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University of Fort Hare (2016)

Effect of Acacia Karoo encroachment on grass production in the semi-arid savannas of the Eastern Cape, South Africa

Magandana, Thabo Patrick

Titre : Effect of Acacia Karoo encroachment on grass production in the semi-arid savannas of the Eastern Cape, South Africa

Auteur : Magandana, Thabo Patrick

Université de soutenance : University of Fort Hare

Grade : Masters Agriculture (Pasture Science) 2016

Résumé
The objectives of this study were (1) to investigate the influence of individual A. karroo on soil and grasss layer. (2) to investigate the effect of Acacia karroo encroachment levels (open, moderate and severe) on the grass layer in semi-arid communal grazing lands. The first study was conducted at the University of Fort Hare farm located in Alice in the Eastern Cape Province, South Africa. A total of thirty A. karro plants were selected randomly, of which ten trees each having sizes of ( >1.5m – 2m, >2 – 2.5m or > 2.5m ). Two transects radiating out of the tree trunk to open grassland were marked at each woody stand in the north and south directions. Each transect was divided into two sub-transects to represent the under canopy and outside canopy zone. In each sub-transect, two 0.5 x 0.5 m quadrat was laid to record all vegetation and soil data. The tuft diameter of C. plurinodis was significantly (p<0.05) smaller on the open habitats of >1.5m – 2m trees. Tuft diameter of Sporobolus africanus was significantly (p<0.05) smaller under canopies of >2m – 2.5m trees in winter. Tuft diameter of Themeda triandra was significantly lower in the open habitats of >1.5 m – 2m trees in summer. The grass biomass production was significantly (p<0.05) lower under the canopies and open habitats of >1.5m – 2m stands in winter than summer. Soil organic carbon content was significantly (p<0.05) lower under canopy and open habitats of >1.5m – 2m trees. The second study was conducted at Melani communal village which is located approximately 12 km North of Alice Town. Three encroachment sites were selected namely severe (3650 trees/ha), moderate (2521 trees/ha) and open (250 trees/ha). A total of 16 grass species were identified of which 15 were perennials. Grass biomass production was affected (P<0.05) by encroachment being lowest at open sites. T. triandra dominated the moderate and severe encroached sites whereas Digitaria eriantha dominated the low encroached site. Overall decreaser grass species increased with the increase in encroachment levels. On the other hand, the increaser II grass species such as S. africanus and microchloa caffra dominated the open site showing that their abundance decreased with the increase in tree density. In terms of height, grass species at the open site were shorter (P<0.05) than the moderate and severe encroached sites. Basal cover improved with the increased encroachment levels. Grass biomass production was affected (P<0.05) by encroachment being lowest at open sites. A. karroo improves grass production. Grass layer improves under tree canopies with the increase in A. karroo up to a point where A. karroo suppresses grass growth. The more palatable grass species occurred under canopies than open habitats. T. triandra was dominant under tree canopies than open habitats. The grass biomass production and basal cover improved under canopies than open habitats.

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