VARIATION IN CREOSOTEBUSH (LARREA-TRIDENTATA) CANOPY MORPHOLOGY IN RELATION TO HABITAT, SOIL FERTILITY AND ASSOCIATED ANNUAL PLANT-COMMUNITIES

Differences in creosotebush (Larrea tridentata) crown morphology may r eflect changes in die relative demand for water vs. nutrient resources , coinciding with shrub growth and development. Creosotebushes with in verted cone-shaped crowns were more abundant in water-limited environm ents whereas hemispherical shaped creosotebushes were more abundant in less water-limited environments. Cone-shaped creosotebushes accumulat ed substantially less litter under their canopies than did creosotebus hes with hemispherical shaped crowns. Soil nutrient concentrations und er conical shrubs were similar to those in intershrub spaces and both of these were significantly less than soil nutrient concentrations und er hemispherical shrubs. In ecosystems where overland flow of water ex erted a greater influence on the movement of organic litter than did w ind, shrub shape had little effect on long-term litter accumulation. N o persistent differences in the biomass or diversity of ephemeral taxa exploiting undershrub areas were found, probably because the positive effects of greater nutrient resources under hemispherical shrubs were offset by the limitations imposed by the larger, more dense canopies of hemispherical shrubs. Overall, creosotebush morphology affected lit ter accumulation patterns and soil nutrient patterns, and must be cons idered when assessing the heterogeneity of desert ecosystems in the so uthwestern USA.