Abstract
Exotic plantation forests have high biomass and contribute to significant economic impact of many countries in the World. This is due to the fact that the species have an ability to grow very fast in introduced areas compared to many native species. However, they might also escape from plantations through seeds regeneration and spread into natural habitats. Their expansion outside plantation may have huge negative impacts on biodiversity and ecosystem functioning, and thus has become a major concern for many scientists. The major planted species worldwide are eucalyptus, pines and cypress. This study aimed to investigate the regeneration potential of four exotic planted species (i.e., Eucalyptus grandis, Pinus kesiya, Pinus caribaea and Cypress lustanica) at the Sao Hill forest plantation, Tanzania and try to record any evidence of self-regeneration of the species into its adjacent natural areas. The study proposed that: “if these species can withstand conditions of plantation areas where no prior treatment of soil, watering, or fertilizer applications, may have the potential to have natural regeneration into natural areas upon plantation escape”. The study was done by conducting censuses of all regenerated exotic individuals into both plantation and natural areas. In total, there were 4 districts (with 12 transects). Three line transects were set up at each district. The distance from plantation boundary was 100 m and 200 m in plantation and natural areas, respectively. The study found that the species have self-regenerated and have the potential of becoming invasive. Three species (i.e., Eucalyptus grandis, Pinus kesiya, and Cypress lustanica) were found into both plantations and natural areas, while few individuals of Pinus caribaea were recorded. The results further showed a positive skewness trend of individual recruits towards natural areas. The majority of the individual recruits were found close to the plantation edge. Moreover, results on maximum diameter at breast height (DBH) on individual recruits showed that, individual’s diameter in two species (i.e., Eucalyptus grandis, Pinus kesiya,) increased with distance from plantation boundary and thus indicating severe invasive potential. Thus, having seen the successful natural regeneration of the species, this study urges further studies to identify traits of species related to invasion and composition of native forests. Nevertheless, identifying the details of germination ability and processes associated with seeds dispersal, seedling survival and mortality are crucial. The current results of this study can help plantation managers to easily identify fast spreading species into natural areas and thus, take responsible measures of control.

Table of Contents
Acknowledgement i
Abstract iii
Table of Contents v
List of Figures vi
List of Tables vii
1. INTRODUCTION 1
1.1. The ecology and economic impacts of plantation species 1
1.2. Pattern and mechanism of species invasion 2
1.2.1. Casual arrival 3
1.2.2. Naturalize 3
1.2.3. Invasive 4
1.3. Plantation status in Tanzania 6
1.4. The Sao Hill forest plantation 8
2. MATERIAL AND METHODS 11
2.1. Study Area 11
2.2. Climate and Soils 11
2.3. Vegetation 12
2.4. Study Species 12
2.5. Sapling recruitment 16
2.6. Canopy height and openness 19
2.7. Litterfall coverage 21
2.8. Data analysis 21
3. RESULTS 22
3.1. Self-regeneration pattern of individual species 22
3.2. Recruitment of individuals in relation to distance from plantation boundary 22
3.3. Species diameter in relation to distance from plantation boundary 24
3.4. Recruitment patterns related to environmental factors 29
4. DISCUSSION 33
4.1. Recruitment of exotic plantation species into natural areas 33
4.2. Recruitment as a source of habitat establishment 34
4.3. Recruitment differences between inside plantation and into natural habitat 35
4.4. Species traits and characteristics 35
4.5. Environmental factors affecting recruitment of individuals 37
4.6. Study limitation 37
4.7. Conclusion and way forward 38
5. REFERENCES 40
6. APPENDIX 43

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