Tree invasion in a semi-arid savanna in Zimbabwe : seedling recruitment of Acacia karroo

摘要: In this thesis Chirara reports on his study the competitive interaction between savanna grasses and young tree seedlings of Acacia karroo, from hereon indicated as ' seedlings' . is one species that dominates grassland in situations overgrazing (bush encroachment). The discussion whether invasion predominantly caused by decreasing light competition or water overgrazed situations. So, studied: -Acacia seedling survival field under different grazing intensitie -Acacia an experimental set up with grass clipping regimes -Water availability relation to regimes effect it for survival -Interaction limitation survival -Effect defoliation survival. Surprisingly, low cover well a high facilitated establishment. Most probably shade reduces evaporation hence demand very seedling. This will establishment rather than long run. Young develop quickly thin taproot search deeper soil. enables survive during dry season. In deep (less 6% full sunlight) growth much hampered independent soil level. These less are not exceptional field. However, slightly higher levels, shortage more determining growth. Depressed due their can lower probability season spells wet season. Grazing 90% finally did recovers quickly. In conclusion, effects considering plasticity allocation pattern especially ability produce early its life cycle, accommodate stress competition. Competition important suppressing seedlings, but only mechanism.