Dispersal of white spruce seed in mature aspen stands

Abstract

The dispersal of white spruce (Picea glauca (Moench) Voss) seed through trembling aspen (Populus tremuloides Michx.) forests was investigated by releasing artificial seed (confetti) from different heights on a meteorological tower, and, secondly, by observing the distribution of spruce regeneration along transects radiating out from small isolated patches of mature spruce seed trees. Mean dispersal distance of confetti increased with height of release. Before leaf fall of the aspen canopy, most confetti landed close to and in all directions around the tower. After leaf fall, no confetti was observed upwind from the tower and the mean dispersal distance increased, with peak densities occurring at a distance of 15 m in the downwind direction. The rate of decrease in regeneration density with distance from patches of mature, seed-bearing white spruce was much less than that observed during confetti release experiments. Furthermore, regeneration densities were significantly greater in the prevailing downwind direction (toward the east). The results indicate that stronger than average winds, primarily from the northwest, west, and southwest, play a major role in the dispersal of white spruce seed. Simulation modelling of the observed distribution of regeneration suggests that long-distance (>250 m) dispersal may be an important mechanism for the persistence of white spruce in the fire-prone boreal forest of western Canada.Key words: seed dispersal, boreal forest, mixedwood, wind dispersal, artificial seed.