Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 8
Forum: Issues, management, PolIcy, and oPInIons
HUMAN FIRES AND WILDFIRES ON SYDNEY SANDSTONES: HISTORY INFORMS MANAGEMENT
Vic Jurskis1* and Roger Underwood2
1 6 Cocks Lane, Eden, New South Wales, 2551 Australia
2 7 Palin Street, Palmyra Western Australia, 6157 Australia
*Corresponding author: Tel.: 61-2-64961121; e-mail: [email protected]
ABSTRACT RESUMEN
There is a concept in fire ecology that En ecología del fuego se plantea que algunos some natural (pre-European) fire -re regímenes de fuego naturales (pre-europeos) gimes were dominated by infrequent fueron dominados por incendios poco frecuen- high intensity fires ignited by light- tes de alta severidad causados por rayos. En ning. In Australia, some ecologists Australia, esta idea ha sido aplicada por ecólo- extend this to most or all ecosystems gos y ecólogas a la mayoría de los ecosistemas across the landscape. They regard en el paisaje, quienes consideran que los in- contemporary human burning or pre- cendios de origen humano y las quemas pre- scribed burning as an unnatural distur- scritas contemporáneas son disturbios no natu- bance that threatens biodiversity. rales que amenazan a la biodiversidad. Su Their particular concern is the poten- principal preocupación es que los incendios tial extinction of slow maturing obli- frecuentes pueden causar la extinción de plan- gate seeders by frequent fire. Howev- tas semilladoras obligadas de crecimiento len- er, a completely different picture to. Sin embargo, estudios ecológicos de la his- emerges from study of Australia’s eco- toria y prehistoria australiana muestran una logical history and prehistory. There imagen completamente diferente. Existen evi- is ample evidence that Australian veg- dencias de que la vegetación australiana se ha etation was shaped by thousands of formado a lo largo de miles de años de quemas years of frequent mild burning by Ab- frecuentes y de baja severidad iniciadas por origines. Infrequent, high intensity grupos aborígenes. Los incendios de alta se- lightning fires affected only small ar- veridad y baja frecuencia causados por rayos eas of wet forests in refuges that were han afectado solo áreas pequeñas de bosques physically protected from mild fires. húmedos en refugios que estuvieron física- We present a case study of ecosystems mente protegidos de los incendios de baja se- on the Sydney sandstones to demon- veridad. Presentamos un estudio de caso de strate that a regime of infrequent high ecosistemas en las areniscas de Sidney para intensity wildfires since European set- demostrar que los regímenes de incendios de tlement has caused structural changes baja frecuencia y alta severidad, a partir de la and reduced spatial diversity. This has colonización Europea, han causado cambios put many fire dependent plants at a estructurales y reducción de la diversidad es- competitive disadvantage and in- pacial. Esto ha puesto a muchas plantas de- creased their susceptibility to disease. pendientes del fuego en desventaja competiti- Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 9
We argue that biodiversity, ecosystem va, incrementando su susceptibilidad a enfer- health, and fire safety are threatened medades. Argumentamos que la biodiversidad, by lack of frequent mild fire. Ecologi- salud y resistencia de los ecosistemas se ven cal theory should build on ecological amenazadas por la falta de incendios de baja history. Australia is fortunate in hav- severidad. La teoría ecológica debe basarse en ing comprehensive historical records la historia ecológica. Australia tiene la fortuna of Aboriginal burning against which de contar con registros completos de las que- paleoecological data can be calibrat- mas aborígenes para calibrar los datos paleo- ed. We emphasize the importance of ecológicos. Enfatizamos la importancia del using historical information to inter- uso de información histórica para interpretar pret ecological studies and inform fire estudios ecológicos y proveer información para management. manejo del fuego.
