PHLOEMAP · Hydraulic functional traits as determinants of forest function and drought responses. Putting xylem and phloem attributes into the functional trait map.

Hydraulic functional traits as determinants of forest function and drought responses. Putting xylem and phloem attributes into the functional trait map.

Forests provide key ecological services such as the regulation of energy, carbon and water balances from local to global scale. These are however under severe pressure due to climate and land use changes, especially in the Mediterranean basin where limited water availability is prominent. It is thus crucial to identify the forest species and areas that are likely to be more vulnerable to reduced water availability and establish how changes in forest composition and structure will impact key ecosystem services. In this project, we used the functional trait concept to bridge between tree, population, species and forest level to enlarge our capacity to predict where and when dramatic changes in forest ecosystem services are likely to occur. We focussed on the role of the xylem and phloem tissue and cells in tree and forest functioning in relation to drought. Our objectives were to (1) compile an extensive dataset of xylem and phloem trait values representing the trait variability existing along gradients in water availability at regional scale addressing both within-species and between-species variability; (2) integrate this set of xylem and phloem traits with a comprehensive set of other hydraulic and functional traits; (3) use the integrated dataset to study trait relationships and describe tree responses to drought so to determine the combination of traits that is the best predictor of drought resistance at intra- and interspecific level; and (4) test how and to which extent variability in xylem and phloem traits influences forest performance at different ecological scales and forest vulnerability under climate change scenarios. The expected final conclusions of the project are: - About one fourth of trait variability can be attributed to the within-species level and should thus not be neglected when forecasting responses of trees and forests to climate change. - Trait variation is larger between species than between populations of the same species with water availability not having a large direct effect on branch tissue proportions and conduit sizes lowering forest adaptation possibilities to environmental changes. - Strong conclusions on whole-tree performance under changing environmental conditions should at least incorporate several hydraulic traits.

Data: CORDIS, © European Union