1925: A paper published by Thorvald Schantz-Hanson in 19311, with data collected in 1930 representing 5 years of growth since the initial treatment, noted favorable increases in individual tree yield in the heavily thinned plot, but no improvement in overall yield at that time. The paper noted that at the time of publication, such a pre-commercial thinning of jack pine would not be economically in most silvicultural environments. By 1945, however, a mention in Technical Bulletin 1712 noted that the heavily thinned stand increased growth and improved structure. Individual tree data continued to be collected up to 1960, although no further publications resulted from this experiment. The data presented shows the continued improvement of the heavily thinned plot over the other plots in terms of cumulative mortality, mean DBH, stems per acre, and basal area (Figs. 1, 2, 3, & 4, respectively). The author visited these plots in August 2016, and noted considerable visible difference in the forest environment, as well as measurable differences in surviving basal area of jack pine. The heavily-thinned stand was more open, with minimal hazel or other understory shrubs, and few understory balsams. The moderately thinned plot had a fair amount of balsam regeneration, but had also visibly been affected by a wind event. The check plot was thick with balsam (>350/ac, >1in DBH) regeneration, and had only one living jack pine in the measured area.
2015: Measurements were taken of DBH by a group of undergraduate forestry students at the Cloquet Field Session in August of 2016. They determined that after 1 year, there was a statistically significant (P<0.05) difference between the control plots and the 7x7ft thinned plots, but no significant difference between the 7x7ft and 9x9ft thinnings (Fig.6). Measurements are scheduled to continue in 2018, 2020, 2025, and 2050 before scheduled final harvest in that year.
1Schantz-Hansen, Thorvald. "Some Results of Thinning 27-Year Old Jack Pine." Journal of Forestry 26 (1931): 544-550.
2Allison, J. H., and R. M. Brown. Mangement of the Cloquet Forest: Second Ten-Year Period. University of Minnesota Agricultural Experiment Station, 1945.