Factors affecting survival of California juniper in its lower elevational range in the northwestern Sonoran Desert

Abstract

Juniperus californica (California juniper; Cupressaceae) occurs in a variety of habitats, including pinyon-juniper woodlands and high elevation desert scrub in the northwestern Sonoran Desert. The goal was to determine how much physiological and structural plasticity and microclimate allow J. californica to survive in desert scrub. We hypothesized that individuals in the desert scrub (Agave Hill) coped with greater water stress by limiting xylem cavitation and exhibiting greater stomatal control than individuals in the pinyon-juniper woodland (Pinyon Crest). Additionally, J. californica were expected to occur in cooler microhabitats in the desert scrub, which should have more available soil water than the surroundings. Hypotheses were tested by examining climate data, as well as the morphology, physiology, wood anatomy, and canopy and soil temperatures for individuals at both sites. Agave Hill received less rainfall and the air and soil temperatures were significantly warmer than at Pinyon Crest. Individuals were larger at Pinyon Crest than at Agave Hill; however, water relations and maximum quantum efficiency of Photosystem II did not differ between sites. Plants at Agave Hill had lower CO2 uptake in the autumn and suffered greater dieback during the study; stomatal conductance was also lower at Agave Hill. Average native xylem embolism and wood anatomy did not differ with site; however, xylem embolism did increase as plant shoot volume decreased at Agave Hill. The results indicate that J. californica exists in desert scrub by occupying washes and altering its morphology through reduced growth and dieback during stressful periods.