Vegetation of the Okavango river valley in Kavango West, Namibia

Abstract

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...

Patterns of forest composition and their long term environmental drivers in the tropical dry forest transition zone of southern Africa

“…Strohbach (2013) indicated that 90 % of the Acacia erioloba -S. rautanenii community in the Okavango river valley has already been cleared for agriculture. Environmental impact studies for agricultural development projects should advise preservation and establishment of corridors and islands of natural woodland, especially for the B. plurijuga and S. rautanenii communities.…”

“…Future MAP is based on the B1 SRES emission scenario for 2080 (HADCM3 model,WorldClim) national economies through ecotourism focused on large mammals, and the provision of fuel, construction wood and fodder (Barnes et al 2010). Some detailed studies on forest composition in this area focused on smaller study areas (Childes and Walker 1987;Strohbach and Petersen 2007;Aarrestad et al 2011;Strohbach 2013;Revermann and Finckh 2013). Few studies have examined the longterm changes in the composition of late successional forest (e.g.…”

“…Mosugelo et al 2002). Detecting forest patterns in the study area is complicated by 1) a lack of obvious environmental gradients with exception of a few rivers and dunes and 2) the difficulty to distinguish tree communities with small datasets (<200 plots) (Childes and Walker 1987;Strohbach 2013;De Cauwer 2013). Regional studies indicate that forest dynamics are mainly driven by fire, drought and browsing (Burke 2006;Archibald et al 2009;Fanshawe 2010).…”

Species richness and evenness respond to diverging land‐use patterns – a cross‐border study of dry tropical woodlands in southern Africa

“…Mean annual precipitation is approximately 570 mm, and mean annual temperature ranges from 22 to 23°C (Weber, ; Harris et al ., ). The vegetation of the floodplain and the river banks varies over short distances and is primarily determined by topographic position above river level (Strohbach, ). In contrast, the vegetation of the vast sandy plains of the hinterland, the Kalahari Sandveld, is relatively homogeneous and is dominated by dry deciduous tropical Baikiaea–Burkea woodlands (De Cauwer, ; Revermann & Finckh, ).…”

Biodiversity observation - an overview of the current state and first results of biodiversity monitoring studies

“…Also, several regional descriptions have been published in this country over the past few years, or are in the process of being published (e.g. Strohbach, , 2014. Here, the work is advancing from making pure C A Biodiversity baseline descriptions to developing a tool for land use planning (Strohbach, 2017c).…”