Poster, BayCEER-Workshop, Bayreuth, Geo-Gebäude, H 8: 2012-10-11
Introduced mammalian herbivores are considered one of the major threats to native island ecosystems and biodiversity. Environmental isolation is exceptionally high in high-elevation ecosystems on oceanic islands, thus, resulting in a high proportion of endemic plant species. As a consequence of the evolutionary history in the absence of mammalian herbivores endemic plant species are considered poorly adapted to herbivory. Here, we present data from an 11-year exclosure experiment in the high-elevation ecosystem of La Palma, Canary Islands, where rabbits and goats have been introduced but do not naturally occur. Our aim is to investigate the effect of herbivory and fire on seedling establishment and species diversity. Results show that overall species richness and seedling establishment are positively affected by the absence of herbivores. Furthermore, species richness was significantly increased by a wildfire that occurred in parts of the study area six years before sampling. We conclude that since human colonization competitive balance of the high-elevation ecosystems has been severely altered by the introduction of non-native herbivores. Although it is banned today, goat herding probably induced a shift in species composition with detrimental effects to several single island endemics. Presumably, only total eradication of introduced herbivores will allow a protection and even reestablishment of the highly endangered endemic flora. In contrast, fire seems to influence seedling establishment and diversity positively.