Regeneration of grassland after removal of pine plantations in the north eastern mountain grasslands of the Drakensberg escarpment, Mpumalanga, South Africa

Abstract

Concern for the severe loss of biodiversity of grassland species is often voiced. Plantation forestry is known to cause extensive and long lasting disturbance of the natural environment in particular in areas such as the mountain grassland of the Drakensberg escarpment. The survey was conducted in the Graskop area on sites within pine plantations along the Treur River bordering the Blyde River Nature Reserve. The results showed that restoration of plant species biodiversity through natural succession, on cleared plantation sites, required periods longer than seven years and that the regeneration of a great many of the indigenous forb species remained uncertain. Two survey areas were selected and within each survey area, sampling sites were selected to represent three categories of vegetation namely, undisturbed grassland and sites where pine trees had been removed three and seven years previously. Samples of plants were collected from each of these sampling sites. Analysis by means of a classification technique determined the species composition of the disturbed sites in relation to that of the intact grassland. Wheel point surveys were also carried out on these sites to provided information on the vegetation cover, as well as the degree of species regeneration on each site. The variation in vegetation composition of the various plots was ana lysed by means of Detrended Correspondence Analysis (DCA) and Two-Way Indicator Species Analysis (TWINSPAN). The results showed three distinct species assemblages which corresponded with the three categories of sampling sites. Also that the indigenous forbs species comprised 68% of all the sampled species most of which had failed to regenerate in either the three or seven year cleared plots. The most successful grass species in establishing and persisting in all sites were, Eragrostis curvula and Loudetia simplex. The fern, Pteridium aquilinum had a high prevalence on the disturbed grassland plots and the threat of its invasion of these habitats is compounded by the physical disturbance which eradication methods cause. Planning for grassland restoration involves cognizance of the complexity of grassland ecology, the influence of a multiplicity of environmental factors and the proximity of donor sites to the disturbed areas. Applying international restoration techniques used in grasslands of different origins to those of South African landscapes could result in disappointing and costly efforts. At best any attempt at managing grassland diversity should be preceded by an holistic investigation into the environmental conditions particular to the specific terrain and thereafter maintaining a conservative approach of allowing natural succession. The threat of invasive exotic species should be integral to conserving the integrity of the remaining intact natural grasslands in South Africa. It is acknowledged that in this study regeneration of grassland species on plantation sites cleared of pine trees three and seven years previously does not include a long time span such as needed for succession to take place but is useful in showing a trend in species re-colonization to resemble the vegetation of intact grassland, as well as highlighting the absence of a great number of indigenous forb species. Copyright