Inter-and intra-annual patterns of seed rain in the black spruce stands of Quebec, Canada

Abstract

Divergent reproductive strategies of tree species generate differences in the dynamics of seed production and dispersion. The spatial and temporal variability in seed rain abundance and viability was monitored during the period 2000-2007 in four boreal stands in Quebec, Canada. The aim was to compare the interand intra-annual patterns of seed dispersal between species with diverging adaptive characteristics and reproductive strategies by testing the hypothesis that sympatric species can exhibit different patterns of seed dispersal according to specific ecological adaptations. The coefficient of variation (CV), representing the inter-annual variability in seed rain, was close to or higher than 1 in balsam fir (Abies balsamea [L.] P. Mill.) and white birch (Betula papyrifera Marsh.) and confirmed the mast seeding habit of the two species. In contrast, CV in black spruce (Picea mariana [Mill.] BSP) ranged between 0.24 and 0.54, indicating a more homogeneous inter-annual amount of seed dispersal because of its semiserotinous cones that preserve seeds for an indefinite period of time. The species showed divergent intra-annual patterns of seed dispersal. Most seed dispersal of the companion species was observed in September-November, while black spruce concentrated seed rain in spring, when the proportion of germinated seeds was higher. Boreal stands experience annual seed rains constituted by a gradual dispersal of seeds of dif ferent ages and originating from cones belonging to multiple cohorts. However, asynchronous seed rains in terms of quantity and quality can occur if companion species are associated to the dominant black spruce.