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Extramural Research

Grantee Research Project Results

Grantee Research Project Results

Spatial and Temporal Quantification of Bush Encroachment in Overgrazed South African Rangelands

EPA Grant Number: U914998
Title: Spatial and Temporal Quantification of Bush Encroachment in Overgrazed South African Rangelands
Investigators: Hudak, Andrew T.
Institution: University of Colorado at Boulder
EPA Project Officer: Edwards, Jason
Project Period: January 1, 1996 through December 7, 1999
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996)
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology and Ecosystems



The objectives of this research project are to: (1) quantify the effect of chronic overgrazing on carbon sequestration in semiarid savannas; and (2) recommend remediatory measures.


An automated textural analysis of historical aerial photography will be used to quantify the spatial and temporal extent of bush encroachment across two study landscapes (each one approximately 100,000 hectares). Soil and litter samples gathered at field sites representing various degrees of bush encroachment will be analyzed for total carbon and stable carbon isotope ratio to estimate potentially longer term changes to the soil carbon pool. Aboveground biomass was estimated at these same field sites. Canopy fractional interceptance of photosynthetically active radiation (FIPAR) characterized along 240-m transects will be related to Landsat satellite-derived vegetation indices (VIs). These FIPAR-VI relationships will be used as a tool to scale between field and remotely sensed data. Carbon pools characterized for four major soil/vegetation community types then will be extrapolated across both landscapes using the satellite data and a geographic information system. Finally, a Markov-type transitional matrix model, driven by cattle stocking, fire, and rainfall variables, will be constructed to simulate changing tree densities. This model will be linked to the Century ecosystem model to further explore how bush encroachment may alter savanna ecosystem processes.

Supplemental Keywords:

fellowship, overgrazing, bush encroachment, savanna ecosystem, soil carbon pool, photosynthetically active radiation, FIPAR, vegetation indices, geographic information system, GIS.

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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