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Layout of logs on one of the three 1 ha plots in the Warra area. |
Image: Gemma Woldendorp |
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Project summary:
This study is part of a larger one that investigated efficient sampling methods for coarse woody debris (CWD, larger dead logs and branches on the forest floor) in Australian forests. CWD debris is an important component of forest ecosystems. It can contain a significant proportion (up to 20% and sometimes more) of the total forest biomass and is important habitat for native wildlife.
The forest types surveyed were eucalypt-dominated woodlands in south central Queensland (Injune), eucalypt open forest (dry sclerophyll forest) in south coastal New South Wales (Kioloa) and tall open forest in southern Tasmania (Warra and environs). CWD is generally assessed using the ‘line intersect’ approach or by measuring logs and branches on fixed area plots. There have been varied recommendations in the literature on the number of lines (transects) to use and their length and arrangement. Recommended plot size has also varied considerably. Several one-hectare plots were established in each region. All CWD, stumps and standing dead trees above 10 cm diameter in the woodland, and 15 cm in the other forest types were measured and mapped.
These data were used to analyse the effect on precision of estimates of the CWD volume using alternative approaches to the line intersect method and different sizes of fixed area plot. Mean volume of CWD sampled on the plots was 26 m3 ha-1 at the woodland site, 117 m3 ha-1 at the open forest site, and 1351 m3 ha-1 at the tall open forest site. Mean mass of CWD was 12 t ha-1at the woodland site, 52 t ha-1 at the open forest site, and 500 t ha-1 at the tall open forest site. These were generally within the range from other studies in similar forest types of Australia. CWD levels at the Tasmanian site were some of the highest recorded in Australia and among the highest reported in the world. Variability of CWD volume in forests is very high and achieving estimates with a precision (coefficient of variation) less than 50% of the mean will require a high sampling intensity. In analysis of the line intersect method, precision of volume estimates decreased as total transect length increased. In denser forests, transects of at least 100 m are required to achieve a precision of less than 100% of the mean.
One long transect resulted in a lower coefficient of variation than a number of short transects and is more cost effective. There was no improvement in precision by arranging the total transect length in a ‘V’, a triangle or a square. In woodland vegetation (20-50% canopy cover) the amount of CWD is relatively low and variability is high. Very long lines (>200 m) would be required to achieve estimates with a precision below 100%. In these situations fixed plots are preferred. using a larger fixed area plot improved precision of estimates. Plots 20×20 m can give estimates with precision less than 100% in forest structures but well over 200% in woodlands. Measuring all pieces on a 50×50 m plot in woodlands gave estimates with a precision of +/- 21-73% of the mean. These results will be incorporated into future sampling for the National Forest Inventory and other studies of biomass and carbon stocks in Australian forest and woodlands.
Methodology: CWD is generally assessed using the ‘line intersect’ approach or by measuring logs and branches on fixed area plots.All CWD, stumps and standing dead trees above 10 cm diameter in the woodland, and 15 cm in the other forest types were measured and mapped. Data were collected in three forest types in different parts of Australia and analysed using a computer-based system to test alternative sampling approaches.
Datasets: None available.
Publications: Grove, S.J. (2009). A decade of deadwoodology at Warra. The Tasmanian Naturalist 131: 25-35.
Woldendorp, G. & Keenan, R.J. (2005). Coarse woody debris in Australian forest ecosystems: a review. Austral Ecology 30: 834-843.
Woldendorp, G., Keenan, R.J. & Ryan, M.F. (2002). Coarse Woody Debris in Australian Forest
Ecosystems. Bureau of Rural Sciences, Canberra.
Woldendorp, G., Spencer, R.D., Keenan, R.J. & Barry, S. (2002). An analysis of sampling methods for coarse woody debris in Australian forest ecosystems. Bureau of Rural Sciences, Canberra.
Woldendorp, G., Keenan, R.J., Barry, S. & Spencer, R.D. (2004). Analysis of sampling methods for coarse woody debris. Forest Ecology and Management 198: 133-148.
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