Population structure of a fleshy-fruited species at its range edge -: the case of Prunus mahaleb L. in northern Switzerland

Little is known about age structure and reproduction in small populations of woody species at their range edge. Here, we report on the demographic structure of the fleshy-fruited Prunus mahaleb at the margin of its distributional range in northern Switzerland. The aim of the study was to investigate distribution patterns, age structure and plant performance as affected by population size and isolation, altitude and climate. Fifteen small populations were chosen in the Swiss and French Jura, where the species is rare and restricted to exposed cliffs and scree slopes, which are surrounded by beech and oak forests. Plant distribution within populations was often clumped or linear. Irregular recruitment was indicated by uneven age structures with a low number of young plants and missing age classes in some populations. Mean plant age per population ranged from 14 to 42 years. Plant age, stem length and diameter, photosynthetically active crown volume and annual growth increment all differed significally among populations albeit without correlation to population size or altitude. However, recruitment was highest at altitudes between 500 and 600 m, and recruitment and mean plant age were negatively correlated with precipitation during the vegetation period. Plant size was negatively correlated with distance to the nearest population, and positively correlated with nearest neighbour distance. As a conservation tool, forest tree removal may reduce shading and thus increase both vegetative and sexual recruitment in P. mahaleb.