The ecology of edges in Tasmanian wet forests managed for wood production

The study addresses microclimate and vegetation changes in the edges of logged coupes in southern Tasmanian wet forests artd discusses general questions relating to forest edges. _ Seasonal patterns of microclimate were investigated using a Before and After, Control and Impact (or \BACI\") approach and a study of edg~s across a range of ages; less than 1 \"year25 and 15 years old. There was a loss of canopy buffering of t~mperature an~ humidity in the ~dersto~ey in warmer-seasons which extended up to 10 m distance into the undisturbed forest from the edge regardless of its age. Otherwise gradients in microclimate within controls and at th~ BACI site prior to logging were analogous to those measured at forest ?oupe edges .. Influences on the flora in the edge were thus considered likely to occur only during extreme climatic conditions (e.g. very hot dry windy days). Apart from seasonal differences height above ground was also found to have a very· important influence on the microclimate _ in the edges of forest coupes. Vegetation changes were explored through surveys of the bryophyte and epiphytic vascular plants (otherwise described as \"epiflora\") again employing a BACI design and edges of different ages. The epiflora was found to have very low survival rates on coupes and was therefore considered the most likely element of the flora to respond.to microclimate changes at least in the short term .. Changes in the epiflora in forest edges were correlated w:ith the microclimate response but also corresponded to the' mechanical disturbance at both the canopy and grolind lev~I' that resulted from the adjacent logging and firebreak construction. Epiflora composition did not alter with age of the edge but appeared to respond more to large-scale c;hanges in the composition of the associated vascular flora and· related substrates (dead logs and litter). Edge effects in southern Tasmanian wet forests in both microclimate and epiflora thus extended only a short distance into the intact forest ( < 10 m) but were maintained for a prolonged period (at least 15 years) . . There was no 'indication of increased seedling recruitment in the vascular flora-within the edge which may explain the lack of any apparent side canopy development that has been noted in other research. However as with much of the Australian flora successful recruitment for many species in southern Tasmanian wet forests requires or is enhanced by destructive wildfires. A lack of woody plant recruitment within the firebreaks constructed at the edge of coupes may also play a role. It was considered that edge effects in tree and tall shrub components of the flora were expressed mostly in terms of mechanical damage that was partly due to adjacent logging but mostly a response to prolonged exposure to increased windthrow and. may penetrate up to 50 m in from the forest edge. Outcomes from this research highlight deficiencies in other published research of forest edges. These relate to a lack of information on 1) the nature of forest systems before edge establishment (a priori measurements) 2) appropriate levels of control (background variability) and 3) age related responses (succession). There is little comparable research on changes in microclimate with season in forest edges or on the relative importance of mechanical damage to forest edges on the changes in . microclimate and flora. Future research should focus more on longer terms studies combining floristic microclimatic and disturbance information with repeated measurements over several years or even decades."