Fire history and frost in a semi-arid savanna woodland: Understanding their impacts on vegetation structure and species composition in the Waterberg Plateau Park, Central Namibia (Poster)

Fires are inevitable in savanna ecosystems and play a major role in shaping vegetation structure. Thus, fire cannot be disregarded when considering the management of rangelands for both domestic livestock and wildlife. Furthermore, a disturbance that is rarely studied and may be important to understand is frost occurrence in savannas. In the study area frost occurs frequently, particularly in low-lying areas (interdunes) during winter when temperatures are at or below freezing point. The study was done at the Waterberg Plateau Park, a semi-arid savanna woodland considered the south-western limit of the "Tree savanna and Woodland" zone. The park experiences a range of fire frequencies, both natural and of anthropogenic origin, and its fire history (time since last burn and fire return interval) is relatively well known. A total of four sites with the following fire histories were surveyed: fire treatments burned 1 year, 2 years, 14 years and 24 years ago and with mean fire return interval of 6.2 years, 9.3 years, 9.3 years and 18.5 years respectively. The frost study was carried out in an area with a clear dune-interdune effect. Findings show that fire positively (p 0.05) reduce overall woody density but maintained an open savanna through top-kill, thus woody plants persist as gullivers. Woody species composition was also not altered by the current fire history, but a well-adapted woody plant Terminalia sericea dominated the study area. The frost study showed that, frost indirectly influences the grass component positively through top-kill of woody plants that allows more light penetration to the herbaceous layer. This was evident as the interdune areas had significantly (p 0.05) reduce overall woody density. Frost is also an important limiting disturbance that influences woody species composition by favouring more tolerant woody species such as T. sericea and limiting the occurrence of less frost tolerant woody species such as Acacia ataxacantha and Ochna pulchra.