Spatial variation of the influence of distance from surface water on riparian plant communities in the Okavango Delta, Botswana

Gaolathe Tsheboeng

doi:10.1186/s13717-018-0140-x

Abstract

IntroductionUnderstanding the environmental factors that influence riparian vegetation community composition and distribution is important for understanding wetland ecosystem functioning. This understanding can further serve to inform policy aimed at conserving wetlands such as the Okavango Delta. In the Okavango Delta, information on the influence of distance from surface water on vegetation community composition and structure is limited. The objective of this study was to determine the relationship between distance from surface water and riparian plant communities at different sites in the Okavango Delta.MethodsVegetation sampling was conducted in four sites in 20 m × 10 m belted plots placed perpendicular to the river bank at 0–10 m, 10–20 m, 20–30 m, 30–40 m, and 40–50 m distance classes. At each site, 10–15 plots were sampled at each distance class. Basal area, species richness, cover, and plant diversity were determined for each plot. Indicator species analysis was used to determine the characteristic species at each distance class. One-way analysis of variance and Tukey post hoc analyses were used to compare species diversity, richness, cover, and basal area between distance classes. Generalized linear mixed (GLM) model was used to test for the overall impact of site and distance on each plant parameter.ResultsMean species richness was significantly (p < 0.05) higher at 0–10 m than at 20–30 m, 30–40 m, and 40–50 m in Boro. There was no significant difference within other sites. Mean species diversity also varied significantly (p < 0.05) in Boro where it was higher at 0–10 m and 10–20 m than at 30–40 m. Mean basal area differed significantly within Jao and Upper Panhandle. In Jao, it was higher (p < 0.05) at 0–10 m than at other distance classes. Mean percentage canopy cover differed significantly within all sites. In addition to this, plant species composition also changed along distance from surface water within each site. From GLM analysis, both distance and site significantly (p < 0.05) influenced diversity and basal area. Species richness and cover were significantly (p < 0.05) influenced by site only.ConclusionDistance from surface water and site are important determinants of riparian plant dynamics in the Okavango Delta.

Highlights

Understanding the environmental factors that influence riparian vegetation community composition and distribution is important for understanding wetland ecosystem functioning
Plant species composition changed along distance from surface water within each site
In areas with relatively shallow groundwater, declining groundwater depth can lead to a reduction in plant species richness and total cover due to a decrease in the availability of a permanent water source to promote primary production (Stromberg and Richter 1996)

Summary

Introduction

Understanding the environmental factors that influence riparian vegetation community composition and distribution is important for understanding wetland ecosystem functioning This understanding can further serve to inform policy aimed at conserving wetlands such as the Okavango Delta. Depth to groundwater influences the distribution of plant species, density, and size structure in riparian zones because it determines the availability of a permanent surface water source (Stromberg and Richter 1996). In areas with relatively shallow groundwater (i.e., where plants are using it as a source of water), declining groundwater depth can lead to a reduction in plant species richness and total cover due to a decrease in the availability of a permanent water source to promote primary production (Stromberg and Richter 1996)

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