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Tunnel Road Pine Spacing Trials and Student Thinnings
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The overstory red pine present along Tunnel Road naturally regenerated following clearcut logging in 1911 during a good seed year. Logging slash was piled and burned on site. Regeneration in the stand was quite uneven and in 1927 some dense portions ran as high as 20,000 trees per acre (Schantz-Hansen 1933). The overstory scotch pine intermixed with the red pine on the north end of Tunnel Rd were part of experimental plantings established in 1915–17.

Experimental thinnings first occurred here in 1927 that included the removal of tens-of-thousands of 15 year old red pine to create growing space for residual trees left in four spacings (4x4, 6x6, 7x7, and 9x9 feet). The effects of the various spacings on red pine growth are evident today.

Image 1: Dr. Thorvald Schantz-Hansen stands in a red pine thinning plot ca. 1928. (Image: University of Minnesota Archives, Cloquet Forestry Center Collection)

In 1950, the first set of student thinnings was marked and carried out by U of MN forestry students as part of their coursework. The thinnings removed low-value, high-risk trees, as well as some high-value, low-risk trees. This approach ensured that natural thinning mortality was captured as timber and the residual stand was left with a desirable spacing for increased tree productivity. Additional thinnings occurred in 1960, 1970, and 1985, each removing commercial materials and increasing the overall value of the stand long-term.

The pine along Tunnel Road will see a final regeneration harvest in the coming years using variable retention harvesting techniques that favor the perpetuation of red pine and associated native tree species and the reduction of the non-native scotch pine.

Image 2: View of Tunnel Road looking north, October 2020.


T. Schantz-Hansen, Observations on the Thinning of Fifteen-Year-Old Norway Pine, Journal of Forestry, Volume 31, Issue 7, November 1933, Pages 838–841,