Growth limitations for conifer regeneration under alternative silvicultural systems in a coastal montane forest in British Columbia, Canada

Abstract

In coastal montane British Columbia (BC), Canada, alternative silvicultural systems that retain varying levels of overstorey structure and employ different gap sizes may provide means to promote regeneration of shade-tolerant conifers. In this study, part of an operational trial of Montane Alternative Silvicultural Systems (MASS), foliage morphology and physiology of planted Abies amabilis and Tsuga heterophylla were measured in conjunction with shade, soil and tree water status, and soil temperature to compare above- and below-ground growth limitations under Clearcut (CC), Green Tree (GT), Patch Cut (PC) and Shelterwood (SW) systems. Three years after planting, both A. amabilis and T. heterophylla seedlings in the SW had smaller height increments (mm) than in any of the other treatments. Acclimation of specific leaf area (SLA, cm 2 g −1) indicated that there were above-ground limitations on foliage growth and development in T. heterophylla in the SW. In A. amabilis, despite an increase in photochemical efficiency ( F v/ F m), above-ground growth limitations in the SW were not alleviated. There was no differential acclimation in the maximum light saturated rate of photosynthesis ( A max) or in foliage nitrogen concentrations (%N) in either A. amabilis or T. heterophylla among the silviculture systems. This, combined with the lack of differences in soil water or soil temperature, may indicate that nutrient availability was not different among the silvicultural systems. Foliar morphological and physiological acclimation showed that the source of seedling height growth limitations in the SW system 3 years after planting was above- and not below-ground. Therefore, retention of 25% of the pre-harvest overstorey stand structure in a dispersed pattern can limit the early growth of regenerating montane conifer seedlings presumably as a result of a 47% reduction in available light and not as a result of reduced nutrient availability.