Effects of woody plants on microclimate in a semiarid woodland: Soil temperature and evaporation in canopy and intercanopy patches

The canopies of woody plants in semiarid ecosystems modify the microclimate beneath and around them, with canopy patches usually having lower soil tem peratures than intercanopy patches. However, lacking are studies that have evaluated how heterogeneity in soil temperature, induced by woody plant can opies, influences soil evaporation rates and the consequent effects on plan t-available water. Soil temperatures were measured and soil evaporation rat es were estimated for canopy and intercanopy patches in a semiarid pinon-ju niper woodland (Pinus edulis and Juniperus monosperma) in northern New Mexi co. Soil temperature was measured at 2-cm depths in four canopy and four in tercanopy locations during 1994. Maximum soil temperature in intercanopy pa tches was greater than in canopy patches between May and September, by as m uch as 10 degrees C, while soil temperatures in intercanopy patches were lo wer than in canopy patches during colder parts of the day in the fall and w inter months. Equations for soil drying rates for sandy loam soil samples w ere determined in laboratory experiments over a range of temperatures and s oil water contents. Drying rates were disproportionately greater at high so il moisture and high soil temperature. Intercanopy patches were predicted t o dry more than canopy patches for days in April through September by as mu ch as 2% volumetric soil water content per day. The difference between patc hes was amplified at lower soil water contents when expressed as soil water potential, which more directly determines plant-available water. Our resul ts quantify the effects of woody plants on the microclimate with respect to soil temperature and evaporation, which in turn affect herbaceous and wood y plants by modifying factors such as germination, the potential for facili tation, and the amount of plant-available water.