Overview

Project Highlights:

  • This project will for the first time characterise how future CO2 levels impact tree water storage.
  • These results will better inform tree response to drought, and exactly how their water content can be used to characterise stress, and even death
  • This project will provide experience in multiple methods and techniques (e.g. sonic tomography, eddy flux, direct moisture sensing, modelling, remote sensing) and the opportunity to work in a globally-unique experimental forest.

Tree death in extreme droughts and heatwaves has been widely reported across all major forest biomes over the last few years (e.g.Hartmann et al., 2018; Lewis et al., 2011; Peng et al., 2011; Stovall et al., 2019), and the frequency and severity of such events is expected to increase in many regions. Yet our ability to predict how our forests will respond to extreme heat and drought is very limited. Major unknowns are how much water do trees hold inside themselves, under what conditions do they draw on these internal stores, and how will this be impacted by future environmental change? Whilst these are apparently simple questions, the water held by trees remains largely ‘hidden’ both for individual trees, and across entire forests. Yet we know water content is closely linked to drought resilience (e.g. Rao et al., 2019) and the hydraulic strategies of trees (Konings and Gentine, 2017). In addition, forests of the future may use water differently, depending on their climate and levels of carbon dioxide to which they are exposed. Therefore, a better understanding of how much water trees hold and when they draw on it will help improve everything from local forest and water management, to models of global vegetation dynamics and climate interactions. This project will look deeper into this hidden dimension of trees and the water they hold, and how this will change in the future, using multiple methods and techniques (e.g. sonic tomography, eddy flux, direct moisture sensing, modelling). In addition, it will provide a fantastic opportunity for the student to work at a globally unique experimental facility that is artificially enhancing the CO2 concentrations of an old growth oak forest in central UK (BIFoR FACE), and is producing ‘trees of the future’.

Trees can store a lot of water! Top right Image source: https://en.wikipedia.org/wiki/Terminalia_elliptica, installation of accelerometers in trees (left image, courtesy Tim van Emmerik), and the BIFoR experimental forest facility (bottom right).

Methodology

The BIFoR experimental forest contains mature oak trees subjected to either ambient or elevated atmospheric CO2 concentrations within an otherwise undisturbed setting. The student will utilise and contribute to relevant measurements already being conducted at the site (e.g. eddy covariance flux measurements, sap flow monitoring, soil moisture probes) and supplement these with direct measurements of tree water content using either sonic tomography or direct moisture sensors, or a combination of the two, depending on the outcome of exploratory tests. These will be used to develop a simple quantitative model of tree water storage to identify explicitly under what conditions trees draw on internal water storage as opposed to soil water. Parameters will thus be developed to inform representations of water storage in dynamic vegetation modelling. Connections with radar remote sensing will be investigated to potentially estimate tree water storage over large scales (in cooperation with a parallel project at Dresden).

Training and Skills

This is a fantastic opportunity to learn and apply a variety of measurement techniques to constrain tree water content. Learn both ‘big data’ methods and quantitative modelling. There will be substantial opportunities for travel and to build strong international links, collaborating with partners from across Europe.

The Doctoral Researcher will be supported in developing research communication skills, including presenting their work at international conferences and publishing their findings in high-impact journals.

Timeline

Year 1: Begin instrument installations and site measurements at the BIFoR FACE experiment.

Year 2: Continue field measurements, develop simple tree water balance model.

Year 3: Consolidate final field results, parameter development for vegetation models and comparisons with remote sensing. Work with project partners on policy implications

Partners and collaboration (including CASE)

A big emphasis of this project will be the opportunity to collaborate with international partners (Germany and Netherlands), as well as participate in a unique ecosystem level experiment to simulate trees of the future (BIFOR FACE).

The student will have the opportunity to interact with groups at Exeter University, Met Office and the JULES community, who have a similar interest in the effect of incorporating plant hydraulics into land-surface modelling.

The student will benefit from the large network of scientists taking part in the FACE project, based at Birmingham.

Further Details

To discuss the project, please contact:

Tom Pugh (t.a.m.pugh@bham.ac.uk) or Josh Larsen (j.larsen@bham.ac.uk)