Form and function of grass ring patterns in arid grasslands: the role of abiotic controls

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.

The effect of sand grain size on the development of cyanobacterial biocrusts

“…Ring diameter is species-dependent and varies over two orders of magnitude, from about 0.1 m in the case of plant species Poa bulbosa to about 10 m for Larrea tridentate (Sheffer et al, 2011). One of the suggested mechanisms for ring formation is an aeolian feedback between plants and wind (hydrologic-aeolian process) suggested by Ravi et al (2007Ravi et al ( , 2008Ravi et al ( , 2010 Class weight (%) Fig. 8.…”

“…to lower infiltration and lower hydraulic conductivity at the ring's center compared to the edges. The retention of moisture at the surface by the finer soil deposited at the center of the ring enhances the formation of physical crusts and biocrusts, resulting in a central die-back and the development of surface-runoff source-sink relations between the ring's center and its fringes (Ravi et al, 2008). The final result of this process is the formation of two micro-environments in the patch: the patch center, characterized by low soilwater content, and the patch fringes, characterized by higher soilwater content (Ravi et al, 2008).…”

Dryland ecohydrology and climate change: critical issues and technical advances

“…The dichotomy between shrub canopy and interspace is a major determinant of ecosystem productivity and diversity. The heterogeneous nature of the vegetation in drylands is thought to be controlled by processes of upslope water erosion and sedimentation, and complex interactions among individual plants and the surrounding soil matrix (Puigdefébregas and Sanchez, 1996;Bochet et al, 1999;Reid et al, 1999;Wang et al, 2007;Ravi et al, 2008). Both the movement and storage of water within shrublands is highly variable (e.g., Breshears et al, 2009).…”

Dynamic interactions of ecohydrological and biogeochemical processes in water‐limited systems

“…These interactions can lead to the formation of areas of ''hydrologically enhanced plant productivity'', a common characteristic of many arid and semi-arid landscapes (Ludwig et al 2005, Puigdefabregas 2005. The examples of the vegetation-sediment transport interactions are well documented in drylands including the formation and expansion of coppice dunes, and the ring pattern formation in certain grass species (Ravi et al 2008, Ravi et al 2009). Disturbances, natural or anthropogenic, can impact the sediment transport-vegetation v www.esajournals.org interactions at different scales (Breshears et al 2003, Ravi et al 2009).…”