PARENT SESSION
Oral Session # 93: Vegetation Change and Response.
Presiding: B Parry Hecht
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 105.

Grassland productivity responses to individual and combined global changes: four years at Jasper Ridge.

Dukes, Jeffrey^*,1, Shaw, M.^{1, 2}, Chiariello, N.³, Field, C.¹, ¹ Carnegie Institution of Washington, Stanford, CA, USA² The Nature Conservancy of California, San Francisco, CA, USA³ Department of Biological Sciences, Stanford, CA, USA

ABSTRACT- While many studies have examined ecosystem responses to individual global environmental changes, few have examined responses to multiple changes. Because many global changes are happening simultaneously, our ability to predict ecosystem functioning depends on an understanding of responses to interacting changes. Here we show how net primary productivity (NPP) of a California grassland responded to four individual and interacting global changes over four years of exposure. While simulated nitrogen deposition consistently increased NPP, warming and increased precipitation generally had little effect. Elevated atmospheric carbon dioxide concentrations had increasingly negative effects on NPP over the course of four years. Each of the four factors had more consistent and usually more positive effects when applied individually than when applied in combination with other factors. Collectively, results from the Jasper Ridge Global Change Experiment suggest that productivity responses to global changes are less than additive, and are harder to discern when factors interact.

Key words: elevated CO₂, climate change, global change, annual grassland