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Irl, S*; Steinbauer, M; Beierkuhnlein, C; Jentsch, A: Dynamics of an island endemic shrub: Herbivores a threat to island biodiversity?
Vortrag, 41st Annual Meeting of the Ecological Society of Germany, Austria and Switzerland (GFÖ), Oldenburg: 05.09.2011 - 09.09.2011

Plant species and ecosystems on oceanic island have generally evolved in the absence of strong herbivorial pressure. Yet, around the globe introduced herbivores have caused severe damage to natural island ecosystems with a particularly detrimental effect on island endemic species. Interestingly, the spatially isolated, high‐elevation desert (codesar) of La Palma (Canary Islands) is dominated by Adenocarpus viscosus ssp. spartioides, one out of several other endemic shrub (sub‐) species, while the other shrubs of this ecosystem are highly endangered or even close to extinction. We assessed the population dynamics and spatial pattern of A. viscosus ssp. spartioides. Habitat and vitality characteristics were investigated assessing spatial topographic features and tree ring based age estimates. In addition, we analysed plant diversity patterns and growth height of shrubs in communities dominated by A. viscosus ssp. spartioidesas a function of herbivore exclosure. Mean age increased with altitude although vitality analyses indicated that the codesar is elevated above the growth optimum of A. viscosus ssp. spartioides. All investigated non‐dominant shrub species reached a larger canopy height in the exclosures than A. viscosus ssp. spartioides, but were absent elsewhere, even though these effects were depended on altitude and island orientation. Introduced herbivores (rabbits and goats) seem to be the major disturbance in this ecosystem and pose the biggest threat to native ecosystem biodiversity. Recently, increased fire frequency and recurrent ice storms probably further alter the disturbance regime. This high‐elevation desert is an ideal model system for investigating interactions of fundamental processes in nature, due to its small species pool exposed to key ecosystem disturbances.
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