Sir

The fires that ringed Sydney in December and January were as intense as any in the past 70 years (see Nature 415, 105; 2002). Over half a million hectares of bush land burnt and more than 10 times this area threatened but saved; about 100 houses were destroyed. The fires have stimulated strident demands for more frequent and extensive burning off ('hazard reduction burning'), especially in national parks, to protect property.

Most authorities agree, though, that protection is not guaranteed by this approach. The way forward is not simple. It must include strategic (not broad-scale) hazard reduction, continued emphasis on fire-fighting, education and better town planning in areas of high fire risk.

The urban areas of Sydney and Wollongong are surrounded by large conservation areas: a World Heritage Area, several national parks and water catchments. The principal objective of the New South Wales National Parks & Wildlife Service, the agency responsible for most of this land, is "to protect and conserve natural and cultural heritage", including natural ecosystems, biodiversity in general, and species and communities listed as vulnerable and endangered. Although the proximity of the threatened conservation areas to Sydney makes the city stunningly beautiful, the variegated boundaries create an unenviable challenge for land managers, who have to protect the native biota inside the boundaries from big fires while protecting people outside.

Many plant and animal species are threatened by too-frequent fires, even though they evolved with fire as a natural disturbance. Paradoxically, some plants most favoured by fire are actually killed by it. They re-emerge, phoenix-like, from seeds that were protected from heat in woody fruits or the soil. The juvenile period — the time needed for the new recruits to develop a seed bank of their own — can exceed 10 years for some species. A second fire during this time could spell local extinction. Also, animals requiring dense habitat are confined to areas that do not burn frequently. These species need long-unburnt refuges from which to re-invade, once the burnt vegetation recovers to an appropriate stage. Frequent burning sustains unsuitable habitat. The current state of knowledge is summarized in Flammable Australia: The Fire Regimes and Biodiversity of a Continent, edited by R. A. Bradstock, J. E. Williams and A. M. Gill (Cambridge University Press, 2001).

The primary conservation objective of the national parks is that of managing too-frequent fires, so managers and politicians must resist the demand for broad-scale hazard reduction. Perhaps neighbouring property and lives can be protected by attention to the boundaries of conservation areas, without burning frequently throughout the parks. This strategy has been pursued in New South Wales national parks, to the extent that biodiversity conservation in these boundary zones may be sacrificed to protect property. Backed by a well trained, resourced and coordinated fire-fighting effort, this strategy meant that remarkably few houses were lost in the recent fires.Now it is time to find and defend solutions that also protect the parks.