- Title:
-
Effects of Repeated Low-intensity Fire on Tree Growth and Bark in a Mixed Eucalypt Foothill Forest in South-eastern Australia
- Date:
- December 2003
- Organisations
- DSE
- Authors:
- Karen Chatto, Tina Bell, John Kellas
- Location:
- Victoria, VIC, Australia
Overview
This study was designed to determine the effects of repeated low-intensity fire on the growth and bark thickness of trees in a mixed eucalypt foothill forest in Victoria. Research elsewhere is ambiguous as to whether regular burning affects the long-term productivity of trees. About 700 individually tagged trees were included in this study in the expectation of being able to detect any changes in growth rates of as small as 10%, but at least 20% across the forest. Two tree species were included in the study—Messmate Stringybark (Eucalyptus obliqua) and Candlebark (E. rubida). Messmate was chosen because of its commercial value, its extensive distribution in Victoria and the fact that it is a ‘stringybark’ species, while Candlebark was chosen because it also is widespread but is a ‘gum-bark’ species.Five burning treatments were replicated in each of five Fire Effects Study Areas in this study: long-unburnt, short-rotation (or frequent) spring burning, short-rotation autumn burning, long-rotation (or infrequent) spring burning and long-rotation autumn burning.
Bark loss due to burning was shown to depend significantly on burning treatment. Both season and frequency of fires could be considered to be important in the loss and recovery of bark after fire. Bark loss was found to be greater as a result of autumn burning compared to burning in spring. This seasonal effect was more strongly related to soil dryness index than fire intensity. Bark loss on regrowth trees could be explained to some extent by fire intensity (r2 = 0.46; autumn fires averaged 259 kW m–1; spring fires averaged 152.3 kW m–1) but was not a valid explanation for overwood trees. Longer rotations (i.e. 10-year) caused greater bark loss than shorter rotations (3-year) for both spring and autumn burning.
In the current study, prescribed burning provided a significant stimulus to tree growth. Trees in all burning treatments showed greater increases in stem diameter for the period 1985–99 compared to unburnt trees. (Earlier in the study, it was suggested that one or two low-intensity fires had no major impact on the growth of overwood or regrowth trees. But with additional burning and further measurements, it was possible to elaborate on the preliminary conclusions to incorporate the prolonged effects of prescribed burning regimes on tree growth.)
It is envisaged that repeated short-rotation burning would eventually result in stem damage. Already, results from this study have shown the mortality of the above-ground stems of some of the smaller trees. The full impact of a regime of short-rotation burning has not yet been shown in this study.
