Seedling size and woody competition most important predictors of growth following free-to-grow assessments in four boreal forest plantations

Improvements to forest management decisions require accurate and quantifiable information. We examined the effects of various classes of competitors on crop tree growth in the context of free-to-grow standards using regression analysis. We found that seedling size accounted for most of the variation in height and volume growth of jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] BSP) plantations. Including herbaceous and woody competition as explanatory variables explained the additional variation on crop tree growth significantly. In the plantation initiation phase (years 2 to 6), the presence of herbaceous competitors generally reduced conifer growth but in the first part of the stem-exclusion phase (years 7 to 12) increased their growth. In all four boreal plantations in this study, woody competitors reduced conifer growth in both the initiation and stem-exclusion phases. These results have relevance to forest managers who develop and/or use free-to-grow surveys. Key words: vegetation management, silviculture, effectiveness monitoring, forest management, regeneration success, competition effect