Arboretum Dendrochronology Workshop by Dr. Brita Lorentzen, May 5, 2018

The following is a summary of the Dendrochrology workshop conducted at the Arboretum on May 5, 2018, by Dr. Brita Lorentzen of Cornell University:

Cored 4 trees southwest of the Learning Center:

  1. Bur oak: minimum age= 1893 (125-year sequence) (reasonably close to the center, so we’re probably within ~10 years of the center)
  2. Red cedar: actually rather young, considering; minimum age is 1926 (92-yr sequence), and it’s reasonably close to the center (within a few years, plus adding in a few years for it to reach chest height)
  3. White oak: minimum age is 1905 (113 year sequence), but this core didn’t go in very far because we hit a rotten patch ~1905
  4. Red oak: minimum age of 1912 (106 year sequence), but again, this core is probably a bit further from the center, given that we were concerned about rot in the center and stopped


  1. The bur oak has an injury that caused callus tissue to form in 1956; this is a rather non-specific injury signature, so there’s some sort of disturbance but hard to say what
  2. There’s a cambial injury to the white oak in 1905; with a core, it’s hard to see the entire structure of it, so I can’t tell whether it’s just something like bark getting stripped on part of the trunk or a deer rubbing its antlers on the tree, etc.  Doesn’t look like a fire related injury, though.
  3. Overall the bur oak has fat rings; its average ring width is 4.02 mm, vs. 2.30 (white oak) and 2.57 mm (red oak)
  4. The red cedar is most “sensitive” to changes in environment from year to year (it has the strongest reaction to 1988)
  5. The bur oak has several “density fluctuations,” late in the growing season in 1900, 1907, 1931, 1961, and 1973, so there’s some sort of disruption to the regular growing regime.  I’ll get you a photo of one under the microscope tomorrow morning when I’m back in the lab.  There’s a few different things that can cause these, so I’ll need to look up climate, etc. to get a better idea of the culprit, unless you’re aware of any management history changes in those years, too.
  6. 1988 does indeed show up as a bad year, although far more noticeable are the effects of the Dust Bowl years of 1934 and 1936 in creating narrow rings in all of the samples; based on what I see from the notable good and bad years, I’d say that the tree-ring widths are mostly changing in response to summer moisture availability, which is pretty typical for mesic forests in the Upper Midwest.




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