Effects of Thinning on Dynamics and Drought Resistance of Aspen-White Spruce Mixtures: Results From Two Study Sites in Saskatchewan

Drought stress associated with warm temperatures is causing increased mortality and reduced growth of trees in drier portions the boreal forests western Canada both warming drought expected to increase over coming decades. While thinning often shown reduce stress, there little information on its effects stands comprised mixtures trembling aspen white spruce that are common this region. This study examined pre-commercial growth, response stand dynamics for two sites located Saskatchewan, Canada. In unthinned plots densities declined from initial 40,000 200,000 ha ?1 2,639 at age 26. Twenty-one years after (i.e., 26) diameter had increased, largest being found lowest (200 0 spruce). Aspen density affected average height but not top trees. Spruce decreased significantly increasing density. Crown width live crown ratio Data cores collected indicate significant positive tree size (basal area beginning year), CMI (Climate Moisture Index) basal increment while (m 2 ) negative growth. Increasing area) competition resistance resilience spruce. Yield projections provided by Mixedwood Growth Model (MGM) suggest mixture 1,500 1,000 has potential provide a 23% total mean annual (MAI) single harvest 100, compared stands, 44% reduction MAI pure stands. Thinning below 4,000 5 resulted yields yields.