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

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.

Managing forest harvesting to maintain old growth in boreal and sub-boreal forests

“…Subalpine fir is prolific at producing seedlings, but a high proportion of spruce seedlings are apparently recruited into the canopy too (Kneeshaw and Burton 1997), indicating that both species could be successfully managed using partial cutting methods. Subalpine fir was the only species to consistently exhibit an all-aged population structure required for formal uneven-aged management.…”

“…stands in northern Wisconsin, U.S.A., to accelerate the development of old-growth attributes. Kneeshaw and Burton (1997) suggest that the creation of canopy gaps in Sub-Boreal Spruce stands could accelerate the attainment of old-growth status in mature stands, similar to the impact of bark beetles and to pockets of root rot. Runkle (1991) and Coates and Burton (1997) advocate the mimicry of gap dynamics in designing silvicultural systems for ecosystem management objectives.…”

“…Characterised by long, cold winters and moist cool summers, this region of interior plateaux can be considered intermediate between true boreal forest (located further north and east) and subalpine sprucefir forest found above 1100 m to 1300 m elevation in this area (Meidinger et al 1991). Analysis of tree population structures revealed that these stands had individualistic development histories, but were generally characterised by long periods of establishment, decreasing amounts of Populus and Pinus over time, increasing amounts of Abies over time, and the persistence of Picea in some old stands but not in others (Kneeshaw and Burton 1997). Descriptions of the population structures of these stands were subsequently correlated with a number of structural attributes to devise old-growth rating schemes Coates 1996, Kneeshaw andBurton 1998).…”

“…In order to understand these dynamics in a particular forest type, Kneeshaw and Burton (1997) reconstructed the stand development patterns of several mature and old-growth stands in the moist cold subzone of the SubBoreal Spruce biogeoclimatic zone (SBSmc) of central B.C. (53' to 55'N lat., 124" to 128'W long.).…”

Wood production, wood technology, and biotechnological impacts

“…In Finland, other species in mature conifer stands (Scots pine -Pinus sylvestris, lodge- Fig. 2 Views of a spruce with heart rot fallen in 1999 by the storm "Lothar" on the Dinkelberg close to Rheinfelden, south of the Black Forest (photos: Wolfgang Helle) peratures, water regimes, nutrient composition and soil strength, well suited for example for the regeneration of various types of spruces (Anderson & Winterton 1996, Lieffers et al 1996, Kneeshaw & Burton 1997, Ulanova 2000, Ruel & Pineau 2002. Especially in subalpine spruce stands and at dry places, natural regeneration is successful when the seedlings grow on rotten wood.…”