ecosystem health and water resources inforested catchments (Kinal and Stoneman 2012).Declining autumn rainfall has also extended the length ofthe high-risk bushfire period into April and occasionally tothe beginning of May, with the result that opportunities forsafe and effective prescribed burning in the fall may be lim-ited to only a handful of days in some years.

Figure 1. (a) Tall open forest of karri (Eucalyptus diversicolor) with a dense understory of large shrubs and a well-developed near-surface fuel layer of bark, twigs, and leaf litter. (b) Open forest of jarrah (Eucalyptus marginata) and marri (Corymbiacalophylla) with a low-intensity prescribed fire burning in the surface fuel layer of leaf litter and twigs.

(a) (b)

N Burrows and L McCaw Prescribed burning in southwestern Australian forests

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Prior to European colonization of the southwest ofAustralia in 1828, fires ignited by lightning and by theindigenous Noongar people maintained a patchwork ofvegetation at different stages of post-fire development,from recently burned to long unburned (Hallam 1975;Abbott 2003). Burning by the Noongar occurred mainlyduring the dry summer months, from December to March(Abbott 2003), coinciding with the peak period of light-ning ignition (McCaw and Read 2012). The preferenceof the Noongar to burn throughout the dry summermonths indicates a profound understanding of fire behav-ior and ecosystem responses to fire, and demonstrates thatthe fuel age mosaic maintained by this burning limitedthe impact of intense bushfires that might otherwise havethreatened the safety of the Noongar and the resourceson which their communities depended (Gammage 2011).

n Prescribed burning for fuel management

Stand flammability and bushfire behavior depend on thestructure, amount, distribution, and dryness of the fuel.Fine fuels (<6 mm diameter) in eucalypt forests are com-prised predominantly of leaf litter, twigs, and bark, and canbe categorized according to their vertical structure andcomposition (Gould et al. 2011). Bark on standing trees isalso an important fuel component in eucalypt forestsbecause it facilitates the vertical extension of flames intothe forest canopy and provides a source of firebrands thatcan propagate spot fires ahead of the flame front, a processknown as “spotting” (McCaw et al. 2012). The rate atwhich fuels accumulate following a fire event is deter-mined by the density of the forest canopy and the compo-sition of the understory shrub layer, which are strongly cou-

pled to the amount of annual rainfall and site fertility(Burrows 1994; Sneeuwjagt and Peet 1998). Fine fuelsaccumulate for several decades after fire, by which timefuel loads may approach 20 metric tons ha–1 in jarrah forestand 40–50 metric tons ha–1 in karri forests that have adense understory of woody shrubs. Rates of fine fuel accu-mulation may be modified by outbreaks of defoliatinginsects and drought that reduce canopy density, and bytimber harvesting and silvicultural treatments that alterstand structure and fuel arrangement (McCaw 2011). Barkon standing trees and coarse woody fuels that are highlyresistant to decomposition may continue to accumulateover much longer periods than is typical of fine fuels.

Prescribed fire has been used extensively to managefuels in southwestern forests since the 1960s (see Figure 2;see also Panel 1). Reducing fuel loads and altering fuelstructure mitigate key aspects of wildfire behavior,including the rate of spread, flame dimensions, spotting,and fireline intensity (Byram 1959; McCaw et al. 2012).The contribution of prescribed fire to mitigating theeffects of extensive, high-intensity fires can be quantifiedin a variety of ways, using basic combustion science, well-documented case studies, analysis of fire statistics, andcomputer simulations (Underwood et al. 1985; Fernandesand Botelho 2003; Cheney 2010). Fuel reduction canimprove the safety, efficiency, and effectiveness of firesuppression, although these effects may be subtle and dif-ficult to quantify for fires burning during severe weatherconditions and in eucalypt forest fuels older than about 5years (McCaw 2013).

