Banded Vegetation, Circles, and Geomorphic Couplings Inferred from Remote Sensing

Abstract:

Patterned vegetation has been studied for at least 70 years. Patterned vegetation is a self‑organized mosaic of bare or nearly bare ground and patches of vegetation, typically stripes or holes (such as fairy circles), that is distinct from patterns caused by bedrock contrasts or features such as fissures, bedding planes, and dunes. It is well established that self-organized dryland patch patterns are usually found on very shallow slopes in climates with a moderate excess of evapotranspiration, where the water supply is insufficient to permit full ground cover but local runoff routes flow to the vegetation. Often the bare areas are less permeable than the vegetated areas. Numerical modeling indicates that feedbacks tend to perpetuate developed patterns and patterns may spontaneously generate, but the precise conditions fostering self-organized vegetation are less established. To examine the geomorphic conditions more closely, patterned vegetation locations with stripes or holes were visually identified in an extensive worldwide search, digitized using Google Earth™ and Google Earth Engine™. Heuristics for locations conducive to patterned vegetation formation were developed to take advantage of digital elevation models and radar backscatter, as well as derived products such as vegetation and soil classifications derived from machine learning and gridded climate and NDVI products. The resulting database of >4,000 locations includes extensive swathes of Africa, central Asia, Australia, and North America. The database also includes patterned fens in North America and from Scandinavia through central Russia, which exhibit very similar banding patterns and occur on eolian deposits that were arid during the late Pleistocene and subsequently flooded. The collection of locations strongly suggests that wind patterns and the presence of a moderate amount of fine eolian-transported sediment are important initiating factors in patterned vegetation, although aqueous reworking may be important as well. Banded vegetation appears to be related to sediment transport and deposition processes, whereas many of the swarms of circular holes appear to be small deflation hollows related to sediment erosion processes.