Vegetation and fuel dynamics following clearfelling of dry Eucalypt forests on Dolerite in Southeastern Tasmania with special reference to the use of fire in forest regeneration
thesisposted on 2023-05-26, 00:06 authored by Dickinson, KJM
In order to supply eucalypt pulpwood to an expanding woodchip industry the silvicultural management practice of clearfelling followed by slash-burning was adopted in the dry eucalypt forests on dolerite in southeastern Tasmania. To provide data on the vegetation and fuel dynamics following dry forest utilisation, a study area with comparable sites that were (a) unlogged, (b) clearfelled, (c) clearfelled and slash-burned, was monitored over a 24 month period. Detailed records were made of plant species composition and cover on floristically similar permanent plots on each of these sites. Fuel levels, fuel structure and fuel composition were measured at the study area, and at other East Coast sites of varying ages since slash-burning. A monthly bird census was conducted in the main experimental area to establish the inter-relationships of the avifauna with particular plant species and habitats. Following clearfelling there was found to be marked variation in the growth response of plant species, due to environmental situation, degree of disturbance, and intensity of slash-burn. Moreover, the effect of these factors on individual species was greatly influenced by selective grazing and browsing, predominantly by native fauna. The combination of burning and predation tended to favour unpalatable species which recovered rapidly by vegetative means. The succession of plant species following fire in dry forest communities most closely approximated the initial floristic composition model. Most of the plant species recovered rapidly with a progressive increase in species richness for at least two years after disturbance. Slash-burning was found to reduce the levels of fine fuel (2.0cm in diameter or thickness) left as a result of clearfelling, but the practice was ineffective in reducing the volume of coarse fuel (2.0cm in diameter or thickness). However, over time, this relative reduction of fine fuel was only persistent in the compacted ground fuel layer, as the regenerating stand rapidly recovered the above-ground, vertical fine fuel structure. Experiments were conducted on various dry forest and wet forest plant species and fuel components, in order to establish their energy content and relative flammability. It was found that eucalypt dry forest species and fuel components had the highest energy content and the greatest tendency to propagate fire, whereas species from wet forest and Casuarina dry forest communities propagated fire less readily. Species from dry habitats had, in general, low ash contents, high energy levels, high volatile oil contents and low moisture contents. Wet habitat species had high percentages of moisture and ash. As a result, general support could be given to the hypothesis that natural selection has favoured flammable characteristics in fire-dependent plant communities. The gains from the retention of natural eucalypt regeneration after clearfelling (i.e. forest management in the absence of hot, slash-burns) may generally offset the short-term advantage of reduced fire hazard which results from slash-burning.
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