At the regional scale, application of prescribed burningover broad areas of southwestern forests since the 1960s hasreduced the area burned by wildfire. Boer et al. (2009)

Panel 1. Origins of prescribed fire in forest management

Systematic protection of forests against fire in southwestern Australia began with the formation of the Western Australian ForestsDepartment in 1918. Up to that time, intense bushfires often followed in the wake of unregulated exploitation of forests for timber,seriously damaging extensive tracts of forest regenerated after logging (Kessell 1920; Burrows et al. 1995). Colonial foresters weretrained in Europe and viewed fire as a threat to the forest, depleting soil nutrients and organic matter and slowing the growth oftrees (Kessell 1920). Foresters argued that fire prevention and suppression were entirely possible, while practitioners experiencedin local conditions advocated a return to the Aboriginal practice of frequent “light” burning of the forest. By the late 1920s, fire pol-icy and practice sought to exclude fire from young regrowth forests by installing firebreaks and burning narrow strips between pro-tected compartments, with limited prescribed burning carried out in older regrowth and uncut forests. Extensive and damagingwildfires in 1949 and 1950 led to the realization that excluding fire from the forest ecosystem was impractical and unsustainableover the longer term (Wallace 1965). In 1954, broad-area prescribed burning to reduce fuel loads was endorsed as a fundamentalcomponent of fire management. However, limited resources and a rudimentary understanding of weather and fire behavior proveda daunting challenge to implementation. In the summer of 1961, multiple wildfire outbreaks resulting from dry lightning stormsburned approximately 150 000 ha of forest under severe fire weather conditions. Although the area treated with prescribed fire waslimited in extent, the reduction in fire intensity and damage to the forest was clearly apparent (McArthur 1962). A RoyalCommission inquiry into the fires recommended that the Forests Department make every endeavor to improve and extend thepractice of controlled burning to ensure that the forests receive the maximum protection practicable consistent with silviculturalrequirements (Rodger 1961). The Forests Department rapidly expanded its prescribed burning program, supported by research todevelop reliable fire-behavior guides and aerial ignition techniques that enabled large areas of forest to be ignited in a day, takingmaximum advantage of suitable weather conditions required for low-intensity, cost-effective, and low-risk prescribed burning(McCaw et al. 2003). The 1960s also saw the beginnings of an understanding of fire ecology, which expanded in scope and becameintegrated into fire-management practice in subsequent decades.


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showed a strong inverse relationship between the extent ofprescribed burning and unplanned fire in a 0.93 million haforested region of the southwest over a period of 45 years,during which the fraction of the study area burned annuallyby prescribed fire varied from 4% to 11%. Prescribed burn-ing reduced the mean number, extent, and frequency–sizedistribution of unplanned fires; furthermore, over theperiod of the study, the length of time that sites remainedunburned by wildfire doubled to approximately 9 years. Fuelreduction had a detectable effect on the incidence andextent of unplanned fires for up to 6 years after prescribedburning, consistent with scientific knowledge of fueldynamics and field observations of the contribution of fuel-reduced areas to fire suppression (Burrows 1994; Cheney2010; Gould et al. 2011). The extent to which fuels olderthan 6 years were spatially connected had a significanteffect on the annual extent of wildfire (Boer et al. 2009).

An inverse relationship between the extent of prescribedburning and unplanned fire is also evident at the whole-of-forest scale over six decades (Figure 2). Over the period1951 to 2012, the average annual area burned by prescribedfire and unplanned fire was ~291 000 ha (or ~11.6% of theforest region) and ~7140 ha (or ~0.3%), respectively. From1962 to 1990, the proportion of the region burned by pre-scribed fire each year ranged from 7.6–18.1%, with anannual average of 12.5%. Over the same period, the propor-tion of forest burned each year by wildfire ranged from0.1–1.1%, with an annual average of 0.3%. Since the1990s, the area burned intentionally through the use of pre-scribed fire has been reduced, leading to longer intervalsbetween fires and increased mean fuel ages (Figures 2 and4). From 1991 to 2012, the area burned by prescribed fireranged from 4.1–9.2%, averaging 6.6% annually, and thishas been accompanied by an increase in the area ofunplanned fire ranging from 0.2–4.7%, averaging 1.1%annually. Individual forest fires >20 000 ha were uncom-mon in the 1970s and 1980s but have occurred every sec-ond or third fire season since 1997.

