The eucalypts from the wet forests exhibited the slowest decomposition rates known for flowering trees. The CWD of both New South Wales and Tasmania had comparable decomposition rates (the slight difference between the areas was not significant). In the relatively undisturbed forests of southern Tasmania, this resulted in the highest accumulation of dead wood for any forest ecosystem reported anywhere. The tropical rainforest CWD decomposed the fastest, and decays at a rate comparable to other tropical rainforest ecosystems elsewhere in the world. The fast decomposition results in much less wood lying of the forest floor, in undisturbed sites, compared to the undisturbed sites in the eucalypt forests. The rainforest CWD loading is about one-fifteenth that of the relatively-undisturbed southern Tasmanian eucalypt forests. The woodland CWD (central Queensland) decomposition was so slow, that most loss to the surrounding environment was due to fragmentation and incorporation into the soil; this is undoubtedly due to the prevailing harsh-climate of the region (high temperatures and low moisture availability). Consequently, due to the extremely slow decomposition of the woodland CWD, and the unavailability of old samples, a decomposition rate could not be established. Modelling of the Tasmanian eucalypt tree-growth and CWD-decay, shows that including CWD in carbon accounting can provide an increase of up to 40% of the long-term carbon that is stored in living trees. If change can be made to the current practice of excluding CWD from carbon trading, then managers of nature parks and reserves, where wood clearing has occurred in the past, may be able to increase their potential income by including CWD-carbon in their tradable-carbon stocks.

The slow decomposition of the eucalypts poses several management problems. Generally, it has been found that the most decayed wood contains the highest number of different species of resident organisms. However, due to wood removal in several areas of Australia, it will take a long time for forest regeneration, tree death, and decomposition to the most decayed stage to occur. This means that the organisms that rely on the most-decayed logs may become locally extinct if a region has had extensive wood-removal in the past. This may require that some select-trees be felled periodically within nature parks, in order to generate CWD earlier than would occur naturally in regenerating forests. This is especially relevant for the larger trees, which are also favoured by many of the organisms found in rotting logs. The felling of trees in nature parks is a contentious issue within the community, but may be necessary as the ‘lesser of two evils’.

Besides being important as a habitat for many forest organisms, CWD performs other important functions. The logs act as slow-release fertilisers, continually releasing nutrients back to the forest environment as they continue through the slow decomposition process. The logs also act as obstacles to water flowing over the soil, reducing the speed of the water, which in turn reduces erosion, albeit to a small extent. Any reduction in erosion will help, to some extent, reduce the soil and nutrients from being transported into creeks and other water bodies, which, in turn, helps to reduce turbidity and nutrient loading of the aquatic environment. Turbidity of the aquatic environment reduces the light received by aquatic plants, reducing their ability to photosynthesise, and produce their own food. Increased nutrient loading of aquatic environments leads to increased intensity of algal blooms, which reduces the drinking-quality of the water. (Increased algal blooms can also lead to a dramatic increase in the zooplankton which prey on the algae, which can, in turn, lead to a depletion of the oxygen content of the water, subsequently resulting in the death of aquatic animals that require oxygen; the so-called ‘fish kills’.) Coarse woody debris is an extremely important element in the terrestrial environment, which has generally been ignored by environmental managers in the past. The impact of the slow decay of the eucalypts requires that environmental managers need to take CWD seriously, and formulate extensive management strategies to overcome the effect of environmental degradation caused by extensive log removal in the past, especially in nature parks and reserves, and water catchment areas.

This work is supported by The Australian National University, the Cooperative Research Centre for Greenhouse Accounting, and Forestry Tasmania.

This page is reproduced from the SRES 2005 Yearbook – above details as at time of publication [July 2005].

An important requirement of this study was the availability of an approximate time-of-death for each sample. This allowed the tracking of CWD through each decay class as decomposition proceeded through time. This then allowed the determination of decomposition constants and the flux of C back into the surrounding environment.

The preferred transect design is in the form of an equilateral triangle. This minimises the effects of slope on the orientation bias of the CWD. The preferred length of each transect is 300 m, with each side of the triangular-transect being 100 m. Two samples were collected from each sample CWD piece. A disc, or slice, was collected for volume and mass measurement; for determining wood density. A smaller sample was collected for chemical analyses.

Returned samples were stored in a dark cool room at 5ºC during the sampling period, to minimise (macroarthropod) deterioration of the sample, and to prevent any photo-degradation of chemical constituents, prior to laboratory analyses. During laboratory analyses, the ‘density’ samples were soaked overnight to saturate the wood before having the volume determined using the water-displacement method. After volume was determined, the wood was dried in an oven at 105ºC ±5ºC until daily mass loss was <1%. The smaller chemical samples were dried in a separate oven at 75ºC ±5ºC. Chemical analyses of the samples for C, N, P, K, Ca, Mg, lignin, cellulose, and soluble fraction were performed.