Canopy and age structures of some old sub‐boreal Picea stands in British Columbia

Abstract

Abstract. 14 old, unlogged, Picea‐dominated stands in the moist cool Sub‐Boreal Spruce biogeoclimatic subzone of central British Columbia, Canada, were sampled to describe canopy heterogeneity, regeneration patterns and tree population age structures. These stands are composed of Picea engelmannii × glauca hybrids, Abies lasiocarpa and lesser amounts of Pinus contorta and Populus tremuloides, and had survived 124–343 yr since the last stand‐destroying wildfire. Canopy cover was patchy and highly variable (ranging from 30.5 % to 86.4 %) but was not significantly related to stand age. Vertical canopy structure was less variable, reflecting the shade‐tolerance and live crown ratios (length of live canopy expressed relative to tree height) of component species: 18.8 % for Populus, 20.2 % for Pinus, 46.7 % for Picea and 51.4 % for Abies. Individual stands varied considerably in their population structures and in their stand development trajectories, yet some patterns are evident. Survivors of the initial post‐disturbance cohort of trees took 51 to 118 yr (mean = 80, s.d. = 20) to establish. Some stands had all tree species present during stand initiation, while other stands indicated early successional roles for Populus and Pinus, or a late successional role for Abies. Abies recruitment, while often slow in the beginning, occurs uniformly throughout the history of most stands, reflecting the high shade‐tolerance of this species. Picea is often recruited in high densities early in stand development, and then (after long periods of exclusion) may be displaced by Abies in some stands but maintains itself in others. Minor, single‐tree disturbances (due to bark beetles, root rot, and windthrow) were important in accelerating the reinitiation of Picea in the understory. Results thus suggest that stands from this region can be self‐perpetuating in the absence of fire. Yet, post‐fire tree populations still clearly dominate these spruce‐fir forests, for only the oldest stand had greater basal area in the replacement cohort than in the initial cohort.