Investigating the role of fire in soil biotic processes and carbon storage at tropical grassland-forest transitions

Overview

Fire is an important process that shapes the structure, biodiversity and function of many ecosystems on Earth. In fire-prone systems, residues of incompletely burned biomass can form an important store of carbon (C) in soils and sediments, with inherently slow turnover times of its highly aromatic components (Bird et al., 2015). There is also a significant redistribution of nutrients associated with aerial deposition of ash, and lateral transport of fire residues by wind and water that impacts on ecosystem productivity. Projected changes in fire frequency and biomass production will likely impact on the size of this globally important soil C pool, but we so far lack an understanding of processes of stabilisation or decomposition of pyrogenic carbon (PyC) in soils to even predict the direction of this change. Key gaps in our understanding include:
• What are contributions of PyC to long-term soil carbon storage?
• What are roles of soil animals and soil microbial groups in the processing of fire-derived carbon in soils?
• What is the spatial distribution of mineral nutrients associated with wind and air-borne movement of fire residues?
• What is the role of fire return frequency on ecosystem productivity, nutrient availability and soil carbon storage?

Aim
This studentship addresses some fundamental knowledge gaps relating to the impact of grassland fires on ecosystem function. A strong focus of the proposed research programme will be on field-based observations, supported by lab-based process studies and advanced analytical techniques to elucidate the way in which pyrogenic carbon relates to carbon storage and other ecosystem functions.

Methodology

Field work for this project will be based in the Lope National Park in Gabon, which offers an ideal opportunity to investigate mechanisms by which biotic processes impact on the formation and decomposition of soil PyC. Situated in the middle Ogooue region of central Gabon, it covers almost 5000 km2 of equatorial tropical forest interspersed with a mosaic of savannahs in its northern and eastern parts. To protect savannahs from forest encroachment and maintain habitat diversity at the forest-savannah edge, a prescriptive fire management program has been in operation since 1993, where the majority of savannahs are burned annually, and a smaller area of around 7.9 km2 savannah units are either burned with a 2-3 year fire return frequency or completely protected from burning (Jeffery et al., 2014).

There has so far not been a comprehensive assessment of soil C stocks in the savannah-forest transition at Lope, and one aim of this project is to carry out a targeted soil C assessment in relation to fire frequency and vegetation biomass. In addition to this spatial survey of C stocks, we envisage a determination of other nutrients (primarily P and N) in relation to landscape position, fire interval and vegetation cover. For a sub-set of samples, we intend to determine the content of PyC within the soil profile.
Further experimental approaches include the determination of soil faunal abundances (or mostly invertebrate fauna) and microbial biomass. The in-situ assessments will be supplemented by lab-based studies in the UK on the interactions of PyC with soil fauna and specific microbial groups found in savannah soils.

Project Timeline

Year 1

Identification of field sites and detailed planning of sampling strategy; Method development for PyC sampling and analytical detection; skills training (elemental analysis, soil fractionation, CO2 flux measurements)

Year 2

Main sampling campaign; soil profiles of C and N stocks in relation to fire management; continued skills development (Spectral techniques to quantify PyC) and lab-based studies

Year 3

Finishing lab and field experiments; data evaluation, and publication of results

Year 3.5

Final stages of publications and thesis writing

Training
& Skills

1. Field work methods, including soil coring and processing, soil CO2 flux measurements and experimental design.
2. Soil faunal identification of key groups
3. General laboratory skills, including C, N and P determinations
4. Application of specialised analytical methods such as hydrogen pyrolysis for PyC determination in soil samples and stable isotope techniques.
5. Numeracy, data analysis, ecological modelling & informatics. These skills will be gained through targeted training courses within the IAPETUS2 consortium and available at Stirling.
6. Complementary training in transferable skills and core scientific skills (data management, analysis, presentations, paper writing).

References & further reading

Bird, M.I., Wynn, J.G., Saiz, G., Wurster, C.M., McBeath, A., 2015. The pyrogenic carbon cycle. Annual Review of Earth and Planetary Sciences 43, 273-298.

Jeffery, K.J., Korte, L., Palla, F., White, L.J.T., Abernethy K.A., 2014. Fire management in a changing landscape: A case study from Lope national park. PARKS 20, 35-48.

Further Information

Please contact Dr Jens-Arne Subke with any queries regarding this project:
jens-arne.subke@stir.ac.uk

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