Slope-aspect induced climate differences influence how water is
exchanged between the land and atmosphere
Abstract
High resolution air temperature, relative humidity, soil moisture,
insolation, and sap velocity observations on 14 madrone trees spanning
adjacent north and south slopes at the University of California’s Angelo
Coast Range Reserve show that cross-slope climate differences in the
mid-latitudes are ecologically important, and impact vegetation-mediated
water balance between the earth surface and the atmosphere. In this
paper, we describe the cross-slope differences in direct observations of
vapor pressure deficit (VPD) and sap velocity, which we use as a proxy
for transpiration. We use a hybrid observation/model approach to
estimate cross-slope insolation variations. We show that trees on
opposing slopes do not follow a shared pattern of physiological response
to transpiration drivers, meaning that the observed sap velocity
differences are not due entirely to observed microclimate differences,
but also due to population-level physiological differences, which may
indicate acclimation to inhabited microclimate. While our present
dataset and analytical tools do not positively identify any mechanism of
possible acclimation, we speculate that differing proportions of
sun-adapted and shade-adapted leaves, differences in stomatal
regulation, and cross-slope root zone moisture differences could explain
some of the observed and modeled differences.