Long-term differential stem growth responses in mature eastern white pine following release from competition

Abstract

The magnitude and duration of the growth response in residual trees following silvicultural release treatments are measures used to assess the success of silvicultural practices. Eighty-eight eastern white pine (Pinus strobus L.) trees, representing three different dominance classes, were sampled destructively from stands from a single study site that included areas of both unharvested (control) and silvicultural release treatments. The study area consisted of several pine mixedwood stands with understory white pine growing in association with an overstory of predominantly intolerant hardwoods. Annual height, diameter, basal area, stem and sawtimber volume increment, pattern of stem increment allocation along the bole, stem form, and height–diameter ratio were reconstructed over a postrelease period of 23 years using detailed stem analysis. Within 3 years of release, white pine in all dominance classes showed significant increases in diameter, basal area, and volume increment compared with control trees. Differences in the volume increment between released and control trees varied with canopy position, with emergent trees showing the greatest increased volume growth, followed by dominant and intermediate classes, respectively. A temporary shift in the growth allocation pattern along the bole varied depending on crown class, suggesting a period of growth adjustment during which trees are acclimating to changes in resource availability and wind exposure. The shift in growth allocation contributed to increased stem taper, resulting in decreased form class and height–diameter ratios in the released trees.