Fighting drought with fire: Can prescribed fire increase forest resistance to drought?

A century of fire exclusion across many forest types in the western U.S. has resulted in unforeseen changes, including high fuel accumulations, high densities of trees, and increasing dominance of fire-intolerant species. These changes are particularly acute in forests that historically experienced high frequency and low severity fires. In response, the NPS Pacific-West region supports a large prescribed fire program to reduce understory fuels and forest density. Prescribed fire has been generally successful at reducing understory fuels and threats of catastrophic fire, and treated stands are expected to be more resistant to future wildfire. Less well understood is how well prescribed fire confers resistance to other forest stressors, such as drought. Chronic drought caused by long-term warming trends is believed to be an underlying cause of increased ‘background’ (non-catastrophic) tree mortality across western North America, and co-occurrence of reduced precipitation and high temperatures can lead to massive forest die-back, where entire stands are lost.

Has prescribed fire removed enough small trees so that remaining trees have sufficient moisture to survive the extended drought? The answer to this question has profound implications for forest management over the coming decades as drought stress on our forests is expected to increase rapidly.

The severe drought extending from 2012 to 2015 across much of California provides a remarkable natural experiment to test whether prescribed fire creates conditions where forests are resistant to drought. In this project, researchers at Sequoia and Kings Canyon National Parks will address this question, using access to several ongoing long-term forest monitoring projects that have tracked tree survivorship both with and without fire for over 30 years. Comparisons of survivorship across these sites will inform us how well prescribed burning influences drought responses and how this response varies across treatment intensity (number, size class, and basal area of trees removed) and forest type.