Keywords: Aborigines, biodiversity, European settlement, fire regimes, history, prehistory, sand- stone, Sydney, vegetation change, wildfires
Citation: Jurskis, V., and R. Underwood. 2013. Human fires and wildfires on Sydney sandstones: history informs management. Fire Ecology 9 (3): 8–24. doi: 10/4996.fireecology.0903008
INTRODUCTION example, Matthew Flinders (1814) described thickly wooded vegetation and evidence of in- Many Australian ecologists have assumed frequent high intensity lightning fires on the that ecosystems showing little evidence of hu- uninhabited Kangaroo Island in 1802. He con- man activity (usually characterized as “distur- trasted this environment with continental Aus- bance”) represent the natural (pre-European) tralia where human fires were prevalent. state (e.g., McElhinney et al. 2006, Gibbons et The view of a thickly wooded Australian al. 2008, Killey et al. 2010). This hypothesis landscape shaped by infrequent and intense portrays stands of native vegetation that have wildfires is unsustainable for two reasons. been dramatically altered as a consequence of Firstly, it is totally inconsistent with historical more than a century of fire suppression as records of Aboriginal fire regimes and vegeta- benchmarks of natural conditions. In fire ecol- tion (e.g., Tench 1793; Flinders 1814; Mitchell ogy, the assumption has led to conclusions that 1839, 1848; Curr 1883; Howitt 1891; Pyne prescribed burning reduces densities of woody 1998; Gammage 2011); secondly, it ignores plants and quantities of litter, fallen timber, the widespread woody thickening that oc- and soil nutrients below natural levels, and that curred after Aboriginal culture was disrupted this threatens biodiversity (e.g., Morrison et and frequent mild fires no longer maintained al.1996, Henderson and Keith 2002, Tasker the Australian landscape (Mitchell 1848, How- and Bradstock 2006, Christie and York 2009, itt 1891, Gammage 2011). Tasker et al. 2011). Dense and homogeneous stands of trees or This assumption implies that the natural woody shrubs created by post-European man- (pre-European) fire regime was one of infre- agement have been studied as if they were nat- quent (at least decadal), extensive, high inten- ural ecosystems, and some fire management sity wildfires ignited by lightning, and that the guidelines have been devised to maintain these natural vegetation was mostly thickly wooded. artificial assemblies and structures. Unnatural However, prehistoric and historic records of processes have been described as if they were fire regimes and vegetation contradict this. For natural. For example, Cohn et al. (2011) de- Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 10
scribed the response of unnaturally dense stone formations around Sydney (e.g., Keith et stands of Callitris (Callitris glaucophylla Joy al. 2002: Figure 17.2a). We examine this work Thomps. & L.A.S. Johnson) to unnaturally se- in the context of historical information about vere fires as though it were a natural process. vegetation and fire regimes in the area. In fact, these conifers were attuned to occa- sional low intensity fires that killed seedlings THE FIRE HISTORY OF SYDNEY’S and maintained the health of scattered mature SANDSTONE vEGETATION trees with thick, insulating bark that protected them from damage by quick moving fires in When Europeans settled at Sydney in 1788, grassy fuels (Jurskis 2009, 2011a). their agricultural activities were virtually con- The argument (e.g., Mooney et al. 2001, fined to the Cumberland Plain, which is encir- 2011) that Australian Aborigines did not burn cled by large areas of Triassic sandstones. frequently and extensively because sustained These rugged and barren areas have remained high levels of biomass burning were not evi- largely undeveloped and now form an exten- dent as charcoal in sediments post-dating Ab- sive system of national parks including the original occupation cannot be sustained. The Blue Mountains to the west, most of the land prehistory of fire in Australia can only be re- between Sydney Harbour and the Hawkesbury solved by calibrating sedimentary charcoal re- River to the north, and Royal National Park cords against historical records. Charcoal de- immediately south of Sydney. The conse- position increased markedly at the time, about quently long interface between urban and wild- 40000 years ago, that Aborigines occupied land around Australia’s largest city has led to Australia (Mooney et al. 2011: Figure 2); after extensive debate about the fire history, ecolo- the demise of the Aboriginal population on gy, and management of Sydney’s wildlands. Kangaroo Island about 2500 years ago (Singh Detailed observations of Aboriginal culture et al. 1981); and after European settlers dis- in this region were made by Captain Lieuten- rupted Aboriginal culture on the mainland ant Watkin Tench (1793) during the first four (Howitt 1891, Mooney et al. 2011). Charcoal years of European settlement at Sydney Cove deposition was reduced after extensive pre- (1788−1791). Tench was an officer in the sec- scribed burning was reintroduced by forest ond rank of the new colony’s military depart- managers in the mid-twentieth century (Jurskis ment. He reported that Aboriginal people car- et al. 2003, Mooney et al. 2011). Increased ried fire wherever they went, noting that “they deposition