A window of vulnerability: Fire causes short-term reduced tree growth and elevated drought stress

Photo Credit

USDA Forest Service Photo by Charlotte Reed

Field technician installing a rain-exclusion shelter around a study tree after a prescribed burn.

It is often assumed that the thinning effects of fire mean that surviving trees grow more and have more water available to them. However, fire may also come with costs. Trees that survive fire, but sustain fire-caused injuries, may experience a temporary period of reduced growth and greater vulnerability to drought before they are able to take advantage of the effects of stand density reduction (such as less competition for water). This window of vulnerability is due to negative effects from fire-caused injuries like crown scorch, with more severe injuries likely having a stronger negative impact. 

In this study, we monitored ponderosa pine and Douglas-fire trees before and after a prescribed burn to assess the short-term changes in water status and growth. We found a temporary window after fire where the effects of fire injuries dominate. This means a period where trees not only grow less, but where drought vulnerability is higher. These costs will likely dissipate as trees recover from injuries. This work, combined with ongoing research on longer-term growth patterns after fire will help to improve current operational models of post-fire growth. It also informs our evolving understanding of how fire and drought can interact. There are many clearly demonstrated benefits of prescribed burning, thus our results should be placed in the context of larger efforts to restore vast areas of fire-prone forests.