Desert pavements stabilise arid vegetation patterns

Ida Gaulke, Alisha Matheson, Leloba Jefferis, Dominik Nommensen, Josh Evans, Victoria M Fernandes, David Dunkerley, Patrick Leo Taggart, Andrew Gunn 

Some vegetation patterns have aridity-dependent morphology. On low-angle arid hillslopes, vegetation organises into bands which follow topographic contours. Terraces emerge with these bands due to vegetation’s drag on sediment-laden runoff, creating a topographic signature of life diagnostic of precipitation rate. Another widespread feature of arid environments is desert pavement, surficial pebbles that armour finer-grained sediments, which is considered a hallmark of landscape stability. Banding and pavement often co-occur, however their interaction has not been studied. Here we show that vegetation-induced topographic terracing is stabilised by pavement development. In proximal field sites with varying pavement coverage, we illustrate that pavements suppress seed germination and reduce sediment erosion between vegetation bands, stabilising terrace morphology. Despite sites experiencing consistent contemporary precipitation, they exhibit relationships between terrace morphology, topographic slope, and band spacing consistent with patterns formed under wetter conditions at sites with greater pavement coverage, implying aridity has increased as pavements emerged. This suggests that pavements preserve terracing and spacing diagnostic of paleoprecipitation. Because pavement age, band spacing, and topographic slopes are readily observable, we believe our study identifies a new widespread paleo-precipitation proxy in arid environments where conventional alternatives are often unattainable.