Similar treatments, based on the felling or ring-barking of diseased, suppressed or malformed trees and the thinning of regrowth, both seedling and coppice, were also adopted by the other State forest services to rehabilitate some of the more important dry sclerophyll forest areas. The labour requirement for this mammoth task was high and progress slow. Some of the cost was recovered from the sale of timber that was suitable for poles, posts or firewood, but many of the felled trees were just left or burned in the forest. Fortunately, however, when the Depression of the 1930s arrived this work of rehabilitation was regarded by governments as a desirable form of relief employment and larger areas were able to be treated right to the outbreak of the Second World War.

In the 1920s and 30s the forest services also sought to develop improved management methods to ensure that harvesting and related operations were conducted in a manner consistent with the principles of sustained yield forestry, a policy that had been first strongly advocated for Australia by Lane Poole in Western Australia and since widely accepted. Selection logging was still generally practised but under closer supervision by the forest services. Sustained yield forestry requires the adoption of logging regimes which ensure that adequate regeneration will take place to maintain the productivity of the resource by natural seeding, coppice growth from stumps or by the sprouting of lignotubers (swellings which develop around the base of seedlings of many eucalypt species and which can be dormant in the soil for years even after repeated destruction of their shoots by fire or other causes). Where these natural methods are not adequate they must be supplemented by additional seeding or planting.

Fire is an integral part of the natural regeneration process for eucalypt forests as it stimulates the opening of the seed capsules in the trees and prepares a receptive seed bed by removing undergrowth and increasing light access, which not only assists seedling growth but also stimulates any lignotubers present to develop shoots. The WA Forests Department was probably the first to use fire in a systematic way in its forest management practices when it introduced, in the 1930s, the controlled burning of coupes before logging and timed the burning of logging residues to coincide with years of abundant seed on the remaining trees. This was done primarily to reduce fire danger, although the regeneration benefits from the treatment were also recognized. The regeneration areas were protected by firebreaks, which were burned every three years.

The wet sclerophyll forests of Victoria and Tasmania were extensively exploited from the end of the 19th century, but with the exception of some regrowth thinning little effort was made to ensure sustained yield, as knowledge of their regeneration requirements was inadequate. However, with the introduction in 1938 of pulp mills based on these forests and the disastrous Victorian bushfires of 1939, a new incentive arose for the development of appropriate management methods. After the Second World War the regeneration of these forests became a major research activity for both the Victorian and Tasmanian forest services, assisted by the sponsorship of university research by the pulp and paper industry. Ashton, Cunningham and Grose in Victoria and Gilbert in Tasmania, all made important contributions[3] on which the silvicultural methods that are in use today for wet sclerophyll forests have been based. Their work showed that ash species will not regenerate adequately unless a heavy cut is made, the under-storey largely removed and an effective seed bed prepared. In practice these conditions were met by clear-felling in coupes, each about 50 ha in area, in which some trees were left for seeding purposes, burning the understorey and logging residues in a hot fire, if necessary mechanically scarifying to expose the mineral soil and, where economical, felling the seed trees when the regrowth became well-established. Where natural seed supply was inadequate it was supplemented by broadcast seeding or by seedlings. Some protection against browsing animals and seed-eating insects was sometimes needed.

Australian Academy of Technological Sciences and Engineering