Effects of forest fragmentation on log-dwelling invertebrates at Tumut, NSW

Research Project 2

This work was funded by the Australian Research Council 2003-2005.

Project summary

Clearing of Australian native forests continues apace. This leads to declines in total forest area and creates isolated remnants with depleted woody debris. Critical forest processes driven by invertebrates occur in this debris. Despite its major economic and conservation significance, there is little information on the impacts of habitat loss and alteration on organisms in decomposing logs. We will utilize recent advances in population genetics to compare impacts on a suite of log-dependent invertebrates in an islands-of-bush-in-a-sea-of-pines model. This will facilitate improvements in conservation and sustainable management outcomes in forests.


Clearfell pine logging poses considerable barriers for organisms with low dispersal ability Pine-eucalypt interfaces are typically abrupt and the habitat in the two forest types very different The study area & its history of fragmentation: ‘islands of bush in a sea of pines’ The area targeted for the study of habitat fragmentation is the Buccleuch State Forest (BSF) near Tumut, NSW, which encompasses a unique model that has been intensively developed, with data collected for many plant and vertebrate groups (program of Dr David Lindenmayer). Approximately 50,000 ha of BSF were converted from eucalypt forest to a softwood plantation of exotic radiata pine (Pinus radiata). Clearing native forest occurred from the 1930s to mid-1980, leaving 192 remnant patches of the native forest embedded in a pine matrix. These patches range from 0.2 to 124 Ha. The fragments vary in shape: half are elongated strips that follow creek lines, and the other half are elliptical. The date of fragmentation for each remnant is known from records of State Forests of NSW, and range from 15 to 65 years. Extensive areas of contiguous native eucalypt forest lie adjacent to the N, E & S borders of the plantation, and are suitable control regions in quasi-experimental designs.

Early progress on this work was made by the Honours research of Sean MacEachern in 2001. Sean focussed his research on a large, flightless, wood-boring cockroach Panesthia australis that lives in the saproxylic habitat. The main outcomes are summarized below:

The consequences of habitat fragmentation on the wood-dwelling cockroach Panesthia australis

The only significant predictor found of cockroach abundance or genetic diversity was the amount of coarse woody debris on the forest floor
Genetic differentiation was significantly positively correlated with distance, at > 10km.
P. australis was found in nearly all patches, the continuous forest, and within the pine matrix in pine logs as well as eucalypt logs
Nonetheless, isolation-by-distance slopes were significantly steeper for sets of samples from the remnant patches than in the continuous forests over the same spatial scale, indicating restricted gene flow among fragments.

It was surprising that P. australis showed restricted gene flow in forest fragments. With the exception of its being flightless, the species has characteristics that would tend to predict high dispersal ability: we found the insect to be broadly-distributed and not highly specialized in its habitat requirements, and although flightless, it is large, robust and has a desiccation-resistant cuticle. Thus P. australis would be predicted to be relatively immune to the effects of habitat fragmentation, yet still showed impediments to gene flow that arose in only 20-30 years (a mere handful of generations, given time to maturity is a much as 10 years). The impacts on mobility were detectable with only 4 polymorphic allozymes.
For development of the work see the pages of Christina Schmuki.

We hope that our research will contribute insights to the vital goal of sustainable use of forests. Without this, maintenance of the organismal diversity that underpins natural values (biodiversity, enjoyment by people etc) as well as forest production will suffer.

Publications

Publications of impacts of fragmentation of forests on invertebrates

MacEachern, S. (2001). The effects of habitat fragmentation on the wood dwelling cockroach Panesthia australis (Blattaria, Blaberidae, Panesthiinae). Honours thesis, Department of Genetics. Bundoora, La Trobe University . (DOC 1.1MB)
Woodman, J. (2003) Population structure in a funnel web spider (Hexathelidae:Hadronyche). Hons thesis, ANU (PDF 972KB)
July 2003: International Congress of Genetics, Melbourne (poster). Boring blaberids in bits of bush: how habitat fragmentation has moulded the genetic structure of a log-dwelling Australian cockroach Panesthia australis . Runciman, D., Sunnucks, P. & MacEachern, S. (DOC 3.6MB)
Schmuki, C. (2003). Impacts of habitat fragmentation on two species of Adeliini beetles at Tumut, NSW. Honours thesis, Department of Genetics, La Trobe University. (PDF 2MB)
Watson, S. (2003). Population genetic structure, gene flow and dispersal in the saproxylic beetle Prostomis atkinson. Honours thesis, Dept of Genetics, La Trobe University (DOC 1.2MB)