Effects of drought and defoliation on moisture and energy balances in a tropical mountain cloud forest

Forested mountain slopes with prevailing wind patterns are often enveloped in clouds formed from orographic uplift. Over the elevation range where the lifting condensation level intersects the land surface, frequent cloud-immersed conditions affect the water balance, with persistent soil moisture, fog/cloud interception and foliar uptake, and transpiration suppression during cloud-immersed periods. From April 2014 - November 2018 we collected data to characterize cloud immersion and its role in the ecohydrology of the Luquillo Mountains. A significant drought occurred Jun 2015-Feb 2016, and on Sep 20, 2017 Hurricane Maria made landfall, resulting in widespread canopy defoliation and tree mortality. Our observations of temperature, relative humidity, time-lapse imagery (in-situ cloud immersion at 1000 m and 675 m) and ceilometer cloud base height cover both these disturbance periods, including 14 months post-hurricane. Clouds produced by orographic uplift were determined by comparing ceilometer and camera observations; the frequency of forest-immersing clouds was higher than over the coastal plain. Changes in moisture and energy balances from drought and defoliation resulted in complex effects on the orographic cloud system. After defoliation, diurnal temperature cycles were amplified and vapor pressure deficit increased from undisturbed levels. Overnight post-hurricane cloud immersion frequency at the 1000 m site was above mean levels, while overnight immersion at the 675 m site showed lower frequencies during the post-hurricane period and during the drought. These results offer insight on the effects of changes in regional climate, land use, disease, or prolonged drought on ecohydrology and water resources in forested mountains with cloud water inputs.