Survival and growth response of seedlings in root disease infected partial cuts in the Interior Cedar Hemlock zone of southeastern British Columbia.

摘要

Widespread concern about the sustainability of clearcut regeneration systems has led to the increased use of partial retention systems in British Columbia. In particular, uncertainty surrounds the relative performance of tree species of different shade tolerance, prompting increasing interest in seedling response to a range of light environments. Even more uncertainty surrounds our understanding of the development of trees in partially cut stands infected with the root diseases, Armillaria ostoyae and Inontus tomentosus [Inonotus tomentosus]. The survival and growth responses of different species of planted and advanced conifer regeneration to 3 levels of overstorey retention and 2 levels of root removal system, were examined. We compared light retention (25% of the original basal area), heavy retention (50% of the original basal area), and clearcut treatments at 2 sites (the Mount Seven site and the Ice Road site) in the Interior Cedar Hemlock zone in eastern British Columbia, Canada. Plug stock of Douglas fir [Pseudotsuga menziesii], western larch [Larix occidentalis] and interior spruce [Picea glauca x Picea engelmannii] were planted in Mount Seven, while Douglas fir, western larch and western red cedar [Thuja plicata] were planted in Ice Road. A root removal technique (pushover felling) was used for root disease mitigation. Light levels were measured using hemispherical photography. Growth rate increased as the level of canopy openness increased, but did not vary among species differing in shade tolerance. The root removal treatment, by contrast, had no effect on seedling survival after 5 years. Development and expression of the root diseases over the longer term may alter these results. Our findings demonstrate that a variety of partial retention systems can be used to regenerate mixed species forests in the Interior Cedar Hemlock zone.