Small-Scale Droughts Limit Sagebrush Recovery After Wildfires

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new study supported by the Southwest, Northwest, and North Central CASCs found that a few days of water scarcity during critical growth periods dramatically limited post-fire sagebrush regeneration across the Great Basin. 

Five mule deer stare at the camera as they stand in a field of dry sagebrush

Mule deer move through a sagebrush ecosystem in eastern Oregon.

(Public domain.)

Water is one of the most critical resources in any ecosystem. Past a certain threshold, a lack of water can permanently alter plant and animal communities, causing ecosystems to fundamentally and sometimes permanently change in structure and function. Like all droughts, transformative ecological droughts are becoming increasingly common in the modern era of climate change and intense fire seasons. Yet ecological droughts are particularly hard to study – they occur on spatial and time scales that are difficult to measure, and the unique community dynamics specific to each ecosystem can make insights hard to generalize. As such, little is known about the specific drivers of ecosystem transformations caused by droughts. 

In a recent study supported by the Southwest, Northwest, and North Central CASCs, a group of federal and academic researchers investigated the role of small-scale ecological droughts on post-fire sagebrush recovery. They measured sagebrush regrowth in previously-burned plots across the Great Basin and compared these measurements to two metrics of drought: a broad-scale drought index measuring regional water availability on a monthly basis (Standardized Precipitation Evapotranspiration Index, SPEI) and a fine-scale drought index measuring soil water content on a daily basis (soil-water potential).  

They found that daily soil-water availability measurements during the March germination window was a strong predictor of sagebrush regrowth, while monthly drought measurements were not. This indicates that, even though droughts are usually thought of in terms of months or years, water scarcity over short time periods can dramatically decrease plant survival post-fire. These results emphasize that drought has profound, long-lasting impacts on sagebrush ecosystems, both by increasing the frequency and intensity of wildfires and by altering the ecosystem’s ability to regenerate. The authors hope these insights aid resource managers in the Great Basin improve sagebrush recruitment after wildfires. 

This study is part of the “Improving the Success of Post-Fire Adaptive Management Strategies in Sagebrush Steppe” project funded jointly by the Southwest, Northwest, and North Central CASCs.  

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