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Cryptogam succession in relation to forest age and log decay progression in Tasmanian wet eucalypt forest


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Browning, Belinda Jayne 2009 , 'Cryptogam succession in relation to forest age and log decay progression in Tasmanian wet eucalypt forest', Research Master thesis, University of Tasmania.

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Cryptogam communities on coarse woody debris persist in forests regenerating after the
first clearfell, burn and sow harvesting rotation due to harvest residue. The habitat
disturbance dynamics in a regenerating forest is different from the natural wildfire
disturbance, as is the dynamics of coarse woody debris, which, while different, also
provides an opportunity for new bryophyte community development. How bryophyte
communities develop in response to this new system dynamic is largely unexplored.
Community development may depend on time since disturbance and/or the degree of
decomposition of the coarse woody debris. For individual species and communities as a
whole, it is not known which of these two effects dominates or what environmental
attributes affect the resulting communities. This research attempts to tease apart these
issues by examining the time dependent response of cryptogamic communities growing on
coarse woody debris to first rotation clearfell, burn and sow harvesting and the relative
significance of forest age and log decay progression on community succession.
Subsequent to clearfelling, cryptogamic communities on coarse woody debris were
compared from wet eucalypt forests of increasing age. There were significant differences
in species richness and community composition between forest age and between log decay
stage. Older forests were the most species rich. More individual species had significant
associations with logs of intermediate decay classes than with logs of an earlier decay class.
The ecology of individual species varied considerably for forest age and log decay class
associations and there were distinct early, middle and late successional species identified.
Forest climate measures of temperature and vapour pressure deficit were used as an
indication of the variation in large scale habitat conditions over time between forests of
each age and to examine the influence of habitat conditions associated with forest age on
of coarse woody debris. There were significant changes over time for temperature and
vapour pressure deficit where mesoclimatic conditions became less variable as forest age
increased. Log moisture was a direct measure of the fine scale habitat conditions
influencing cryptogam communities of coarse woody debris, especially in relation to log
decay stage. Log moisture had a significant influence on bryophyte community
composition over time and was important for determining the succession of cryptogamic
communities when combined with mesoclimatic conditions.
The effect of forest age and log decay stage on cryptogam communities of coarse woody
debris suggests that both of these time dependent processes play an important role in
community succession, and that the distinction between the two habitat variables may vary
depending on time since clearfell, burn and sow disturbance. Fine scale community
analysis revealed that at any forest age and at any decay stage there were significantly
associated species. While this study has shed some light on how succession plays out in the
first decades of the first clearfell, burn and sow rotation, it also suggests that communities
follow a predominantly similar successional pathway as would occur in a forest
regenerating after natural wildfire disturbance; however, it is likely that successive
harvesting events based on 100 year rotations will result in the loss of some cryptogam
species. Managing forests after clearfell, burn and sow for the development of mature
stands and for actively facilitating the persistence of a range of decay stages and coarse
woody debris habitat structures at the site and landscape levels may be appropriate, and the
findings of this study are discussed in this context.

Item Type: Thesis - Research Master
Authors/Creators:Browning, Belinda Jayne
Copyright Holders: The Author
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Copyright 2009 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
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