Canadian Forest Service Publications
A study in sampling of pre-commercial thinned plots in New Brunswick. Internal Report. 2007. Swift, D.E.; Bourque, C.P-A.; Toole, D. Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre, Fredericton, N.B.
Issued by: Atlantic Forestry Centre
Catalog ID: 26942
In recent years, inconsistent assessment results from routine harvest block surveys for different parts of New Brunswick have raised concerns among foresters about the required sampling intensity for pre-treatment precommercial thinning conditions in softwood and hardwood stands. The primary objective of this report is to determine the required sample plot number for four groups of harvest blocks size (10, 20, 30, and 40 ha) at three confidences levels (90, 95, and 99%) at the request of the New Brunswick Silviculture Technical Group. A secondary objective of this report is to determine the influence of limiting to the upper level of 33 crop-tree stems/plot (49 5000 stems / ha) on density determination and required sample plot number. The required number of sample plots is determined by classic statistical methods and Monte Carlo modelling techniques. High variation in stem densities of all species combined, softwoods, and hardwoods was observed for individual regeneration plots and harvest blocks. Between one to two regeneration plots / ha for all species and hardwoods at 90% confidence level appears to provide a reliable estimate of the mean crop-tree density for most harvest blocks of this study. For softwood mean density estimates, between two to three regeneration plots / ha are required for adequate sampling of most of the harvest blocks. Although the analysis of an upper limit of 33 crop-trees / ha showed no significant differences to an actual density count at the harvest block level, the impact on the productivity of the silvicultural worker conducting per-commercial thinning prescriptions is beyond the scope of this report. The impact on productivity of the silvicultural worker because of significant stem density differences at the regeneration plot level is not known. Extreme variation of individual regeneration plots and some harvest blocks may be reduced by fewer and larger sample plots or stratification of the harvest blocks based on ecological or landscape features, such as the Depth-to-water Map.