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Title: DROUGHT AND GRAZING INTERACTION AND RECOVERY IN SHORGRASS STEPPE: A DAYCENT MODELING ANALYSIS

Author
item Grant, Douglas
item Del Grosso, Stephen - Steve
item PARTON, W - COLORADO STATE UNIVERSITY
item Reeder, S
item Morgan, Jack

Submitted to: Shortgrass Steppe Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 1/5/2005
Publication Date: 1/14/2005
Citation: Grant, D.W., Del Grosso, S.J., Parton, W.J., Reeder, S.J., Morgan, J.A. 2005. Drought and grazing interaction and recovery in shorgrass steppe: a DAYCENT modeling analysis. Shortgrass Steppe Symposium. Reeder Abstract.

Interpretive Summary:

Technical Abstract: Global climate change may result in a warmer drier climate with more frequent drought episodes in the North American Great Plains. Plant productivity decreases during drought conditions, reducing OM inputs from grasses and decreasing forage production. We used the DAYCENT model to examine the potential responses of SOM to increased drought frequency and the interaction between drought and rest from cattle grazing. Weather data from 1950 through 2002 were categorized as drought or non-drought years based on three criteria: 1) early-season precipitation, 2) total annual precipitation, and 3) early-season actual evapotranspiration. These criteria categorized drought as occurring in 9 of 53 years. A subset of the weather data (1955 to 1974) was used to analyze how SOM dynamics would be affected if drought frequency increased to one out of four years and this weather cycle was repeated to simulate 60 years. Grazing during drought years followed by a year of rest was compared to rest during the year of drought and continuous season-long grazing to look at the interaction between drought and rest from grazing. This analysis revealed that rest during the year of drought did not significantly enhance C sequestration potential of the soil compared to continuous grazing, while rest the year after drought slightly improved soil C sequestration or offset the increase of SOM losses associated with increased drought frequency. This response was largely attributable to the rareness of consecutive drought years and increased potential for C sequestration from rest in non-drought years resulting from increased plant inputs.