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Scrubbing up: multi-scale investigation of woody encroachment in a southern African savannah

Marston, Christopher G.; Aplin, Paul; Wilkinson, David M.; Field, Richard; O'Regan, Hannah J.

Authors

Christopher G. Marston

Paul Aplin

David M. Wilkinson



Abstract

Changes in the extent of woody vegetation represent a major conservation question in many savannah systems around the globe. To address the problem of the current lack of broad-scale cost-effective tools for land cover monitoring in complex savannah environments, we use a multi-scale approach to quantifying vegetation change in Kruger National Park (KNP), South Africa. We test whether medium spatial resolution satellite data (Landsat, existing back to the 1970s), which have pixel sizes larger than typical vegetation patches, can nevertheless capture the thematic detail required to detect woody encroachment in savannahs. We quantify vegetation change over a 13-year period in KNP, examine the changes that have occurred, assess the drivers of these changes, and compare appropriate remote sensing data sources for monitoring change. We generate land cover maps for three areas of southern KNP using very high resolution (VHR) and medium resolution satellite sensor imagery from February 2001 to 2014. Considerable land cover change has occurred, with large increases in shrubs replacing both trees and grassland. Examination of exclosure areas and potential environmental driver data suggests two mechanisms: elephant herbivory removing trees and at least one separate mechanism responsible for conversion of grassland to shrubs, theorised to be increasing atmospheric CO2. Thus, the combination of these mechanisms causes the novel two-directional shrub encroachment that we observe (tree loss and grassland conversion). Multi-scale comparison of classifications indicates that although spatial detail is lost when using medium resolution rather than VHR imagery for land cover classification (e.g., Landsat imagery cannot readily distinguish between tree and shrub classes, while VHR imagery can), the thematic detail contained within both VHR and medium resolution classifications is remarkably congruent. This suggests that medium resolution imagery contains sufficient thematic information for most broad-scale land cover monitoring requirements in heterogeneous savannahs, while having the benefits of being cost-free and providing a longer historical archive of data than VHR sources. We conclude that monitoring of broad-scale land cover change using remote sensing has considerable potential as a cost-effective tool for both better informing land management practitioners, and for monitoring the future landscape-scale impacts of management policies in savannahs.

Citation

Marston, C. G., Aplin, P., Wilkinson, D. M., Field, R., & O'Regan, H. J. (2017). Scrubbing up: multi-scale investigation of woody encroachment in a southern African savannah. Remote Sensing, 9(5), https://doi.org/10.3390/rs9050419

Journal Article Type Article
Acceptance Date Apr 22, 2017
Publication Date Apr 29, 2017
Deposit Date May 11, 2017
Publicly Available Date May 11, 2017
Journal Remote Sensing
Electronic ISSN 2072-4292
Publisher MDPI
Peer Reviewed Peer Reviewed
Volume 9
Issue 5
Article Number 419
DOI https://doi.org/10.3390/rs9050419
Keywords Savannah; woody encroachment; land cover change; multi-scale; elephant herbivory; shrubs
Public URL http://eprints.nottingham.ac.uk/id/eprint/42735
Publisher URL http://www.mdpi.com/2072-4292/9/5/419
Copyright Statement Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by/4.0

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Copyright Statement
Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by/4.0





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