Regeneration from seed of six tree species in the interior cedar-hemlock forests of British Columbia as affected by substrate and canopy gap position

Abstract

Canopy gap size can play a major role in determining composition of tree regeneration after disturbance. The effect of different positions within gaps and within the intact forest has received less study. We seeded six tree species onto two substrates (organic and undisturbed moss) in three positions along a north-south gradient within eight replicate 600-m2 canopy gaps and in the intact forest south of each gap (the gap positions), in 1995 and 1996. Emergence of all species was strongly affected by gap position, seedbed substrate, and year, but there was little evidence of partitioning by gap position among the species. Average emergence was higher in the shady southern position in gaps and within the intact forest and significantly higher on organic than undisturbed moss substrates (with the exception of Abies lasiocarpa (Hook.) Nutt., which showed no preference for seedbed). Seedling survival was greatest for all species in the south end of the gap, where soil moisture remained highest and light levels of approximately 20% full sun were adequate for survival. A species trade-off was observed in the understory of the intact forest, where differential survival based on shade-tolerance ranking occurred. To predict regeneration success in these forests, for either silvicultural purposes or to permit a better understanding of community dynamics and succession, it is important to consider the influence of position inside and outside of gaps and the nature of the seedbed substrate.