- Title:
-
Effects of Repeated Low-intensity Fire on Carbon, Nitrogen and Phosphorus in the Soils of a Mixed Eucalypt Foothill Forest in South-eastern Australia
- Date:
- December 2003
- Organisations
- DSE
- Authors:
- Peter Hopmans
- Location:
- Victoria, Australia
Overview
The impact of repeated prescribed fires on total carbon (C) and nitrogen (N) and extractable phosphorus (P) in soil profiles was evaluated at five Fire Effects Study Areas in the Wombat State Forest, north-west of Melbourne. Soil profile samples were collected in 1985, prior to the commencement of trial applications of prescribed low-intensity fires in spring and autumn at three-year and ten-year intervals, and again in 1998.Comparison of initial soil properties between fire treatments across the five study areas showed close agreement, although variability was generally high, with coefficients of variation ranging between 20% and 30%. Because of the low replication within treatments, it was therefore important to examine the effects of fire on soils across the full range of study areas rather than just one or two areas.
Based on a comparison of soil profiles collected in 1998, extractable P was not affected by any of the fire regimes. Phosphorus showed a substantial decline across all treatments after 1985, including the unburnt control, which could not be attributed to the prescribed fire treatments.
In the absence of fire, total C and N in the surface soil increased by 16 g kg–1 and 0.47 g kg–1 respectively, equivalent to a change of 14% and 11% relative to their initial levels. In contrast, burning at three-year intervals caused a decline in both C and N in surface soils; estimated at 15 g kg–1 (13%) and 13 g kg–1 (12%) for C, and 0.31 g kg–1 (7.8%) and 0.27 g kg–1 (7.6%) for N in spring and autumn burning treatments respectively. At the less-frequent burning intervals (10 years nominally), changes were negligible for the spring burning treatment. However, small increases in C of 10 g kg–1 (9.5%) and in N of 0.28 g kg–1 (7.4%) were noted for autumn burning.
A slight change in the C/N ratios was observed, indicating an increase in C relative to N where there was an accumulation of organic matter, such as in the unburnt controls. In contrast, a decrease in C relative to N was observed where there was a loss in organic matter due to frequent low-intensity fires. While these changes in C/N ratios were small, it is suggested that they are indicative of subtle changes in the pools of labile C and N important to
