|
Project summary:
The objective of this study is to model the decay-class and diameter-class distributions of coarse woody debris (CWD) in an unmanaged, even-aged tall lowland E. obliqua forest subject to cyclical stand-replacing wildfire by both volume and mass. Modelling the dynamics of CWD is an important step towards understanding how disturbance, both natural and anthropogenic, affect this substrate as it supports many different types of organisms, performs valuable ecosystem services and is a significant proportion of the biomass of many forests.
The honours thesis arising from this work is presented in three sections.
The first section covers the CWD collected from lowland wet E.obliqua forest in the Warra Long Term Ecological Research site in Southern Tasmania, and deals with measurements of the proportions and densities of ‘rot types’ within the five decay-classes of CWD. It demonstrates that, although there is some overlap, the standard five-point decay classification system used by Forestry Tasmania (FT) is a valid surrogate for ‘internal decay state’ and for relative wood density. Comparisons of CWD sampled from different locations within Warra, and logs of different diameters, show that the sites selected had little influence on the internal decay state, but that log diameter did.
The second section employs the five-point decay-class system to construct a stage-based decay model to simulate temporal change in CWD volume and mass. Key parameters were populated with data describing the density of CWD in each decay-class and diameter class obtained from the first part of the study. A forest growth model and a stagfall model for even aged tall wet E. obliqua forests, derived from models developed within FT, were then combined with the decay model to enable modelling of stand-level CWD dynamics over single or multiple cycles of wildfire and regrowth. Some of the important findings that emerged from this section are:
It is possible to model CWD using a stage-based model in which the rates of transition of CWD through stages of decay vary by decay-class and diameter-class
The mean volume of CWD decreases with decreasing wildfire return interval
CWD is more abundant in larger diameter-classes under longer wildfire return intervals
Volume and mass of CWD follow different trajectories
The third section presents a synthesis of the previous two sections, and briefly discusses the ways in which the CWD model could be applied in order to facilitate a better understanding of the impacts of natural disturbance and forest management on CWD dynamics within tall lowland wet eucalypt forests in Tasmania.
Methodology: Sampling was carried out at four sites located within the Warra Long-Term Ecological Research (LTER) site. For this study, 64 logs were sampled covering a range of decay-classes and diameters. At each site, sampling was conducted in a way that evenly sampled a spectrum of decay-class and diameter-classes present. Logs that were longer than 10m were preferentially sampled as well as logs that were relatively intact ie. did not break into pieces upon falling to the forest floor. The majority of sampling occurred in site 1 because this site was the easiest to access and contained a wide range of diameters and decay-classes of logs. The decay state of each log was assessed and classified into one of five decay-classes: decay-class 1 is a freshly fallen tree, decay-class 5 corresponds to a mostly amorphous humus-like remnant of the original log. As well as recording the decay-class, other characteristics of the log were recorded such as the average log elevation and canopy cover at that location. Three cross sectional slices (‘biscuits’) of approximately 5cm in width were then cut from each log corresponding to points near the base, middle and top sections of the tree bole that gave rise to the log. The biscuits were sampled at least 2m from a log end and the majority of the biscuits were greater than 3m apart within a log. Occasionally, only one or two biscuits were sampled (from the logs of length <10m). In total 169 biscuits were cut.
Datasets: None available.
Publications: Grove, S.J. (2009). A decade of deadwoodology at Warra. The Tasmanian Naturalist 131: 25-35.
Grove, S.J., Stamm, L. & Barry, C. (2009). Log decomposition rates in Tasmanian Eucalyptus obliqua determined using an indirect chronosequence approach. Forest Ecology and Management 258: 389-397.
Grove, S.J., Stamm, L. & Wardlaw, T.J. (2011). How well does a log decay-class system capture the ecology of decomposition? – A case-study from Tasmanian Eucalyptus obliqua forest. Forest Ecology and Management 262: 692-700.
Stamm, L. (2007). Decomposition in Tasmanian Eucalyptus obliqua coarse woody debris. Honours thesis, University of Tasmania, Hobart.
Wardlaw, T., Grove, S., Hopkins, A., Yee, M., Harrison K. & Mohammed, C. (2009). The uniqueness of habitats in old eucalypts: contrasting wood-decay fungi and saproxylic beetles of young and old eucalypts. Tasforests 18: 17-32.
|
