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Accueil du site → Doctorat → États-Unis → 2005 → Response of a mesquite community to groundwater deficiency, Mojave Desert, California

UNIVERSITY OF CALIFORNIA, LOS ANGELES (2005)

Response of a mesquite community to groundwater deficiency, Mojave Desert, California

Campbell, Jonathan Edward

Titre  : Response of a mesquite community to groundwater deficiency, Mojave Desert, California

Auteur  : Campbell, Jonathan Edward

Université de soutenance : UNIVERSITY OF CALIFORNIA, LOS ANGELES

Grade : Doctor of Philosophy (PhD) 2005

Résumé
Edwards Air Force Base, in the Mojave Desert, provides a refugium for mesquite trees approaching their range limit in the arid southwest United States. Unfortunately, the health and fecundity of these widely-spaced trees appear to be diminishing as mature and old individuals dominate the community. This study represents an effort to understand better mesquite trees at their range limit and determine what environmental factors contribute to and detract from their selection of germination sites and subsequent long-term persistence. In addition, this study examines the feasibility of planting mesquite in a nearby establishment site in order to reduce anthropogenic pressures on the extant community. Analysis of aerial photographs shows the spatial extent of themesquite community grew vigorously from 1956 to 1968, while it contracted from 1984 to 2000. An age-class analysis confirmed that the existing community is made up largely of mature, old, and dying trees. Soil fertility, salinity, texture and moisture values in the rooting zone, along with water-table depths, were examined to determine if local’ differences affect germination site selection and/or long-term persistence of individuals. Although water-table depths have dropped significantly in this region over the past century, values in the study site were found to range from 7.7 to 20 m. Soil water in the vadose zone was relatively abundant in areas where the groundwater table was shallow and mature mesquite trees flourished, whereas areas dominated by old, dying or dead trees were located in sites where there was less soil water. Little variation existed in soil- water content between Beneath-Canopy and Between-Canopy sites. Although occasional spikes in various soil parameters were present in some areas, neither soil fertility, salinity, nor texture concentrations appear to limit germination sites or growth, as the differences between Beneath-Canopy and Between-Canopy sites also showed little to no variation. Results show that the establishment of a mesquite community to the south of Rosamond Dry Lake appears to be feasible. Surface and subsurface variations for all soil and water parameters analyzed herein are minimal between the extant mesquite community and the proposed establishment area.

Mots clés : BIOLOGY, ECOLOGY ; GEOGRAPHY

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Page publiée le 20 septembre 2005, mise à jour le 18 janvier 2017