Why are some trees more sensitive to climate than others?

Why are some trees more sensitive to climate than others? A study on the functional linkage of tree hydraulics and their sensitivity to climate

Trees are amazing! Over the course of their life, trees transport millions of liters of water from the soil through their vessels and leaves into the atmosphere. They play an important role in the regulation of the earth’s climate by affecting the hydrological cycle, cooling the earth, and by storing large amounts of carbon. Understanding the response of trees to a changing climate is therefore important to predict how forests and the earth will look like in the future.
Trees show strong differences in their responses to climate. While some trees succumb even under mild drought others are able to survive and even continue growing under severe droughts. These differences are related to the trees’ specific properties or traits. One important plant trait explaining differences in trees climate response is that linked to their water transport, and the trade-off between water transport efficiency and safety (Sperry et al. 2008). Trees that are more efficient at water transport due to greater hydraulic conductance are believed to be more sensitive to inter-annual variation in climate. In contrast, trees with more conservative water use strategies and a “safer” hydraulic transport system may maintain a positive water balance throughout drought periods. Recent studies show that forests with more diverse hydraulic traits are more buffered to changing drought conditions. Thus, hydraulic traits play an important role in forest functioning.
At the same time, there is also evidence for an important role of carbohydrate reserves (eg. starch) for tree functioning. Carbohydrate reserves can be used in bad years thus providing resilience to inter-annual variation in climate. Thus, besides hydraulics other traits may also play an important role in protecting trees from the impacts of strong year-to-year climate variation.

The aim of this PhD project is to
1. Assess the global linkage between trees’ climate sensitivity and their functional traits;
2. Evaluate how functional traits and climate sensitivity change with tree size and age.
3. Provide recommendations for Improving predictions of trees’ responses to future climate.

Despite, recent progress in understanding trees’ physiological responses to variation in climate, the governing principles to predict trees’ resilience to climate remains poorly quantified. In this study, you will provide the first global assessment of trees’ climate sensitivity and link these to species’ functional traits. To this end, you will use the International Tree Ring DataBase (ITRDB) to assess the inter-annual response of trees to climate, and link those responses to the trees functional characteristics, especially those traits related to hydraulics. In addition to using existing datasets, you will in this PhD also collect new tree ring and trait data on a few tropical and temperate tree species. This will involve fieldwork in the tropics (most likely in the Amazon) and in Europe.

You will work under the supervision of a strong team of earth system dynamics experts within the Ecology and Global Change research group of the School of Geography. Direct daily supervision will be done by Dr. Roel Brienen, Prof. Emanuel Gloor and Dr. David Galbraith. You will also benefit from working within a highly active and multidisciplinary group of scientists in the Leeds Ecosystem, Atmosphere & Forest (LEAF). The school of geography has excellent and state-of-the-art laboratory facilities including a full equipped tree ring lab.
You are expected to have strong interests in environmental and earth system science and global change. You also should have some background in disciplines such as mathematics, physics, geography, biology, or environmental science. Strong analytical skills are required.