Abstract
Forests experience major changes in climate worldwide, but boreal, temperate and tropical forests are expected to be affected in different ways. Understanding the responses of these biomes to climate change, and reducing uncertainties therein, should be based on the growth mechanisms of trees. The Forest Ecology and Forest Management Group at Wageningen University leads projects that address the issue of impacts of climate change and extreme events on trees and forests across the globe, for example in China, Europe and the tropics, including in Brazil. We have shown possible impacts of climate on growth mechanisms of trees in those areas, but for improving our understanding and predictions, we require better, comparative, information on hydraulic bottlenecks in trees, which act as key drivers of tree responses to drought and warming. Rafael Oliveira is a world leading expert in those hydraulic bottlenecks in plants, and in upscaling such relationships to whole plant performance and species distributions. We therefore invite him to participate in our projects, participate in discussions on results and new plans, and participate in some of the research papers that we are currently writing. In addition, Oliveira will train the FEM team in the latest techniques, developed by Oliveira and his team (Pereira et al. 2016), for measuring hydraulic bottlenecks in trees, and thus transmit this crucial knowledge, and test the equipment, during his visit for later implementation in our projects worldwide. Over the past years, our studies have shown that drought is a major driver of variation in the performance of trees and tree species along climate gradients both in Europe and across the tropics, and that functional traits and physiological mechanisms underlying the hydraulics of plants are key for understanding such variation (e.g. Markesteijn 2011, Sass-Klaassen et al. 2016, Schippers et al. 2015, Sterck et al. 2011, 2014, 2016, van der Sleen et al. 2015, Zuidema et al. 2013). Yet, these studies also showed that there are major gaps in such understanding: while we can upscale hydraulic bottlenecks to entire trees (e.g. Sterck and Schieving 2011, Sterck & Zweifel 2016), the uncertainly on predicted growth rates remains high (Zuidema et al. 2013), particularly because we lack sound comparative information on the hydraulic bottlenecks in trees (van der Sleen 2015, Steppe et al. 2015, Sass-Klaassen et al. 2016). Over the coming years, we aim at measuring the conductivity of stems and the vulnerability of stem to drought (via cavitation of water column in the stem) in a comparative way in our different study systems. The most advanced and practical methods for this have been developed in the lab of Rafael Oliveira, and we will take the opportunity to establish this equipment with him in our labs, and start testing a series of measures with him on a sample of our species. This critical information is required for better quantifying key bottlenecks in the hydraulics and their consequences for the growth of trees and forests.
Netherlands