Drought in tropical forests: the role of tree height and wood density for hydraulic efficiency, productivity and vulnerability to cavitation of trees along a lowland precipitation gradient (tropical moist to seasonally-dry)

• Applicant: Professor Dr. Bernhard Schuldt
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 253019017

Several studies have reported accelerated tree mortality in tropical moist as well as dry forests in response to severe drought periods in the past. Although it still remains unclear how tropical trees will respond to increased drought frequency as predicted by several climate change scenarios, it is safe to conclude that drought will cause major shifts in community composition and ecosystem functioning in tropical forests in the future. The mechanisms leading to drought-induced mortality in trees are far from being understood, but it appears that large and tall tropical trees are carrying a disproportionally higher risk for drought-induced tree mortality than smaller and understory trees, both in seasonally-dry and in perhumid tropical environments. Tropical trees with light wood seem also to be at greater risk of drought-induced die-back, but the related findings are less consistent. Both tree height and wood density are thus thought to be key functional traits influencing growth and survival, but they have rarely been studied in adult trees along environmental gradients in combination with hydraulic measurements with the aim to predict the trees susceptibility to drought. In the light of climate change, there is an urgent need to identify easily measurable functional traits that determine the drought sensitivity of tropical trees of contrasting tree functional types and communities in order to assess the vulnerability of tropical forests.The proposed project aims at examining the interrelationship between hydraulic architecture, water consumption, productivity, carbon investment in storage pools and vulnerability to cavitation and their assumed control by wood density and tree height in a large sample of tropical trees across a precipitation gradient in Costa Rica. In close collaboration with Costa Rican scientists, 40 tree species (200 mature trees) will be studied comparatively in five perhumid to seasonally-dry lowland forests. By measuring a set of productivity-related (wood production, non-structural carbohydrates, tree height), hydraulic (hydraulic conductivity, P50, sapflux density) and anatomical parameters (vessel dimensions, wood density) from the stem and sun-canopy branches, 12 hypotheses on the interrelationship between anatomy, carbon relations and water relations in the trees with different phenology (evergreen vs. deciduous), physiological constitution (isohydric vs. anisohydric) and drought exposure will be tested. These findings will help to clarify whether hydraulic failure and/or carbon starvation are the primary causes of drought-induced die-back, and to identify easily accessible key functional traits that determine the drought-sensitivity of tropical trees in perhumid to semi-arid climates.

• DFG Programme: Research Grants
• International Connection: Costa Rica
• Participating Persons: Dr. Dagoberto Arias Aguilar; Professor Dr. Henrik Hartmann; Oliver van Straaten, Ph.D.; Dr. Nelson Zamora