Seed abundance versus substrate limitation of seedling recruitment in northern temperate forests of British Columbia

We examine the influence of (i) the spatial distribution and abundance of p arent trees (as seed sources) and (ii) the abundance and favourability of s eedbed substrates, on seedling recruitment for the major tree species in no rthwestern interior cedar-hemlock forests of British Columbia, under four l evels of canopy openness (full canopy, partial canopy, large gap, and clear cut). Substrate distribution varied with canopy openness, and substrate fav ourability was a function of both canopy openness and seedling species. Lac k of suitable substrates was the predominant factor limiting seedling densi ty under full canopies. Partial canopy and gap sites provided a broad range of favourable substrates in close proximity to parent trees, resulting in the highest observed seedling densities. There was much higher effective di spersion of seedlings away from parent trees in gaps than in the partially cut stands. Seedling dispersion to clearcut sites was poor with seedlings b eing tightly restricted to a narrow band along the forest edge. Thus, seedl ing recruitment in these forests was a reflection of the interaction betwee n the abundance of seed and substrate favourability, and the relative impor tance of these factors varied significantly with canopy structure.