Current fire-management policy has a prescribed burn-ing target of 200 000 ha per year for southwestern forests,representing ~8% of the public forest estate. Based on thefinding of Boer et al. (2009) that each unit area reductionin unplanned fire required about four units of prescribedfire, a prescribed burning program of this scale would beexpected to reduce the area of unplanned fire by about50 000 ha. A reduction of this scale is substantial, both interms of the area burned by unplanned fire and theexpected impact of fire, given the potential of intensesummer wildfires to damage human communities andecosystem services.

n Prescribed burning for biodiversity conservation

While the use of prescribed burning to mitigate wildfirerisk focuses on managing the accumulation of fuel, applica-tion of fire for biodiversity conservation focuses on manag-ing components of the fire regime considered important formaintenance of ecosystems and selected species. Thesecomponents include the interval between fires togetherwith seasonality, intensity, scale, and patchiness of burn-ing. Fire management for biodiversity conservation out-comes is guided by biodiversity conservation objectivesoperating at a range of spatial and temporal scales (Burrowsunpublished). These objectives have a foundation in eco-logical theory and are based on knowledge gained throughexperiments, retrospective studies, and monitoring in theforest ecosystems of the southwest. Responses to fire havebeen documented for many species of flora and fauna –including threatened taxa – in these forests and associatedecosystems (Friend and Wayne 2003; van Heurck andAbbott 2003; Burrows 2008; Wittkuhn et al. 2011; Pekin etal. 2012; Burrows 2013).

Populations of many plants and animals require sufficienttime between successive fires to attain reproductive matu-rity (Whelan et al. 2002). Plants that are obligate seedersare vulnerable when intense fires recur at short intervals

Figure 2. Proportion of the southwestern Australian forest region (~2.5 million ha) treated with prescribed fire (PF) and wildfire(WF) per year since 1951–1952.

PF WF

20181614121086420

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1951/52

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1978/79

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because seed banks cannot be replenished. Conversely, toolong an interval between fires may eliminate plant taxa thatrely on fire for reproduction, particularly obligate seedersthat store seed in woody capsules (serotinous taxa) and lackthe capacity to maintain a store of viable seed once the par-ent plant dies and seed is released (Whelan et al. 2002;Keith 2012). Burrows et al. (2008) compiled a database ofthe post-fire regeneration requirements of some 700 speciesof vascular plants, representing about one-third of theknown flora found in southwestern forests. From this data-base it was determined that approximately 97% of under-story species reach flowering age within 3 years of theoccurrence of fire and all species reach flowering age within5–6 years of a fire; about 3% of species are fire-sensitiveobligate seeders that have primary juvenile periods longerthan 3 years. Most of these latter taxa inhabit areas that areless prone to fire because they remain moist for a longerperiod each summer or because surface fuels tend to besparse and discontinuous due to low site productivity orextensive rock outcropping (Burrows 2013).

Fauna with low fecundity and poor dispersal abilitiesare vulnerable to large-scale, high-intensity fires thatoccur at short intervals (Friend and Wayne 2003).

