Effects of shelterwood and site preparation on microclimate and establishment of white spruce seedlings in a boreal mixedwood forest

Microclimate and seedling response of planted white spruce were investigated under four canopy densities (control - a 120-year old uncut aspen/white spruce stand, low and high residual densities of shelterwood canopy, and clearcut) and three site preparation treatments in the Lower Foothills of central Alberta. The partial canopy of the shelterwoods had a less extreme environment than the clearcut: higher humidity and soil temperature, lower maximum air temperature and occurrence and severity of night frost, and a light regime that was nearly optimum for height growth of juvenile white spruce. Planted white spruce seedlings had earlier bud break, lower seedling mortality and terminal bud mortality, higher rates of photosynthesis and stomatal conductance, and greater height and diameter increments under shelterwoods than those in either clearcut or control. Site preparation increased soil temperature, decreased seedling mortality and improved growth, especially diameter growth. This study demonstrates how shelterwoods and site preparation can improve the establishment of white spruce. The findings of this study can be applied to the situations where white spruce establishes in the understory.