Tree growth response at stand edges in gap cutting in Finland

This study provided the models to quantify the edge effect of gap cuttings on surrounding trees growth for pine, spruce, and birch. The developed models predict tree level growth as a function of tree distance from the gap edge with other commonly used growth factors. The models were based on data from 21 gap cutting experiments of pine and spruce dominated stands located in Central and Eastern Finland. Gap cutting had a significant positive effect on tree diameter growth for all tree species in the remaining edge stand. The trend was nonlinear, i.e. the growth acceleration was greatest in the immediate vicinity of the gap, diminishing rapidly towards stand interior, and was virtually extinguished 10 m away from the edge. The effect of distance from the gap edge on height growth showed to be negative for birch and positive for pine and spruce. Despite the large range of gap size (0.1–0.6 ha) in the study material, the growth response showed to be insensitive to gap size. The detected diameter growth response means also increased stand basal area growth of nearby the gap edge. If the edge effect is not addressed basal area growth of the surrounding trees are underestimated. In our study this underestimate was on average by 7 % and 11 % for pine and spruce stands. Although natural regeneration is the most essential aim in gap cutting, the edge effect on the surrounding trees growth needs to be considered especially when assessing profitability of whole management chain for long run. Lack of suitable growth models for gap cuttings has caused challenges for predicting reliably stand developments in Finland.