New subject: Fwd: Dark rings in red oak logs PLUS other oak dendrochronology question: enclosed phloem

19 Nov 2009

      Any idea what would cause dark rings in red oak logs as in the attached pictures? 

The dark rings run the length of the logs.  So far this has been seen on a number of sites
in 3 or 4 counties in Minnesota.  Not all red oak trees on a site have the dark rings. 

My first guess is that it is a barrier zone resulting from a wound or injury of some type.
 However it seems strange that it forms a complete cylinder that reaches the ends of the
logs.  I didn't see any logs where the dark ring only went part way around a log. 
Also there were some logs that had obvious injuries with decay and discoloration but these
logs did not form rings or even have distinct barrier zones going even part way around the
log.  

I've only looked at logs like this while in the mill, not on the site where they were
harvested. At first, the thought was that these rings were the result of something
happening 16 to 17 years ago.  This will take more investigation, but it looks to me like
the time period varies anywhere from 6 to 35 years.  Also at this time I can't say if
the time period varies ibetween sites, or if the time period varies from log to log on the
same site.

Any suggestions would be appreciated.  

Mike Albers
Forest Health Specialist
MN  DNR-Forestry
1201 E. Hwy.  # 2 
Grand Rapids, MN   55744
(218)-327-4115