DESERT PAVEMENT SURFACE CHARACTERISTICS AND THEIR CORRELATIONS WITH SOILS AND PLANT DISTRIBUTIONS, CIMA VOLCANIC FIELD, CALIFORNIA

Desert pavement, a surficial feature widespread throughout the world's arid lands, plays a dynamic role in geomorphic, hydrologic, and ecologic processes. The spatial patterning of desert pavement surfaces is generally barren stone (clast) covered expanses surrounding 'islands' of shrubs and bare soil, reflecting the dominant control of rainfall redistribution by the soil surface. Our objective was to determine the relation at a scale of meters between the physical surface characteristics of a single-aged desert pavement landscape, water movement, underlying soils and desert flora distributions. A desert pavement mantling a 560 ka basalt flow in the Mojave Desert of California was delineated into six large-scale surface map types, termed clast mosaics, using mean clast size, degree of clast sorting and percent of bare ground. Clast mosaics abut with sharp boundaries and capture subtle, yet consistent, variations in soil surface characteristics.

Chemical and morphological characteristics of underlying soils (Aridisols), formed in eolian parent material, were compared within and between delineated clast mosaics and then related to percent surface cover by desert scrub. Soil properties are consistently more similar within, rather than between, clast mosaic map units and are strongly linked to measured biotic components. The differences between the soil properties of abutting mosaics are sufficient for their soil classifications to range from Typic Haplargids to Calcic Paleargids. Plant cover inversely relates to clast cover, reflecting the surface's control of available water. Surface cover by desert plants varies from scarce (0.4% cover by ephemerals) where clast cover and concentrated soil salts are high, to as much as 50% cover by vascular plants where clast cover is low and soils are leached to at least the 50 cm depth.

While desert pavement may appear as a monotonous, barren feature, we find that instead desert pavement surfaces are complex associations of landscape elements. Strong linkages between surface clasts, the genesis of underlying soils, and desert flora distributions have initiated and reinforced these distinct, yet intricately associated, landscape elements, which currently determine surficial processes, such as eolian deposition, and leaching regimes.