Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Premise of the study: In ecosystems where seed production is low and masting years are sporadic, or with species that have short-lived seeds, regeneration is assured by seedling banks rather than seed banks. Seedling establishment and survival play a critical role in determining the composition of these plant communities by supplying new individuals for their maintenance. Seedling emergence and mortality were investigated to test the hypothesis that recruitment into the seedling bank is periodic.

Materials and methods: Seed production and seedling emergence and survival was monitored during 1994-2007 in balsam fir (Abies balsamea) and white spruce (Picea glauca) in four pristine stands of the boreal forest of Quebec, Canada. Measurements were collected twice per month by sampling one permanent plot of 20 × 20 m per stand.

Key results: Seed-rain abundance reached 9 × 103 seeds m-2 year-1, and was characterized by synchronous sequences of low and high seed production. New seedlings appeared only during the year following a seed production of at least 1 × 103 and 1.5 × 102 seeds m-2 year-1 for balsam fir and white spruce, respectively. Seedlings emerged in July and survived 34-52 d on average, with balsam fir showing a longer lifespan and lower mortality, although 85-99% of seedlings died before completing one year of life.

Conclusions: The emergence of young seedlings was coupled with massive seed rains, which allowed synchronous replenishment of the seedling banks among stands and species, and generated different cohorts, yielding a discontinuous age structure.