New Research Shows Soil Moisture Can Diminish Drought Effects, Depending on the Plant Species

Release Date:

Vegetation abundance has been declining due to drought in the western U.S. where the landscape is predicted to become dryer and hotter. This project offers information on tracking the conditions that can cause significant vegetation declines.

Comparing changes in plant abundance, soil content and regional climate could help managers plan for and adapt to the effects of drought, according to a new study co-authored by the National Climate Adaptation Science Center researcher Seth Munson.

In a small canyon, yellow trees pop through various and brown shrubs growing around a dried up river.

 Shrublands in part of the Colorado Plateau in Utah. Credit: Deborah Lee Soltesz

Reduced vegetation has been linked to the recent rises in both temperature and drought frequency in forests and shrublands of the southwestern United States. Within this region, an increasingly dryer climate is predicted by mid‐century, which will further impact plant life and maintain a negative influence on the region’s ecosystems and economy. Researchers and managers alike have highlighted a need for greater, faster understanding of the vulnerability of regional vegetation to drought so that land management actions can be implemented at the right place and time.

The amount of water available to plants is controlled not only by precipitation, but also by soils, vegetation traits, topography, and land use. In this study, annual vegetation production was compared to water availability across seven national park units on the Colorado Plateau. To do this, researchers used satellite technology to determine vegetation responses to water availability across the study sites, taking location-specific measurements of variables such as water availability, precipitation and soil moisture. From here, the researchers determined how vegetation responded to the different water levels at each site, and at which point plant production fell below average.

In arid regions, plant life depends on a balance of growth and reproduction during wet conditions yet durability during dry periods. However, the vegetation responses from this experiment were found to also largely depended on the dominant vegetation and soil types of each study area. For example, Blackbrush shrublands had generally high drought resistance, possibly due to the plant’s deep-growing roots, but showed less resistance to drought in areas where the soil was sandy. On the other hand, sagebrush shrublands were less drought resistant overall, but showed an increase in drought resistance in soils heavy with clay.

Current strategies employed by land managers to assess vegetation conditions are often based on weather and climate monitoring. Results of this research show that the accuracy of these location-specific weather and climate assessments can be improved if used in conjunction with water level tracking, referred to as ‘the pivot point approach’. In the event of a decrease in regional plant production, further measures can then be taken to prepare for the effects of drought, including minimizing human disturbances or controlling invasive species growth to reduce competition for water. Overall, taking full advantage of the information that can be gleaned from closely monitoring water levels, especially in various soil types, would allow land managers to identify early warning signs of increased risk to vegetation, so that they can focus their resources more quickly and effectively.

Learn more about the National CASC project that this study was a product of here!