of charcoal was clearly associated always, if possible, carry a lighted stick with with intense fires in heavy accumulations of them, whether in their canoes or moving from fuel (woody biomass), whereas reduced depo- place to place on land.” He saw Aborigines sition was associated with long term Aborigi- “perpetually setting fire to the grass and bush- nal burning and broad area prescribed burning es” and noted that “it is a very common cus- by forest managers. tom” for “the Indians in their hunting parties” The reported negative impacts of frequent to “set fire to the surrounding country”. Ab- mild burning (at intervals less than about ten origines used fire for warmth, cooking, hunt- years) have been based on comparisons of fre- ing, signaling, lighting their way, managing quently burnt vegetation against infrequently vegetation and fauna, and in celebration as burnt or long unburnt areas inappropriately well as in conflict (e.g., Tench 1793; Flinders designated as controls (Turner et al. 2008, Jur- 1814; Mitchell 1839, 1848; Curr 1883; Howitt skis et al. 2011). Much of this work has fo- 1891; Gammage 2011). Fire was integral to cused on non-resprouting, bradysporous shrubs the mental and material existence of Australian (seeds retained for long periods in aerial, Aborigines (Pyne 1998). woody fruits unless released by fire) on sand- Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 11
On 11 April 1791, Tench left Rose Hill (now Parramatta) with a party of exploration. Each member of the party except Governor Phillip carried about twenty kilograms of bulky equipment and provisions. Once they reached the sandstone country (at what is now known as North Rocks), the terrain became, “very bad, being full of steep barren rocks, over which we were compelled to clamber for seven miles”. However, the only references by Tench to difficulties occasioned by vegetation were along the Hawkesbury River where they were “plagued and entangled … stung … with Figure 1. Dense undergrowth on the approach to nettles and ridicule,” (by their Aboriginal the summit of Tench’s Prospect Mount. Note large guides) “and shaken nigh to death” by tripping dead banksia in left foreground. No large live banksias were present. over obstacles. Once more in rocky sandstone country with “nothing but trees growing on precipic- sandstone in New South Wales because “con- es”, Tench “saw a tree on fire here and several flagrations take place so frequently and exten- other vestiges of the natives.” Scrambling to sively … as to leave very little vegetable mat- the top of a sandstone mountain “with infinite ter to return to earth.” Travelling the Great toil and difficulty”, Tench had an extensive Northern Road, Mitchell described the country view “in almost every direction, for many between Parramatta and the Hawkesbury River miles.” Governor Phillip named this “pile of thus: desolation” Tench’s Prospect Mount (Tench 1793). … no objects met the eye except barren The “infinite toil and difficulty” faced by sandstone rocks, and stunted trees. Governor Phillip’s party in scrambling up With the banksia [Banksia spp.] and Tench’s Prospect Mount was as nothing com- xanthorhaea [Xanthorrhoea spp.] al- pared to the task that would confront them in ways in sight … The horizon is flat ... the current dense vegetation (Figure 1). Fur- thermore, the toil would be wasted because the Mitchell had surveyed the continuation of party’s objective—Richmond Hill (now En- the road through the sandstone country north field Hill)—is no longer visible due to the thick of the river, and recounted that: growth. Gregory Blaxland (1823) led the first Eu- … the whole face of the country is com- ropean crossing of the Blue Mountains in posed of sandstone rock, and but par- 1813. He described thickets of “brushwood” tially covered with vegetation. ... on that impeded the packhorses. However, in un- many a dark night … I have proceeded known territory, a few men were able to clear on horseback amongst these steep and and blaze a track through this tall shrubland rocky ranges, my path being guided by for four heavily laden packhorses at the rate of two young boys belonging to the tribe one mile (1.6 km) per hour, suggesting that the who ran cheerfully before my horse, al- shrubs were not very dense, and certainly not ternately tearing off the stringy bark as dense as they are today. which served for torches, and setting Surveyor General Thomas Mitchell (1839) fire to the grass trees xanthorhaea( ) to observed that “no vegetable soil is formed” on light my way. Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 12
Today, Mitchell’s Aboriginal assistants … were compelled to seek a precari- would not be able to run “cheerfully before” ous shelter amidst the close thickets his horse, lighting grasstrees because the vege- and rocky fastnesses which afforded tation is too thick and fully grown grasstrees them a temporary home, but scarcely a are rare as are large banksia trees. In fact, any- subsistence … I knew this unhappy one would have great difficulty riding a horse tribe, and had frequently met them in through the current vegetation, even in broad their haunts. In the prosecution of my daylight (Figure 2). surveys I was enabled to explore the wildest recesses of these deep moun- tainous ravines, guided occasionally by one or two of their number.
