Fig. 2: Graphical concept.

Based on the altitudinal-niche-breadth hypothesis and a positive specialization-species richness correlation, we expect both decreasing (H I) habitat specialization and (H II) species richness with elevation. Given decreasing specialization with elevation, we expect (H III) decreasing community dissimilarity across developmental stages with elevation. Given decreasing community dissimilarity with elevation, we finally predict that (H IV) differences in species richness among forest developmental stages are strongest at lower elevations and decrease towards the tree line.