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Title: Climatic controls of aboveground net primary production in semi-arid grasslands along a latitudinal gradient portend low sensitivity to warming

Author
item MOWLL, W - Colorado State University
item Blumenthal, Dana
item CHERWIN, K - Colorado State University
item SMITH, A - University Of Oklahoma
item SYMSTAD, A - United State Geological Service
item Vermeire, Lance
item COLLINS, S - University Of New Mexico
item SMITH, M - Colorado State University
item KNAPP, A - Colorado State University

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2015
Publication Date: 2/12/2015
Citation: Mowll, W., Blumenthal, D.M., Cherwin, K., Smith, A., Symstad, A.J., Vermeire, L.T., Collins, S.L., Smith, M.D., Knapp, A.K. 2015. Climatic controls of aboveground net primary production in semi-arid grasslands along a latitudinal gradient portend low sensitivity to warming. Oecologia. 177:955-969.

Interpretive Summary: Although climate models forecast warmer temperatures, precipitation is the primary driver of plant productivity in most grasslands. Forecasting responses to warming is a challenge, and raises the question: how sensitive will grassland productivity be to warming? We evaluated climate and productivity data from eight western US grasslands arrayed along substantial temperature and precipitation gradients. Growing season temperature was negatively related to total and graminoid (grass and sedge) productivity, but precipitation was a better predictor than either temperature or indices that incorporate precipitation, evaporation and transpiration. We conclude that warming will affect ANPP in these grasslands, but that predicting temperature effects from natural climatic gradients is difficult. This is because unlike precipitation, warming effects are likely to be complex and site specific as well as moderated by regional shifts in the C3/C4 ratios of plant communities.

Technical Abstract: Although climate models forecast warmer temperatures with a high degree of certainty, precipitation is the primary driver of aboveground net primary productivity (ANPP) in most grasslands. In contrast, variations in temperature seldom are related to patterns of ANPP. Thus forecasting responses to warming is a challenge, and raises the question: how sensitive will grassland ANPP be to warming? We evaluated climate and multi-year ANPP data (67 years) from eight western US grasslands arrayed along substantial mean annual temperature (MAT, ~7-14 °C) and mean annual precipitation (MAP, ~300 – 500 mm) gradients. We used regression and analysis of covariance (ANCOVA) to assess relationships between ANPP and temperature, as well as precipitation (annual and growing season) to evaluate temperature sensitivity of ANPP. We also related ANPP to the Standardized Precipitation Evaporation Index (SPEI), which combines precipitation and evapotranspiration estimates. Regression models indicated that variation in growing season temperature was negatively related to total and graminoid ANPP, but precipitation was a better predictor than temperature. Growing season temperature was also a significant parameter in more complex models, but again precipitation was consistently a stronger predictor of ANPP. Surprisingly, neither annual nor growing season SPEI was as strongly related to ANPP as was precipitation. We conclude that warming will affect ANPP in these grasslands, but that predicting temperature effects from natural climatic gradients is difficult. This is because unlike precipitation, warming effects are likely to be complex and site specific as well as moderated by regional shifts in the C3/C4 ratios of plant communities.