Research confirms fire as essential to eucalypt regeneration

Dr Steve Read
Chief Scientist

A 12-year study undertaken by Forestry Tasmania’s Principal Research Officer (Native Forests), Dr Mark Neyland, has confirmed the fundamental relationship between fire and the successful regeneration of wet eucalypt forests after harvesting.

Mark was awarded his Doctor of Philosophy by the University of Tasmania on 21 August for his research, which has made an invaluable contribution to our understanding of the ways in which wet eucalypt forests respond to different harvesting and regeneration methods. Specifically, Mark’s work has further increased our expertise in variable retention.

The key finding is that, far from being unnecessary, regeneration burns are the best way to ensure healthy regrowth in wet eucalypt forests.

Mark’s study, carried out at the Warra Long-Term Ecological Research site in the southern forests, looked at the effects of different variable retention harvesting regimes on structural and biological diversity in forestry coupes:

• Clearfell burn and sow with understorey islands, in which 40-metre by 20-metre patches of the understorey were retained undisturbed by harvesting machinery within the otherwise clearfelled coupes, followed by a high-intensity burn.
• Stripfells, in which 80-metre wide strips were felled with unfelled strips of equal width retained between them, followed by a moderate-intensity burn.
• Dispersed retention, in which 10 per cent of the original trees were retained evenly distributed throughout the coupe, followed by a low-intensity burn.
• Aggregated retention, in which 30 per cent of the coupe was retained in unfelled aggregates of about one hectare each, followed by a low-intensity burn.
• Single-tree/small-group selection, in which gaps and ‘fairways’ of varying size were created, followed by no burn or a low-intensity burn.

Mark found a direct relationship between the density and growth of eucalypt seedlings and the type of harvesting and regeneration technique. The highest densities and fastest growth rates for eucalypt seedlings occurred in the coupes that had been subjected to high-intensity burns, and which also had the largest areas of burnt seedbed. Adequate regeneration was achieved in the coupes with low-intensity burns, where the burnt ground was evenly distributed throughout the harvested area. Very little regeneration, growing very slowly, was observed following single-tree selection harvests with no burning.

The program of research at Warra, including Mark’s work, has demonstrated that aggregated retention is the alternative method to clearfelling that is most likely to be able to achieve the desired balance of retaining structural and biological diversity within the coupe, whilst still meeting timber production and eucalypt regeneration goals. Forestry Tasmania has also signalled its intention to introduce variable retention, typically in its aggregated retention form, in areas of regrowth forests available for harvesting, as well as old growth forests for which it was developed (Click Here).

Mark and his Mother at the graduation ceremony

The research at Warra, and more recent research from throughout Tasmania, has shown that variable retention – and most typically its aggregated retention form - provides the best balance of social, environmental and economic benefits for Forestry Tasmania and the wider community. However, high-intensity burning cannot be used as a regeneration technique in variable-retention coupes, due to the likelihood of burning the patches of forest retained in the coupe. Mark has shown us, that if we are to retain forest productivity in variable-retention coupes, we need to develop regeneration burning techniques of sufficient intensity to provide optimum eucalypt regeneration in these areas, whilst still retaining the aggregates in good condition.

 More information:

To read the abstract of Mark’s PhD thesis, click here.

The following papers have been published from Mark’s research:

Neyland MG (2001) Vegetation of the Warra silvicultural systems trial. Tasforests 13: 183-192.

Neyland MG (2004) Selection, harvesting damage, burning damage and persistence of retained trees following dispersed retention harvesting in the Warra silvicultural systems trial in Tasmania. Tasforests 15: 55-66.

Hickey JE, Neyland MG, Grove SJ, Edwards LG (2006) From little things big things grow: The Warra Silvicultural Systems Trial in Tasmanian wet Eucalyptus obliqua forest. Allgemeine Forst und Jagdzeitung 177: 113-119.

Neyland M, Hickey J, Beadle C, Bauhus J, Davidson N, Edwards L (2009). An examination of stocking and early growth in the Warra silvicultural systems trial confirms the importance of a burnt seedbed for vigorous regeneration in Eucalyptus obliqua forest. Forest Ecology and Management 258: 481-494.

Neyland MG, Hickey JE, Edwards LG (2009) Safety and productivity at the Warra silvicultural systems trial. Tasforests 18: 1-16.