The microenvironment of a desert hackberry plant (Celtis pallida).

Abstract

Evapotranspiration rates of plots with vegetative cover and evaporation rates from bare soil differed during the active growing season of desert hackberry (Celtis pallida) plants but total water losses from both plots for the year were the same. Thermally induced vapor flux appeared to contribute insignificantly to moisture movement under the desert hackberry plant. The difference in measured available soil moisture was independent of location from the plant center during the growing season. During the winter months, when the plants were semidormant, soil moisture measurements had more variability and measurement locations appeared to be important due to differential rainfall input. The determined soil moisture release curve and soil water conductivity values (using an in situ technique) appeared to be representative of the conditions at the study site. A model using soil and plant parameters predicted evapotranspiration rates during the active growing season of the plants when water was not a limiting factor. Calculated results using the model were unreliable when plants were under stress -- very low soil water content. Monitoring of climatic parameters delineated only major differences in surface albedo and net radiation between plant cover and bare ground. Potential evapotranspiration estimations were high but within acceptable bounds for desert conditions. Plant diffusion resistance for the desert hackberry plant, determined from a climatological model and measured soil moisture changes, appeared to increase linearly with decreasing soil moisture until it reached a critical value, below which it rose sharply.