Potential for red spruce (Picea rubens Sarg.) establishment from natural seed dispersal in old fields adjacent to forest stands

摘要

Red spruce can establish on abandoned agricultural land only from seed, unlike in logged environments where red spruce forests can establish from seedlings that survived the harvest. In this study we collected seeds from the seed rain and from soil cores to examine the abundance and distribution of the red spruce seed rain and the seed bank along a gradient from the forest interior to adjacent old fields in Greenwich, Prince Edward Island National Park (PEINP), Canada. In addition, we examined the temporal abundance and distribution of the seed rain through the seed-fall season. We subsequently tested the germination potential of red spruce seeds from the forest portion of our sites. Because red spruce seeds are usually viable for only one year, we expected the seed bank to be either very small or non-existent. We found 39 red spruce seeds in the seed bank, distributed over 13.1% of the sampled area; 37 of these seeds were definitely nonviable. From the seed rain, we collected 224 red spruce seeds, distributed over 29.4% of the sampled area; 213 of these seeds were definitely nonviable. Nearly all of the red spruce seed rain fell within the forest; differences in abundance among collection dates were not statistically significant. Our seeds had a low germination rate of 0.004%, in part because red and black spruce commonly hybridise in our study area. Despite the low rates of red spruce seed dispersal and viability, the presence of red spruce saplings in our two longest-abandoned fields shows that the species is able to slowly colonise some old fields in PEINP.