Tench and Judge Advocate David Collins recorded the first European observations of fire behavior under drought and extreme weather conditions at Sydney. Aboriginal fires were burning in bushland northwest of Rose Hill (Parramatta) on 10 and 11 February 1791 un- der extreme temperatures (>40 oC) and searing northwesterly winds, conditions that caused fruit-eating bats and parrots to drop dead from Figure 2. This is the forest type and locality that the sky. However, the fires did not affect the Mitchell traversed on horseback in the dark of settlement (Tench 1793, Collins 1798). There night and described in daylight as follows: “no ob- was another “blow up day” (a day when high jects met the eye except barren sandstone rocks, and stunted trees. With the banksia and xantho- temperatures, low humidities, and strong winds rhaea always in sight … the whole face of the can cause extreme fire behavior) on 5 Decem- country is composed of sandstone rock, and but ber 1792 when a grass fire at Sydney burnt one partially covered with vegetation”. house and several fences before being con- trolled (Collins 1798). Extensive fires at Par- When Charles Darwin travelled the road ramatta and Toongabbie on the same day also blazed across the Blue Mountains by Blax- had relatively minor impacts. They were land’s party, he described “scrubby trees of the thought to be controlled until a firebrand from never-failing Eucalyptus family”. Clearly the the crown of a tree ignited a spotfire on a patches of shrubland made little impression. thatched roof, leading to the destruction of a When he descended to the granite country of hut, outbuildings, and a stack of wheat (Col- the central tablelands he noted “the trees were lins 1798). The minimal impact of these fires, both finer and stood farther apart; and the pas- burning under extreme conditions, demon- ture between them was a little greener and strates that they were generally burning in more plentiful” (Darwin 1845). light, discontinuous fuels, and thus did not at- Though the sandstone country was not tain high intensity (e.g., Jurskis et al. 2003). generally thickly wooded, thickets occurred in some rocky or sheltered sites. Mitchell noted MODERN HISTORY AND ECOLOGY OF that after European settlers occupied their kan- SYDNEY SANDSTONE vEGETATION garoo grounds, the displaced Aborigines: After disastrous fires around the mid-twen- tieth century, Australian foresters introduced Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 13
broad area prescribed burning, including aerial ing shrubs showed the opposite response, and ignition, as a major facet of fire management resprouting trees were unaffected (Knox and (Jurskis et al. 2003). Ecologists began to raise Morrison 2005). Knox and Morrison (2005) concerns about the potential environmental speculated that there may be rapid selection impacts of prescribed burning, and in 1976 the for early maturity of obligate seeders in fire Scientific Committee on Problems of the Envi- prone environments. ronment initiated an international fire ecology A number of studies demonstrated that project (Gill et al. 1981). In this project, Gill short intervals between fires disadvantaged (1981) reviewed responses to fire of Australian large shrubs and favoured smaller shrubs or plants. He suggested that plants be classified herbs (e.g., Siddiqi et al.1976, Cary and Mor- as sprouters or seeders and their life cycles an- rison 1995, Morrison et al. 1995, Bradstock et alysed in the context of fire regimes to assess al. 1997) and grasstrees (Xanthorrhoea resino- their likely persistence. This suggestion was sa Pers.; syn. X. resinifera Sol. ex C.Kite enthusiastically adopted by many ecologists, E.C.Nelson & D.J.Bedford) (e.g., Tozer and particularly in regard to non-resprouting bra- Bradstock 2002, Tozer and Keith 2012). Not dysporous shrubs, which form a major compo- surprisingly, plants’ responses to fire varied nent of Sydney’s sandstone vegetation. with growth stage (e.g., Siddiqi et al. 1976) as The nub of their concern was that burning well as with fire intensity (Bradstock and My- at intervals shorter than the time taken for erscough 1988). It also emerged that media- these shrubs to develop from seedlings to sex- tion of interspecific competition by fire re- ual maturity would eliminate them, reducing gimes was equally or more important than in- biodiversity (e.g., Benson 1985, Bradstock and dividual species responses to direct physical O’Connell 1988, Cary and Morrison 1995, impacts of fire (e.g., Bradstock et al. 1997, Keith 1996, Keith et al. 2002). Dangerous fuel Tozer and Bradstock 2002, Tozer and Keith loads were found to accumulate within two to 2012). four years after fire, leading Morrison et al. It is indisputable that the time between (1996) to suggest that fuel reduction burning fires can influence the abundance of particular was incompatible with conservation of biodi- species and consequently the floristic compo- versity. Keith et al. (2002) claimed that Sid- sition of the vegetation (e.g., Bradstock and diqi et al. (1976) had “demonstrated” local ex- O’Connell 1988; Cary and Morrison 1995; tinctions by frequent fires. However, Siddiqi Morrison et al. 1995, 1996; Bradstock et al. et al. (1976) actually reported that a “fierce” 1997). Bradstock and O’Connell (1988) pre- wildfire eliminated some plants from a few dicted that densities of large shrubs on Syd- small plots where they had been present as ney’s sandstones would increase if fires -oc seedlings before the fire, whilst the same spe- curred at fifteen to thirty year intervals, and cies regenerated close by, within the fire -pe their prediction was found to be correct by ret- rimeter, in a more sheltered plot where they rospective studies (e.g., Conroy 1996). There had been present as mature plants. Thus the was no evidence that a reduction in density of purported extinctions (Keith et al. 2002) oc- some species by frequent prescribed burning curred at a minutely small scale and could be would lead to local extinctions and reduced more aptly described as reinstatement of the biodiversity. Cary and Morrison (1995) re- natural species pattern. ported that frequent, intense fires (intervals Another study found that obligate seeders less than ten years, understory completely de- produced more seeds under a regime of short stroyed across at least five hectares) reduced fire intervals (three or four years) than under species richness, whereas Morrison et al. longer intervals between fire, whilst resprout- (1995) found that this regime favoured ten Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 14 small plants and disadvantaged six large after a 17 year interval between fires. They shrubs. Morrison et al. (1996) found that, of found higher mortality of grasstrees with less seven plants whose abundance was affected by frequent fire because of competition from large fire frequency, the least abundant across all shrubs, and they considered that presence of sites were two plants favoured by frequent Phytophthora would exacerbate the effects of fires (less than seven years), and one of these competition. species was not found on sites with longer fire The endangered broad-headed snake (Hop- intervals (Morrison et al. 1996: Table 2). locephalus bungaroides Wagler), is thought to Bradstock et al. (1997) concluded that fre- be extinct in sandstone vegetation north of quency of fires affected floristic composition Sydney (Pringle et al. 2009). Remotely sensed but not species richness. Frequent fires at short chronosequences in sandstone woodlands to intervals (one or two years) reduced the densi- the south revealed that its habitat of bare exfo- ty of seven shrubs and increased the density of liated sandstone, critical for thermoregulation, one grass. The most common shrub in the area was substantially reduced between 1941 and was the most reduced. Bradstock et al. (1997) 2006 as a consequence of shading by encroach- emphasized the highly heterogeneous nature ing shrubs under a wildfire regime (Pringle et of site effects on fire regimes and vegetation, al. 2009). and that it was difficult to extrapolate conclu- The aforementioned ecological studies sions from fine scale studies to the landscape have assessed the role of recent fire history in scale. shaping ecosystems, but they have largely ne- Grasstrees were a prominent component of glected to assess changes in fire regimes and Sydney’s sandstone vegetation at the time of biota consequent to European settlement. European settlement (Mitchell 1839), and al- However, records of charcoal deposition in a though still common, are suffering decline as a lagoon within Royal National Park were used consequence of modern fire regimes, competi- to infer long term fire history. Mooney et al. tion from large shrubs, and disease associated (2001) found evidence of many fires during the with infection by Phytophthora cinnamomi previous seven decades but of only one “con- Rand (Tozer and Bradstock 2002, Regan et al. flagration” during the 1600 years before Euro- 2011, Tozer and Keith 2012). Tozer and Brad- pean settlement. This led them to suggest that stock (2002) found that fully grown live either Aborigines did not burn much or they grasstrees were virtually absent from patches burnt in a way that delivered little charcoal. of large shrubs, although there were many Mooney et al. (2001) concluded that “the idea dead stems, “consistent with suppression by of the ubiquitous use of fire by Aboriginal peo- overstorey species”. ple should be further, and critically, analysed”. Regan et al. (2011) sampled the demo- In contrast, Clark and McLoughlin (1986) graphics of grasstrees and Phytophthora under presented historical evidence that Aborigines the recent wildfire regime. They considered burnt Sydney’s sandstone vegetation frequent- that grasstrees were threatened by an adverse ly and that less frequent fire after European fire regime as well as by the fungal pathogen. settlement caused woody thickening and Simulated populations of grasstrees declined upslope expansion of gully vegetation at the in the long term under all fire management expense of groundcover plants. Conroy (1996) scenarios (burning at 5 yr, 12 yr, 20 yr, and 30 analysed the fire history of Ku-ring-gai Chase yr intervals with and without wildfires and to- National Park between 1943 and 1994. He tal fire exclusion), even in the absence of dis- concluded that wildfires were more frequent ease (Regan et al. 2011). Tozer and Keith and less intense prior to 1970, after which stra- (2012) reported a local extinction of grasstrees tegic burning and fire suppression were intro- Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 15 duced. After 1970, reduced frequency and in- of their ‘job’ (e.g., Jurskis 2009, 2011a). creased intensity of fire resulted in increased Where they made no such records, there were cover of woody shrubs that impedes bushwalk- clearly no such impediments to be recorded. ers, shades out some attractive small flowering Mooney et al. (2001) used paleological plants, and reinforces a regime of high intensi- data on charcoal accumulation to question the ty fires (Conroy 1996). historical record. Physical records such as The significance of the change in fire re- charcoal deposits (e.g., Mooney et al. 2001, gimes and vegetation over the longer term can 2011) or fire scars on trees (e.g., Banks 1989, be appreciated by comparing the situation on von Platen et al. 2011 ) have often been misin- blow up days