Growth of understory Piceaglauca, Calamagrostiscanadensis, and Epilobiumangustifolium in relation to overstory light transmission

Abstract

The potential for use of a partial canopy for controlling growth of Calamagrostiscanadensis (Michx.)•Beauv., and Epilobiumangustifolium L. among regenerating Piceaglauca (Moench) Voss saplings was assessed in the understory of 24 established stands in the P. glauca–Viburnum–Rubuspubescens association of the lower boreal cordilleran ecoregion of Alberta. Stand overstories were dominated by Populustremuloides Michx., P. glauca, or were a mixture of these two species The composition, basal area, and light transmission of the overstory of each stand were measured. Hardwood-dominated overstories transmitted between 14 and 40% of incoming light while P. glauca canopies transmitted between 5 and 11 % of light. Cover and height of C. canadensis and E. angustifolium decreased with decreasing light transmission; at 40% light, both species were greatly reduced compared with open-grown conditions and both were virtually eliminated from stands with less than 10% light. The annual height increment of P. glauca saplings increased from 5 cm at 10% light to 25 cm at 40 % light; the latter increment was approximately equal to growth in 100% light conditions. The number of buds, the diameter of the current leader, and the height to diameter ratio of the tree also increased with light transmittance.

Managing understory light conditions in boreal mixedwoods through variation in the intensity and spatial pattern of harvest: A modelling approach

“…6A). Light levels predicted by SORTIE-ND in the pre-harvested stand were similar to those reported by Messier et al (1998) for mixed stands in the same region (i.e., on average 7.2%), and in the same range as those observed by Lieffers and Stadt (1994) in western aspen-spruce mixedwood stands with a 20-80% deciduous proportion (i.e., ∼5-12%).…”

Describing condition-specific determinants of competition in boreal and sub-boreal mixedwood stands

“…Peak height growth for some boreal conifers (e.g., white spruce and balsam fir) has been shown by some studies to occur between 40-60% full light (Shirley 1945, Logan 1969, Lieffers and Stadt 1994, Comeau 2001, while Jobidon (2000) found that height increments for white spruce increased all the way to full sun. Peak stem radial and/or volume growth among many boreal and western conifers appears to occur near full light (Eis 1967, Logan 1969, Lieffers and Stadt 1994, Wright et al 1998, Jobidon 2000, Comeau 2001). However, stem radial-growth trajectories in response to light availability differ among ecologically distinct conifer species (Wright et al 1998).…”

“…Light interception in the overstory increases with broadleaf stem density (or basal area), while light interception in the understory decreases (Comeau 2001, Comeau andHeineman 2003). Consequently, conifer survival, height growth and stemvolume increments in the understory have been shown to be negatively correlated with broadleaf stem density or basal area (Lieffers and Stadt 1994, Man and Lieffers 1997b, Jobidon 2000, Comeau 2001, Lieffers et al 2002. Minimum understory light thresholds for conifer survival may be exceeded in dense broadleaf stands (Pinno et al 2001) with light levels observed as low as 2% full light (Lieffers et al 2002), which can result in high mortality among the most shade-tolerant conifers.…”

“…For example, Eis (1970) found that the critical light threshold for white spruce survival in central B.C. (about 15% full light) was nearly twice that observed in boreal forests by Lieffers and Stadt (1994). Additionally, Awada and Redmann (2000) reported considerable variation in mortality at low light levels among different populations of white spruce from western and central Canada.…”

“…These relations have been characterized in numerous mixedwood stands (e.g., Lieffers and Stadt 1994, Comeau et al 1999, Messier et al 1999, Jobidon 2000, Brandeis et al 2001, Prévost and Pothier 2003, Valkonen and Ruuska 2003. Current management guidelines in Alberta and British Columbia, which are used to describe the "competition neighbourhood" around conifer crop trees in mixedwood stands (i.e., freegrowing stocking standards), rely on distance-dependent relations confined to a small area around crop trees (MacIsaac andNavratil 1996, Lieffers et al 2002).…”