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

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.