While the growth of individual plants often responds quickly to experimental climate change, changes in plant community composition occur over longer time scales. We established a long term warming and precipitation change experiment along the C. Hart Merriam elevation gradient in Northern Arizona, which encompasses a broad range of ecosystems and climactic conditions. 20 intact plant-soil mesocosms were transplanted downhill, warming them by 4 °C, and 20 were excised and placed back into the native site as controls. Clear acrylic rain collectors (50% increase) and interceptors (30% decrease) were installed at each site to simulate long term shifts in precipitation. We asked: 1) What are the long term effects of climate warming and altered precipitation on aboveground primary productivity (ANPP)? 2) What features of the vegetative community influence ecosystem responses to climate change?
Results/Conclusions
Across the elevation gradient, warming initially increased ANPP up to 125% during the first three years. However, the response of ANPP to warming and precipitation change declined 7% per year from 2002 to 2017, and by 2010, the effects of warming on ANPP switched from positive to negative. Preliminary analyses suggest that plant community composition mediated long term effects of warming on ANPP: at high elevations, plant communities shifted significantly in response to warming, which was correlated with a 20% loss in ANPP in 2017. However, at middle elevations, changes in the plant community were minimal, and ANPP was not affected by warming in 2017. We expect that ANPP responses to climate change will depend on ecosystem type and survivorship rates of dominant native plant species. Ongoing work will address whether re-ordering of plant functional groups drives the progressive trend in ANPP responses to climate change in high elevation ecosystems.