under Aboriginal management terpreted as providing a complete prehistory of against the current situation. Fires on blow up fire when, in fact, mild fires in open vegetation days in 1791 and 1792 caused little damage to burn relatively low quantities of mostly fine settlements at Parramatta and Sydney, and and herbaceous fuels, leaving little charcoal or were easily controlled (Tench 1793, Collins scarring (e.g., Burrows et al. 1995 , Mooney et 1798). In contrast, fires under similar condi- al. 2011, Jurskis and Underwood 2012). Ab- tions in January 1994 (Speer et al. 1996: Fig- original burning was ubiquitous and prehistory ure 3) were mostly uncontrollable, burning shows that, after the period when the continent more than thirty thousand hectares around was initially occupied, subsequent burning de- Sydney, claiming hundreds of houses and three livered little charcoal (e.g., Mooney et al. lives despite the efforts of a well-equipped 2011: Figure 2). Interpretation of charcoal in army of firefighters (NSW Rural Fire Service sediment cores should be informed by histori- 1998). cal observations. Taken together, paleological The difference in 1994 was that firestorms and historical records indicate that Aborigines developed in the dense, three dimensionally altered vegetation pattern and structure using continuous fuels produced by modern misman- high intensity fires when they originally occu- agement of the native vegetation on sandstone pied Australia, after which they maintained the surrounding Sydney (e.g., Figure 1). The fire new pattern using frequent mild burning. Fol- storms caused showers of embers and long dis- lowing the initial peak in biomass burning, tance spotting of fires. For example, a run of there was a sustained reduction (e.g., Mooney fire that claimed human lives spotted 800 me- et al. 2011: Figure 2) as dense woody vegeta- tres across a major watercourse (Hurditch and tion was restricted to physical refugia (e.g., Hurditch 1994). However, Conroy (1996) list- Singh et al. 1981, Kershaw et al. 2002). ed four localities where runs of these fires un- McLoughlin (1998) inferred the Sydney der extreme weather conditions were effective- region’s early European fire history using only ly contained as a result of prior hazard reduc- individual records that identified the date. She tion burning. found 31 records between 1788 and 1845 (an average of one fire somewhere in the region DISCUSSION every two years). The more general observa- tions of explorers and settlers indicate that fires It is clear that Aboriginal burning main- were very common, so that specific fires were tained Sydney sandstone vegetation in a gener- unremarkable unless they were damaging or ally very open condition. Tench, Mitchell, had been set maliciously. There were certainly Darwin, and others described vastly different many more fires than those listed by McLough- vegetation to that currently occurring on sand- lin (1998) (e.g., Tench 1793, Mitchell 1839). stone around Sydney. Explorers systematical- Since the 1970s, a plethora of ecological ly and meticulously recorded impediments to studies has purported to examine the impacts travel and visibility because it was a large part of frequent fires on Sydney sandstone vegeta- Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 16
tion. However, the results of these studies tween fires would not ensure the persistence of have not been interpreted in the context of Ab- grasstrees, but they suggested that further stud- original fire regimes and the historical, ecolog- ies are required to establish what patterns of ical consequences of their disruption including shrub densities will promote the coexistence of woody thickening and outbreaks of pests, par- contrasting species. However, there is no need asites, diseases, and megafires (e.g., Mitchell for further studies because the landscape pat- 1848; Howitt 1891; Jurskis 2002, 2009, 2011a, tern established by thousands of years of fre- b; Jurskis et al. 2003, 2011). Furthermore, quent burning by Aborigines allowed grasstrees these studies examined wildfire regimes or and shrubs to coexist. Shrubs occurred in mixed fire regimes dominated by intense wild- much lower densities on most sites. fires, whilst the abundance and richness of spe- Fire suppression can promote Phytophtho- cies have been measured at a fine scale so the ra root-rot by increasing topsoil moisture lev- conclusions have little relevance to consider- els and changing soil chemistry, with adverse ation of the effects of frequent, mild, and impacts on roots and direct benefits to the patchy burning (e.g., Penman et al. 2007) on pathogen (Jurskis 2005). Increasing fuel loads the natural (pre-European) composition and promote high intensity fires that can raise wa- structure of the vegetation across the landscape ter tables by interrupting transpiration and fur- (Jurskis et al. 2003, Bradstock et al. 1997, Jur- ther benefit the pathogen (e.g., Fagg et al. skis 2011b). 