Edge effects on between-fire interval in landscape fragments such as fire-prone terrestrial conservation reserves

When a parcel of land, a reserve, is isolated from its fire-prone landscape context, its fire interval can potentially be altered simply due to diminished access to external fire. A model is developed to depict this situation. Cutting off the external access of randomly-oriented fires along an infinite edge reduces the proportion burnt per year at the edge to one half; the average interval doubles there. Well away from the edge, the fire interval remains the same as it was before fragmentation. When very long strips from which external fires are cut off from both sides are considered, edge effects from the two sides overlap internally such that the average interval between fires in the strip, overall, increases. Overlap increases as width decreases. The same phenomenon occurs in a modelled circular, or other shaped, reserve with the central area being the least affected. Modelled results, expressed as average interval per reserve, were consistent with changes in fire interval in fragments of different size in a mallee-vegetation complex of the wheat belt of south-western Western Australia. Such effects would be at a maximum in small irregularly-shaped reserves. If historical fire regimes are to be maintained for biodiversity conservation purposes, then management intervention will be necessary where this effect occurs.