Background/Question/Methods: Tropical montane cloud forests make up only 1.4% of the world’s tropical forests, yet despite their rarity they make a tremendous contribution to global biodiversity with large numbers of endemic species. These critically threatened forests perform ecosystem services important to many people in developing countries, including cloud-water interception which reduces downstream erosion damage and river flooding, and aids in the supply of drinking water year-round. Climate change is predicted to cause an increase in global temperature and a rise in elevation and disappearance of the cloud-base that supplies water to these forests. This saturated cloud-base and the nutrient-rich water subsidies it provides are principally what define a cloud forest, and are essential to the growth and survival of cloud forest species. As such, it is critical to study the vulnerability of cloud forest trees to shifting water availability in order to predict how these forests might respond to a changing climate. Plant sensitivity to water deficit can be directly measured by uncovering their strategy for maintaining a balance between water conservation and growth. For each species, this tradeoff defines its hydraulic strategy. Here we investigated the plant hydraulic strategies of congeneric pairs of tree species in differing cloud forest and premontane habitats along a Costa Rican tropical montane gradient by quantifying vulnerability to embolism and stomatal regulation in response to water loss. These measurements allowed us to create a hydraulic “safety margin” for these tree species that assess how vulnerable or resilient they are to drought.
Results/Conclusions: Our results show a diverse number of hydraulic strategies and safety margins between congeneric species pairs, indicating differing levels of vulnerability between habitats. Most notably, cloud forest species showed greater safety margins than hypothesized, which may suggest greater resilience to drought than previously anticipated. This research will address knowledge gaps regarding the vulnerability of tropical trees in response to drought, and contribute to the conservation of forests in the face of climate change