As most have already heard, I've been living upside down in the Southern Hemisphere on the incredibly beautiful island of Tasmania. As incredible a place as it is, somehow I've gotten myself wrapped up in a project far far away...in Arnhem Land.
here's some background for the current adventure:
The eucalypt-grassland savannas that sweep across tropical northern Australia are one of the world's most flammable ecosystems. Unlike the rest of the continent, the climate there is governed by the Asian monsoon so that 90% of the annual rainfall occurs between December and May. The ecological significance of this is simply that lots of grass grows in the Wet, resulting lots of cured fuels in the Dry. A third “season,” which many folk call the Buildup, is marked by incredibly high humidity and dry lightening storms for about a month before the onset of the rains. This creates the perfect recipe for the landscape-scale wildfires which rage across much of the landscape every year - dwarfing the bushfires in southern Australia which get all the media attention. Yet while these wildlfires seem quite beyond human control, ecologists reckon this wasn't always the case.
Arnhem Land sits squarely in the middle of northern Australia. It is home to one of the oldest continuous cultural groups on the planet with evidence of Aboriginal occupation extending beyond 50,000 years. Think about that number for a minute – its hard to imagine. The stories still sung by these people predate the rise of agriculture, all the world's major religions, civilizations and empires, even the last ice age. What has come from this incredibly long occupation is a very refined set of knowledge and tools for survival in this landscape. And one of the most significant of Aboriginal tools is fire.
Historical and contemporary descriptions of “traditional” management by Aborigines in Arnhem Land and elsewhere in Australia involves burning country – mostly in the early dry season when the weather keeps fire size and intensity low, but some Aboriginal elders maintain that people set fires year-round. Coined as “fire-stick farming,” Aboriginal burning accomplished many things. Fires were lit for communication and driving game animals like goanas (monitor lizards). Flushes of fresh grass after burning attract kangaroos for hunting. Preventative burns also protect sacred site and valued resources like stands of edible fruit trees. “Cleaning country” with fire improves access to fishing holes and other resources like turtles and yams. The landscape-level effects of these management activities, which ecologists are still trying to understand, were likely a reduction in the occurrence of large, destructive wildfires and an increase in the diversity of habitat patches. This last feature – the so-called “habitat mosaic” of mixed age patches of vegetation – has become a key argument in explaining patterns of diversity of plants and animals in savannas across the world.
Unfortunately these days much of Arnhem Land stands empty of people, especially in the “Stone Country” of the Arnhem Plateau – the rugged country of western and central Arnhem which straddles the east edge of Kakadu National Park. Aborigines along the Arnhem coast enjoyed trading relations with Indonesian sailors coming for sea cucumbers at least since the 16th Century, however, white Australians only began “developing” the region around the 1900s. As is too often the case with colonization, the immigration of cattle ranchers and prospectors painted a pretty grim history. Vindictive and often inhuman retaliations by the newcomers against Aborigines defending their lands ravaged entire clans and disrupted ancient trade relationships. In the aftermath of the 1920s and 30s, missionaries further broke apart culture and family, discouraging traditional song and ceremony and forcibly removing “half-caste” children from their Aboriginal mothers. By the 1940s and 50s, as the taste for “western” goods grew and local economies shifted away from subsistence, most remaining families had walked off their ancestral lands in the heart of Arnhem Land towards permanent settlements nearer to the coast. Despite the disruptive and conflictual history, Arnhem Land was officially returned to Aboriginal Traditional Owners in 1976. More recent infrastructure development has provided a few scattered “outstations” where some family groups still hunt and gather traditional foods on ancestral estates. However, the current patterns of human settlement in Arnhem Land are dramatically different than they were into the first half the 1900s.
The cultural and economic marginalization of Aboriginal communities in Arnhem Land may be less severe than elsewhere, but the conditions of health and education are poor overall. There is effectively a “third world” population within Australia (arguably not unlike the situation for many ethnic groups in “first world” nations). The problem is directly related to lifestyle and livelihoods – those families fortunate enough to live at outstations on ancestral lands and maintain some degree of subsistence activity are generally much healthier and happier. Unfortunately, many Aborigines in the larger coastal settlements face myriad problems brought about by welfare dependence, poor nutrition, alcohol, and the imposition of European social structure on traditional relationships and taboos. Integrating or even establishing common ground between “whitefella” and “blackfella” culture – to provide the educational and economic opportunities of “Western” society and maintain the values, ceremony, and connection with country that define Aboriginal identity – is still a hugely daunting challenge.
