Female-biased sex ratio despite the absence of spatial and niche segregation between sexes in alpine populations of dioecious Salix lapponum (Salicaceae)

Dioecious plants often exhibit deviations from expected 1:1 sex ratios. Genus Salix is a notable example of the female-biased sex ratio. Quite surprisingly, there are very few studies retesting observed bias patterns from the different parts of the species range. We have determined whether isolated subalpine populations of Salix lapponum exhibit a biased secondary sex ratio, measured the size of the plants, and tested the spatial and ecological correlations of the bias at fine and broad scales. Males were generally taller than females, suggesting that a different allocation of resources may occur in both sexes. Despite this, we found consistent female bias with females on average twice as common as males in most populations studied. No correlations of sex ratio with elevation as a proxy of environmental harshness and proportion of non-flowering individuals were found. Additionally, no differences in spatial sex segregation and microhabitat preferences were found between males and females at a fine scale within the studied populations. Our results suggest that the biased sex ratio in S. lapponum is not environment-dependent and probably originates during early stages of ontogenetic development (seeds).