Environmental factors that influence diversity of floodplain communities in different phases in the Okavango Delta, Botswana
Background and objectives: Species composition and distribution in seasonal floodplain plant communities are influenced by variation in flooding. However, the influence of intra-flooding variation phases on the diversity of seasonal floodplain plant communities has not been studied in the Okavango Delta. The objective of this study was to investigate environmental factors that influence species composition and distribution of seasonal floodplain communities before
and after flooding. It was hypothesised that environmental factors that influence the species composition and distribution in seasonal floodplain communities will vary with intra-flooding seasons.
Methods: Flooding depth was measured in May (before flooding) and September (flood recession/after flooding) in forty 25 m2 plots. Flooding duration was recorded as the number of weeks in which the plots were inundated. The soil was sampled before and after floods and analysed for pH, extractable P, K, Mg, Ca and Na. Plant identification and estimation of percentage cover were done in the 25 m2 plots in which environmental variables were sampled. The relationship between environmental variables and seasonal floodplain plant community composition and distribution was sought using Non-metric Multi-dimensional Scaling. Paired Student’s t test was used to compare the means of environmental variables before and after flooding.
Results: Factors that influenced the distribution of species before flooding were Na, K, water depth and flooding duration. After flooding, the factors that influenced species composition and distribution were K, Na, Mg, pH, water depth and flooding duration.
Conclusion: These results suggest that during flooding K and Mg are deposited in the floodplains due to lateral water flow. Our results also suggest that any water abstraction from the Okavango River Basin should take into consideration the
importance of flooding duration and depth in sustaining species composition and distribution of seasonal floodplain plant communities so that such developments do not disturb the ecological functioning of the Delta.
Biggs, R.C., 1976, ‘The ecology of chief’s island and adjacent floodplains of the Okavango Delta’, Proceedings of the
symposium on the Okavango Delta and its future utilization held in Gaborone, Botswana. Gaborone, Botswana.
Bonyongo, M.C., Bredenkamp, G.J. & Veenendaal, E., 2000, ‘Floodplain vegetation in the Nxaraga Lagoon area, Okavango
Delta, Botswana’, South African Journal of Botany 66, 15–21, DOI: 10.1016/S0254-6299(15)31046-2.
Cronk, J.K. & Fennessy, M.S., 2001, ‘Wetland plants: biology and ecology’, CRC Lewis Publishers, New York.
Davis, S.M. & Ogden, J.C., 1993, ‘Everglades: The ecosystem and its restoration’, St. Lucie Press, Delray Beach, Florida
De Oliveira, M.T., Damasceno-Junior, G.A., Pott, A., Filho, A.C., Suarez, Y.R. & Parolin, P., 2014, ‘Regeneration of riparian
forests of the Brazilian Pantanal under flood and fire influence,’ Forest Ecology and Management 331, 256–263, DOI: 10.1016/j.foreco.2014.08.011.
De Simone, O., Junk, W.J. & Schmidt, W., 2003, ‘Central Amazon Floodplain Forest: root adaptations to flooding’, Russian
Journal of Plant Physiology 50, 848–855, https://doi.org/10.1023/B:RUPP.0000003285.70058.4c.
Edwards, P.J. & Kollman, J., 2002, ‘Life history of evolution in Lodoicea maldivica (Arecaceae),’ Nordic Journal of Botany
22, 227–238, https://doi.org/10.1111/j.1756-1051.2002.tb01371.x.
Ellenbroek, G.A., 2012, ‘Ecology and productivity of an African wetland system: the Kafue Flats, Zambia’, Dr W. Junk
Ellery, K., Ellery, W.N., Rogers, K.H. et al., 1991, ‘Water depth and biotic insulation: Major determinants of backswamp
plant community composition’, Wetlands Ecology and Management 1, 149–162, https://doi.org/10.1007/BF00177289.
Ellery, W.N. & Tacheba, B., 2003, ‘Floristic Diversity of the Okavango Delta, Botswana’, In: Alonso, L.E. & Nordin, L.A (eds), ‘A rapid biological assessment of the aquatic ecosystems of the Okavango Delta, Botswana: High water survey’, RAP-Bulletin of Biological Assessment 25, 69–96.
Ellery, W.N., Ellery, K. & McCarthy, T.S., 1993, ‘Plant distribution in islands of the Okavango Delta, Botswana: determinants
and feedback interactions’, African Journal of Ecology 31, 118–134, https://doi.org/10.1111/j.1365-2028.1993.tb00526.x.
Flowers T.J. & Colmer, T.D., 2008, ‘Salinity tolerance in halophytes’, New Phytologist 179, 945–963, https://doi.org/10.1111/j.1469-8137.2008.02531.x.
Gregory, S.V., Swanson, F.J., Mckee, W.A. & Cummins, K.W., 1991, ‘Ecosystem perspective of riparian zones’, Bioscience
41, 540–551, DOI: 10.2307/1311607.
Growing, D.J.G., Spoor, G. & Mountford, O. 1998, ‘The influence of minor variations in hydrological regime on grassland plant communities: implications for water management’, In: ‘Joyce, C.B & Wade, P.M (eds), European wet grasslands: biodiversity, management and restoration’, Wiley, Chichester, 217–227.
Gumbricht, T., McCarthy, J. & McCarthy, T.S., 2004, ‘Channels, wetlands and islands in the Okavango Delta, Botswana, and their relation to hydrological and sedimentological processes’, Earth Surf. Process Landforms 29, 15–29, DOI:10.1002/esp.1008.
Hameed, M., Ashraf, M. & Naz, N. 2009, ‘Anatomical adaptations to salinity in cogon grass (Imperata cylindrical (L.)
