School of GeoSciences

School of GeoSciences

PhD Topic: Measuring and Modelling Carbon & Water Dynamics of Longleaf Pine Savannas from a Plant Functional Group Perspective

Jennifer Wright

I am a 4th year PhD student working with Prof. Mathew Williams at the University of Edinburgh, Dr. Robert Mitchell at the Joseph W. Jones Ecological Research Centre and Dr. Gregory Starr at the University of Alabama. Currently, my research focuses on carbon dynamics in savannas, with particular regard to the roles of different functional groups, the influence soil moisture has on these roles, and how they might respond to changing climate. My PhD focuses on combining different datasets (plant ecophysiology, stand inventories, phenology) with a process based model (SPA) to partition eddy-covariance data into the contributions of various functional groups. To do this I am adapting the SPA model to better reflect a savanna ecosystem by allowing simultaneous modelling of C3 and C4 photosynthesis and deciduous and evergreen species. This research has taken place in the longleaf pine savannas of the southeastern US and addresses the following aims:

  1. Modelling the productivity of Pinus palustris across a soil moisture gradient and exceptional drought.
    Paper Title: Measuring and modeling leaf and stand scale productivity across a soil moisture gradient and a severe drought
    In review Plant Cell and Environment

    Pinus palustris is the dominant, by biomass, species in longleaf pine ecosystems and naturally inhabits a wide range of soil moisture conditions, from well drained deep sandy soils known as "sandhills" to wetter, more clay dominant soils known as "flatwoods". This section of my PhD focussed on assessing and modelling the ecophysiology and phenology of longleaf pine at wet and dry sites in both non-drought and drought conditions. Modelling the pine-only component allowed me to determine what proportion of the fluxes measured from eddy-covariance towers at both wet and dry sites were due to pine photosynthetic activity. I also looked at how productivity and its limitations varied from the leaf to landscape scale across this soil moisture gradient and through an exceptional drought.

  2. Comparative ecophysiology of functional groups in a longleaf pine savanna
    Paper Title: Comparing plant hydraulic functional roles across a soil moisture gradient and severe drought

    Building on the work done on pine discussed above, I collected similar data for the other two main functional groups of longleaf pine savannas: oaks and understorey grasses. The main development here was to adapt the SPA model to run with various plant functional types concurrently. This enabled me to model both the canopy and understorey groups and explore the sensitivity of these functional groups to key environmental controls.

  3. Fire and Water: assessing the interseasonal and interannual productivity of longleaf pine savannas

    The final section of my research combines the research described above and examines the seasonal and annual productivity of longleaf pine ecosystems in the context of a biannual burning regime, the soil moisture gradient and the three main functional groups. Flux data from both wet and dry sites for 3 years will be partitioned by SPA and limitations and sensitivities explored. A variety of stand scale datasets have been collected to further constrain the flux data, including crown mapping, stem growth increment data, biomass surveys and canopy and understorey phenology and their responses to fire and drought.

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