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Threatened mammals and birds have attracted consider-able attention in terms of species conservation status andfire ecology research, including life history studies. Withsmall- and medium-sized mammals (< 5500 g) in particu-lar, there is considerable evidence that loss of habitat dueto land clearing for agriculture and predation by intro-duced species such as the red fox (Vulpes vulpes) areimportant causes of population declines (Christensen1980; Kinnear et al. 1988). However, there are threatenedspecies that have special habitat requirements withrespect to post-fire seral (ie developmental) stages (Panel2). These include mammals, birds, and amphibians thatdepend on fires being infrequent, as well as on older andmore complex mosaics of seral stages, ranging fromrecently burned to unburned for many decades (Friendand Wayne 2003; Burbidge et al. 2005). Knowledge of thelife histories of select threatened fauna – especially faunathat are recognized as fire-sensitive or exhibit specificfire-regime habitat requirements – can be used to under-stand species’ responses to fire and to plan fire regimesthat will best support their conservation (Burrows andFriend 1998; Friend and Wayne 2003).

To properly interpret life history attributes of plants and

Panel 2. Managing quokka habitat using prescribed fire

The quokka (Setonix brachyurus; Figure 3) is a small marsupial endemic to the southwestern partof Western Australia. While a large population persists on Rottnest Island, there is evidence thatthe mainland population has declined since European settlement, especially in the northern jarrahforest (Hayward et al. 2004). The species is declared threatened under the 1950 Western AustraliaWildlife Conservation Act.

The conservation status of the quokka requires that particular attention be paid to protectingextant populations and managing habitat. Controlling introduced predators, especially the red fox,and the judicious use of fire are fundamental to quokka conservation. Mainland quokkas inhabitmore mesic parts of the landscape, such as swamps and creeks that support dense vegetation.Fire plays an important role in protecting and maintaining quokka habitat but inappropriate fireregimes, including intense wildfires, can threaten their populations.

Fire management for quokka conservation is based on using prescribed burns to either protecthealthy habitat and populations from harmful wildfires or to regenerate senescent habitat that is nolonger occupied by quokkas. Habitat protection burns are carried out in spring, when upland forestsare sufficiently dry to burn but when creeks and swamps – that is, quokka habitat – are too moist to

burn. Burning the more flammable parts of the landscape extends some protec-tion to quokkas and their habitat against summer wildfires. Creek-line vegeta-tion that has died back and collapsed, usually by about 20–25 years after fire, isunsuitable habitat for quokkas. Habitat regeneration burns are then carried outin autumn, when the entire landscape, including creek systems, is dry enough toburn. The vegetation regenerates vigorously and within a few years it is againsuitable for quokkas. For the next 25 years or so, mild spring burns are imple-mented every 5–7 years to protect riparian and other mesic ecosystemsembedded in the forest. These ecosystems provide habitat for a variety of fire-sensitive organisms, including the quokka. Desired fire intensity outcomes canbe achieved within a prescribed burn unit by manipulating burning conditionsand the pattern of ignition (Figure 4).

Figure 3. A quokka (Setonixbrachyurus).

Mowen Block Prescribed BurnBiomass change after fire

75–100% (Full scorch)

50–75% (High scorch)25–50% (Low scorch)10–25% (Understory burn)1–10% (Patchy burn)0% (Unburned)

0 1 2 3km

ScaleBased on Landsat 17 January 2005

Figure 4. A burn severity map prepared from satellite imagery showingmoderate-intensity burning under dry conditions to regenerate quokkahabitat (red and yellow areas at top of the satellite image) and low-intensityburning under moist conditions to protect healthy habitat and quokkapopulations in the gullies (purple areas at bottom of image).

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animals as a guide to fire management for biodiversity con-servation objectives, it is necessary to understand fire regimecharacteristics. For example, experimental studies on smallplots have shown that repeated burning at 3–4-year inter-vals over a 30-year period has not reduced species richnessbut has substantially reduced the abundance of some oblig-ate seeding shrubs in jarrah forests (Burrows and Wardell-Johnson 2003). This finding is consistent with other studiesthat have reported changes to floristic composition as aresult of single or repeated short-period fire intervals inAustralian ecosystems where obligate-seeders are promi-nent (Morrison et al. 1995; Bradstock et al. 1997; Watson etal. 2009; Russell-Smith et al. 2012). However, Wittkuhn etal. (2011) concluded that occasional short (3–5-year) inter-vals between fires were unlikely to have a persistent effecton plant community composition in jarrah forests and theirassociated shrublands, based on the findings of landscape-

scale studies on fire interval sequences over a 32-year period. This apparent difference in results canbe explained by the fact that experimental studiestend to impose a high degree of uniformity in burn-ing treatments at local scales that is rarely encoun-tered in fires at landscape scales.

