ECOSYSTEM ECOLOGY - ORIGINAL PAPER Form and function of grass ring patterns in arid grasslands: the role of abiotic controls Sujith Ravi Æ Paolo D’Odorico Æ Lixin Wang Æ Scott Collins Received: 17 February 2008 / Accepted: 15 September 2008 / Published online: 15 October 2008 Ó Springer-Verlag 2008 Abstract Ring-shaped growth patterns commonly occur in resource-limited arid and semi-arid environments. The spatial distribution, geometry, and scale of vegetation growth patterns result from interactions between biotic and abiotic processes, and, in turn, affect the spatial patterns of soil moisture, sediment transport, and nutrient dynamics in aridland ecosystems. Even though grass ring patterns are observed worldwide, a comprehensive understanding of the biotic and abiotic processes that lead to the formation, growth and breakup of these rings is still lacking. Our studies on patterns of infiltration and soil properties of blue grama (Bouteloua gracilis) grass rings in the northern Chihuahuan desert indicate that ring patterns result from the interaction between clonal growth mechanisms and abiotic factors such as hydrological and aeolian processes. These processes result in a negative feedback between sediment deposition and vegetation growth inside the bunch grass, which leads to grass die back at the center of the grass clump. We summarize these interactions in a simple theoretical and conceptual model that integrates key biotic and abiotic processes in ring formation, growth and decline. Keywords Aeolian processes  Arid ecosystems  Ecohydrology  Infiltration  Soil moisture Introduction Vegetation patterns such as bands (Leprun 1999; Valentin et al. 1999), stripes (White 1971; Ludwig et al. 1999), spots (Couteron and Lejeune 2001) and rings (Cosby 1960; Sheffer et al. 2007) are a recurrent characteristic of resource-limited arid and semi-arid landscapes (Greigsmith 1979; HilleRisLambers et al. 2001; Rietkerk et al. 2002). Interactions between surface soil moisture, erosion pro- cesses, and vegetation are thought to be the major factors responsible for the formation of these patterns (Valentin et al. 1999). The geometry, spatial distribution and scale of vegetation pattern, which result from interactions between biotic and abiotic processes, affect the spatial patterns of soil moisture, sediments and nutrients in these landscapes (Ludwig et al. 1999; Puigdefabregas 2005). The spatial distribution of water and sediments, in turn, determine plant growth, root biomass and species composition (Val- entin et al. 1999). Thus, vegetation patterns can be considered as biological indicators of abiotic processes such as runoff and infiltration, and of source-sink areas for sediments in dryland landscapes (Ludwig et al. 1999; Imeson and Prinsen 2004). Field studies have shown that in arid landscapes vegetation patterns optimize the capture and storage of water and resources to maximize plant productivity (Ludwig and Tongway 1995). Further, chan- ges in vegetation patterns are thought to be easily Communicated by Alan Knapp. S. Ravi (&) B2 Earthscience and UA Biosphere 2, University of Arizona, Tucson, AZ 85721, USA e-mail: ravi@email.arizona.edu; sr9k@virginia.edu S. Ravi  P. D’Odorico Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904-4123, USA L. Wang Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA S. Collins Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA 123 Oecologia (2008) 158:545–555 DOI 10.1007/s00442-008-1164-1