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Colorado State University (2014)

Temperature sensitivity in aboveground net primary productivity in semi-arid grasslands

Mowll, Whitney Macy

Titre : Temperature sensitivity in aboveground net primary productivity in semi-arid grasslands

Auteur : Mowll, Whitney Macy

Université de soutenance : Colorado State University

Grade : Master of Science (MS) 2014

Résumé
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 ? I 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. I 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. I 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 alone. I 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 C 3 /C4 ratios of plant communities.

Mots clés : Ecology, Semi-arid, Climate, Temperature, Precipitation, Biological sciences, Productivity, Grassland

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