Understorey dynamics following partial logging in Eucalyptus delegatensis forests on the Central Plateau, Tasmania

Partial logging in high-altitude E. delegatensis forests involves the retention of approximately 50 % of original forest basal area, and was implemented to overcome the problem of \growth check\" in regenerating eucalypts following clearfelling. It is increasingly being carried out in these forests in an effort to provide income to landowners while still allowing regeneration of the overstorey eucalypts. This thesis looks at the effects of partial logging on understorey floristics and structure in both the short (-2 years) and the long (15-20 years) term. Analysis of a floristic structural and environmental dataset using multivariate and ANOVA techniques found that two understorey types grassy and shrubby were present and that short term trends included reduced cover of all lifeform groups reduced understorey height species richness and structural complexity and increased bare ground cover and soil disturbance. Four of these trends increased grass and forb cover decreased shrub cover and structural complexity were still apparent 5-8 years after logging and two reduced shrub cover and habitat complexity 16-21 years after logging particularly in shrubby forest. These changes were attributed to the reduced cover of the overstorey and subsequent changes in the light/temperature/moisture regimes of the forest floor microclimate. Effects of plantation establishment in wetter areas of this forest type were similar to those of partial logging but of a greater magnitude and duration. Ecological processes structuring the understorey were examined by first looking at changes in species cover/abundance under individual overstorey eucalypts and in forest gaps in unlogged forest and second with a laboratory shading/disturbance experiment. It was found that canopies of overstorey eucalypts were causing distinct patterns in understorey distribution. Species richness and cover increased moving from trunk to canopy edge to forest gap and from unshaded to shaded sector of forest gaps primarily due to the inhibitory effects of high litter and shade under trees and cold induced photoinhibition in high light areas of gaps. Chlorophyll fluorescence measurements confirmed the requirement of shade for the shrub Lomatia tinctoria and the sedge Lomandra longifolia and the ability of grasses to out compete these species in full sun mimicking the patterns observed logged forest. Results are discussed in relation to the theory of ecological resilience and it is suggested that increasing divergence of understorey will occur with each logging and/or plantation rotation and may lead to shifts in forest/grassland boundaries."