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Results of a lucerne old-field restoration experiment at the Fynbos-Karoo interface


PM Holmes

Abstract

A restoration study was designed to investigate lucerne control and indigenous species re-introduction on previously cultivated land at Matjiesrivier Provincial Nature Reserve, situated at the interface between the Fynbos and Succulent Karoo biomes. The objectives were to compare four lucerne control treatments, and the simultaneous effects of these treatments on the reintroduction of indigenous species by seed, in the presence or absence of brush packs, using a split-plot design. Lucerne was controlled using herbicide, ploughing or a combination of these treatments, and seed collected from target vegetation in the area was applied to half the plots, together with reed mulch. Brush packs, comprising dead shrubs, were added to half the sown and unsown plots respectively. Ploughing significantly reduced lucerne density and projected foliage cover and in combination with herbicide eliminated most lucerne plants. Establishment of indigenous species from sown seed was highest in ploughed plots and comprised both annuals and perennials. There was virtually no establishment in the presence of the alien annual Amsinckia retrorsa. Indigenous perennial plant density, cover and richness were highest throughout the study in the ‘plough plus seed\' treatments, with Athanasia linifolia being the dominant species. Average initial densities of 80 m–2 decreased sharply during the first summer, and at three years averaged 5 m–2. Indigenous canopy cover continued to increase throughout the three years in two of the experimental blocks, and attained that of the target vegetation in ‘plough plus seed\' treatments. Community composition approached that of the target vegetation, although graminoids were under-represented, partly as a result of intensive grazing during the third year, and large, non-Asteraceous shrubs were under-represented. In future restorations at the Fynbos-Karoo interface, it is recommended that the sowing density, particularly of unpalatable pioneer shrubs, be reduced to improve composition and to lower seed harvesting costs. Ploughing is an essential presowing treatment where alien species, especially annuals, dominate the old field. A larger number of species may be established following the creation of different microsites across the field, for example by pitting and brush-packing the surface. Nodes of larger, animal-dispersed species could be established from propagated material to facilitate colonisation of these species across large disturbed areas. It is recommended that sown areas be protected from ungulate grazing until the palatable species have reached maturity.

South African Journal of Botany 2005, 71(3&4):

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