The ‘‘fire stick farming’’ hypothesis: Australian Aboriginal foraging strategies, biodiversity, and anthropogenic fire mosaics R. Bliege Bird*†, D. W. Bird*, B. F. Codding*, C. H. Parker‡, and J. H. Jones* *Department of Anthropology, 450 Serra Mall, Building 50, Stanford University, Stanford, CA 94305; and ‡Department of Anthropology, 270 South, 1400 East, Room 102, University of Utah, Salt Lake City, UT 84112-0060 Edited by Kent V. Flannery, University of Michigan, Ann Arbor, MI, and approved August 1, 2008 (received for review May 15, 2008) Aboriginal burning in Australia has long been assumed to be a productivity of herbaceous plants and increasing in-patch diver- ‘‘resource management’’ strategy, but no quantitative tests of this sity, which tends to peak 2–4 years after a fire (18–20); (ii)in hypothesis have ever been conducted. We combine ethnographic anthropogenic regimes, fires are of lower intensity and occur observations of contemporary Aboriginal hunting and burning more frequently but only in particular types of habitat (8); (iii) with satellite image analysis of anthropogenic and natural land- fire mosaics of burnt and regenerating vegetation are more scape structure to demonstrate the processes through which Ab- fine-grained (17, 18, 21, 22), (iv) which prevents extensive, original burning shapes arid-zone vegetational diversity. Anthro- late-season fires (22), and this in turn (v) prevents the fragmen- pogenic landscapes contain a greater diversity of successional tation and subsequent contraction of Acacia woodlands (23) and stages than landscapes under a lightning fire regime, and differ- other fire-sensitive species (24). ences are of scale, not of kind. Landscape scale is directly linked to These studies quantify the ecological outcomes of anthropo- foraging for small, burrowed prey (monitor lizards), which is a genic fire but not its formation processes, assuming that mosaic specialty of Aboriginal women. The maintenance of small-scale formation is driven by management strategies designed to in- habitat mosaics increases small-animal hunting productivity. These crease the availability of key resources (25). Without sanctions results have implications for understanding the unique biodiver- that exclude free-riders, management produces common-pool sity of the Australian continent, through time and space. In par- resources and thus becomes a collective-action problem (26). ticular, anthropogenic influences on the habitat structure of pa- This problem is further exacerbated if the future benefits of leolandscapes are likely to be spatially localized and linked to less management are heavily discounted, as they might be if indi- mobile, ‘‘broad-spectrum’’ foraging economies. viduals are risk averse for uncertain future rewards. It can be difficult to overcome the dual problems of collective action and fire ecology ͉ human behavioral ecology ͉ hunter–gatherers ͉ future discounting, especially in small-scale, politically decen- resource management tralized societies (27). However, there are conditions that might make management strategies less costly to maintain: if individ- nthropogenic fire is increasingly recognized as an important uals gain more from contributing to construction than they gain Aconstructive force in shaping plant communities around the from free-riding, if the costs of construction are low relative to world (1–3), and its impact in Australia has been argued to be the future benefits gained or if those paying the costs reap more particularly significant (4–6). Fire can act as an ‘‘intermediate of the future benefit. In order for burning to be maintained as disturbance,’’ enhancing biodiversity by disrupting the repro- part of any long-term strategy of ecosystem construction or ductive rate of slowly growing species and promoting greater resource management, there must be future benefits to survival diversity (7–11). Over evolutionary time scales, fire shapes the and/or reproductive success that accrue to those who pay the cost life-history traits of plant communities; thus a change in fire of creating and maintaining mosaics. Although this ‘‘burning as regime should trigger a cascade of population extinctions of resource management’’ hypothesis was first proposed by Rhys those species with incompatible life histories (12). Such a Jones (4) and elaborated by Gould (28), no research has yet ‘‘trophic cascade’’ has been hypothesized to have occurred upon tested this either by quantifying the adaptive benefits or by the colonization of Australia ca. 45–50 ka (5). Paleoecological linking the process of mosaic formation to particular foraging records coincident with the putative arrival of modern humans strategies. show possible changes in burning regimes and subsequent tro- Here, we attempt to address this gap in our knowledge of the phic-level shifts in ecological communities—a fragmentation of processes structuring Aboriginal fire mosaics by linking quanti- woodlands and forests and an expansion of grasses, particularly tative observations of foraging by contemporary Aboriginal Triodia (the inedible spinifex