Growth releases across a natural canopy gap-forest gradient in old-growth forests

• We assess growth releases of trees growing along north–south axes of canopy gaps.
• We examine the duration and magnitude of growth releases.
• Duration and magnitude of releases decreased as distance from gap center increased.
• The effect of distance on duration of releases was greater for trees north of gap center.
• Results can help inform ecologically sustainable forest management approaches.

Canopy gaps created by the death of one to a few trees can exert a dominant influence on forest structure and composition by affecting the growth of nearby trees. Previous research in old-growth forests of coastal British Columbia, Canada indicated that most western redcedar (Thuja plicata Donn ex D. Don), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and Pacific silver fir (Abies amabilis Dougl. ex J. Forbes) growing around, or within, 20 natural canopy gaps of known timing of origin experienced a release (i.e., abrupt increase in radial growth) following gap formation. In that study, tree diameter, growth rate prior to a release, species identity, and interactions between some of these variables influenced the duration and magnitude of releases. In this study, we use trees growing along north–south transects that extend through the 20 gaps and into the adjacent forest to clarify the influence of two additional variables on growth releases: tree distance from the gap center and tree north–south position relative to the gap center. For all trees, predicted duration and magnitude of releases showed a decreasing trend with increasing distance from the gap center. Interestingly, the effect of distance on predicted duration of releases was greater for trees north versus south of the gap center, suggesting a response to additional light availability north of the gap center. These findings, combined with those from our previous study, indicate a strong influence of canopy gaps on growth releases of nearby trees of varying sizes and species in our study area, even trees that extend into the surrounding forest matrix. Our results can help inform ecologically sustainable forest management approaches, including variable retention approaches that aim to emulate the fine-scale, low-intensity disturbances that dominate the wetter forests of coastal British Columbia.