Decreasing precipitation variability does not elicit major aboveground biomass or plant diversity responses in a mesic rangeland

Authors: Derner, Justin; HICKMAN, KAREN - OKLAHOMA STATE UNIVERSITY; Polley, Herbert

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2011
Publication Date: 7/5/2011
Citation: Derner, J.D., Hickman, K.R., Polley, H.W. 2011. Decreasing precipitation variability does not elicit major aboveground biomass or plant diversity responses in a mesic rangeland. Rangeland Ecology and Management. 64(4):352-357.

Interpretive Summary: One aspect of global change is the alteration of precipitation regimes (amount, timing). Since water is the limiting variable on most rangelands, responses of vegetation to altered precipitation regimes can have substantial effects on the productivity and function of these important ecosystems for goods and services desired by society. Here we altered the precipitation regimes in a southern tallgrass prairie in Texas for three years by removing variation among and within years with rainout shelters and added water through sprinkler systems to determine if aboveground biomass becomes more stable (less variable), and if plant diversity was impacted. Altering the precipitation regime by removing variability did not influence total aboveground biomass, the stability of this biomass nor species diversity. Although biomass was reduced for the dominant species, a warm-season perennial grass (little bluestem), compensation occurred with higher biomass for another warm-season perennial grass (yellow indiangrass) and an annual forb (firewheel). This rangeland ecosystem is largely non-responsive to removal of variability in precipitation with competitive interactions among species more important for regulating productivity than precipitation.

Technical Abstract: There is an emergent need to understand how altered precipitation regimes will affect aboveground biomass, stability of this biomass, and diversity in grassland ecosystems. We used replicated 9X10 m rainout shelters to experimentally remove inherent intra- and inter-annual variability of precipitation from 1999 to 2001 on a mesic grassland in central Texas. Within each shelter, three, 3X10 m areas were randomly assigned one of three precipitation regimes: 1) normal distribution with spring-dominated (April-May) and constant annual total amounts (87 cm) to remove inter-annual variability, 2) even distribution with constant annual total amounts (87 cm) to remove both inter- and intra-annual variability, or 3) ambient precipitation amounts (48, 113 and 101 cm in 1999, 2000 and 2001 respectively) and distribution. Removal of intra- and inter-annual variability in precipitation did not influence June, December or total aboveground biomass, the stability of biomass or species diversity across the three years. The dominant species in this grassland ecosystem, Schizachyrium scoparium, a perennial C4 grass, did exhibit reductions in biomass with the removal of inherent precipitation variability. These reductions, however, were compensated by an increase in biomass of the annual forb Gaillardia pulchella in the even precipitation regime, and non-significant increases in biomass of another perennial C4 grass Sorghastrum nutans and annual forbs in the normal precipitation regime. This suggests that species covary negatively to altered precipitation regimes and that abiotic factors such as precipitation are less important than competitive interactions in regulating stability of aboveground biomass in this mesic grassland.