From an ecological perspective, the effect of this marginalization has been a drastic change in the patterns of burning across the savannas. Rather than small patchy fires set by humans widely dispersed over the landscape, the fire regime has shifted towards huge, uncontrolled wildfires lit by lightening strikes in the late dry season. We are only beginning to understand the ecological consequences of this change. There have been recent and marked declines in populations of many plants and animals – a major concern in areas like the Arnhem Plateau, which is considered a center for species endemism (ie, species unique to this region) and part of World Heritage Area Kakadu National Park. However, directly linking these declines to changes in burning patterns remains a challenge for biologists.
Evidence of Aboriginal occupation abounds in Arnhem Land through the rich legacy of rock art depicting the people, animals, and spirits that once filled this country. Evidence of their ecological legacy may also abound, albeit through something less obvious than artwork. Rather, there is a curious old pine tree that seems very much out of place in a tropical savanna dominated by Eucalyptus trees. The Northern Cypress Pine (Callitris intratropica) carries the flag for the ancient flora of Gondwanaland amid the much younger (by evolutionary standards), fire-loving Eucalypts. Whereas the “eucs” can resprout after burning, cypress pines are much less tolerant of fire and reproduce only from seed. For seedlings to reach the point where they can survive even mild fires requires years without burning. So how are they found all across one of the world's most fire prone ecosystems?
Before we surmise an answer, there's a bit more to the story. Aboriginal Land owners were the first point out to biologists that dead Cypress Pines provide evidence of destructive fires and poor land management. You see, another interesting feature of Cypress Pines is that the wood is termite resistant (foresters tried to establish a local industry for its timber in the 1950s) and therefore dead trees can remain standing in the landscape for decades . Running with this idea, counts of dead and living stems across northern Australia has revealed that the species is declining throughout the savannas. What's the upshot of all this? Many ecologists believe the declines in Cypress Pine provide the best evidence of an ecosystem-scale response to the changes in burning patterns mentioned above. Because most of these trees sprouted while Aborigines were still managing their country, the running hypothesis is that Aboriginal patch burning allowed Cypress Pines to establish across the savannas in the first place.
Its a very appealing idea. All the pieces seem to fit the picture. However, ecologists are still trying to prove it beyond a doubt. In spite of the Cypress Pine example, many biologists still contend that Aborigines – and savanna-dwelling people elsewhere – could have had no major effect on the patterns of fire. Or that any effect they did have did not alter plant or animal diversity. Even if we grant that Aborigines did influence fire regimes, merely associating contemporary large-scale wildfires with recent declines in mammals, reptiles, and birds does not explain how these species are affected by fire. Do the fires themselves directly impact populations? Are they causing declines in food plants? Do large fires open habitat and improve hunting conditions for introduced predators like feral cats? The complexity of the issue reveals itself quickly.
Despite the biological arguments, Aboriginal burning patterns provide the framework for current conservation efforts in Arnhem Land and elsewhere in Northern Australia. The sad reality is that Aboriginal people will not likely be returning en masse to their ancestral lands. Knowing this, contemporary land managers are attempting to merge traditional knowledge with modern technology, employing helicopters and Aboriginal ranger groups to set early dry season fires across the landscape. As for the Cypress Pine, we know that dead adults mean poor management. The question now is to see whether the species can be used as a benchmark for good management and whether its presence in the savannas may indicate habitat for other fire-sensitive and threatened species.
There are some cool research opportunities here – comparisons between the national park and Aboriginal estates and hopefully some experimental work directly measuring fire behavior. The ultimate hope is that by addressing these types of questions ecologists can advocate for the increased involvement of Aboriginal landowners in conservation programs in Arnhem Land. The strength of Australian research is that it highlights the ecological significance of both human history and contemporary connections with savannas – ideas that may be extended to other parts of the world.