The vegetation of ash disposal sites at Hendrina power station I: Phytosociology

Abstract

A phytosociological study was conducted as an initial assessment of the vegetation on ash disposal sites to determine the community structure of vegetation and how the communities were related based on their species composition and habitat characteristics. The Braun-Blanquet survey and data analysis method was used to identify and classify plant communities on ash disposal sites and an adjacent natural grassland. Relevés were compiled in 113 survey plots. The TWINSPAN classification algorithm was used as first approximation and results were subsequently refined using Braun-Blanquet procedures. The DCA ordination technique was also used to determine the relationship between communities and whether gradients exist in the study area, α-diversity between communities are statistically compared using the Shannon diversity indices and species richness. The natural grassland sites, rehabilitated ash disposal sites and unrehabilitated ash disposal sites formed three separate communities. The two sub-communities that are described on rehabilitated ash disposal sites are distinguished mainly with respect to age of rehabilitation and level of disturbance. Community structure, on a variant level, is largely determined by different treatments (seed mixtures and soil preparations) that were used in the rehabilitation of the ash disposal sites. Plant communities on recently rehabilitated sites are similar to plant communities on dumps of domestic refuse on some of the disposal sites. Based on the variants described, three homogenous areas on the old rehabilitated sites, which were rehabilitated more than three years ago, can be identified. Vegetation is relatively homogenous and variants are closely related. Differences in rehabilitation treatment, age of rehabilitation and man-made disturbances were some of the important factors determining the establishment of different communities on ash disposal sites. Statistically significant differences are found in the diversity of vegetation studied on a community and variant level. Associations on the ash disposal areas are strongly based on the dominance of particular species rather than specific indicator species.