Microclimatic and spruce growth gradients adjacent to young aspen stands

Effective utilization of a patch or cluster approach to growing aspen-white spruce mixtures in the boreal forest requires an understanding of how the faster growing aspen patches influence microclimate and spruce growth in adjacent spruce patches. In this paper we examine, how young (11–13 year old) aspen (Populus tremuloides Michx) patches influence microclimatic conditions in adjacent openings and how these are reflected in the growth of white spruce (Picea glauca [Moench] Voss) on three boreal mixedwood sites in west-central Alberta, Canada. Light levels increased continuously across the aspen stand boundary and reached maximum levels within the opening, while soil moisture was highest near the edge of the opening and then decreased with distance into the aspen stand or into the adjacent opening north of the aspen stand. Light levels were reduced over a greater distance when moving north from aspen stand edges compared to openings located south of the young aspen. These young aspen stands provided growing season frost protection within one tree length from the edge. The growth of white spruce was positively related to initial crown size and either light levels or distance from the edge. Stem volume growth was best predicted by initial tree size and the light levels at the midcrown of seedlings.