Mesoscale patterns of plant cover, soils, and surface mosaics of a pleistocene desert pavement landscape, Cima Volcanic Field Mojave Desert, California

Desert pavement is a common land surface feature in arid regions worldwide. It is comprised of a surface layer, one to two clasts thick, overlying soils developed in eolian sediments. This research explored how surface clasts, underlying soils, and desert plants are distributed, and interact at the mesoscale (tens of meters) to affect surficial processes, such as eolian deposition, and water infiltration and run-off. The land surface of a 560 ka lava flow in the Mojave Desert was delineated into map units of distinct surface mosaics (defined by clast median size, sorting, and percent cover) to capture the spatial heterogeneity. Chemical, physical and morphological characteristics of underlying Aridisols were consistently and remarkably more similar within, rather than between, surface mosaics. Soils with strong columnar structure, incorporating platy vesicular A horizons and argillic B horizons, developed under a clast cover of ≥87%. At the other extreme, and sometimes sharply adjoining, soils with weak platy A horizons immediately overlying loamy B horizons formed under a clast cover of between 14 and 28%. Material addition to these soils of eolian sands was controlled by clast frequency (N per linear meter) while the depth at which leached salts accumulated was controlled by clast cover. Plant characteristics, also, were distinct for individual surface mosaics. Where clast cover was >65%, soluble salts were concentrated within the top 50 cm of soil, and plant cover was scarce. Where clast cover was <65%, soluble salts were leached to below the 50 cm depth, and plant cover was relatively high. Dynamic feedbacks between the biotic and the abiotic elements of the landscape have evolved. Plant distributions control important pedogenic factors of A horizon soil carbonate and percent sand; and shallow concentrations of soil soluble salts affect important surface physical factors of clast size, percent cover, and frequency, presumably through salt fracturing of surface clasts. Strong linkages between surface clasts, the genesis of underlying soils, and desert plant associations have initiated and reinforced distinct, yet intricately associated, mesoscale landscape elements, each with characteristic ecologic, pedologic, and hydrologic features and functions.