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

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. Rem...

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Bibliographic Details
Published in:International journal of remote sensing 2018-08, Vol.39 (14), p.4761-4785
Main Authors: Mayr, Manuel J., Malß, Sophia, Ofner, Elisabeth, Samimi, Cyrus
Format: Article
Language:English
Subjects:
Disturbance
Disturbances
Dry season
Ecosystem disturbance
Ecosystems
Fires
Grazing
Height
Image segmentation
Instruments
Livestock
Livestock grazing
Navigation
Parameters
Remote sensing
Root-mean-square errors
Savannahs
Scale height
Shrubs
Trees
Unmanned aerial vehicles
Vegetation
Watersheds
Woody plants
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Summary: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 (R 2 ) approximately 0.7, root mean square error (RMSE)
ISSN:0143-1161
1366-5901
DOI:10.1080/01431161.2017.1362132