Raeuschel) from the Salt Range, Pakistan’, Plant and Soil 322: 229–238, DOI: 10.1007/s11104-009-9911-6.
Hameed, M., Ashraf, M. & Naz, N., 2011, ‘Anatomical and physiological characteristics relating to ionic relations in
some salt tolerant grasses from the Salt Range, Pakistan’, Acta Physiologiae Plantarum’, 33, 1399–1409, DOI: 10.1007/
Junk, W.J., 1997, ‘General aspects of floodplain ecology with special reference to Amazonian floodplains’, In Junk, W.J (ed), ‘The central Amazon floodplain: Ecology of a pulsing system – Ecological Studies’, 126, 3–20.
Kozlowski, T.T., 1984, ‘Plant responses to flooding of soil’, Bioscience 34,162–167.
Kruskal, J.B., 1964, ‘Nonmetric multidimensional scaling: a numerical method’, Psychometrika 29, 115–129, https://
MacDonald, G.E., 2004, ‘Cogongrass (Imperata cylindrica) – biology, ecology, and management’, Critical Reviews in Plant Sciences 23, 367–380, https://doi.org/10.1080/07352680490505114.
Marcum, K.B., 1999, ‘Salinity tolerance mechanisms of grasses in the subfamily Chloridoideae’, Crop Science 39, 1153–1160,
Mather, P.M., 1976, ‘Computational methods of multivariate analysis in physical geography’, John Wiley and Sons, London.
McCarthy, T.S. & Ellery, W.N., 1998, ‘The Okavango Delta’, Transactions of the Royal Society of South Africa 53, 157–182, https://doi.org/10.1080/00359199809520384.
McCarthy, T.S., 2006, ‘Groundwater in the wetlands of the Okavango Delta, Botswana, and its contribution to the structure and function of the ecosystem’, Journal of Hydrology, 320, 264–282, https://doi.org/10.1016/j.jhydrol.2005.07.045.
McCune, B. & Grace, J.B., 2000, ‘Analysis of ecological communities’, MjM software, Gleneden Beach, Oregon, U.S.A.
Merritt, D.M., Scott, M.L., Poff, N.L., Auble, G.T. & Lytle, D.A., 2009, ‘Theory, methods and tools for determining environmental flows for riparian vegetation: riparian vegetation-flow response guilds’, Freshwater Biology, 55, 206–
Middleton, B.A., 2009, ‘Vegetation status of the Keoladeo National Park, Bharatpur, Rajasthan, India’, US Geological Survey, Report 2009-5193.
Mueller-Dombois, D. & Ellenberg, H., 1974, ‘Aims and methods of vegetation ecology’, John Wiley & Sons, New York.
Murray-Hudson, M. 2009, ‘Floodplain vegetation responses to flood regime in the seasonal Okavango Delta, Botswana’,
PhD thesis, University of Florida, Florida.
Naiman, R.J. & Decamps, H., 1997, ‘The ecology of interfaces: Riparian zones’, Annual Review of Ecology and Systematics
28, 621–658, https://doi.org/10.1146/annurev.ecolsys.28.1.621.
Oliveira-Filho, A.T., Vilela, E.A., Gavilanes, M.L. & Carvalho, D.A., 1994, ‘Effects of flooding regime on understorey bamboos
on the physiognomy and tree species composition of a tropical semi-deciduous forest in southern Brazil’, Vegetation 113, 99–124, https://doi.org/10.1007/BF00044229.
Parolin, P., Ambrüster, N. & Junk, W.J., 2006, ‘Two Amazonia trees react differently to periodical flooding’, Tropical Ecology
Pinder, L. & Rosso, S., 1998, ‘Classification and ordination of plant formations in the Pantanal of Brazil’, Plant Ecology 136,
Ponce, V.M. & Da Cunha, C.N., 1993, ‘Vegetated earth mounds in tropical savannas of central Brazil: A synthesis’,
Journal of Biogeography, 20, 219–225.
Rees, W.A., 1978, ‘The Ecology of Kafue Lechwe: soils, water levels and vegetation’, Journal of Applied Ecology 15, 163–176, DOI: 10.2307/2402928.
Smith, P., 1976, ‘An outline of the vegetation of the Okavango Drainage system’, Proceedings of the symposium on the
Okavango Delta and its future utilization, National museum, Gaborone, Botswana.
Toogood, S.E., Joyce, S. & Waite, S., 2008, ‘Response of floodplain grassland communities to altered water regimes’,
Plant Ecology 197, 285–298, DOI: 10.1007/s11258-007-9378-6.
Tsheboeng, G., Bonyongo, M. & Murray-Hudson, M., 2014, ‘Flood variation and soil nutrient content in floodplain vegetation communities in the Okavango Delta’, South African Journal of Science 110, 1–5.
Wilson, B.H. & Dincer, T., 1976, ‘An introduction to the hydrology and hydrography of the Okavango Delta’, Proceedings
of the Symposium on the Okavango Delta and its future utilization, National Museum, Gaborone, Botswana.
Wolski, P., Savenije, H.H.G., Murray-Hudson, M. & Gumbricht, M., 2006, ‘Modelling of the flooding in the Okavango
Delta, Botswana, using a GIS model’, Journal of Hydrology 331, 58–72, DOI: 10.1016/j.jhydrol.2006.04.040.
Zeilhofer, P. & Schessl, M., 2000, ‘Relationship between vegetation and environmental conditions in the Northern
Pantanal of Mato Grosso, Brazil’, Journal of Biogeography 27, 159–168, https://doi.org/10.1046/j.1365-2699.2000.00357.x.