Forests in parts of North America are not growing back from wildfires in quite the way they used to, finds a research team by Colorado State University (CSU). More frequent wildfires and warming temperatures are reducing the long-term resilience of forests, and in some cases, stopping them from growing altogether. ‘We can expect some areas to likely never become forests again,’ says Camille Stevens-Rumann, assistant professor of the Department of Forest and Rangeland Stewardship at CSU. ‘Others may eventually become more open, less dense forests dominated by a different sort of species.’

The data comes from 1,500 sites in Colorado, Wyoming, Washington, Idaho and Montana. Fires are not new to the Rocky Mountain region, and forests are usually able to survive and regenerate from them so long as two requirements are met: enough older trees are left standing to drop seeds, and that the climate favours growth of seedlings.

However, the beginning of the 21st century has been much warmer than the end of the 20th, and ‘conditions are becoming increasingly stressful for tree seedlings to establish and survive,’ says Phillip Higuera, co-author of the study. ‘Seedlings are more sensitive to warm, dry conditions than mature trees, so if the right conditions don’t exist within a few years following a wildfire, the seedlings may not establish.’ In one-third of the areas studied, researchers found no seedlings growing at all.

Their results suggest there is a transition underway. Forest ecosystems may be shifting to unforested areas or to species better suited to warm weather, and wildfires are accelerating the process. It means that attempts to replant areas with the current species could be futile – the climate has already moved on. ‘We need to prioritise planting where we will see the most success,’ suggests Stevens-Rumann. ‘Managers may want to plant species that are adapted to the current and future climate, not the climate of the past.’

This was published in the February 2018 edition of Geographical magazine.

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