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Vachellia erioloba dynamics over 38 years in the Kalahari Gemsbok national park, South Africa

dc.contributor.authorVan der Merwe, Helga
dc.contributor.authorVan Rooyen, Noel
dc.contributor.authorBezuidenhout, Hugo
dc.contributor.authorBothma, Jacobus du P.
dc.contributor.authorVan Rooyen, Margaretha W.
dc.date.accessioned2020-11-13T13:54:50Z
dc.date.available2020-11-13T13:54:50Z
dc.date.issued2019-04
dc.description.abstractVachellia erioloba is a keystone tree species in the southern Kalahari. This long-term study over nearly four decades tracks two populations in different landscapes (the interior sandy duneveld versus the clayey Nossob riverbed) of a large conservation area and offers valuable data on this species under natural soil moisture conditions and with limited anthropogenic influences. In 1978, 18 trees were permanently marked in a 1 ha plot in the interior duneveld of the Kalahari Gemsbok National Park (Dankbaar site). In the Nossob riverbed all trees in a 1 ha plot were surveyed in 1979 (Grootkolk site). At both sites, tree height and stem circumference were subsequently measured at irregular intervals until 2016 in order to investigate growth rates and population structure. Of the 18 marked trees at Dankbaar, six died and three showed coppice regrowth following substantial dieback after a fire. A mean height increase of 60 mm/year was recorded and the mean height of the remaining uncoppiced trees was 6.8 m in 2016. Stem diameter growth rate per year varied widely between trees and between years with a mean value of 2.5 mm/year over the 38-year period. Growth rate calculated for three 10-year intervals varied. Using the mean growth rate derived in the current study and stem size of the dead trees, the mean age of the trees when they died was estimated. At the Grootkolk site, the position of the centroid in relation to the midpoint of the diameter class range suggests that this population is gradually becoming a mature to old population with limited recruitment. This was supported by the size class distribution curves. However, no differences between slopes or intercepts of the stem diameter size class distributions were found. CONSERVATION IMPLICATIONS : This study was conducted in a large conservation area, that is, a natural ecosystem excluding most of the anthropogenic threats that are present outside of the park. The study illustrated that in the duneveld the population studied was self-sustaining, with recruitment occurring and large individuals presumably dying of old age. Although fire caused a few individuals to coppice, no fire-related deaths were reported. In the Nossob riverbed, surveys started in a stand of predominantly young trees and the size class distribution at that stage already showed a lack of recruitment. This stand is ageing and will likely disappear at this site; however, new young stands are appearing at other sites in the Nossob riverbed. Under the current conditions with negligible anthropogenic influences, it therefore appears that some V. erioloba populations in the park are increasing in size while others are decreasing, but that overall the species will persist. The impact of global climate change on this species is, however, unknown.en_ZA
dc.description.departmentCentre for Wildlife Managementen_ZA
dc.description.departmentPlant Production and Soil Scienceen_ZA
dc.description.librarianhj2020en_ZA
dc.description.sponsorshipThe University of Pretoria, Centre for Wildlife Management and the National Research Foundation.en_ZA
dc.description.urihttp://www.koedoe.co.zaen_ZA
dc.identifier.citationVan der Merwe, H., Van Rooyen, N., Bezuidenhout, H. , Bothma, J. du P. & Van Rooyen, M.W., 2019, ‘Vachellia erioloba dynamics over 38 years in the Kalahari Gemsbok National Park, South Africa’, Koedoe 61(1), a1534. https://doi.org/10.4102/koedoe.v61i1.1534.en_ZA
dc.identifier.issn0075-6458 (print)
dc.identifier.issn2071-0771 (online)
dc.identifier.other10.4102/koedoe.v61i1.1534
dc.identifier.urihttp://hdl.handle.net/2263/76992
dc.language.isoenen_ZA
dc.publisherAOSIS OpenJournalsen_ZA
dc.rights© 2019. The Authors. Licensee: AOSIS. This work is licensed under the Creative Commons Attribution License.en_ZA
dc.subjectConservation areaen_ZA
dc.subjectGrowth rateen_ZA
dc.subjectKgalagadi Transfrontier Parken_ZA
dc.subjectLong-term studyen_ZA
dc.subjectSize class distributionen_ZA
dc.subjectTree ageen_ZA
dc.titleVachellia erioloba dynamics over 38 years in the Kalahari Gemsbok national park, South Africaen_ZA
dc.typeArticleen_ZA

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