Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2005
Publication Date: 4/1/2006
Citation: Synder, K.A., Tartowski, S.L. 2006. Multi-scale temporal variation in water availability: Implications for vegetation dynamics in arid and semi-arid ecosystems. Journal of Arid Environments. 65(2):219-234. Interpretive Summary: This manuscript summarizes how temporal variability in water availability affects vegetation dynamics in semiarid and arid ecosystems. Variation in water availability is considered at centennial, decadal, annual, seasonal, and within-season scales. The main point is that cross-scale interactions in water availability are an important factor in determining temporal and spatial variation in species composition and structure. The encroachment of shrubs into areas formerly dominated by warm season perennial grasses appears to have been facilitated by changes during the last century in the amount of winter and summer rainfall and decadal scale drought. This manuscript also highlights the potential importance of pulses of rainfall within the growing season. The delivery of pulses--both in terms of the frequency and magnitude of individual storm events affects complex patterns of soil wetting that may differentially affect the ability of shrubs and grasses to use this water for production. Lastly, we present an innovative experiment on the Jornada Range that is manipulating the frequency and magnitude of individual rainfall events throughout the growing season to determine the effects of rainfall frequency and magnitude on the mesquite-black grama ecotone.
Technical Abstract: The objective of this paper is to illustrate the importance of variation in water availability to temporal variation in vegetation dynamics. We hypothesize that fine-scale pulses of precipitation interact with longer-scale variation in climate and weather to generate temporal variation in plant community composition. Arid and semiarid regions exhibit a high degree of temporal variability in water availability as a result of variation in climate and weather at multiple scales and vegetation-soil water feedbacks. The scales of variation include: shifting climate regimes over centuries and decades, inter-annual variation in weather patterns, seasonal differences in winter and summer precipitation, and within-season variability in precipitation frequency and magnitude. In arid and semiarid regions pulses of rainfall are separated by intervening dry periods of variable lengths. This results in fluctuating availability of water that limits plant production and controls other ecological processes, such as rates of nutrient cycling. In many semiarid and arid systems, temporal variation in water availability may create positive feedbacks that facilitate encroachment of C3 woody plant species into areas formerly dominated by C4 grasses. Our ability to predict these complex shifts in vegetation composition may be improved by including temporal variation in climate, weather, and ecosystem processes.