The primary objectives of fire management forconserving biodiversity at the landscape scale are(1) to maintain a diverse representation of ecosys-tem seral states and habitat conditions and (2) toprotect fire-sensitive and fire-independent ecosys-tems and niches, including riparian zones, aquaticecosystems, and peat wetlands. Fire-sensitiveecosystems are characterized as: those containingobligate seeder plant species with long maturationperiods; those that provide critical habitat forfauna with low fecundity, low dispersal capacity,and a preference for vegetation in post-fire seralstages older than the typical fire return interval ofthe surrounding landscape; communities that takedecades or longer to recover to their pre-fire state,such as peat wetlands (Horwitz et al. 2003); andvegetation types that have a lower likelihood ofburning because they either occupy mesic habitatsor have sparse amounts of ground fuels.

Strategies to achieve these landscape-scale objec-tives include maintaining a mosaic of fire-manage-ment units (see below) within the landscape at dif-ferent times since the last fire, including recentlyburned and long unburned units, and units burnedin different seasons. Ideally, the mosaic shouldinclude three biologically important fire regimecomponents: (1) time since last fire, (2) fire fre-quency, and (3) fire season. The geographic extentof these components that are ecologically sustain-able can be determined based on knowledge of theregion’s fire ecology and the life history characteris-tics of taxa occurring within the landscape (Burrowsand Friend 1998; Burrows 2008). Prescribed fireplays a critical role in managing fire regimes but

unplanned fires are also important and may dominate theoccurrence of fire in areas subject to very high rates of delib-erate ignition (such as the forest zone adjacent to the city ofPerth) and in remote areas, where poor access limits theopportunity for rapid initial responses to lightning ignitions(Plucinski et al. in review).

Fire regimes in forests in southwestern Australia havebeen characterized in a variety of ways, including from mapsshowing the spatial pattern of time-since-fire (Hamilton etal. 2009) and by using landscape metrics derived from spa-tial statistics (Faivre et al. 2011). Recognizing patterns inthe landscape is important for biodiversity conservation(Forman 1995; Wardell-Johnson and Horwitz 1996).Operational planning for fire and other management activ-ities is undertaken at the scale of the LandscapeConservation Unit (LCU) (Figure 5; Mattiske and Havel2002). Climate, landforms, soil types, assemblages of local

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Figure 5. Spatial distribution of time since last fire (fuel age) for the CentralJarrah Landscape Conservation Unit (LCU). LCUs have similar biophysicalproperties and thus are appropriate scales at which to develop prescribed fireregimes. (Data are derived from fire history records of the Department of Parksand Wildlife Western Australia and agencies that pre-dated the Department.)

Legend

Locality

Central Jarrah Forest LCU

Time since last burned

0–4 years

5–9 years

10–20 years

21≠ years Mandurah

Pinjarra

Dwelling Up

Waroona

Yarloop

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Australind

Bunbury

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flora and fauna, and disturbance regimes are simi-lar within each LCU, which range between103–105 ha in size. Periodic reporting of the distri-bution of time-since-fire provides a meaningfulway of measuring progress towards both biodiver-sity conservation and fuel management objec-tives at the scale of the LCU (Figure 6), and hasbeen adopted as a reporting protocol for a keyperformance indicator in Western Australia’sForest Management Plan 2004–13 (Conser-vation Commission of Western Australia 2004).The example in Figure 6 shows how the propor-tion of older fuels in the Central Jarrah LCU hasincreased since 2004, leading to greater potentialfor large wildfires. The theoretical distribution offuel age classes under a fire-management zoning strategy,assuming an annual prescribed burning program of~200 000 ha, is shown in Figure 7.

