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Ecosystem Response to Climate Change: Sensitivity of Grassland Ecosystems Across the Great Plains to Variability in PrecipitationEPA Grant Number: F6F10397
Title: Ecosystem Response to Climate Change: Sensitivity of Grassland Ecosystems Across the Great Plains to Variability in Precipitation
Investigators: Heisler, Jana L.
Institution: Colorado State University
EPA Project Officer: Manty, Dale
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $99,958
RFA: STAR Graduate Fellowships (2006) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Terrestrial Ecology and Ecosystems
Water availability is an important determinant (and primary limiting factor) of aboveground net primary productivity (ANPP) in many biomes and strong positive relationships exist between mean annual precipitation (MAP) and ANPP across temperate grasslands within North America. However, increasing evidence suggests that many aspects of ecosystem structure and function are quite sensitive to intra-annual variability in precipitation, even in cases where precipitation quantity remains within normal bounds. Additionally, ANPP pulses and declines in years of extreme wetness or drought are asymmetric, suggesting that potential buffering mechanisms and vegetational characteristics mediate ecosystem response to availability of water.
Projected changes in climate include warming of the atmosphere and increasingly variable precipitation regimes, both of which may affect soil, plant, and ecosystem properties and ultimately impact productivity in terrestrial ecosystems. This experimental study will focus on two aspects of precipitation variability—frequency and quantity—with the overall objective of improving our understanding of basic precipitation-productivity relationships within grasslands of the Great Plains region.
In order to evaluate the impacts of precipitation variability on ecosystem function, I will conduct a series of field experiments in which growing season rainfall will be manipulated through the use of moderate-size low-cost rainout shelters. In shortgrass steppe, mixed grass prairie, and tallgrass prairie ecosystems, I have constructed 45 rainout shelters (15 per site) that deflect all precipitation from 2.25 m2 plots. “Precipitation events” are then applied manually according to an experimental protocol. In 2006, I will focus on precipitation frequency, with plots receiving mean growing season precipitation that is delivered at 10-, 20-, or 30-day intervals. In 2007, I will focus on precipitation amount, with plots receiving either 1) –20% mean precipitation, 2) –40% mean precipitation, 3) mean precipitation, 4) +20% mean precipitation, or 5) +40% mean precipitation. The primary response variables will be ANPP, soil moisture, and N availability; however, in order to understand the mechanistic processes responsible for the patterns that I observe, I have chosen to also focus on plant carbon-water relations as well as soil CO2 flux.
Increasing evidence suggests that terrestrial ecosystems differ in their relative water use efficiency, and this is likely to be influenced by the frequency and size of precipitation events. Across the Great Plains (from shortgrass steppe to tallgrass prairie), plant communities differ in their tolerance to drought as well as their responsiveness to precipitation pulses. Because of this, I expect differences among grassland types in plant, community, and ecosystem-level processes, and I hope to be able to incorporate these differences into predictive models for productivity in this region.