Free-to-grow regeneration standards are poorly linked to growth of spruce in boreal mixedwoods

Abstract

For public lands in Canada, the free-to-grow (FTG) standards are part of regulatory surveys of post-harvest juvenile stands that are designed to assess the level of competition on conifer trees. In this paper we analyzed two data sets to test the ability of FTG standards to predict growth of white spruce saplings. Using data from juvenile permanent sample plots, FTG was assessed at age 13 and subsequent diameter increment and height increment were assessed in the measurement interval after year 18. If the growth of trees was adjusted for differences in height at age 13, FTG status made no difference in predicting subsequent growth. A second data set from operational regeneration surveys of 49, 13-year-old boreal mixedwood stands was also evaluated for evidence of competition across a range of cutblock with different percentages of plots classed as FTG. There was no evidence of an increase in variation in size or growth of leading trees in stands when the plots in a cutblock were evenly split between FTG and not-FTG trees, compared to cutblocks with either few plots FTG or nearly all plots FTG. Height attained at year 13 was a sufficient indicator of future growth. Key words: regeneration, standard, free, grow, productivity, mixedwoods