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Disturbance feedbacks on the height of woody vegetation in a savannah : a multi-plot assessment using an unmanned aerial vehicle (UAV)

Title data

Mayr, Manuel J. ; Malß, Sophia ; Ofner, Elisabeth ; Samimi, Cyrus:
Disturbance feedbacks on the height of woody vegetation in a savannah : a multi-plot assessment using an unmanned aerial vehicle (UAV).
In: International Journal of Remote Sensing. (2017) . - pp. 1-25.
ISSN 0143-1161
DOI: https://doi.org/10.1080/01431161.2017.1362132

Project information

Project financing: Deutscher Akademischer Austauschdienst

Abstract in another language

Disturbances affect the woody, i.e. trees and shrubs, and herbaceous vegetation in savannah ecosystems worldwide. In Northern Namibia, livestock grazing and fires depict two prominent agents of disturbance. These affect the structural parameters of vegetation such as the height of woody species. Remote sensing is a tool to quantify such structural parameters. In particular, Image-Based Point Clouds (IBPCs) obtained from unmanned aerial vehicles (UAVs) are nowadays increasingly used for three-dimensional (3D) remote-sensing applications. Here we aim at deriving the height of woody stands through a multi-plot UAV campaign (n = 19) carried out at the end of the dry season. We use direct georeferencing from the navigation-grade instruments on board the UAV in a Structure-from-Motion (SfM) approach. Watershed segmentation is applied to derive plot-scale height metrics (maximum, mean, and median) based on delineated individuals. Fire and grazing – both individually and synergistically – are then investigated for their impacts on UAV-derived height metrics. The results indicate good agreement between the UAV-derived and in situ-measured height metrics on the plot scale (coefficient of determination (R2) approximately 0.7, root mean square error (RMSE) <1.9 m). Underestimations of height are apparent with large, leafless trees. Clumping of equally sized individuals complicated their correct delineation. Grazing was found to be significant for all height metrics as well as in combination with fire for the plots’ maxima. We conclude that the approach applied here is able to reproduce the plot-scale heights of woody vegetation with acceptable accuracy. We attribute the observed height reductions with the simultaneous presence of disturbances to legacy effects.

Further data

Item Type: Article in a journal
Refereed: Yes
Institutions of the University: Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professorship Climatology
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professorship Climatology > Professorship Climatology - Univ.-Prof. Dr. Cyrus Samimi
Profile Fields > Advanced Fields > African Studies
Profile Fields > Advanced Fields > Ecology and the Environmental Sciences
Research Institutions > Research Centres > Bayreuth Center of Ecology and Environmental Research- BayCEER
Research Institutions > Research Centres > Institute of African Studies - IAS
Faculties
Profile Fields
Profile Fields > Advanced Fields
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 500 Science
500 Science > 500 Natural sciences
500 Science > 550 Earth sciences, geology
900 History and geography
Date Deposited: 11 Aug 2017 08:33
Last Modified: 11 Aug 2017 08:33
URI: https://eref.uni-bayreuth.de/id/eprint/39093