Experimental Manipulation of Variability in Precipitation in a Grassland
Alan K. Knapp, John M. Blair, Phil A. Fay
Project Summary
The structure and function of grassland ecosystems in the
Central Plains are strongly influenced by an extremely variable continental
climate. This is especially true in tallgrass prairie, where many of the
defining characteristics of the ecosystem are a result of interactions
of climate with fire and grazing. Although much of the original extent
of this grassland has been plowed, five million acres occur in Kansas supporting
a livestock grazing industry second only to Texas. Within grasslands, the
importance of both amounts and timing of precipitation inputs as forcing
functions for grassland ecosystems makes them particularly vulnerable to
the changes in precipitation predicted by global climate change models.
For the Central Plains region, these predictions generally include decreased
summer precipitation, increased temperatures and, perhaps most importantly,
increased variability in both the amounts and timing of rainfall events.
This is particularly important, since climatic variability is at least
as important as mean climate values in determining the structure and function
of grassland ecosystems. Major goals of the proposed research are to
determine how key above- and below-ground patterns and processes are altered
in response to changes in two aspects of climate: the (1) amount of precipitation
and, (2) the variability of precipitation inputs, and to identify the potential
consequences of these responses for grassland ecosystem function. Our
approach utilizes field-scale Rainfall Manipulation Plots in which the
timing and amounts of rainfall events are experimentally manipulated, independently
and in tandem, to assess the effects of altered precipitation regimes on
individual plant ecophysiological responses, plant community composition,
and ecosystem-level processes. This multidisciplinary approach will
provide unique insights into the importance of the altering precipitation
amounts and/or variability in grasslands, both predicted to occur under
a variety of climate change projections.
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