A Novel Model to Simulate Water Storage in Epiphytic Mats for Tropical Montane Cloud Forests

Tropical montane cloud forests (TMCFs) are hotspots of biodiversity that are threatened by deforestation, human activities, and climate change. Epiphytes are vascular and non-vascular plants that gain support but not nutrients from trees, creating arboreal microsystem that provide ecological services by capturing and retaining allochthonous nutrients from rain and , and supporting the presence of canopy pollinators and other fauna. However, predicted increases in temperature and rising cloud-based heights, as well as land use changes, threaten the abundance and capacity of epiphytes to contribute to ecosystem functions. It is unclear how the loss of epiphytes will impact microclimate and host tree water status. To investigate how loss of epiphytes might impact canopy water storage, we developed an idealized water balance model for epiphytic mats in TMCFs. We considered epiphytes in the host-tree as a water tank that is filled via rainfall and fog, and depleted via evapotranspiration and host tree water uptake, which results from the presence of canopy host tree roots. We test the model using average dry season conditions for a TMCF in Monteverde, Costa Rica. Results of the idealized model captures how epiphytes regulate water and energy fluxes in the canopy at diurnal scales. Evapotranspiration rates in this simulation matches expected values measured in the field from the literature. This model will aid in our understanding of the effects of climate change on canopy water storage in TMCFs.