Collaborative Research: Dry in the sky? Ecophysiological Strategies and Drought Tolerance among Tropical Montane Cloud Forest Canopy Epiphytes

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Epiphytes, plants that live on other plants, reach their peak of diversity and abundance in Tropical Montane Cloud Forests (TMCF). In this ecosystem, epiphytes play important ecosystem roles because they intercept and hold on to nutrients and water from rain and mist and provide food and resources for many birds, animals and insects. Because these plants do not have access to soils and water from the ground, they are particularly vulnerable to changes in climate, including increases in cloud height and drought. This research will determine the degree to which epiphyte communities are vulnerable to decreases in precipitation or cloud cover, and increased forest fragmentation. This project will also develop a training program in canopy ecology for ecotourism operators in Monteverde, Costa Rica. This region hosts over 100,000 people per year for canopy adventure sports but few tourists or guides get information on the importance of the TMCF in general and the epiphyte community specifically. The team will also provide training and presentations to local research and educational institutions in the Monteverde region including the Monteverde Reserve, the Monteverde Institute and local high schools.Despite evidence that the canopy community as a whole is important to ecosystem processes, there is little information regarding the ability of this community to withstand projected changes in climate and/or increases in exposure due to deforestation. In the TMCF, there is great variation in growth forms in the canopy that may differ in their vulnerability to decreases in precipitation or increases in cloud base heights. Although efforts have been made to understand individual species responses to drought stress, little is known about variability in drought-stress responses and the ability of plants to cope with projected future drought conditions. By working in this hyper-diverse, but relatively understudied system, this research will increase the understanding of a fundamental topic in plant ecophysiology: the diverse ways plants respond to drought. Variability in microclimate across the six sites provides a unique opportunity to identify suites of drought-stress responses across functional groups and determine whether these traits vary, or respond plastically, to changes in the environment. Functional morphological traits, water relations, water use, and vulnerability to drought will be measured across the gradient to document variation in ecophysiological strategies in plants that are exposed to different microclimates. Photosynthetic strategies will also be evaluated along the gradient using stable isotopes. Canopy communities in open pasture trees will also be studied because these exposed communities tend to experience greater water stress within a given precipitation regime and may provide insights on how canopy communities are likely to be affected by increases in drought stress or forest fragmentation. To assess the role of suites of functional traits on drought resistance, a subset of common species from three of the sites (wettest, intermediate, driest) from both forests and pastures will be subjected to a manipulative drought experiment.