Effects of artificially imposed shade on a Sonoran Desert ecosystem: arthropod and soil chemistry responses

Abstract

The responses of arthropod populations and soil chemistry to ameliorated microclimatic conditions and altered vegetation patterns caused by artificially imposed shade were investigated in a Sonoran Desert ecosystem using an array of 12 regularly spaced, opaque structures. Shrub arthropods, particularly the phytophagous Homoptera, responded positively to shade. Arthropods were abundant on the broadleaf shrub Ambrosia deltoidea in shaded microhabitats but not on the xerophytic evergreen Larrea tridentata. Surface arthropods, chiefly tenebrionid beetles, exhibited greater density in the pitfall trapping grid of the experimental site than in a control. Five species of seed harvesting ants were variously affected by artificial shade. Most species showed increased diurnal surface activity in shaded microhabitats, especially in the warm season. Soil microarthropods were more abundant in shaded microhabitats but the density of these organisms may have been stimulated more by the presence of shrubs than by artificial shade. Increases in soil nutrients occurred as a direct result of artificial shade at both beneath-shrub and inter-shrub locations.