Vitality of bog pine and colonising Norway spruce along environmental gradients within a bog

Bog pine is an endangered species in Europe as drainage of bogs permits colonisation by Norway spruce, resulting in severe bog pine habitat loss in marginal bog forests, and a habitat shift towards the bog centre where growing conditions are extreme. Thus, we investigated the physiological causes that limit bog pine regeneration at the bog margins and growth in the centre. We measured needle nitrogen concentration, chlorophyll content, photosynthetic capacity and the morphological traits of bog pine and spruce along transects from the centre to the margin of a bog in the Black Forest, Germany. Needle nitrogen and chlorophyll contents in the bog pine increased from the centre to the margin. However, photosynthesis was independent of chlorophyll content indicating that other factors, such as light rather than nutrients, may limit regeneration of bog pine. Vitality of bog pine was highest at the edge of the bog centre. This zone appears to be a compromise between nutrient limitation and shallow water levels on the one hand, and light limitation caused by spruce on the other. Therefore, in order to conserve bog pine, it is necessary to maintain wet and open bog forests that cannot be colonised by spruce