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Pellegrini Group: The resilience of savanna ecosystems to changing fire regimes

NERC / GFC / OTHER

Supervisor: Adam Pellegrini (Plant Sciences)

Importance of work

Fires are becoming more frequent in many ecosystems across the globe, with uncertain consequences for biodiversity and biogeochemical cycling. Ecosystem responses are critical, however, in part because of their large influence on the global carbon cycle. One hypothesis is that more frequent burning will destabilize ecosystems, resulting in a negative effect of fire on carbon and nutrient cycling and plant composition. The alternative hypothesis is that compensatory responses allow ecosystems to acclimate to the new fire regimes, resulting in long-term stabilization of biogeochemical cycling and composition. However, the tests of these hypotheses are rare because most studies focus on the effect of a single fire and not long-term alterations of fire regimes. This project will utilize a network of long-term (30-50 years) fire frequency manipulation experiments that are distributed across the globe. The broad geographic scope will allow for the evaluation of mechanisms that may lead to generalities in the responses across ecosystems.

Project summary

This project will investigate how changes in fire frequency have influenced the structure and composition of vegetation and soil biogeochemistry in both tropical and temperate savanna ecosystems. The results of this work will address the question of how natural ecosystems will respond to the rapidly changing fire regimes across the globe. Fieldwork will take place in three sites where fire frequency has been experimentally manipulated for >40 years (South Africa, Brazil, and the United States). The fieldwork will characterize the vegetation community to test the hypothesis that frequent burning shifts the plant community to being increasingly sensitive to fire. The labwork involves soil sampling and analysis, which will characterize the storage and turnover of carbon and nutrients via microbial activity assays and organic and inorganic chemistry measurements. These assays will be used to test the hypothesis that fire depletes ecosystem carbon and dampens nutrient turnover, inhibiting vegetation and microbial recovery.

What the student will do

The project will combine both field and lab work.

  1. Fieldwork: Fieldwork will be carried out in field sites in Kruger National Park (South Africa), Cedar Creek Ecosystem Science Reserve (United States), and Instituto Brasileiro de Geografia e Estatística (Brazil). Time will be spent conducting vegetation measurements in the field and collecting soil samples for future analyses in the lab.
  2. Labwork: Analyses of the amount and form of carbon and nutrients in the soil will be carried out in the lab using combustion and gas chromatography. Microbial activity assays will include multi-month jar incubations to measure CO2 respiration, microbial biomass, and extracellular enzyme activities.
  3. Data analysis and model development: Data will be incorporated into an existing ecosystem model to project how future changes in fire regimes will alter ecosystem carbon storage and stability in these savanna ecosystems.

Training to be provided

The student will be trained in field survey and sampling techniques, biogeochemistry (carbon and nutrient measurements in soils, organic matter chemistry, and mineral-carbon interactions), microbiology (microbial biomass, respiration assays, extracellular enzyme assays), and ecosystem modelling. Moreover, the broad geographical scope will give them exposure to working in international collaborations and allow them to create a strong research network.

References

  • Pellegrini, A. F. A., L. O. Hedin, A. C. Staver, and N. Govender. 2015. Fire alters ecosystem carbon and nutrients but not plant nutrient stoichiometry or composition in tropical savanna. Ecology 96:1275–1285.
  • Pellegrini, A. F. A., W. A. Hoffmann, and A. C. Franco. 2014. Carbon accumulation and nitrogen pool recovery during transitions from savanna to forest in central Brazil. Ecology 95:342–352.
  • Pellegrini, A. F. A., A. Ahlström, S. E. Hobbie, P. B. Reich, L. P. Nieradzik, A. C. Staver, B. C. Scharenbroch, A. Jumpponen, W. R. L. Anderegg, J. T. Randerson, and R. B. Jackson. 2018. Fire frequency drives decadal changes in soil carbon and nitrogen and ecosystem productivity. Nature 553:194–198.

 

 

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