Abstract
Vegetation dynamics in savannas are largely determined by water availability as well as soil nutrient dynamics. Species composition differs significantly from nutrient-rich soils to nutrient-poor soils, where the former is dominated by fine-leafed palatable woody species and the latter by broad-leafed and less palatable ones. Whilst this typically occurs at a landscape or catena scale, it is also interestingly observed at a localised and micro scale in areas such as wetlands and termite mounds. Wetlands are important edaphic contrasts in savannas and are paradoxically prevalent in the semi-arid to arid regions. In Southern Africa endorheic (inward draining) wetlands, known as pans, are particularly ubiquitous in arid regions but are not well studied compared to other wetland types. These wetlands were the focus of this study, which took place in the semi-arid savanna of the Limpopo plains, South Africa. The key research aims of this study were to determine how the pans differed from the surrounding terrestrial savanna landscape with respect to soil texture and chemistry, woody plant density and vegetation species composition. Top and sub soil samples were analysed to a depth of 30 and 60 cm and vegetation transects were carried out across three identified ‘hydro-ecological’ zones, i.e. the pan centre, the wooded wetland zone around the pan and representative terrestrial savanna habitat. In addition, drone aerial imagery was utilised to accurately determine woody species density and visually understand habitat changes. As hypothesised, the physiochemical properties of the soils differed along the study gradient from terrestrial to wetland, where in general the soil fertility, clay content and water holding capacity increased. The high clay content of the pans facilitates the surface pooling of rainwater and the possible maintenance of wetland conditions in these depressions which were found to be localised soil nutrient hotspots. The wooded wetland and terrestrial areas differed from each other in woody species composition where the terrestrial areas were largely dominated by broad leafed tree and shrub species and the wooded wetland areas had few to no broad-leafed species present but rather a dominance of fine-leafed Senegalia/Vachelia species. In addition, the Senegalia/Vachelia dominated habitat had a higher tree density than the surrounding bushveld, forming closed canopy patches in some areas. This change in vegetation and soil dynamics are important in savanna ecology as these habitats function quite differently from each other with respect to nutrient cycling, herbivore behaviour and biodiversity. It was concluded that these pans are nutrient-rich hotspots, likely playing an important ecological role in the savanna landscape. Furthermore, as they are likely to be key water sources and preferential forage sites, they could be the first to show signs of degradation and be useful indicators for land managers. These pans should be highlighted as sensitive habitats with regional conservation significance, which are deserving of adequate protection from surrounding threats such as mining.
Similar content being viewed by others
References
Allan DG, Seaman MT, Kaletja B (1995) The endorheic pans of South Africa. In: Cowan GI (ed) Wetlands of South Africa. Department of Environmental Affairs and Tourism, Pretoria
Bell RHV (1986) Soil-plant-herbivore interactions. In: Bell RHV, McShane-Caluzi E (eds) Conservation and wildlife management in Africa. US Peace Corps, Washington, DC, pp 109–130
Bird MS, Mlambo MC, Wsserman RJ, Dalu T, Holland AJ, Day JA, Villet MH, Bilton DT, Barber-James HM, Brendonck L (2019) Deeper knowledge of shallow waters: reviewing the invertebrate fauna of southern African temporary wetlands. J Hydrobiol 827:89–121
Blackmore AC, Mentis MT, Scholes RJ (1990) The origin of nutrient-enriched patches within a nutrient-poor savanna in South Africa. J Biogeogr 17:463–470
Craine J, Morrow C, Stock W (2008) Nutrient concentration ratios and co-limitation in South African grasslands. New Phytol 179:829–836
Day J, Day E, Ross-Gillespie V, Ketley A (2010) The assessment of temporary wetlands during dry conditions. WRC report no. TT434/09. Water Research Commission, Pretoria
Dean WRJ, Milton SJ, Jeltsch F (1999) Large trees, fertile islands, and birds in arid savanna. J Arid Environ 41:61–78
de Klerk AR, de Klerk LP, Oberholster PJ, Ashton PJ, Dini JA, Holness SD (2016) A review of depressional wetlands (pans) in South Africa, including a Water Quality Classification System. Report to the Water research commission. WRC Report No. 2230/1/16
Dini J, Cowan G, Goodman P (1998) South African national wetland inventory: proposed wetland classification system for South Africa. Department of Environmental Affairs and Tourism, Pretoria
Driver A, Sink KJ, Nel JN, Holness S, Van Niekerk L, Daniels F, Jonas Z, Majiedt PA, Harris L, Maze K (2012) National biodiversity assessment 2011: an assessment of South Africa’s biodiversity and ecosystems. Synthesis report. South African National Biodiversity Institute and Department of Environmental Affairs, Pretoria
