An ecological assessment of the genus Cynodon for reclamation and restoration of disturbed areas in Southern Africa

Abstract

A large section of landscape degradation in South Africa resulted from among others, extensive mining activities. Usually these disturbed areas are plagued with a combination of adverse conditions. Revegetation is the most efficient in reducing negative impacts and helps to prevent air pollution, limits water pollution, it is aesthetically pleasing, and sometimes land productivity can be restored. The erosion control effectiveness of Cynodon species is the combined result of a high shoot density and root mass for surface soil stabilisation, plus a high biomass matrix providing resistance to lateral surface water flow. Differences in ecological performance and the high degree of morphological variation within the genus Cynodon, its wide geographic distribution and the presence of different reproductive modes within the genus, imply that an diverse genetic adaptability for survival under fierce environmental conditions exists within this taxon. Various populations belonging to the genus Cynodon was included in a study aimed at acquiring hardier, more viable ecotypes and/or agronomic groups suitable for restoration and reinforcement of degraded land. A taxometric approach was followed w'hereby 23 vegetative morphological characters were used in a Principal Components (PCA) and cluster analysis to assist in the delimitation of five agronomic groups within the genus Cynodon and eight C. dactylon ecotypes occurring in a distinct habitat. These delimited groups and ecotypes were used for further study and in order to determine the reproductive mode and degree of sexuality for each population, scion growth, chromosome number, seed viability and embryo sac development studies v.,ere conducted. It was concluded that three cytogenetic factors i.e. polyploidy,

apomixis and hybridisation are responsible for the variability generated and maintained within this genus. All the populations studied had some means of asexual reproduction, agronomic group Comsutus XX and ecotype Dae 13 proved to be best adapted for vegetative reproduction. The low percentages of seed viability and excellent vegetative reproductive faculties is a indication that stolon and/or rhizome scions should be used to establish Cynodon populations. Finally, investigations aimed at determining the adaptability and resistance of delimited ecotypes and/or agronomic groups were conducted (adaptability and evaluation phase). Regarding drought resistance, the high degree of correspondence and comparableness between data, qualitative and quantitative, were prominent. Ecotypes Dae 16, Dae 116/113 and Dae SR and agronomic groups lneompletus, Bradleyi and Comlemtus appeared to be superiorly adapted for survival in arid environments. Agronomic group Comsutus XX and ecotypes Dae SR and Dae 13 had the highest biomass production during cultivation under uniform environmental conditions and as for pH tolerance ecotype Dae 16 and agronomic groups Comdaetylon ZZ. and Bradleyi displayed outstanding vigour throughout the experiment. Agronomic groups Comdaetylon ZZ. and Bradleyi, and ecotypes Dae 13 and Dae 116/113 displayed superior tolerance to frost. It was concluded that no ecotype or agronomic group were superiorly adapted to withstand all environmental stresses. The selection of a ecotype or agronomic group for reclamation would depend on the major environmental stress factors at the reclamation site. This investigation quantified the tolerance ranges of the ecotypes and agronomic groups and the implementation and rendering thereof must be evaluated by means of field plantings in critical areas.