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.