Ferreira M, Wepenar V, van Vuren JHJ (2010) Aquatic invertebrate communities of perennial pans in Mpumalanga, South Africa: a diversity and functional approach. Afr Invertebr 52(2):751–768
Fey M (2010) Soils of Southern Africa. Cambridge University Press, Cape Town, pp 115–122
Goudie AS, Thomas CG (1985) Pans in southern Africa with particular reference to South Africa and Zimbabwe. Zeitchrift fur Geomorphologie 29:1–19
Grant CC, Scholes MC (2006) The importance of nutrient hot-spots in the conservation and management of large wild mammalian herbivores in semi-arid savannas. J Biol Conserv 130:426–437
Khomo L, Hartshorn AS, Rogers KH, Chadwick OA (2011) Impact of rainfall and topography on the distribution of clays and major cations in granitic catenas of southern Africa. Catena 87:119–128
Khomo L, Rogers KH (2009) Stream order controls geomorphic heterogeneity and plant distribution in a savanna landscape. Austral Ecol 34:170–178
Kotze DC, Marneweck GC, Batchelor AL, Lindley DC, Collins NB (2009) A technique for rapidly assessing ecosystem services supplied by wetlands. Mondi Wetland Project
Land Type Survey Staff (1989–2002) Land type survey of South Africa, 1:250 000 scale. Climate and Water; 1972–2002. ARC Institute for Soil, Pretoria
Levick SR, Rogers KH (2011) Context-dependent vegetation dynamics in an African savanna. Landsc Ecol 26:515–528
Levick SR, Asner GP, Chadwick OA, Khomo LM, Rogers KH, Hartshorn AS, Kennedy-Bowdoin T, Knapp DE (2010) Regional insight into savanna hydrogeomorphology from termite mounds. Nat Commun. https://doi.org/10.1038/ncomms1066
Miller RW, Donahue RK (1990) Soils: an introduction to Soils and Plant Growth, 6th edn. Prentice Hall, Hoboken
Mucina L, Rutherford MC (2012) The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, Pretoria
Nel JL, Murray KM, Maherry AM, Petersen CP, Roux DJ, Driver A, Hill L, van Deventer H, Funke N, Swartz ER, Smith-Adao LB, Mbona N, Downsborough L, Nienaber S (2011) Technical report for the National Freshwater Ecosystem Priority Areas. Springer, New York
Scholes RJ (1990) The influence of soil fertility on the ecology of Southern African dry savannas. J Biogeogr 17:415–419
Scholes R, Archer S (1997) Tree-Grass interactions in savannas. Ann Rev Ecol Syst 28:517–544
Scholes RJ, Walker BH (1993) An African savanna: synthesis of the Nyslvley study. Cambridge University Press, Cambridge
Scholes M, Scholes RJ, Otter L, Woghiren A (2003) Biogeochemistry: the cycling of elements. In: du Toi JT, Rogers KH, Briggs HC (eds) The Kruger experience: ecology and management of savanna heterogeneity. Island Press, Washington
Simmons R, Barnard P, Jamieson I (1999) What precipitates influxes of wetland birds to ephemeral pans in arid landscapes? Observations from Namibia. Ostridge 70(2):145–148. https://doi.org/10.1080/00306525.1999.9634531
Tessema ZK, de Boer WF, Baars RMT, Prins HHT (2011) Changes in soil nutrients, vegetation structure and herbaceous biomass in response to grazing in a semi-arid savanna of Ethiopia. J Arid Environ https://doi.org/10.1016/j.jaridenv.2011.02.001
Tooth S, McCarthy TS (2007) Wetlands in drylands: geomorphological and sedimentological characteristic, with emphasis on examples from southern Africa. Prog Phys Geogr 31(3):3–41
Treydte AC, van der Beek JGM, Perdok AA, van Wieren SE (2011) Grazing ungulates select for grasses growing beneath trees in African savannas. Mamm Biol 76:345–350
Venter FJ (1990) A classification of land for management planning in the Kruger National Park. Unpublished Ph.D. Thesis, University of South Africa
Venter FJ, Scholes RJ, Eckhardt HC (2003) The abiotic template and its associated vegetation pattern. In: du Toit JT, Rogers KH, Biggs H (eds) The Kruger experience: ecology and management of savanna heterogeneity. Island Press, Washington, DC, pp 83–129
Acknowledgements
This serves to acknowledge that the research results presented herein were completed as part of a Master’s of Science Degree in Environmental Science (University of the Witwatersrand, Johannesburg, South Africa). The manuscript containing the results of this research is thus acknowledged and referenced.
Funding
Research funding received from the South African Systems Analysis Centre and SARChI (DST/NRF) chair in Systems ecology (Grant No. 101057) awarded to Prof Mary Scholes.
Author information
Authors and Affiliations
Contributions
CAW: conceptualization; data curation; formal analysis; investigation; methodology; validation; visualization; writing. Prof. MCS: funding acquisition; investigation; methodology; supervision; review.
Corresponding author
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Wallington, C.A., Scholes, M.C. Pans as possible pedological hotspots in an arid African savanna. Wetlands Ecol Manage 29, 519–530 (2021). https://doi.org/10.1007/s11273-021-09798-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11273-021-09798-5