Structure of high-elevation, old-growth stands in west-central British Columbia

We described quantitatively the height distributions of three high-elevation, old-growth stands in the Engelmann Spruce – Subalpine Fir zone of west-central British Columbia. The stands were composed of subalpine fir (Abies lasiocarpa (Hook.) Nutt.), with very few Engelmann spruce (Picea engelmannii Parry ex Engelm.) trees; had a two-storied canopy; and were multiaged. The height distributions were quantified by fitting curves to the cumulative frequency distributions. The diameter distributions of the study stands were reverse-J shaped and similar to those of other old-growth Engelmann spruce – subalpine fir stands in the Pacific Northwest; however, the height distributions were different, indicating the presence of two canopy layers. We suggest that high-elevation, subalpine boreal, old-growth stands composed of shade-tolerant tree species may display a modal height distribution instead of a reverse-J shape. This structural pattern is suggestive of the transition between the gap-phase and tree-island regeneration models and of the cyclic mode of succession.