1986, Davison 1997, Jurskis 2005). Thus the The theory of extinctions of plant species inoculum level and extent of the Phytophthora (loss of biodiversity) as a result of frequent fire has probably increased compared to natural (e.g., Benson 1985 , Keith 1996, Keith et al. levels (e.g., Pratt and Heather 1973, Jurskis 2002) relies on the untenable assumption that 2005). It is likely that the health of grasstrees the current vegetation in national parks repre- on Sydney’s sandstone is generally reduced sents the natural (pre-European) condition. It and that current mortality rates used in model- also relies on the unlikely assumption that fre- ing by Regan et al. (2011) are unnaturally quent prescribed burns are sufficiently hot and high. There is strong evidence that Phytoph- uniform to kill or substantially damage most thora is indigenous to eastern Australia and plants irrespective of life form or growth stage that natural vegetation patterns reflected genet- but not sufficiently hot and uniform to stimu- ic susceptibility of plants as well as suitable late their reproduction or establishment (Jur- soil conditions for the pathogen (Pratt and skis et al. 2003, Jurskis 2011b). Another im- Heather 1973, Jurskis 2005). The history of plicit assumption is that direct impacts of fire grasstrees at Sydney strongly suggests that are the major influence on plant demography. modern fire regimes disrupted these natural Competitive interactions between species have patterns. been neglected (Bradstock et al. 1997). This The ecological studies have shown that in- is particularly apparent in the case of grasstrees teractions between fire regime and interspecific on Sydney’s sandstones, which are declining competition are important (e.g., Bradstock et as a result of damage by high intensity fires, al.1997) because absence of fire favours larger competition from thickening woody vegeta- plant species over smaller species (Clark and tion, and a disease that is favoured by infre- McLoughlin 1986, Cary and Morrison 1995, quent, high intensity fires (that is, by modern Morrison et al. 1995, Morrison et al. 1996, fire regimes) (e.g., Tozer and Bradstock 2002, Conroy 1996, Bradstock et al. 1997, Tozer and Jurskis 2005, Regan et al. 2011, Tozer and Bradstock 2002, Tozer and Keith 2012) and Keith 2012). other fire studies in dry eucalypt forests have Tozer and Keith (2012) recognized that a confirmed that many small groundcover plants focus on minimum allowable intervals be- decline rapidly after fire as larger shrubs de- Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 17
velop (Jurskis 2011b). Thus biodiversity is cally inaccessible to mild fires. A small num- likely to decline with less frequent fire because ber of plants on Sydney’s sandstones are asso- many smaller species are shaded out by fewer ciated with wetter soils or dense shrub cover larger species and spatial heterogeneity due to (Tozer and Bradstock 2002). Disruption of site factors (e.g., Siddiqi et al. 1976, Bradstock natural fire regimes has allowed these fire sen- et al. 1997, Keith et al. 2002) is obliterated (e. sitive species to escape their refuges and inter- g., Siddiqi et al. 1976, Clark and McLoughlin fere with fire management across the landscape 1986, Conroy 1996, Jurskis et al. 2003, Jurskis (Clark and McLoughlin 1986, Conroy 1996, 2011b). Fire regimes also mediate intraspecif- Jurskis et al. 2003). ic competition. Frequent mild fire regimes fa- The results of recent ecological studies are voured mature plants over juveniles irrespec- entirely consistent with the recorded history of tive of species, whilst a regime of fire suppres- Sydney’s sandstone vegetation, but the way sion can have the reverse effect, causing loss that these results have been interpreted to in- of mature trees and shrubs, and initiating fluence fire management is not, because the changes in species composition (Jurskis 2009, historical context has not been appreciated. 2011a). For example, Morrison et al. (1996) claimed Some proponents of the theory that pre- that there is “a clear conflict in south-eastern scribed burning threatens biodiversity have Australia between fire management practices used a circular argument around species that based solely on prescribed burning for hazard are long lived obligate seeders (e.g., Benson reduction and the fire management practices and Redpath 1997, Enright et al. 2005). They necessary to maintain ecosystem biodiversity”. claim that persistence of these species in the However, this proposal fails to recognize that landscape is evidence that Aborigines did not the current high fuel accumulation rates and burn frequently because burning at shorter in- extreme fire behavior during severe weather tervals than their maturation period would are products of changed vegetation structure eliminate them. Clark and McLoughlin (1986) and composition consequent to less frequent recognized the historical evidence for frequent and more intense fire regimes. For example, burning by Aborigines, but used the same cir- Cary and Morrison (1995) studied sites where cular argument to overestimate intervals be- the understorey had been completely destroyed tween Aboriginal burning at seven to fifteen across at least five hectares by severe fires. years. The persistence of the slow maturing Their finding that short intervals between these obligate seeders on Sydney sandstone and of fires reduced species richness has no relevance naturally rare plants (e.g., Keith et al. 2002) to low intensity prescribed burning. Post-Eu- despite thousands of years of frequent Aborigi- ropean fire management in national parks nal burning provides clear evidence that both around Sydney has initiated a vicious circle the theory and the circular argument should be that threatens biodiversity and human socio- discarded. It is apparent that slow maturing economy. The historical evidence indicates obligate seeders, once mature, are very toler- that Aboriginal burning favoured biodiversity ant of frequent mild fires (e.g., Jurskis 2009, over biomass and that there is no conflict be- 2011a) and that fire sensitive obligate seeders tween the socioeconomic and environmental mature rapidly (e.g., Knox and Morrison objectives of low intensity prescribed burning. 2005). Aboriginal burning over thousands of Keith et al. (2002) acknowledged that the years undoubtedly selected genotypes attuned current Australian biota persisted through Ab- to frequent low intensity fire. Genotypes that original fire regimes for tens of thousands of were not so attuned, that is fire sensitive spe- years, but argued against reinstating those re- cies, persisted in limited areas that were physi- gimes because: Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 18
