Revegetation of Artificial Disturbances in Grasslands of the Serengeti National Park, Tanzania: I. Colonization of Grazed and Ungrazed Plots

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Abstract
(1) The effects of small, physical disturbances on the structure and species composition and of grazing on colonization and regrowth of tropical grasslands were investigated in four communities in the Serengeti National Park, Tanzania. The species composition and densities of seedlings, surviving sprouts and invading ramets were recorded throughout the first growing season following disturbances. Soils, seed banks and natural disturbances were also investigated. (2) All species that grew in the disturbed plots were present prior to the treatments and, in most cases, the most abundant colonizing species were previously abundant also. (3) Seedlings were more abundant than vegetative sprouts and ramets on disturbed plots in all communities. (4) The densities of seedlings, sprouts and invading ramets decreased along a gradient of increasing rainfall and soil moisture. This decrease in revegetating plants was not correlated with soil type, persistent seed bank (which was negligible in all sites), or frequency of disturbance, but it was partially correlated with the composition of the undisturbed vegetation. (5) The depth of disturbance affected significantly 28% of the species; seedlings were more abundant in the deeply disturbed and sprouting species were more abundant in shallowly disturbed plots. (6) Grazing affected significantly 23% of the species. Most species escaped the effects of grazing by being prostate, resprouting from ground-level or underground organs, or by growing before or after the periods of heaviest grazing. (7) Large mammals were not responsible for the rich community pattern found in most Serengeti grasslands.