Influence of Tree Density on Vegetation Composition and Soil Chemical Properties in Savanna Rangeland of Eastern Cape, South Africa

Sive Tokozwayo,Keletso Mopipi,Eric Cofie Timpong-Jones

doi:10.4236/as.2021.1210064

Abstract

The proliferation of woody species alters the vegetation structure, leading to loss of rangeland productivity. It aimed to assess the influence of tree density on vegetation and soil chemical properties at three levels of encroachment; open, moderate and dense. Each level of encroachment was replicated 3 times, a 5000 m2 plot was marked per replicate. Four belt transects 200 m2 were placed per plot. Woody species within each belt transect per replicate were identified and recorded to evaluate woody species composition. Grass species composition was assessed using a step point method. Soil was sampled per replicate and analysed for chemical properties. Results showed that 71% of grasses were increasers and 29% decreasers. Digitaria eriantha and Eragrostis obtusa were the most dominant species. Vachellia karoo and Aloe ferox were the most dominant woody species. The dense had high nitrogen (1.48%) compared to the moderate (0.23%) and the open (0.17%). Increaser species, soil carbon, soil pH increased with the increase of tree density. It was concluded that the replacement of highly palatable grasses with inferior ones was due to improper rangeland management practices. It was recommended that land users form rangeland management associations and set up conservation agreements for proper management of resources.

Highlights

Savannas are described as biomes with continuous herbaceous vegetation strata and discontinuous trees or shrubs strata [1]
Open had more decreasers species compared to moderate and dense, respectively. This indicated that the frequency of Digitaria eriantha and Themeda triandra decline with the increase of tree density, except for Panicum maximum
An increase of tree density has resulted in a gradual change of both herbaceous vegetation and soil nutrients

Summary

Introduction

Savannas are described as biomes with continuous herbaceous vegetation strata and discontinuous trees or shrubs strata [1]. This biome covers 33% of the surface area of South Africa [2], delivers a wide range of ecosystem services to humans and supports a wide variety of flora and fauna [3]. Tree-grass co-existence is a widely and often controversially discussed concept [5]. Walter’s two-layer hypothesis has been used to clarify tree-grass eco-existence. Walter’s hypothesis proposed that tree roots occupy the surface and deeper layers of the soil whereas grass roots only occur on the top layer [4]

Methods

Results

Conclusion