• they are difficult to specify precisely; Clearly, the guideline is intended to maintain • they may have different consequences the status quo, and this will perpetuate the ac- today because of habitat fragmentation cumulation of woody vegetation, dangerous and introduction of exotic biota; fuel loads, and pathogenic inoculum at the ex- • they were implemented to provide food pense of understory diversity and healthy soil whereas conservation has “very differ- conditions. The guideline is apparently based ent goals” such as protecting rare on a philosophy of minimizing human “inter- plants, which may have had no value to ference” rather than on any historical or eco- Aboriginal people and may have been logical foundation. disadvantaged by their burning; • they may be too expensive to apply CONCLUSIONS across the landscape because of their fine scale. Contrary to the views of many modern fire ecologists, human ignitions were the dominant However, the concept that frequent mild cause of fire in most Australian ecosystems for fire regimes would need to be defined precisely thousands of years (Pyne 1998; Kershaw et al. before they could be successfully implemented 2002; Gammage 2011; Jurskis 2011a, b). is not valid. These fires are inherently patchy Patchy Aboriginal burning undoubtedly limited (e.g., Penman et al. 2007) and fire behavior recruitment of woody plants by killing seed- varies with site factors at a fine scale (e.g., lings on sandstone around Sydney as it did Bradstock et al. 1997). Habitat fragmentation elsewhere (Mitchell 1848, Howitt 1891, Noble is irrelevant to the discussion for the same rea- 1997, Jurskis 2009). Frequent, mild, and sons. Invasion by exotic biota can be mini- patchy fires in sparsely shrubbed vegetation mized under natural fire regimes (e.g., Jurskis leave many established woody plants unscathed 2012). Exotic plant invasions on Sydney’s (e.g., Jurskis et al. 2003, Penman et al. 2008). sandstones depend on unnatural nutrient en- Thus, recruitment after such fires is not a con- richment (Lake and Leishman 2004), whereas servation issue as has often been suggested. frequent burning at intervals around five years Studies of prescribed burning have con- can maintain stable nutrient cycles on such low firmed that most obligate seeders are favored nutrient sites (Turner et al. 2008). by frequent mild fire whilst a few common There is no doubt that Aboriginal burning large shrubs are disadvantaged (Jurskis et al. was economically and culturally motivated 2003; Penman et al. 2008, 2009; Jurskis (e.g., Pyne 1998, Gammage 2011) and it is 2011b). In the absence of frequent burning, clear that the best way to conserve ecosystems these few shrubs have commenced to shade shaped by about forty thousand years of Ab- out many smaller and less common species original burning would be to continue in a within three or four years, reducing diversity similar vein. Infrequent burning obliterates (Penman et al. 2008, 2009; Jurskis 2011b). fine scale environmental variation (e.g., Clark Other studies of fuel accumulation (Birk and McLoughlin 1986, Conroy 1996), whereas and Bridges 1989), fire risk (Boer et al. 2009) frequent mild burning enhances it and facili- nutrient cycling, and tree health (Turner et al. tates low input and low cost management (Jur- 2008) in dry eucalypt systems have shown that skis et al. 2003). burning at three to six year intervals can main- Kenny et al. (2004) reviewed the fire ecol- tain dynamic stability and ecological resilience ogy of Sydney sandstone vegetation and con- in these systems (Jurskis 2011b). Physical re- cluded that the “domain of acceptable fire in- cords (e.g., Singh et al. 1981, Burrows et al. tervals” was 7 yr to 30 yr and that some inter- 1995, Ward et al. 2001, Hassell and Dodson vals greater than 20 yr were “desirable.” 2003, Mooney et al. 2011: Figure 2) and his- Fire Ecology Volume 9, Issue 3, 2013 Jurskis and Underwood: Human Fires, Wildfires doi: 10.4996/fireecology.0903008 Page 19
torical records (Mitchell 1848, Curr 1883, tions that favour ancient trees, small understo- Howitt 1891, Abbott 2003, Gammage 2011) rey plants, and bare ground as well as the rare support these studies of ecological processes species that depend on them (Jurskis 2009, pointing to ecosystems shaped by extensive, 2011a, b). In eastern Australia, these include frequent Aboriginal burning. Hastings River mouse (Pseudomys oralis) Australia is fortunate in having good his- (Tasker and Dickman 2004), the orchid Praso- torical records of Aboriginal fire regimes and phyllum correctum (Coates et al. 2006), superb vegetation before they were impacted by Eu- parrot (Polytelis swainsonii) (Manning et al. ropean settlement (e.g., Pyne 1998, Gammage 2006), eastern brown treecreeper (Climacteris 2011). These show that prehistoric physical picumnis victoriae) (Ford et al. 2009), and evidence cannot provide a reliable record of broad-headed snake (Pringle et al. 2009). In- mild fire regimes. Even though historical re- formed application of human fires could also cords may be scant, such records should guide reverse declines in common species such as interpretation of physical evidence as well as grasstrees. interpretation of ecological studies. Human fires can support biodiversity by restoring and maintaining natural, open condi-
ACkNOWLEDGEMENTS
Constructive criticism by B . Gammage, A. Stirling, and two anonymous referees helped us to substantially improve this article.
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