Each LCU is further subdivided into smaller fire-man-agement units that are bounded by roads, tracks, or nat-ural fuel breaks (such as extensive sand dunes) to limitfire size. Fire-management units typically vary in size from102–103 ha and include a variety of landforms, ecosys-tems, and vegetation complexes (Mattiske and Havel1998) representative of the LCU in which they occur.Management objectives for individual units include usingprescribed fire to maintain a variety of habitats, seralstates, and vegetation structures through time (usingpatchy burning), and to protect fire-sensitive and fire-independent ecosystems and niches within the unit fromfrequent fire and large, high-intensity wildfires. Strategiesused to achieve these objectives include:• Varying the season, frequency, and interval of fire

application to a unit within fire regime bounds basedon knowledge of fire responses and life history charac-teristics of key fire regime indicator taxa (Burrows andAbbott 2003; Burrows 2008).

• Implementing mostly patchy burns within the unit tomaintain a mosaic of time-since-fire. Small-grained,fire-induced mosaics can be created in several ways,including (but not limited to) introducing fire into thelandscape where fuel flammability differentials exist as aresult of variability in fuel moisture or continuity. Thiswill also serve to protect fire-sensitive and fire-indepen-dent ecosystems, which are usually found in less flam-mable parts of the landscape (Burrows et al. 2008).

• Burning flammable, drier, and fire-resilient habitats atintervals ranging from frequent to infrequent, depend-ing on life history characteristics of key taxa (Burrowsand Friend 1998; Burrows 2008).

• Burning less flammable habitats (eg riparian zones,some swamps, valley floors, granite outcrops) less fre-quently and by exploiting flammability differentialsthat exist across the landscape in different seasons,based on life history characteristics of key taxa(Burrows 2008).

• Sporadically applying moderate-intensity fires under

dry conditions to promote regeneration of many oblig-ate and facultative seed species and their associatedhabitats (Keith et al. 2002; Burrows 2008).

n Integrating community protection and biodiversityconservation imperatives

The management of fire in fire-prone landscapes requiresthat multiple objectives be met, including the protectionof human communities, the environment, and biodiver-sity. Mitigating the impacts of unplanned fires is anessential prerequisite to managing fire for other out-comes. No single fire regime will achieve all manage-ment objectives but the experience of managing fire insouthwestern Australia has shown that a sound under-standing of fire ecology can provide the basis for fireregimes that achieve both biodiversity conservation andfuel management objectives. When implemented withinan adaptive management framework, these regimes pro-vide opportunities for continuous learning and betterfire-management outcomes.

An important strategic issue for fire and land managers isthe extent to which the perceived wildfire threat tohumans, which is highly variable in both space and time,overrides biodiversity conservation objectives. The plan-ning approach adopted in the southwest is to devise pre-scribed burning programs based on ecological principles,followed by a systematic risk analysis to determine thethreat posed by these regimes to human communities andenvironmental values. The Wildfire Threat Analysis tool(Muller 1993) is a structured process for considering thethreat from and response to wildfires. It provides a frame-work for analyzing available information on all factors con-tributing to the wildfire threat and allows for the evalua-tion of alternative responses. Fire management can then bemodified where the risk or threat of wildfire, and potentialdamage, is deemed unacceptable.

n Prescribing fire in a changing world

Implementing prescribed burning over the areal extentnecessary to protect communities, the environment, and

2004 2013 Zoning

0–3 4–6 7–9 10–12 13–15 16–18 19–21 22–24 25–27 28–30 >30

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Figure 6. Actual distribution of fuel age classes in 2004 and 2013 and thetheoretical distribution under a zoning fire-management strategy (assuming200 000 ha annually was prescribed burned) for the Central Jarrah LCU.


