Conservation conflicts over burning bush in south-eastern Australia
Morrison, DA, Buckney, RT, Bewick, BJ, & Cary, GJ 1996, Biological Conservation, vol. 76, pp. 167-175.
In fire-prone regions of south-eastern Australia, nature reserves and national park managers face conflicts between fire management practices for fire hazard reduction and biodiversity preservation. Accumulation of fuel load can reach a level that is sufficient to result in severe fires as little as two years after low-intensity fires in sclerophyll forests. At the same time, in order to preserve woodland and shrubland communities’ species composition and structure, an inter-fire interval period of at least seven years is required. The conflicting requirements for achieving these management objectives raise serious concerns.
Presently, prescribed fires are carried out in fire-prone vegetation of the Sydney region to reduce the risk of intense wildfires and to maintain ecosystem biodiversity. Low-intensity fires, if they occur too frequently, can have adverse impacts on the abundance of many plant species and subsequently alter the composition of woodland and shrubland communities. In this study, the authors identified the minimum inter-fire interval time required to achieve each objective (fuel reduction to prevent severe non-prescribed fires and species preservation), and they found a clear conflict between the two objectives. The model revealed that a fuel load capable of creating a severe fire hazard can be built up as soon as two years after a low-intensity fire, which is the typical period between prescribed burns aimed for hazard reduction. Prescribed low-intensity fires are often only able to consume a small proportion of fuel load (that was available before the fire), and this can result in a large amount of leftover post-fire fuel. Furthermore, low-intensity fires can also convert non-available fuel into available fuel, for example by bringing down canopy branches that were previously unburnt to the ground. This counteraction between fuel consumption and creation contributes greatly to the rapid fuel accumulation and can affect the timing and effectiveness of hazard reduction burning. On the other hand, a longer inter-fire interval (seven to nine years) is required for maintaining biodiversity without compromising the integrity of vegetation communities. An inter-fire interval of less than seven years may pose significant threats to fire-sensitive shrub and woody species as the time required for them to grow and reach first reproduction can be longer than this period. Similarly, local extinction of fire-tolerant species may also occur if the inter-fire intervals are shorter than the time required for them to become fire-tolerant.
The authors of the study suggested that land managers should make clear decisions about whether an area is to be managed for hazard reduction or biodiversity preservation as there is no simple compromise that will allow both objectives to be achieved. Moreover, managers should consider creating a mosaic effect by prescribing fires of different intensities and frequencies at different patches.
Summarised by Cherie Chan
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