A review of revegetation techniques in the tropics
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Internal Report 333
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results indicate that a single insect species is unlikely to prove totally effective in the control of mimosa. The trials, including up to six species of insects and two species of fungi, appear to be effective. Each species of insect affects a different aspect of the plant's life cycle and, as a result, contributes to the overall decline of the species. Presently, the insect Carmenta mimosa is proving to be very effective (G. Farrell; pers. comm.) whilst the potential of the other species and the fungi have yet to be tested on a field scale. The field studies indicate that the delay in the effectiveness of an insect-based control method can be attributed to the relatively slow rate at which the insects are spreading rather than any inability of the insects to attack plants. A further example of biological weed control is found at the Nabarlek minesite. The weed spiny head sida (Sida acuta) is being controlled by an introduced beetle, Cal/igrapha pantherina. The beetle was introduced to the site in 1990 with the assistance of the Northern Territory Department of Primary Industry and Fisheries. To date the creature has performed well with effective control of the weed being established and maintained (P.Bailey, pers.com.) 2.9 Species 2.9.1 Species selection The choice of species to be used in revegetation is influenced by its aim. If the aim is to restore the site to a woodland ecosystem, then only local native species can be used in the revegetation program. If the land is to be restored to agriculture, pasture or forest, then different principles apply. Likewise, the species to be used will differ if the land is to be returned to multiple uses involving forestry, woodland, pasture, animal production and recreation. Regardless of the aims of revegetation, there is a need to match species to site conditions because disturbed sites are highly variable. The success of establishment, or ensuring that the established vegetation is viable in the longer term, will depend upon how well the species are matched to site conditions. The species-site matching is extremely important in the case of restoration of native woodland ecosystems where restoration requires the establishment of self-sustaining ecosystems. Greater emphasis should be placed on the use of local native species in ecosystem restoration (Bell 1984). This limits the range of species one could use in revegetation. Nevertheless, there is much natural variability within a given ecosystem and this provides an opportunity to select genotypes for specific site conditions. If a specific quality is not found within the local plant community (eg tolerance to heavy metals, salinity, acidity etc) and if the sites have these characteristics, then the use of tolerant non-local native species or even exotic species should be considered. This site-genotype/species matching principle applies even if a single species is to be established on the site (egPinus radiata or 34 I I I I I I I I I I I I I I I I I I I I I