OOS 20-3 - A novel model for epiphytes as canopy water tanks

Tropical Montane Cloud Forests (TMCFs) are the headwaters of globally important watersheds, including the Amazon and Congo rivers, and serve a source of fresh water to populations downstream. TMCFs are hotspots of biodiversity, and epiphytes are a common component of these ecosystems. Epiphytes are vascular and non-vascular plants that exist in forest canopies attached to the branches of host trees. They promote improved microclimatic conditions for neighboring plants by regulating air temperature and humidity. However, the physical processes by which epiphytes control canopy microclimate are not well understood. Here we present a physical-based, uncalibrated model to simulate how epiphytes store water and exchange energy within the canopy. In the model, we conceptualize epiphytes as a water tank where water enters via fog, precipitation, and dew deposition. Water exits the epiphyte tank primarily through evapotranspiration, but we also consider host-tree water uptake by aerial roots. Preliminary results demonstrate that epiphyte temperatures have a phase lag with air temperature, and this lag is responsible for regulating diurnal conditions within the canopy. Under clear sky conditions, epiphytes increase humidity in the canopy during the afternoon, and reduce evapotranspiration at night. This work will improve our understanding of canopy-atmosphere interactions that enable TMCFs to support high biodiversity, which is important as these areas are threatened by climate change and land conversion.