A transition from gap to tree-island regeneration patterns in the subalpine forest of south-coastal British Columbia

Abstract

We examined regeneration patterns and their relationships to snow and microsite factors in subalpine old-growth stands in the Coast Mountains near Vancouver, B.C. Regeneration patterns resembled those in tree islands of the subalpine parkland more than those in gap-driven stands at lower elevations. Regeneration was overrepresented on mounds and close to a canopy tree where snow melted earliest. In contrast to lower elevation stands, canopy cover was mostly unrelated to regeneration patterns, a result that we attribute to relatively homogeneous light levels in the understory and to the confounding influence of late-melting snow, especially in canopy gaps. The absence of colonization in some gaps and very slow colonization in others further demonstrated that gap creation is not required for canopy turnover. Tree-island regeneration patterns were more clearly expressed by Alaska yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach), a species near the upper limit of its elevational range, than by mountain hemlock (Tsuga mertensiana (Bong.) Carr.), a species in the middle of its range. We conclude that cutting is inappropriate in stands where tree-island regeneration patterns predominate because of the uncertainty of regeneration success.