Ring formation in Stipagrostis obtusa in the arid north-eastern Negev, Israel

Abstract

In drylands, particularly in sandy environments, clonal plants occasionally develop into ring patterns that slowly expand radially, leaving bare soil in the ring's center. Several mechanisms have been suggested to explain ring formation, and yet it is very difficult to find out the dominant driving mechanism for each specific ecosystem. This study is the first to assess the rings of Stipagrostis obtusa in the north-eastern Negev of Israel, an arid region with mean annual precipitation of ≈65 mm. Our results propose that S. obtusa rings form in response to the infiltration feedback, which is enhanced by microtopography; the rings developed on small mounds due to continuous deposition of sand and dust. The infiltration feedback is caused by the sharp contrast in water infiltrability between the rings and the inter-ring spaces, where infiltration is lower. In addition, during heavy rainstorms, runoff generated in the inter-ring spaces partially percolates in the rings’ periphery and enhances radial expansion. These source–sink relations increase water availability for the S. obtusa plants, increasing their resilience to the harsh dryland conditions.