Forest colonization of savannas : patterns and process

Includes abstract.Includes bibliographical references (leaves 95-102).In this study, I explored factors that influence forest colonization in a South African savanna. I used a 50 year fire experiment in the Kruger National Park to explore patterns of forest colonization in a mesic Terminalia sericea savanna. I studied woody seedling and sapling distribution in relation to different burning treatments, including no burning, and microsite position - in the open or under the canopy of tall trees. The study showed that species richness and abundance was greatest under Sclerocarya birrea, low under Terminalia sericea and lowest in the open habitats. Low fire frequency increased species richness and abundance under S. biirea, but not under T. sericea or the open habitats. Fire sensitive or fire-intolerant species were highest under tree canopies on unburnt and triennial burn plots, whereas frequently burnt (annual or biennial) plots, had fire tolerant and typical savanna species. Frequent burning reduced woody plant biomass by killing seedlings, saplings and adult trees. Fire exclusion led to a higher seedling and sapling recruitment under S. birrea and T. sericea than open habitats