Legacy effects of fire on the invertebrates of Alpine Tasmania

Fire has a major influence on terrestrial ecosystems. Its effects on vegetation are becoming increasingly well known, while its effects in invertebrates are only starting to be studied. Much of the study of invertebrates has focused on immediate changes following fire in either contrived or natural experiments. As the majority of global ecosystems return to pre-fire conditions within several years, there is little data on the multi-decadal post-fire succession of invertebrate communities.
Tasmanian coniferous heath and scrub are the most fire-sensitive ecosystem in Australia. They have been well studied and shown to require hundreds of years to recuperate from burning. With climate change altering fire regimes globally, including Tasmania’s palaeoendemic alpine ecosystems, I endeavoured to investigate the long-term succession of the invertebrate community associated with this habitat.
My original data was collected over 12 months (separated into six continuous sampling periods) from 33 quadrats which straddled a 52-year-old fire boundary, in sub-alpine central Tasmania. Quadrats from the burned half of the site contained highly floriferous regrown heath vegetation. Quadrats from the unburned half of the site contained a mixture of heath and scrub vegetation characterised by fire sensitive and palaeoendemic evergreen and deciduous plant species. The site was located on the Tarn Shelf, Mount Field National Park which is part of the Tasmanian Wilderness World Heritage Area. Each quadrat contained an experimental sampling method, the Alpine Malaise Trap (AMT), which collected aerial invertebrates across the whole year. Vacuum samples were taken from a subset of quadrats in three of the six sampling periods so that any impact on the results from different sampling techniques could be investigated.
Most Tasmanian alpine invertebrates displayed warm-season peak abundance. The few invertebrate taxa which were most abundant during colder seasons were also palaeoendemic. Palaeoendemic plants significantly co-occurred with more palaeoendemic invertebrates than expected by chance, as well as hosting a cohort of non-palaeoendemic invertebrates which displayed high fidelity with the unburned quadrats and fire-sensitive vegetation. Heath-associated invertebrates were more likely to be generalists visiting burned and unburned heath, except for one which was significantly affiliated with unburned heath only. The overall effect of fire-history on invertebrate distribution and community composition was statistically significant, although not as strong as that of vegetation type, both of which were less influential than season. Vacuum samples proved more sensitive to post fire influence than aerial trapping. The experimental Alpine Malaise Traps collected data and results which similar local surveys were not able to produce.
This work revealed that long-lasting post fire habitat changes in fire-sensitive vegetation were translated into the community composition of both flying and sessile invertebrates. This is in contrast to many researchers who report vegetation and invertebrate return to pre-fire conditions within decades. My data also showed that the regrown heath is not equivalent to unburned heath, 52 years post-burn, both in terms of vegetation resources, and in terms of invertebrate habitat. I also revealed a cohort of generalist invertebrates which have not historically been associated with Tasmanian palaeoendemic vegetation. Their apparent reliance upon this fire-sensitive ecosystem infers an extinction cascade which is not currently considered in the conservation and management of these host plants.