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


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Westphalen, Grant 2003 , 'The ecology of edges in Tasmanian wet forests managed for wood production', PhD thesis, University of Tasmania.

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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 "year, 2, 5, and 15 years old. There was a loss of canopy buffer,ing 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
, 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.

Item Type: Thesis - PhD
Authors/Creators:Westphalen, Grant
Keywords: Vegetation and climate, Forest ecology, Forest microclimatology
Copyright Holders: The Author
Copyright Information:

Copyright 2003 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references

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