How do advance regeneration and planted seedlings of Thuja occidentalis and Picea rubens acclimate under a first irregular shelterwood cut?

Abstract

Eastern white cedar ( Thuja occidentalis) and red spruce ( Picea rubens) contribute to the biodiversity and resilience of mixedwood forests. However, cuts that remove most or all the forest cover can cause the decline of these species. Among partial cutting options, the irregular shelterwood system (ISS) can create successful conditions for the development of advance regeneration and enrichment planting. We studied 6 years of ecophysiology of lower advance regeneration and planted seedlings of eastern white cedar and red spruce growing under a first ISS cut according to three cutting intensities: light cut (35% removal, 20 m2·ha−1 residual basal area), moderate cut (42%, 18 m2·ha−1), and heavy cut (52%, 15 m2·ha−1). Light-saturated photosynthesis and height growth of planted cedar and both spruce types decreased with increasing cutting intensity, in response to an increase in competing vegetation. Therefore, to limit the negative impact of competing species on cedar and spruce regeneration, we recommend protecting tall advance regeneration (2 m+) during partial cut operations and using large-sized containerized seedlings (40–50 cm height) for enrichment planting. Results also suggest that a mechanical release could help optimize the physio-morphology and growth of both regeneration types of cedar and red spruce.