biodiversity is becoming increasingly challenging, andthe annual target of burning 200 000 ha in the southwesthas only been achieved twice since 2000 (Figure 2). Thisdecline in prescribed burning has been driven by con-straints on burning brought about by increased popula-tion size at the peri-urban interface, concerns from com-munities and some industries about poor air quality andsmoke (Reisen et al. 2011), and by land-use changes,including greater fragmentation of forest areas due tobauxite mining and the establishment of even-agedregrowth stands following timber harvesting. The chang-ing climate of southwestern Australia has also altered thetiming and opportunity to undertake prescribed burningwith a level of risk acceptable to government and thecommunity (Keelty 2012). Following recent bushfireinquiries and concerns raised by communities, prescribedburn planning, risk management, and decision makinghave become more complex, further impeding the imple-mentation of prescribed burns.

Because of these constraints, it is unlikelythat the current target of 200 000 ha will bereached in most years. Given this and therenewed emphasis on the protection of humancommunities, it is prudent to consider an alter-native approach for deciding which areas areto be burned as a matter of priority. A zoningapproach based on values at risk has beenemployed in the state of Victoria (Departmentof Sustainability and Environment 2012); herewe present an example of similar zoning forrisk management and resource allocation insouthwest forests:

• Zone 1: Community protection zone, wherefuels are maintained at <4 years old, estab-lished within a 5-km radius of towns andother human settlements.

• Zone 2: Bushfire modification zone, where fuelsare mostly maintained at 5–7 years over afurther 20-km radius to modify bushfirebehavior, reduce damage, and increase likeli-hood of suppression. The fuel age class distri-bution would take the form of a negativeexponential, with most of the landscape car-rying young fuels (< 4 years old) but withsome parts, such as rock outcrops and ripar-ian zones, going unburned for longer periods.

• Zone 3: Biodiversity management zone, whereit is feasible to maintain a diversity of fireregimes and fuel ages (particularly throughmosaic or patch burning) in situations wherethere is negligible wildfire risk to publicsafety and amenities. In this zone, about one-third of the area would carry young fuels (<4years old), one-third intermediate age fuels(4–7 years old), and the remaining third car-rying older fuels.

Figure 7 is an example of zoning to manage risk and toprioritize the use of opportunities and resources for pre-scribed burning. Under the scenario in Figure 7, a total of~200 000 ha would need to be burned per year to achievethe fuel age objectives in each zone. This comprises~50 000 ha in Zone 1, ~100 000 ha in Zone 2, and~50 000 ha in Zone 3. The resulting theoretical distribu-tion of fuel age classes is shown in Figure 6. If it is unlikelythat the 200 000 ha target will be achieved, the zoningframework identifies areas that are a priority for fuelreduction investment to afford the highest degree of com-munity protection, being Zones 1 and 2. Zoning is a con-troversial fire-management strategy but deserves properevaluation as a risk-management approach if communityprotection is paramount and landscape-scale prescribedburn targets cannot be met.

Looking to the future, fire management in a changingworld will require greater understanding of fuel dynamics,

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Figure 7. An example of zoning as one approach to prioritize prescribedburning. This approach recognizes the paramount importance of communityprotection, the ecological role of fire, and constraints to prescribed burning.

LegendTownsite boundary

DEC Region

DEC managed vegetationZone 1 (5 km)

Zone 2 (20 km)

Zone 3 (remainder)

Privately managed vegetation

0 25 50 kilometers


fire behavior and ecosystem responses to fire in a warmer,drier climate. A commitment to science, practical experi-ence, adaptive management, and flexible institutionalresponses provide the fundamentals for ongoing develop-ment of prescribed fire management in the southwesternforests of Australia.

n Acknowledgements

We thank J Russell-Smith, R Thornton, R Sneeuwjagt, RArmstrong, and T Howard for their valuable commentson a draft manuscript. We also thank G Daniel and MPorter for mapping.

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