Print PageFragmented landscapes are vulnerable to habitat loss, and over-utilisation of remaining resources. Sand Forest, which only occurs in South Africa and Mozambique, is a typical example. It is a highly fragmented forest type, surrounded by savanna woodland. It has a low resilience to any type of disturbance (e.g. fire or herbivory), and the more recent protection of Sand Forest fragments within protected game reserves has increased browsing pressure by herbivores. Sand Forest is known for its poor regeneration, and size classes are missing within the population structure for many species. The aim of this study was to determine the effect of the dry season and herbivory on tree recruitment. To this end, we made use of a long-term exclosure experiment, which experimentally separates the browsing effects of two herbivore species (i.e. elephant Loxodonta africana, a mega-herbivore and the medium-sized nyala Tragelaphus angasii). In each treatment all woody individuals under the height of 1.5m were measured, counted and identified to species. In addition, any damage was recorded. We conducted three surveys during 2011 and 2012.
Results/Conclusions
Seedling species compositions were different between seasons. Seedling abundance was lower after the dry season. In one species more than 95% of the seedlings did not survive the dry season due to climatic constraints. During these surveys, nyala affected seedling regeneration but not saplings. The results indicate that dry season coupled with herbivory were responsible for inhibition of regeneration of certain woody species, and may as such affect the sustainability of Sand Forest fragments. This may also facilitate invasion of savanna species, which are better adapted to drier conditions. The effect of herbivores may be managed according to set targets, however the results suggest that, in the case of Sand Forest, the future consequences of climate change may cause an irreversible landscape alteration from forest to savanna.
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