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Overview

What exactly are the climate benefits of forests? This project seeks to train a student to answer this question for temperate forests using the latest analytical techniques to examine how trees exchange powerful greenhouse gases with the atmosphere. In doing so they will add to existing knowledge on CO2 exchange and sequestration in forests. Trees are well known to exchange CO2 and water vapour with the atmosphere. However, it has recently been shown by the Open University group that trees on free draining soils can also exchange the powerful trace greenhouse gases methane (CH4) and nitrous oxide (N2O). This overturns our current understanding of how forest ecosystems function since only forest soils are currently considered as exchange surfaces for these gases.  This is important as 1) CH4 and N2O are ~30 and 300 times more powerful than CO2 at trapping incoming solar radiation and 2) tree stem surfaces can represent a much larger exchange surface than the soil surface. With a limited number of flux measurements from upland tree stems in the Amazon, Panama, the UK and Sweden, there is evidence that tree trunk bases can emit CH4 and N2O but this switches to uptake above breast height. The net effect for tropical and boreal forests is that trees can enhance uptake of CH4 which makes the trees as large a methane sink as the soils in which they are growing.  Our limited studies of UK forest, however, show that trees can switch from net sinks to sources of CH4 depending on the season. It is therefore critical to identify the direction of exchange of fluxes of CH4 and N2O in UK forests and their controlling variables since this has important implications for the UKs greenhouse gas inventory as well as for properly quantifying the climate impact of the biofuel and timber industries. Should UK temperate forests show a similar net uptake of CH4 as tropical and boreal forest this would mean that natural forest and the timber and wood-based biomass industries may be more climatically beneficial than previously thought.

Methodology

The student will quantify methane and N2O exchange at a range of scales over full annual cycles at a Forest Research managed oak woodland in Surrey, UK (Alice Holt).  There, two methods will be employed, firstly eddy covariance using the latest analytical instruments positioned on a tall tower to measure ecosystem scale exchanges of methane and N2O and secondly, flux chambers at the forest floor/tree stem level in order to quantify the various exchange paths of the greenhouse gases in question and reconcile them with the tower measurements. The chamber measurements will be made using a combination of syringe sampling (for later analysis at the Open University) and in situ sampling and analysis using laser spectrometers.

Training and Skills

The student will gain training in the latest equipment for the measurement of N2O and CH4 using both eddy covariance (EC) and chamber methods at the Forest Research field site at their Alice Holt site in Surrey. The OU researchers specialize in chamber methods from soils and tree stems whereas Forest Research have an eddy covariance tower in operation and the latest optical methods for measuring N2O at high temporal resolution integrating over a large forest footprint. VG and SY have been developing the project for some time and all required expertise to train the student is in place. KM is a plant physiologist with expertise in EC across a range of landscapes.

NERC CENTA students are required to complete 45 days training throughout their PhD including a 10 day work 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 CENTA research themes. 

Timeline

Year 1: Perform a literature review, identify monitoring sites. Learn the eddy covariance technique and establish the soil and tree collar setup to commence monitoring.

Year 2: Perform the bulk of the measurements of methane and N2O. Identify, for a single measurement campaign, how the bottom-up and top-down measurements correspond.  Submit manuscript 1 on initial findings/early campaign. Present at British Ecological Society.

Year 3: Finalise data collection and analysis, submit manuscripts 2 and 3 on each of CH4 and N2O fluxes at all scales, and complete thesis, present at European Geophysical Union in Vienna.

 

Partners and collaboration (including CASE)

The project benefits from close collaboration with the CASE partner institution Forest Research. They have excellent access to well instrumented and monitored forests and they have expertise in eddy covariance methods of quantifying GHG exchange at the ecosystem level.

 

Further Details

Students should have a strong background in ecology/geography/environmental science be numerate together with an enthusiasm for fieldwork. Experience of fieldwork is desirable. A full UK driving license is essential. The student will join a well-established team researching forest ecosystems at the Open University and at Forest Research.

Please contact Prof. Vincent Gauci (v.gauci@open.ac.uk) for further information.

Applications should include:

 

Applications should be sent to

STEM-EEES-PhD-Student-Recruitment@open.ac.uk  

by 5 pm on Monday 22nd January 2018