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Harvard Forest Research Project 2022

  • Title: Xylem vulnerability in trees: linking xylem connectivity with patterns of vascular failure
  • Principal investigator: Michele Holbrook (
  • Institution: Harvard Forest
  • Primary contact: Michele Holbrook (
  • Team members: Craig Brodersen; Kate Johnson
  • Abstract:

    Increasingly frequent and severe drought events are leading to forest mortality around the world (Brodribb et al. 2020; Pachauri and Meyer 2014) making it critical to understand how drought leads to tree death. Failure of the plant water transport system (vascular failure) is a major driver of drought induced plant death but the basis and dynamics of this process are poorly understood (Anderegg et al. 2016; Choat et al. 2012). Powerful new optical and X-ray imaging technologies allow us to visualise the functional status of the plant water transport system and vascular failure under drought conditions in real time, for the first time (Brodribb et al. 2016a; Brodribb et al. 2017; Cochard et al. 2015). This presents the opportunity to investigate mechanistic links between the physical properties of the plant water transport system and vascular failure.

    Uncovering which species are vulnerable to drought (and why) will allow us to predict the compositions of our forests in the future. Thus, understanding the links between anatomy and the process of vascular failure will have critical implications for predicting and mitigating the impacts of drought on forests and the many climatic and ecological processes that they underpin.

    Here we propose a novel application of recently developed, non-invasive imaging techniques to investigate the link between the anatomy of the water transport system and the process of drought-induced vascular failure leading to tree death. We expect that differences in connectivity of the water transport system will be associated with both distinct patterns in the spread of vascular failure and the speed of drought induced death. By combining real-time observations of vascular failure data from both northern and southern hemisphere tree species with high resolution information on the arrangement of the plant water transport system, this project aims to:

    1. To determine whether differences in the anatomy of the plant water transport system are driving differences in the spread of vascular failure within and between tree species and whether this affects the vulnerability of trees to drought-induced death.
    2. To investigate the stark differences observed in the progression of vascular failure in the two main tree groups, flowering trees and cone-bearing trees.
    3. To use the information generated in (1) and (2) to parameterize a forest mortality model that specifically considers vascular failure and the environmental conditions that push trees beyond their tipping point.