Overview

The world’s forest ecosystems provide or mediate many services to society, and to the planet, including removing huge amounts of CO2 from the atmosphere every year1, modifying water runoff, and fundamentally influencing the local climate. Yet it is highly uncertain whether forests will continue to function as they do now under the changing environmental conditions projected for the coming century and beyond.

The behaviour of mature trees in particular is not well established, because the experiments required are of a magnitude very seldom seen in terrestrial ecology (Figure 1). Free-Air Carbon Dioxide Enrichment (FACE) facilities are the most direct and robust platform to study the effects of elevated CO2 on woodland/forest ecosystems, benefitting directly land surface models2.
The Birmingham Institute of Forest Research (BIFoR) FACE facility forms part of a unique global machine investigating forest response to elevated CO2 (ref. 2). Set in temperate broadleaf oak-with-hazel woodland (Mill Haft, Staffordshire, UK3), BIFoR-FACE tests hypotheses derived from models, lab-based and mesocosm studies of forest carbon and water cycling in a fully-open and complicated real-world ecosystem.
This doctoral project focuses on the impacts of drought and heat, and the effect of outbreaks of insect pests on forest biogeochemistry (i.e., C, N, P cycling). These processes have caused widespread forest mortality in recent years, and their incidence is expected to increase in the future, as extreme environmental conditions become a more frequent occurrence. Yet existing global projections of future carbon storage and climate are based on models that do not capture how real trees die, omit major disturbance forms, fail to capture interactions between drought, insects, and other stressors, and perform poorly in comparison to observations of mortality events4.

Research Questions:

  1. Can a large-scale terrestrial ecosystem model simulate forest stress and mortality in present environments?

  2. How does a more accurate model of forest stress & mortality modify projections of global biogeochemical and hydrological cycles, and thus climate?

Objectives:

  1. To improve representations of tree stress & mortality within the dynamic global vegetation model LPJ-GUESS

  2. To validate the new model against existing mortality datasets and against detailed stress data from BIFoR FACE; and

  3. To produce global estimates of the impact of forest mortality on the carbon, water, and nutrient (N, P) cycles.

Clockwise from top-left: schematic of leaf gas-exchange showing the fundamental connection between carbon assimilation and water loss; BIFoR research woodland Mill Haft; schematic of land surface model processes; and BIFoR FACE ring foundations at Mill Haft.

Methodology

This PhD connects to a major international modelling programme using the LPJ-GUESS global vegetation model, and the possibility to run this coupled to an Earth System Model. It is also integral to a major FACE programme investigating the response of mature forest ecosystems to elevated CO2.

Modelling
LPJ-GUESS is a world-leading model for simulating vegetation dynamics such as establishment, mortality, and plant succession, along with the resultant effects on biogeochemical and hydrological cycles. LPJ-GUESS also includes models of nitrogen cycling, fire, and anthropogenic management. The project initially requires the design of experiments for the current model, and then developments of the model code for subsequent steps.

Fieldwork
It is vitally important that modellers understand the strengths and weaknesses of the observational data they use to develop and challenge their models. The student will work alongside fieldwork researchers carrying out studies of the ecophysiology of mature woodland under climate change at BIFoR FACE, and be involved in the interpretation of results.

Training and Skills

The Doctoral Researcher will receive key training from the University of Birmingham in Earth system modelling, and associated visualisation systems. There will be close cooperation with researchers working at Mill Haft, and participation in interpreting BIFoR FACE data. The Doctoral Researcher will be supported to present their work at international conferences and publish their findings in high-impact journals. There will be the opportunity to attend selected modules from MSc courses taught within the School.

CENTA students will benefit from 45 days training throughout their PhD including a 10-day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Training will progress from core skills sets to a bespoke set of master classes specific to the student's project. Attendance at the national Earth system modelling summer school will be obligatory and attendance at other relevant training schools will be strongly encouraged.

Timeline

Year 1: Induction, literature review, simple initial model runs, CENTA training. Fieldwork shadowing. Study visit to Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany.

Year 2: Model development. Analysis of BIFoR FACE ecophysiology data.

Year 3: Final model runs, conference attendance, thesis and publication preparation.

Partners and collaboration (including CASE)

Supervisory team: Dr Tom Pugh is vegetation modeller with expertise in the LPJ-GUESS global vegetation model and EC-Earth Earth System Model; Dr Jeremy Pritchard is a plant scientist with experience in plant hydraulics; Prof Rob MacKenzie leads BIFoR.

CASE partner the UK Met Office will provide additional modelling training and advice on forest ecophysiology under climate change.

Further Details

The PhD studentship with be held at the University of Birmingham, linking strongly to the LPJ-GUESS team at the Karlsruhe Institute of Technology, IMK-IFU, Germany.