Are mima-like mounds the consequence of long-term stability of vegetation spatial patterning?

The origins of large (> 5 m diameter, > 1 m height) and regularly spaced (i.e. over-dispersed) non-anthropogenic earth mounds (e.g. mima mounds, heuweltjies, nabhkas) that occur across all biomes remain unresolved. An extensive literature documenting diverse explanations for mound genesis has accumulated that primarily ascribes mound formation to faunal agents. Recent modeling efforts suggest that both abiotic and biotic processes commonly interact to produce striking vegetation patterning (e.g. spots, labyrinths). The hypothesis that many earth mounds, apart from those with a clear faunal genesis (e.g. termitaria), may result from vegetation trapping of sediment or aeolian dust and/or protection of soil from erosion is reviewed here. The literature on the occurrence and properties of some of these mima-like mounds is reviewed, and the evidence for their origins evaluated. Some mounds, such as coppice dunes (otherwise known as nabkhas), clearly form as a consequence of aeolian deposition of sediment around vegetation patches. However, the clay, stone and rock content of some mima-like mounds is not consistent with purely aeolian origins. Instead it is suggested that non-aeolian mound over-dispersion, elongation, volumes, soil properties and stratigraphy are consistent with vegetation patches protecting soil from erosion, resulting in preferential erosional deflation of the inter-mound area leaving regularly spaced mounds. Although mima-like mounds around the world are formed in diverse vegetation types, climates and edaphic conditions, many may be long-term products of vegetation spatial patterning in which plant canopies and root systems increase sediment capture and reduce erosional losses.