Dynamics of Savannas in Swaziland: Encroachment of woody plants in relation to land use and soil classes and indigenous knowledge on plants utilization

Abstract

A study was conducted to assess woody vegetation pattern in the semi-arid savannas of Swaziland under three land use systems (communal land, government ranch, game reserve) and three soil classes (vertisol, lithosol and raw mineral). Communal perceptions towards the indigenous use of woody plants were also assessed. A total of 90 woody plant species were identified. Fifty eight percent of the identified woody plants have browse value to livestock. The mean density of total woody plants combined ranged between 1352 TE ha-1 and 11 533 TE ha-1. In severely encroached area, the total woody plant density was greater (p<0.001) on communal land (8578 TE ha -1) than in the ranch (5608 TE ha-1) and game reserve (4123 TE ha-1) and on raw mineral soil than lithosol. In less encroached areas, land use had no significant differences, but lithosol (2024 TE ha-1) had greater density (p<0.05) than vertisol (1237 TE ha -1). The most important encroaching species in the study areas were: A. tortilis, A. nilotica, C. odorata, A. burkei, C. apiculatum, S. caffra and D. cinerea. All the sites in the current study were dominated by height class of >0.05 -2 m, which suggested the potential for long-term increase. There is an indication that bush encroachment showed non to significant variations at small scale (between land uses, soil classes) and large scale levels of resolution (between study areas). At small scale level, significant variations may be due to past and present grazing pressure as well as inherent diversity and nature of the soil. This study suggests in severely encroached area in particular that generalized statements about the relatively bad condition of any land use system and the permanence of any specific condition must be treated with caution. © 2008 Academic Journals Inc.