The impact of fire, in oldgrowth forest of the Walpole-Nornalup National Park, on short-range endemic invertebrates and their forest floor communities.

The Walpole-Nornalup National Park contains large areas of oldgrowth Karri, Jarrah, and Tingle forest. The forests of the Walpole-Nornalup area are estimated to have a high proportion (approx. 75%, Van Heurck, Burbidge and Wheeler 2000) of arthropod species with Gondwanan affinities, the majority of which are new or undescribed species. Also contained within these forests are a number of threatened and short-range endemic species. Short-range endemics make up the majority of species in the following invertebrate groups: Gastropoda (snails), Oligochaeta (earthworms), Onychophora (velvet worms), Araneae (trapdoor and other spiders), Diplopoda (millipedes), Phreatoicidea (slaters) and Decapods (freshwater crayfish) (Harvey 2002). Little is known of the ability of these short-range endemic species and their litter communities to survive both wild and managed fires. No long-term systematic survey of the fire impact on the species composition of the litter invertebrate communities of these forests has been carried out to date.

Recent worldwide estimates of the number of species of living organisms (Stork, 1999) are of the order of 12.5 million species (invertebrates, vertebrates and plants), of which 11 million are arthropod species. The inventory of arthropod species is therefore critical to the State's requirement to conserve the biodiversity of regions such as the oldgrowth forests. Recent advances in bio-survey methods allow the simultaneous study of fire impacts on the majority of species of an entire ecosystem component such as the forest floor litter community. The advantage is that a rapid inventory of species of a wide range of arthropod groups in the litter community of each site is achieved. In addition, fire impacts on any short-range endemic species at each site can be determined, while also comparing the post-fire species composition between sites with a wide range of fire regimes. This allows extrapolation to other similar oldgrowth forest ecosystems containing similar short range endemic species, as well as predicting the impact of fire regimes and post-fire ages on the richness and species composition of entire litter arthropod communities in these nearby forests.

Following the March 2001 wildfire in the Nuyts Wilderness, a large group of local volunteers from the Walpole Community and Walpole Nornalup National Parks Association (WNNPA) have been trapping and inventorying the litter arthropod species of these forest sites, as well as long unburnt sites nearby. Paul Van Heurck from the Science Division, Department of Parks and Wildlife was asked to advise on the technical methods to carry out this survey. This survey is establishing a comprehensive collection of undescribed local arthropod species and allowing the fire tolerances of these species to be determined. The outcome should be adaptive fire management of these oldgrowth areas to conserve the full range of arthropod biodiversity. The extension of this study over a three year period will allow documentation of the early post-wildfire species succession.