Biogeochemistry of Kalahari sands

Wang, Lixin; D’Odorico, Paolo; Ringrose, Susan; Coetzee, S. H.; Macko, Stephen A.

doi:10.1016/j.jaridenv.2007.03.016

Cited by 98 publications

(126 citation statements)

References 52 publications

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“…and 61% at Tshane and Mongu, respectively (Table 1); these results are similar to those reported for soil %C in an earlier study (Wang et al 2009c). The lower soil δ 15 N CV value at the dry site is unexpected since resources are usually more heterogeneous at the dry end (Wang et al 2007b (Table 1), as found in an early report with a non-spatial explicit sampling design (Wang et al 2007b). The same principle but converse trend (higher rainfall and lower δ 15 N CV value) applies to the dry site, as the rainfall amount is larger than the MAP at the drier site.…”

Section: Resultsmentioning

confidence: 55%

“…The physical parameters such as soil texture (>96% of sand) and bulk density (around 1.4-1.5 g cm -3 along the whole transect) do not have significant variations along the KT (Wang et al 2007b;Thomas et al 2008). (TRMM), and was reported earlier (Wang et al 2010b).…”

Section: Field Sites and Field Samplingsmentioning

confidence: 57%

“…The KT is one of a set of IGBP (International Geosphere-Biosphere Programme) "megatransects" (Koch et al 1995) identified for global change studies. There are several unique aspects of this transect making it ideal for the ecosystem-scale characterization of the spatial patterns of soil δ 15 N: 1) the soil substrate consists of Kalahari sands, which are consistent and homogeneous along the entire transect (Wang et al 2007b); 2) the topography across the transect is flat with gentle slopes (<1%), minimizing the interactive effects of rainfall and topography on soil moisture. In the south (the dry end of the transect), it is a fineleaf savanna with several potential N-fixers such as Acacia mellifera Benth.…”

mentioning

confidence: 99%

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Ecosystem-scale spatial heterogeneity of stable isotopes of soil nitrogen in African savannas

et al. 2012

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Section: Resultsmentioning

confidence: 55%

Section: Field Sites and Field Samplingsmentioning

confidence: 57%

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confidence: 99%

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Ecosystem-scale spatial heterogeneity of stable isotopes of soil nitrogen in African savannas

et al. 2012

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“…The exact reason is unclear, but it is speculated that growing crops in the sandy soils does not produce a large yield, and that yields deteriorate with time, leading to the abandonment of these fields. This assumption is supported by the fact that the Kalahari sands are known to contain little nutrients (Pröpper et al 2010, Thomas et al 2000, Wang et al 2007). Fears of further soil degradation, through a potential "slash and burn" type of agriculture on these sands will lead to further, and extensive, desertification through a continuing process of denitrification and a biological feedback loop in the desertification process (Schlesinger et al 1990, Schlesinger & Peterjohn 1991, Thomas et al 2005 Conversely, the floodplains and wetlands are mainly used for grazing purposes, both in the wet and dry season.…”

Section: Land Use and Conservation Statusmentioning

confidence: 99%

“…Their description follows below. No attempt was made to formally describe these associations following the rules of the International Code for Phytosociological Nomenclature (Weber et al 2000), as a number of these association descriptions are still based on a very limited number of relevés, whilst some clusters displayed a high internal variation (likely due to the degraded nature of the vegetation), that no clear conclusions can be made at this stage to the syntaxonomic status of it. The numbering of the associations follows that of the initial classification as displayed in Figure 4, and as used in the remainder of the results.…”

Section: Vegetation Associations Of the Western Okavango River Valleymentioning

confidence: 99%

Vegetation of the Okavango river valley in Kavango West, Namibia

Strohbach¹

2013

Biodivers. Ecol.

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Abstract:The vegetation of the Okavango River Valley has previously only been described in general terms along the gradient from base of the valley to the top of the sand plateau, without the clear definition of different vegetation types or distinct vegetation composition. Yet the valley bottom supports a large part of the population within the region, who are dependent on ecosystem services provided by the vegetation. A Braun-Blanquet type survey was conducted to describe the vegetation of the Okavango River Valley in the Kavango West Region of Namibia, with special emphasis on the floodplain vegetation. The survey followed the guidelines set out for the "Vegetation Survey of Namibia" project. The data was classified using the modified TWINSPAN procedure in Juice, resulting in four higher-order syntaxa and 11 vegetation associations. We described these associations informally according to diagnostic species, species richness and environmental variables. In the case of floodplain and wetland associations, information regarding the flooding regime (depth, duration and probability of flooding) is provided. Although the higher-order groupings within this association come out very clearly, only the wetlands could be related to similar higher-order syntaxa described for the oshana wetlands in the Cuvelai delta. The placement and validity of the other three higher-order syntaxa is unclear at this stage, and needs to be addressed in a synopsis of all existing vegetation descriptions for the greater Kalahari ecoregion. The various vegetation associations can very clearly be associated with distinct positions in the landscape. The degree of flooding at the one extreme, and the sandiness of the soil on the other extreme, defines the vegetation type and composition. The Acacia erioloba-Schinziophyton rautanenii association (7) has been cleared and ploughed to at least 90%, with only small patches of this vegetation remaining. Expansion of fields into the sands of the terrace embankment is worrisome, leading to fears of further soil degradation and ultimately desertification. Although signs of overgrazing are visible within the floodplains, this cannot be distinctly quantified as yet. Overgrazing in the wetlands will lead to the destruction of fish spawning and breeding habitats, damaging the other major food source of the people of the region.Keywords: Braun-Blanquet; desertification; floodplain vegetation; flooding regime; land degradation; land use; phytosociology; seasonal wetland vegetation. A vegetação do vale do Rio Okavango no Kavango West, NamíbiaResumo: A vegetação do vale do Rio Okavango foi apenas descrita previamente em termos gerais ao longo da encosta, da base do vale até o topo do platô de areia, sem uma definição clara dos diferentes tipos de vegetação ou sua composição distinta. No entanto, o fundo do vale auxilia uma grande parte da população da região, que é dependente dos serviços ecosistemicos fornecidos pela vegetação. Uma pesquisa do tipo "Braun-Blanquet" foi feita para descrever a vegetação do vale...

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An ecohydrological framework for grass displacement by woody plants in savannas

D’Odorico

2014

JGR Biogeosciences

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During the past several decades, woody plants have been encroaching into grasslands around the world. This transition in plant dominance is often explained as a state shift in bistable ecosystem dynamics induced by fire-vegetation feedbacks. These feedbacks occur when woody plants are able to displace grasses because of their better access to soil water and light. On the other hand, grasses can displace woody plants because of their ability to increase fire frequency and of the higher susceptibility of woody plants to fire-induced mortality. In this study, we present an ecohydrological framework to investigate the displacement of grasses by woody plants. Considering the effect of lateral root spread and of soil water and light limitations, we found that woody plant encroachment can substantially suppress grass production even without the presence of grazers. Bistable dynamics emerge as a result of the grass-fire feedback for a wide range of rainfall conditions, fire susceptibility, and woody plant growth rates.

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Biogeochemistry of Kalahari sands

Cited by 98 publications

References 52 publications

Ecosystem-scale spatial heterogeneity of stable isotopes of soil nitrogen in African savannas

Ecosystem-scale spatial heterogeneity of stable isotopes of soil nitrogen in African savannas

Vegetation of the Okavango river valley in Kavango West, Namibia

An ecohydrological framework for grass displacement by woody plants in savannas

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