South Sister St. Marys, Tasmania

Diminishing the biodiversity

diversity of life in weld valley

BIODIVERSITY IMPACTS and SUSTAINABILITY IMPLICATIONS of CLEARFELL LOGGING in the WELD VALLEY, TASMANIA

Summary

This study was undertaken in the Weld River Valley, an area of largely pristine forest located in Tasmania's southern forests just north of the Tahune Airwalk tourism venture. The study was conducted in order to compare and contrast the botanical diversity, soil ecology, invertebrate biodiversity and timber values of old growth forest in the valley with a nearby forest coupe that was clearfelled in the 1980s.

The findings of the study are used to give an independent critique of the scientific basis used to justify the 'clearfell, burn and sow' silvicultural system which dominates forestry in Tasmania today.

The study demonstrated that logging old growth forest in the Weld Valley significantly alters the diversity and abundance of plants and invertebrates. Poor soil structure and lack of soil humus following the clearfell burn and sow treatment appears to adversely affect forest health and its ability to produce good timber. In sites regenerated following clearfelling there was significant root and crown competition resulting in slow and poor tree growth.

A key measure of sustainability is that no species are lost from an ecosystem. The claim that 'no species are known to have been driven to extinction by forestry practices in Tasmania' heavily relies on the lack of knowledge about the species which live in Tasmania's native forests, and the fact that we know little about the long-term effects of forest fragmentation and conversion to plantations of exotic species.

The sampling of nocturnal insects at old-growth and regrowth study sites in the Weld Valley highlighted the stark differences in the diversity of animals present. Using native moths as an indicator of biodiversity it was revealed that:

Native forests managed on short rotation cycles will never reproduce the diverse micro-habitats which characterise old forests.

This study brings in to question whether the forests allocated for timber production under the Regional Forest Agreement (RFA) have been managed in an ecologically sustainable way, that is, in a way that maintains species diversity, water resources, and soil structure and quality.

Forest health, and the ability of the forest to continue to produce healthy timber in perpetuity, is intimately linked to the maintenance of biodiversity and soil health. If biodiversity is compromised, then timber production will become more degraded with each clearfell rotation. This has serious implications, not just for forest ecology and biodiversity, but also for a suite of social and economic values such as: future timber quality, aesthetics, ecotourism opportunity, beekeeping and pollination services, and water supply.

The scientific basis for clearfelling derived from research undertaken in the 1950s must now come under question and should now be critically reviewed in light of the biodiversity implications highlighted in this study.

The study has provided a strong case for a moratorium on logging in the Weld Valley which is an area that has been identified for its high conservation values and significant ecotourism potential. The case for a moratorium on logging is strengthened in light of the current sawlog oversupply and glut in specialty timbers.

- by Green, G., Timber Workers for Forests
Gray, A., Consultant Entomologist and Forest Ecologist
McQuillan, P., Ph.D., Entomologist, University of Tasmania
March, 2004.

[Summary republished with permission of Timber Workers For Forests; the full report is available in pdf (793KB).
For anyone wishing to peruse the matter further we can heartily recommend E. O. Wilson's seminal work The Diversity of Life, ISBN 0-393-31940-7 or Peter J. Bryant's online book Biodiversity and Conservation.]

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