grass)—which may have contrib- people (Martu) in the Western Desert of Australia with remotely uted to Australia’s late Pleistocene extinctions (6, 13). Further- sensed measures of landscape heterogeneity to test three pre- more, some propose that with the establishment of anthropo- dictions derived from Jones’ ‘‘fire-stick farming’’ hypothesis: (i) genic fire mosaics throughout the continent, flora and fauna anthropogenic landscapes (as compared with those shaped coevolved with human behavior to such an extent that the through ‘‘natural’’ or lightning fire) are associated with greater cessation of burning with European incursion into the continent precipitated a second major trophic collapse, leading to se- vere declines in small-to-medium-sized mammal populations Author contributions: R.B.B. and D.W.B. designed research; R.B.B., D.W.B., B.F.C., and C.H.P. (7, 14–17). performed research; R.B.B., D.W.B., B.F.C., and J.H.J. analyzed data; and R.B.B., D.W.B., Models of the prehistoric shift from lightning to anthropo- B.F.C., and J.H.J. wrote the paper. genic fire regimes rely on analogies with modern Australian The authors declare no conflict of interest. Aboriginal burning. Previous work has examined the correlation This article is a PNAS Direct Submission. between Aboriginal presence and landscape-level effects, con- †To whom correspondence should be addressed. E-mail: [email protected]. cluding that (i) in both regimes, fire increases nutrient availabil- This article contains supporting information online at www.pnas.org/cgi/content/full/ ity and removes ‘‘climax’’ vegetation (more slowly growing 0804757105/DCSupplemental. hummock grasses and woody shrubs), enhancing the short-term © 2008 by The National Academy of Sciences of the USA 14796–14801 ͉ PNAS ͉ September 30, 2008 ͉ vol. 105 ͉ no. 39 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0804757105 Downloaded by guest on October 2, 2021 habitat heterogeneity at the spatial scale of the human day range; fires can be set so that they burn out relatively quickly against a (ii) reductions in scale and increases in diversity in a local downwind firebreak. Being able to control a fire is important landscape are linked to time spent foraging for resources for because the rights to burn country for hunting are held collec- which burning offers an immediate increase in foraging returns; tively, but individual hunters are responsible for fires that burn (iii) increases in landscape diversity as encountered by human areas to which they do not hold such rights. A hunter whose fire foragers increase foraging efficiency. We first describe the shifts with the wind and threatens a sacred site in an area where ethnoecological context of Martu foraging before turning to tests his/her burning rights are deemed less than legitimate is subject of the predictions listed above. to severe punitive procedures by the collective body of owners, which today involves ritualized physical punishment and mone- The Ethnoecological Context of Aboriginal Fire tary compensation to owners. The use of fire thus has social and Martu are the indigenous owners of estates that comprise Ϸ150,000 ritual meaning that accompanies its immediate hunting utility: km2 in Australia’s Western Desert [supporting information (SI) Fig. Burning is a signal of coownership and obligation and an S1]. In the 1980s, Martu established three permanent settlements expression of one’s commitment to upholding the Yulupirti, the (‘‘outstations’’) in this region when they returned to their home- law handed down from the Jukurrpa, or ‘‘Dreamtime.’’ The lands after a mid-20th century exodus into missions and pastoral mosaic that develops as a result of repeated burning is a signal stations on the western and northern fringe of the desert (29, 30). of its use: It represents the number of hunters and the frequency Each outstation has a population that fluctuates between 50–200, with which they hunt on the land. with people routinely shifting between communities and traveling Martu often stress the short-term utility derived from winter- extensively throughout the Western Desert and Pilbara regions on time burning: ‘‘Today, we often make a nyurnma to hunt in logistical, social, and ritual business. Most Martu based in these during the winter months, because there is too much old spinifex remote communities hunt and gather daily, acquiring 1,700 kcal per and not enough ground already burnt. We prefer to burn a small capita per foraging day from bush foods (31), purchasing the patch of old spinifex, if it is surrounded by younger growth that remainder from the small outstation stores or on visits to towns in won’t burn, to keep the fire from spreading or burn when the the Pilbara. Contemporary daily foraging typically involves travel by grass is green and doesn’t move very far or very fast. You get vehicle from an outstation to a foraging camp, which establishes a more goanna that way—Goanna like to hide in the small patches central place for search and pursuit of hunted and collected of unburnt spinifex inside a nyurnma.’’ (Karrimarra, June 2003).