Most conifer seeds die as seeds or seedlings within 5 years after dispersal. Understanding what factors keep a few of them alive is essential if natural regeneration is to be maintained in managed forests. For example, decaying logs and the conifer seedlings that often grow on them are rare under certain canopies such as deciduous trembling aspen (Populus tremuloides Michx.). We conducted a seeding experiment to evaluate the role of certain substrates, and litterfall, on early conifer survivorship. Seeds of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss), and eastern white-cedar (Thuja occidentalis L.) were sown during 2 consecutive years on mineral soil, relocated logs, and litter in deciduous aspen and coniferous (Thuja occidentalis dominated) stands. Seedling survivor ship was monitored at the end of the first growing season and 1 year after each sowing. Conifer seedling survivorship was equivalent or greater under aspen than under cedar-dominated canopies. Picea and Thuja survivorship was highest on decaying logs of approximately 9 cm high (compared with logs buried at forest floor level) and lowest on forest floor litter during both the first growing season and the following autumn-winter. Abies survivorship was little affected by substrate type, except for low autumn-winter survival on litter. Thuja autumn-winter survival was significantly reduced by litterfall in both deciduous and coniferous stands.©2003 NRC Canada

In order to explain conifer species recruitment in Canada's southeastern boreal forest, we characterized conifer regeneration microsites and determined how these microsites vary in abundance during succession. Microsite abundance was evaluated in deciduous, mixed and coniferous stands along a 234-yr postfire chronosequence. Conifers were most often found in relatively well-illuminated microsites, devoid of litter, especially broad-leaf litter, and with a reduced cover of lower vegetation (< 50 cm tall). Although associated with moss-rich forest floor substrates, Abies balsamea was the most ubiquitously distributed species. Picea glauca and especially Thuja occidentalis seedlings were frequently found on rotten logs. Light measurements did not show differences among seedling species nor between stand types. The percentage cover of broad-leaf litter decreased significantly during succession. Also, rotten logs covered with moss occupied a significantly larger area in the mid-successionnal stands than in early successional deciduous or late successional coniferous stands. The results suggest that the presence of specific forest floor substrate types is a factor explaining low conifer recruitment under deciduous stands, conifer codominance in the mid-successional stage, and delayed Thuja recolonization after fire. Results also suggest that some facilitation mechanism is responsible for the observed directional succession.