Vortrag, Gesellschaft für Ökologie (GfÖ) Annual Meeting 2015, Göttingen: 31.08.2015 - 04.09.2015
Abstract:
Treelines are fundamental borders in ecology and have been investigated for centuries. Most studies investigated the fundamental environmental causes of treelines whereas geographic drivers such as isolation, continentality and mass elevation effect (MEE) were rarely studied but may be relevant to understand global patterns of treeline occurrence. So far the effect of isolation on treelines has been shown only for islands but it might occur on continents as well. The MEE, which ameliorates growing conditions through increased solar radiation within large mountain chains, has often been described but quantifications are still rare and often unsystematic. To evaluate the importance of these biogeographic drivers on a global scale, we sampled one of the largest treeline elevation data sets (n = 672) using an innovative and systematic sampling approach (GoogleEarth). This enables a global coverage of treeline samples (74°N to 66°S) and a quantification of the influence of isolation (i.e. the nearest distance to a mountain region with similar elevation), continentality (i.e. distance from the ocean) and MEE (i.e. area of mountain chains) on treeline elevation. The global latitudinal pattern showed a distinct double hump, which may result from a tropical depression or from the lack of high mountains in the equatorial tropics. We showed a significant decreasing of treeline elevation with increasing isolation on both, islands and continental mountains. The negative effect of isolation on treeline elevation was stronger on islands and with decreasing distances to the equator. Treeline elevations decreased with increasing continentality for treeline samples located outside of mountain chains. MEE increased treeline elevations significantly. Our results showed that MEE is the most important driver of treeline elevations beside their latitudinal location. We provide new insights into the global patterns of treeline elevations considering underrepresented biogeographic drivers.