|Miller, Richard - OREGON STATE UNIVERSITY|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 5, 2004
Publication Date: September 20, 2005
Citation: Bates, J.D., Svejcar, A.J., Angell, R.F., Miller, R.F. 2005. The effects of precipitation timing on sagebrush steppe vegetation. Journal of Arid Environments. 64:670-697. Interpretive Summary: The timing of precipitation has the potential to alter Great Basin rangelands. We used "rainout shelters" and sprinkler systems to exclude natural precipitation and create different precipitation timing treatments. Our results demonstrate that a shift to less winter and more summer precipitation would have negative consequences for sagebrush/bunchgrass communities. A shift to more winter and less spring/summer precipitation had minimal impact on the plant community. Species change is often used to evaluate rangeland health and response to management. Our results show that changes in precipitation pattern can also have an impact on rangeland.
Technical Abstract: Changes to precipitation timing patterns as predicted by general circulation models has the potential to cause major changes in productivity, composition, and diversity of terrestrial plant communities. These ecosystems are often important to pastoral agriculture systems, thus testing plant community response to altered precipitation timing is necessary for developing predictive models that may describe community responses to shifts in climatic regimes. Plant community response to altered timing of precipitation was assessed during a six year period in the Artemisia tridentata spp. Wyomingensis ecosystem of the Northern Great Basin, USA. Five permanent rainout shelters were used to control water application and seasonal distribution. Water was applied by an overhead sprinkler system. Precipitation treatments under each shelter were WINTER, SPRING, and CURRENT. The WINTER received 80% of its water between October and March; 80% of the SPRING treatment was applied between April and July; and the CURRENT treatment received precipitation matching long-term (50 years) distribution patterns at our experimental range. A CONTROL treatment was placed outside each shelter replicate and received natural precipitation. Plant community composition and productivity were significantly influenced by the precipitation treatments. All shelter treatments tended to have greater ground cover than the CONTROL treatment as a result of higher herbaceous and/or litter cover. Herbaceous biomass production, reproductive effort, and cover were reduced under the SPRING moisture pattern compared to other treatments. Forb species were most sensitive to the SPRING water application. Forb density and cover were lower in the SPRING treatment compared to the other treatments in all years. The SPRING application pattern was more to favorable for Artemisia tridentata spp. Wyomingensis reproductive success and shoot weights than the other treatments. Summer moisture was an important factor in the reproductive effort of sagebrush and winter/early spring moisture is important to the reproductive effort of the herbaceous component. A shift to spring/early summer precipitation patterns would reduce herbaceous productivity and cover, and negatively alter species composition in Artemisia tridentata spp. Wyomingensis communities. A greater percentage of precipitation arriving during winter months should not alter species composition in Artemisia tridentata steppe communities.