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Organized Oral Session

Session: : Living on the Edge: Resilience, Vulnerability and Ecosystem Feedbacks in Epiphyte Communities

OOS 20-6 - Epiphyte removal alters host tree microclimate and physiological processes in a Costa Rican tropical montane cloud forest

Tuesday, August 8, 2023
11:15 AM – 11:30 AM PDT
Location: 253
With cloud base height expected to rise in tropical montane cloud forests (TMCFs) as a result of climate change, epiphytes could be cut off from a vital source of water, leading to widespread mortality. The loss of these epiphytes could potentially affect the host trees on which they live, but little is known about epiphyte-host interactions in these systems. Our study seeks to address this knowledge gap with a whole-canopy epiphyte removal experiment in the TMCF region of Monteverde Costa Rica.

We selected ten pairs of trees; in each pair one canopy was completely stripped of epiphytes (“experimental tree”) and the other served as a control. Pairs were stratified by land use; five pairs were located within intact forest while five pairs were isolated in pastures. We instrumented all 20 trees with microclimate, sapflow, soil moisture, and growth sensors and began building a continuous dataset that will be collected until 2025. This presentation will focus on insights gained from the first year of data collection.

Preliminary results of the tree-level time series show that sap flux velocity correlates strongly and positively with solar radiation and vapor pressure deficit (VPD). The effect of experimental treatment was much stronger in pasture trees than forest trees, which was likely due to the buffering effect of neighboring canopies. Comparing experimental trees to control trees in the pasture, solar radiation, VPD and leaf wetness were all higher. In contrast, sap flux velocity was lower in pasture experimental trees. In forest trees there was a small increase in solar radiation (comparing experimental to control trees), but no change in VPD, leaf wetness, or sap flux velocity.

The slower sap flux velocity in pasture experimental trees suggests that these trees may be regulating water loss as a result of the increased atmospheric water demand brought about by the loss of the epiphytes. The implication is that the loss of epiphytes in pasture ecosystems could harm the ability of host trees to photosynthesize, potentially starving them of carbon .