PhD Research Project: NERC CENTA - Death and the carbon cycle: Hydraulic failure and recovery of tr

Location
United Kingdom
Posted
Nov 30, 2016
Closes
Jan 23, 2017
Organization Type
University and College
Hours
Full Time
Details

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 the hydrological cycle, 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.

One crucial question is whether increased temperatures will lead to a large increase in drought-related mortality in trees. Such an outcome could transform the shape and function of global forests and release a huge amount of CO2 to the atmosphere.
The mechanisms by which trees dies from drought have long been controversial2, but recent evidence strongly indicates that hydraulic failure, i.e. a stress-induced inability to transport water through the plant, is a major cause3. There is evidence that trees may maximise their competitiveness by running very narrow safety margins with respect to drought, yet it is possible that the incredible diversity of tree species in some forests will prevent a wholesale forest die-off under climate change. This exciting doctoral project focuses on trying to answer the pressing question of whether future drought is likely to cause widespread global tree mortality. It will develop a treatment of drought mortality within a state-of-the-art global ecosystem model, and use this model to assess rates of tree mortality under environmental change, and the impact that such mortality has on ecosystem services such as global carbon storage. There will be the opportunity to work with field data from the BIFoR experimental woodland, and on international case studies. The modelling tool used forms part of a major Earth System Model, and thus there will be the potential for developments in this project to propagate directly into the results of major ecosystem and climate assessments, such as future assessment reports of the United Nations Intergovernmental Panel on Climate Change.

Research Questions:
1) Can a large-scale terrestrial ecosystem model simulate drought stress and mortality in present environments?
2) How does a more accurate model of drought mortality modify projections of biogeochemical and hydrological cycles, and thus global climate?

Objectives:
1) To improve representations of plant hydraulics & mortality within the dynamic global vegetation model LPJ-GUESS;
2) To evaluate 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 drought mortality on the carbon, water, and nutrient (N, P) cycles.

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.

Funding Notes

In addition to completing an online application form, you will also need to complete and submit the CENTA studentship application form available from www.centa.org.uk.

CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will receive the following financial support.

Annual stipend, set at £14,296 for 2016/17
Research training support grant (RTSG) of £8,000

CENTA students are required to undertake from 45 days training throughout their PhD including a 10 day placement.

References

1) Ciais, P. et al. Carbon and Other Biogeochemical Cycles. Intergov. Panel Clim. Chang. 465–570 (2013).
2) McDowell, N. G. et al. The interdependence of mechanisms underlying climate-driven vegetation mortality. Trends Ecol. Evol. 26, 523–532 (2011).
3) Anderegg et al., Meta-analysis reveals that hydraulic traits explain cross-species patterns of drought-induced tree mortality across the globe. PNAS. doi: 10.1073/pnas.1525678113
Further details:
The PhD studentship with be held at the University of Birmingham, linking strongly to the LPJ-GUESS teams at Lund University, Sweden, and Senckenburg Biodiversity and Climate Research Centre, Germany.