Windthrow after shelterwood cutting in balsam fir stands

The use of partial cutting in balsam fir stands has been greatly restricted by the fear of windthrow. This applies to shelterwood cutting, for which very little quantitative information on windthrow is available. This study was conducted in 50-yr-old balsam fir stands. The aim of the study was to quantify windthrow losses associated with three patterns of seed cuts. The study consists of five replicates of four treatments: uncut control, uniform shelterwood, group shelterwood, and strip shelterwood. Complete windthrow monitoring was performed at 2, 4, and 6 yr after cutting. The effect of treatment, wind exposure, and stand characteristics was assessed after 6 yr. A simulation with the ForestGales model was conducted to better understand the seed cut pattern effect in identical stands. Results showed that a shelterwood method involving a low intensity seed cut can be applied in relatively sheltered balsam fir stands. Topographic exposure and stand characteristics did not contribute to the amount of windthrow observed. The major factor explaining the amount of windthrow seems to be the presence of adjacent cuts that funneled wind into the plots.