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sur le développement des zones arides et semi-arides

Titre : The competitive effect of vetiver grass on native grasses and implications for grassland rehabilitation in South Africa.

Auteur : Dlamini, Lindokuhle Xolani

Université de soutenance : University of KwaZulu-Natal

Grade : MASTER OF SCIENCE In Grassland Science 2018

Résumé
Vetiver grass (Chrysopogon zizanioides) is a perennial C4 grass that originates from central India. This grass is used worldwide for soil (e.g. erosion control) and water conservation (e.g. wetland and river rehabilitation) because it is a fast-growing tufted grass with a dense root system that reaches 3 meters deep forming a wall-like structure that binds soil particles. Vetiver is a very hardy grass, allowing it to withstand environmental hazards such as drought, frost, and floods. The most commonly used cultivars produce infertile seeds or even no seeds, hence it reproduces vegetatively. To date, no study has investigated the competitive ability of vetiver, factors influencing its competitive ability, whether it inhibits germination and establishment of native grasses, and its role in secondary succession of native grasses. The predicted global increase in atmospheric nitrogen deposition and excessive use of agricultural fertilizers will result in changes in soil nutrient status, hence altering the plant competitive trade-offs that drive species coexistence. Introduced plants, for example, are often more adapted to environmental changes and this may lead to invasion through competition with native plants. This study had three aims ; 1) to examine the behaviour of vetiver and its association with native grasses in the field ; 2) to investigate the effect of established vetiver tufts on native grasses (E. curvula and P. maximum) seed germination and seedling establishment. Within this aim, the effect of different sowing method on seed germination and establishment, and the effect of vetiver tufts when root competition is excluded was also investigated. Lastly, to investigate the competitive effect of established vetiver tufts and soil nutrient status on mature native grasses (Eragrostis curvula, Digitaria eriantha, Panicum maximum, and Hyparrhenia hirta). The last two aims were investigated using a pot trial. The most important results from the surveyed sites were the marked increase in grass species richness with an increase in distance away from planted vetiver, the abundance of bare ground around planted vetiver, and the presence of the recruited vetiver away from planted vetiver.

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