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Spectral reflectance of floodplain vegetation communities of the Okavango Delta

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Abstract

Knowledge of wetland vegetation spectral reflectance signatures can assist in spectral classification of remotely sensed images for monitoring of wetland hydroperiod. This study aimed at assessing the differences between wetland vegetation communities of varying species composition and density in terms of spectral reflectance. The investigation was carried out in floodplains at Nxaraga and Seronga in the Okavango Delta, Botswana. Spectral measurements were conducted during rising and receding flood stages. In each study area, 2 transects were located in homogeneous macrophyte stands, and in each transect 5–10 1 m2 quadrats were randomly set. In each quadrat, water depth and cover percentages (green leaved and senescent) of macrophyte vegetation were recorded, and a full reflectance spectrum between 325 and 1,075 nm wavelengths captured using a handheld spectroradiometer. Multiple regression analysis with stepwise selection of significant variables based on AIC was performed to determine the influence of various stand characteristics on spectral reflectance and vegetation indices (NDVI and EVI). The results showed that stand characteristics explained a large proportion of variance in spectral vegetation indices with r2 = 0.67 for NDVI and r2 = 0.75 for EVI. For NDVI, the significant explanatory variables were percentage green cover, senescent cover and water depth, while for EVI it was the total vegetation cover. Analysis of regression residuals for the various vegetation community classes showed significant differences between the classes in their NDVI, but no differences in EVI, with the exception of the Panicum repens class. Reflectance in visible wavelengths did not vary significantly between sites and seasons, but the NIR reflectance differed across sites and seasons. The results indicate that the simple vegetation indices in the Okavango Delta respond strongly to stand characteristics and thus can be used to derive these from remote sensing imagery. The scope for determination of vegetation communities from these indices is limited, however.

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Acknowledgments

The authors thank the German Ministry for Education and Research (BMBF) for sponsoring this project (TFO). We also thank the field technician for their assistance in field work and herbarium unit (ORI) with their assistant in sample identification. Appreciations to Mr Tsheboeng who aided in cluster analysis. Thanks are also due to two anonymous reviewers whose comments and suggestions on an earlier version helped greatly to improve this manuscript. The work was carried out under Botswana Government Research Permit reference number: EWT 8/36/4 XVI (47).

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Authors and Affiliations

  1. Okavango Research Institute, University of Botswana, Private Bag 285, Maun, Botswana

    K. Thito, P. Wolski & M. Murray-Hudson

  2. Climate System Analysis Group, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa

    P. Wolski

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  1. K. Thito
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  2. P. Wolski
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  3. M. Murray-Hudson
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Correspondence to K. Thito.

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Thito, K., Wolski, P. & Murray-Hudson, M. Spectral reflectance of floodplain vegetation communities of the Okavango Delta. Wetlands Ecol Manage 23, 637–648 (2015). https://doi.org/10.1007/s11273-014-9403-1

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  • DOI: https://doi.org/10.1007/s11273-014-9403-1

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