When to burn and where?

Commentary on Brooke Williams’ article, Optimising the spatial planning of prescribed burns to achieve multiple objectives in a fire-dependent ecosystem by Associate Editor, Cate Macinnis-Ng. Following on from Brooke’s own blog post, Cate gives a personal spin on her own experience of fire events and of editing the paper.

This manuscript arrived in my inbox within days of the Port Hills fire outside Christchurch. When it comes to natural disasters, Aotearoa-New Zealand is a land better know for earthquakes than bushfire. Yet, like much of the world, the incidence of catastrophic fires is on the rise here as droughts increase in severity and frequency, drying vegetation under a changing climate. Hot, dry conditions coupled with strong winds are also exacerbating the problem, causing high intensity fires spreading over vast areas.

Fire is not always bad for ecology and conservation, however. In many parts of the world, including Australia, USA and South Africa, fire-dependent ecosystems rely on frequent, often low intensity burns to maintain biodiversity. A fire event can be vital for germination and stimulation of growth of certain species as the fire makes nutrients more available and prepares the soil for establishment of fire-adapted species. This ecological need for fire can create tension between conservation goals and the desire to protect human activities and infrastructure against fire damage. Hazard reduction burns have been used for decades to reduce fuel loads in an attempt to make fires more manageable and to enhance biodiversity. Yet the question of when to burn and where remains difficult to answer because asset protection and conservation needs are often not aligned.

Balancing the competing goals of property protection and ecological values rarely considers multiple objectives concurrently. To address this, Williams and co-authors have used an integer linear programming approach to assess cost-effectiveness against asset protection and conservation outcomes at their model study area in south east Queensland, Australia. When considered alone, managing for each objective results in poor outcomes for the other objective but when constructed as a multi-objective problem, the approach delivered good conservation outcomes with only a small decline in asset protection outcomes.

By specifically quantifying the trade-offs between competing management goals, this approach was able to identify solutions that could provide good outcomes for both with minimal change in the available budget. The authors indicate that their mathematical optimisation approach will improve scheduling and prioritisation of control burns within a robust framework for decision making. This approach is likely to be valuable to managers working with fire-dependent ecosystems across the world.

Back in NZ, the challenge in the Port Hills is finding ways to regenerate vegetation not well-adapted to intense burning. Invasive species including gorse are likely to flourish after the fire while native species will need some help to reestablish. Work is already underway to replace restored areas of bush that were lost. An alternative approach that could be a powerful control method is to use green fire breaks of less flammable plants in strategic locations in the landscape to reduce spread of fire when it does happen. But that’s a whole different discussion to be had around the plant BBQ!

Whatever the ecosystem type, the key to managing fire well is to be prepared. This paper by Williams and her co-authors is another weapon in the armoury against fire.

The full paper, Optimising the spatial planning of prescribed burns to achieve multiple objectives in a fire-dependent ecosystem , is available in the Journal of Applied Ecology.

Read Brooke Williams’ blog, Prescribed burns for multiple needs … here.

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