From plant traits to vegetation structure/Des traits des végétaux à la structure de la végétation

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I view community assembly as a selection process occurring at the level of individuals belonging to different species, based on the adaptive fit of functional traits to prevailing environmental filters. This general framework, continued in this proposal, has been pursued using a combination of comparative experiments under controlled conditions, manipulative field experiments, observational studies along environmental gradients and mathematical modelling. The general goal of my research program is to answer the following general questions: Given a regional species pool (a list of plant species that are found in a region), a knowledge of the values of key functional traits of these species, and the environmental conditions found in a local community within this region, which species from the species pool will be found at this site? Which of these species will be dominant, subdominant or rare? How will the answers to the first two questions change if we were to change the position of this local community along important environmental gradients? How does the multivariate distribution of trait values within a community affect important ecosystem properties like primary productivity, nutrient cycling and litter decomposition?*I recently (2010) published the general theoretical model of my understanding of trait-based community assembly ("From plant traits to vegetation structure: Chance and selection in the assembly of ecological communities", Cambridge U Press). In this next 5-year proposal my students and I will be testing and expanding this understanding based on five specific research projects. A current PhD student (Jessy Loranger) will use a unique set of 11 long-term field experiments throughout France, involving community composition, plant traits and environmental gradients, to test my general model ("CATS: Community Assembly by Trait Selection"). A second PhD student (Michaël Belluau) will conduct a series of controlled experiments involving 40 contrasted herbaceous dicots, field observations, and multivariate modelling to better link multiple correlated patterns in leaf economic traits and plant hydraulic architecture to precisely measured levels of water stress. This is currently a relatively poorly studied stress in herbaceous species. A third PhD student (Yuanzhi Li) will be exploring a little-recognized implication of trait-based community assembly that is linked to the classical notion of limiting similarity: if communities are assembled while requiring a certain minimum amount of overlap in multivariate trait-space, then the total area of trait-space occupied by communities must expand as species richness increases. Yuanzhi will test these ideas using an existing long-term replicated experiment involving 24 1X1X1 m3 field mesocosms that initially received the same seed mixture but that differ in levels of soil fertility as well as the intensity and frequency of disturbance. The last two projects involve students yet to be recruited. One MSc student will conduct field and mesocosm experiments by manipulating soil water availability in order to test whether the trait syndromes related to water stress of actual and created plant communities, identified by Michaël Belluau (PhD student) change as predicted. A second MSc student will measure ecosystem responses (primary productivity, nutrient loss and litter decomposition) in the longterm mesocosm experiment and relate these responses to differences in community weighted trait values and their variance.*These research projects will contribute to the longterm goal of predicting plant community structure and functioning from generalizable plant traits.