Influence of flood variation on seasonal floodplain vegetation communities in the Okavango Delta, Botswana

Abstract

This study investigated the influence of flooding variation on floodplain vegetation in the Nxaraga Lagoon seasonal floodplains by sampling community composition and soil nutrient content in 1997, when flood levels were unusually low, and again in 2010 when flood levels were unusually high. In each of the eight vegetation zones identified in 1997, five plots were randomly selected. Flooding duration in each plot was estimated as the number of weeks in which the plots were inundated. Multi-response permutation procedures (MRPP) analysis was used to compare vegetation communities under low and high floods. Soil pH, Na, Mg, K, Ca and P content were analysed. The influence of environmental variables on species distribution was investigated using non-metric multidimensional scaling (NMS) ordination. Total plant species richness decreased from 88 during low flood to 53 during high flood, and community co-dominant species changed during high flood. Mean percentage cover decreased for some species, but increased for others. Hydroperiod increased in all zones. During the high flood period the content of Na and K was highest in Zone 8 (tertiary floodplain); Ca, Mg and pH content was highest in Zones 6 and 8 (secondary and tertiary floodplains, respectively), while P was highest in Zone 5. Hydroperiod, Na and pH were found to be correlated with, and are therefore thought to influence, community composition and distribution.

Occurrence and seasonality of internal parasite infection in elephants, Loxodonta africana, in the Okavango Delta, Botswana

“…Wild elephant samples collected in 2010 more commonly contained coccidian oocysts and fluke eggs than in other years, and fluke eggs were also more common than average in 2010 and 2011. Flood levels in the Delta were unusually high in 2010 ( Tsheboeng et al., 2014 ), and this could have favoured parasite transmission through, variously and non-exclusively, more humid soil supporting parasite development and survival, better conditions for snail intermediate hosts of fluke, and higher host population density as a result of lower available land area. A more persistent effect might be expected for fluke than for intestinal coccidia, since flukes are generally longer-lived parasites.…”

Flood variation and soil nutrient content in floodplain vegetation communities in the Okavango Delta

“…The comparison of soil nutrient content between years 2010 and 1997 was done through re-sampling soil from zones sampled during low flood 13 selected on the basis of homogenous vegetation cover along an elevation gradient between a river channel (low) and dry land (high) , and Sporobolus spicatus and Sporobolus acinifolius (Zone 8). 19 Zones 1 and 2 were located in the primary floodplains which are closer to the river channel while Zones 3, 4, 5, 6 and 7 were located in secondary floodplains on relatively intermediately elevated areas. Zone 8 was found in the tertiary floodplains, which are relatively highly elevated areas.…”

The influence of cultivation frequency on weed species composition and diversity in flood recession farming in the Okavango Delta, Botswana

“…Previous studies in the Okavango Delta such as Tsheboeng et al (2014), Murray-Hudson et al (2006), McCarthy et al (2005, Bonyongo (1999) and Ellery et al (1993) have demonstrated that vegetation communities are influenced by flood duration, depth and frequency. In flood recession farming areas of the Okavango Delta, weed species composition and diversity were found to be influenced by frequency of cultivation, suggesting that cultivation frequency can be an important driver of weed species assemblages in flood recession farming.…”

“…Handa et al (2012) showed that facultative upland weeds completely dominated the drained cultivated sites as opposed to permanently inundated areas dominated by either obligate or facultative wetland species. Similarly, in the Okavango Delta, Setaria sphacelata was found to be more pronounced in areas subjected to shallow flooding (Bonyongo 1999) while Eleocharis dulcis and Leersia hexandra were found to be facultative wetland species as they were more tolerant to prolonged flooding (Tsheboeng et al 2014). These studies were focused on the floodplains, and no vegetation studies to date have been done in molapo farming.…”