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

Authors: DE SOYZA, AMRITA - NEW MEXICO STATE UNIV; Whitford, Walter; MARTINEZ-MEZA, ERNESTO - NEW MEXICO STATE UNIV; Van Zee, Justin

Submitted to: American Midland Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Creosotebush is a very common shrub species that occurs in all three warm deserts of North America. Its above-ground stems are often arranged such that the plant looks like a cone (positioned with the sharp end on the ground) or like a half-sphere (positioned with the sharp end on the ground). We found that cone shaped creosotebushes were more common in environments where there was not much water while the hemispherical plants were more common where there was more water. Soil under the hemispherical plants was more fertile than was soil under conical shrubs or in the unvegetated areas between the shrubs. However, the greater fertility under hemispherical shrubs did not support more annual plants, probably because the greater overhang by leaves and stems caused increased shade. This study shows that even areas that appear very homogeneous because they are dominated by a single species such as creosotebush may actually be very variable due to differences in the dominant plant species.

Technical Abstract: Differences in creosotebush (Larrea tridentata) crown morphology may reflect changes in the relative demand for water vs. Nutrient resources, coinciding with shrub growth and development. Creosotebushes with inverted cone-shaped crowns were more abundant in water-limited environments whereas hemispherical shaped creosotebushes were more abundant in less water- limited environments. Cone-shaped creosotebushes accumulated substantiall less litter under their canopies than did creosotebushes with hemispherical shaped crowns. Soil nutrient concentrations under conical shrubs were similar to those in intershrub spaces and both of these were significantly less than soil nutrient concentrations under hemispherical shrubs. In ecosystems where overland flow of water exerted a greater influence on the movement of organic litter than did wind, shrub shape had little effect on long-term litter accumulation. No persistent differences in the biomass or rdiversity 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 litter accumulation patterns and soil nutrient patterns, and must be considered when assessing the heterogeneity of desert ecosystems in the southwestern USA.