Extreme Drought in Grasslands Experiment (EDGE)
Globally, all ecosystems will be impacted to some extent by changes in climate means and more frequent and severe periods of climatic extremes. The goal of EDGE is to understand how and why grassland ecosystems differ in their sensitivity to extreme drought. EDGE employs large rainfall exclusion shelters across six grasslands within the central US from desert grasslands to tallgrass prairie. The shelters intercept ~66% of incoming precipitation over a 4 year period. The sensitivity of different ecosystem processes (soil C and N fluxes, above- and below-ground primary productivity, and biodiversity) are assessed annually throughout the project. This project is funded by the National Science Foundation and is a collaborative effort between researchers at Colorado State University, New Mexico University and Northern Arizona University.
|
|
The role of community functional composition
My contribution to EDGE is to assess the physiological attributes of plant communities by measuring mechanistic traits of the dominant plant species at each of the six grasslands. The goal of this project is to determine whether plant traits, climate, or a combination of variables are best for understanding and explaining ecosystem and community sensitivity to extreme drought (sensitivity assessed as reductions in plant biomass per mm reduction in precipitation). The EDGE trait survey includes commonly measured traits of the leaf economic spectrum (e.g. specific leaf area, leaf nutrients, and maximum photosynthetic rate) as well as several hydraulic traits linked to drought tolerance (e.g. leaf turgor loss point and vulnerability to cavitation). Traits are measured on several species at each site (representing ~90% plant cover) in order to assess community weighted trait means and trait diversity.
|
Main Findings:
- Drought sensitive grassland sites are characterized by both low community functional diversity (i.e. trait dissimilarity between species) and a scarcity of drought tolerant species. Additionally, the four-year experimental drought shifted community functional composition towards reduced drought tolerance and increased functional diversity. Published in Journal of Ecology - download here
- Our experimental drought reproduced the paradoxical responses that were observed during the 1930's Dust Bowl – warm-season C4 grasses replaced by cool-season C3 grasses – which we attribute to changes in precipitation seasonality during drought. Published in PNAS - download here