Overview

Will increased atmospheric CO2 result in increased biomass in forest ecosystems? At the leaf scale, the evidence that elevated CO2 increases photosynthetic rates is overwhelming1. However, evidence of increased biomass is equivocal, particularly in mature stands2 For example, many previous FACE experiments were located in regrowing or disturbed stands. As a result, observed responses may simply have represented accelerated growth, rather than an increase in the long-term carbon store in forest ecosystems.

We know that not all trees benefit to the same extent from additional carbon dioxide2. Where within the forest do the largest growth enhancements due to carbon dioxide occur? Do younger trees benefit more than older ones? What does this mean for the carbon balance across whole ecosystems and even the globe? The work in this project will help to address a big uncertainty regarding the response of mature forest stands to elevated CO2.

This is crucial knowledge, because terrestrial ecosystems currently take up about 30% of all the carbon emitted by human activities each year3, reducing the rate of climate change. In order to understand if this uptake will continue, we have to understand the processes that lead to it.

This PhD project will seek to answer these questions using and developing a state-of-the-art model of terrestrial ecosystems, and combining it with observations from a mature experimental forest in the United Kingdom and other sites worldwide.

Trees within the rings are exposed to elevated levels of CO2. (bottom) Forest landscape as simulated by the LPJ-GUESS ecosystem model.

Methodology

The Free Air CO2 Experiments being conducted at the Birmingham Institute of Forest Research is the only research facility of its kind in the world, focusing on how mature temperate forests are affected by human emissions of carbon4. The LPJ-GUESS ecosystem model scales plant growth and function from the leaf, to the forest stand, to the globe. It is widely used in assessments of the role of terrestrial ecosystems in the global carbon cycle5, one of the largest uncertainties in future projections of climate change. Observations from these forests and other sources will be combined with the LPJ-GUESS model to test hypotheses regarding the role of nutrients, plant allocation decisions and competition between trees in enabling or limiting the growth response of forests to elevated CO2examine the sensitivity of carbon uptake to different forest structures. Ultimately the modelling system will be applied globally, assessing the contribution of different forest states to the global carbon cycle.

Training and Skills

The PhD student will split their time between the United Kingdom and Australia, benefiting from interaction with world-leading scientists in both communities. In addition to extending our knowledge of this exciting aspect of biosphere-atmosphere interactions, they will be exposed to the realities and limitations of gathering experimental data in the field, and develop transferrable skills in data analysis, computational modelling, code development and research communication.

CENTA students are required to complete 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. Throughout the PhD, training will progress from core skills sets to master classes specific to the student's projects and themes. 

Timeline

Year 1: Orientation at Birmingham. Training in use of ecosystem model and application to FACE sites. Opportunity to be involved in sampling work at the BIFoR FACE site and/or EucFACE.

Year 2: Sensitivity studies of forest carbon exchange in a range of forests, working with teams in Birmingham and Sydney.

Year 3: Scaling implications to the global carbon budget.

Partners and collaboration (including CASE)

The student will benefit from the formal collaboration agreement between the University of Birmingham and the University of New South Wales, which enables the exchange in this PhD. De Kauwe has extensive experience comparing ecosystem models to FACE experiements, and is also closely involved with the only other active forest FACE experiment at the University of Western Sydney, Australia. The student will also work closely with other developers of the LPJ-GUESS ecosystem model in Sweden and Germany.

Further Details

For further information please contact Dr Tom Pugh, School of Geography, Earth and Environmental Sciences, University of Birmingham.

t.a.m.pugh@bham.ac.uk