An Investigation into the role of Allelopathy in influencing plant diversity around Lantana Camara groves
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Invasive alien species have become a serious threat to plant biodiversity in many parts of the world. Globally the threat to biodiversity due to invasive alien species is considered second only to that of habitat loss. Invasive species are thus a serious impediment to conservation and sustainable use of global, regional and local biodiversity, with significant undesirable impacts on the goods and services provided by ecosystems. Lantana camara L. is one of the many invasive alien species and has been rated by the IUCN Invasive Species Specialist Group among the world's 100 worst invasive alien species. Zambia's National Biodiversity Strategy and Action Plan of 1998 has identified Lantana camara as one of the introduced invasive plants that negatively impacts on ecosystems and indigenous plant diversity. The overall objective of the study was to investigate L. camara's allelopathic effects on indigenous plants in Zambia. Specific objectives of the study were (i) to determine the effect of L. camara on seed germination of some indigenous plants, (ii) to investigate how L. camara affects growth of seedlings in terms of leaf production, root length, root biomass, shoot length and shoot biomass of Bauhinia petersiana, a woody species that appeared to be negatively influenced by L. camara in the field. The study was conducted in two phases. Phase one involved a field survey to determine whether there was a gradient in indigenous woody plant diversity caused by L. camara invasion and to identify species that appeared to be negatively affected by L. camara. The second phase involved laboratory experiments to determine mechanisms by which L. camara negatively affects B. petersiana seedling growth with regard to leaf production, root length, root biomass, shoot length and shoot biomass . The results in this study showed that L. camara did not necessarily influence plant diversity in its neighborhood. The reasons for L. camara not influencing plant diversity could be that its influence significantly depends on its density and age. It can be assumed that the influence of L. camara occurs at very high density beyond the density of 4 groves per ha at Lilayi Game Ranch where the field survey was conducted. It was also noted that possibly the size of the L. camara groves need to be quite large, beyond the diameter of 4.9 m and 5.3 m for the study groves used in order to have an influence on the floristic diversity at Lilayi Game Ranch study site. The experimental results revealed that germination and seedling growth in terms of leaf production, root biomass, shoot length and shoot biomass of Bauhinia petersiana was reduced by the addition of L. camara leaf and root material to soil which is consistent with results of other studies that have shown that the allelopathic effect of L. camara results in severe reductions in seedling recruitment of nearly all species under its influence. The differences in seedling emergence among the treatments were significant (F = 3.96, p < 0.05) with the Bonferroni all - pairwise comparison test revealing that seedling emergence under the LMT was significantly lower than under the RMT and control but was not significantly different from the LRMT. The findings in this study clearly show that L. camara has allelopathic properties that reduce seed germination and seedling growth in terms of leaf production, root length, shoot length and shoot biomass of B. petersiana. Since L. camara appears to have allelopathic properties that reduce seed germination and seedling growth of some native woody plants, such as B. petersiana, it is therefore recommended that there is prevention of its spread into uninfested areas as this will be the most cost - effective way of conserving indigenous biodiversity. There is also need to use an integrated approach to biodiversity conservation that uses a variety of control methods with a range of methods including herbicides, mechanical removal, fire and biological control. Biological control may not eradicate L. camara but could reduce the plant from a weed to a non-weed status which is then maintained in a steady dynamic equilibrium with the control agent species. In this way, biodiversity may be maintained. In addition, there is need for future studies to consider the effect of L. camara on herbaceous plants and ecosystem functions since these were not considered by the present study.
- Natural Sciences