Cessation of Burning Dries Soils Long Term in a Tallgrass Prairie
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Soil moisture is a critical variable in grassland function, yet how fire regimes influence ecohydrology is poorly understood. By altering productivity, species composition, and litter accumulation, fire can indirectly increase or decrease soil water depletion on a range of time scales and depths in the soil profile. To better understand how fire influences soil moisture in grasslands, we analyzed 28 years of soil moisture data from two watersheds in a central North American grassland which differ in their long-term fire frequency. Across 28 years, cessation of prescribed burning initially led to wetter soils, likely as litter accumulated and both transpiration and evaporation were suppressed. Long-term, cessation of burning led to soils drying more, especially at depths greater than 75 cm. The long-term drying of deep soils is consistent with the increase in woody species in the infrequently burned grassland as woody species likely have a greater reliance on soil water from deeper soil layers compared to co-occurring herbaceous species. Despite the ecohydrological changes associated with the cessation of prescribed burning, watersheds with different burn regimes responded similarly to short-term variation in climate variation. In both watersheds, low precipitation and high temperatures led to drier soils with greater responses in soil moisture to climate variation later in the season than earlier. There is no current evidence that the cessation of burning in this ecosystem will qualitatively alter how evapotranspiration responds to climate variation, but the use of deeper soil water by woody plants has the potential for greater transpiration during dry times. In all, modeling the depth-specific responses of soil moisture and associated ecosystem processes to changes in burn regimes will likely require including responses of plant community composition over short and long time scales.
Key wordsfire soil moisture Konza Prairie critical climate period ecohydrology evapotranspiration woody species
This research was made possible by support from the National Science Foundation over the entirety of the Konza LTER program including the recent grant (DEB-0823341). A number of people including Gene Towne and Amanda Kuhl were responsible for the measurements of soil moisture over the years and maintaining the burn program at Konza. Gene Towne, Nate Brunsell, the editor, and two anonymous reviewers provided helpful comments on the manuscript.
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