Seed dispersal capacity of Salix caprea L. assessed by seed trapping and parentage analysis

Abstract

The natural regeneration of Salix caprea L. in disturbed forest areas is an important ecological phenomenon occurring during succession in temperate and boreal forests. Knowledge of the timing and extent of seed dispersal in goat willow is still rudimentary. We studied seed dispersal and genetic offspring relationships on five storm-disturbed forest sites (4–13 ha) at 715–900 m a.s.l. in the spruce-dominated Thuringian Forest over a 2-year period. The duration of the seed rain was 3 months in 2015, and only 6 weeks in spring 2016. The seed dispersal curve resembled a negative exponential function with a steep slope. The highest seed numbers of 23–156 n per trap occurred close to the base of the seed trees. Farther than 350 m from the seed trees, average numbers of 0.6–2.1 seeds per trap were recorded independent of dispersal distance, inclination, the number of seed sources and the dispersal direction. Trapped seed numbers at the study sites were quite similar within a given year, but differed significantly between years. Parentage analyses were carried out at one of the five study sites. One hundred saplings and all of the 20 potential parent trees located within a search zone distance of 500 m from the edge of the open area were analysed. Twenty-nine per cent of the saplings were assigned to one of the 20 parent trees. The longest confirmed seed dispersal distance was up to 800 m. Saplings showed a higher allelic variation than the 20 parent trees, therefore indicating external gene flow as well as long seed and pollen dispersal distances.