Tropical forest demography and the interactive influences of climate and species traits

International audience

English. Moist tropical forests are some of the most diverse and productive ecosystems on Earth, and are both critical and vulnerable to climate change. Tree demography defines forest dynamics, and is therefore at the core of the response of species, population, and whole communities to environmental changes. Tree growth and survival are two central components of fitness and are greatly responsible for forest composition, diversity, structure and their dynamics. They also control the carbon uptake from, and release to the atmosphere, such that understanding their response to climatic variability is important both to predict tropical forests response to climate change, but also to understand how they will themselves feed back into the changing climate. Because species evolved different life strategies, and allocate resources differently into their growth, defense and survival, and reproduction, and given the huge species diversity of tropical forests, a major challenge remains to understand the diversity of demographic responses to climate observed across species. Using functional traits that approximate some of the allocation trade-offs to different functions could be a way to better understand the mechanisms underlying the variability of tree growth and survival sensitivity to environmental conditions and their variations.I will present work that my colleagues and I did in the old-growth moist tropical forests of northern Australia, where we studied the responses of tree growth and survival to climate, taking advantage of a unique dataset consisting of 50 years of regular censuses for over 20 plots encompassing an elevation gradient, and where morphological, chemical and physiological traits were measured. We will emphasize the importance of species-specific demographic responses to the environment, how functional traits can (sometimes) provide cues to approach potential underlying physiological mechanisms, and will discuss some recent results emphasizing an increasing tree mortality in the past decades in these forests.