HOW OLD IS THAT TREE?

GRAY MORNING

TRUNK OF LARGE WHITE PINE: HOW OLD WAS IT?

36" DIAMETER, APPROXIMATELY 100 ANNUAL RINGS

Thursday, 8;30 AM.  38 degrees F, wind N, calm to very light.  The sky has a high overcast, the humidity is 62% and the barometer is falling, currently at 30.34".  Overcast or not, it will be a warm melt day.

   It's always interesting to guess the age of a large tree.  I am always right, of course, because  there is no way to challenge my guess except to count the annual rings.  That is not possible unless the tree is cut down, or an increment borer is used, an invasive and laborious procedure.  So if I have an opportunity to count the rings on a felled tree I try to do so.

   In this case several large old white pines, Pinus strobus, that were dead or dying were felled by highway crews along Hwy. 13, near the Sioux River.  My guess is that they were killed by road salt over a period of years, white pine being quite intolerant of salt.  I had easy access to one of the trees and I measured the diameter of the trunk and counted the rings.  I had to approximate the core rings as they were deteriorated.  I counted 90 rings and estimated an additional 10, for an approximate age of 100 years old.  The trunk was sawn at somewhere between the root flare and breast height, so my calculations were in pretty good territory.

   I had guessed this tree to be about sixty years old, so it was considerably older than I estimated.  I thought it would have been fast growing in the soil and moisture conditions it grew in but the conditions along the roadside were evidently harsher than I thought and the tree did not grow as fast as it might have, particularly in the last twenty years or so, when the rings were quite close, some years only a sixteenth of an inch or less.  There were a number of years earlier in the life of the tree when the annual rings were more than a quarter of  an inch wide (meaning that the tree increased in diameter a half an inch in each of those years).  As an aside, I noted that the sap had begun rising in this tree, another sign of spring.

   In retrospect I think a 36" diameter white pine would be about 100 years old, adding or subtracting some guess years in consideration of growth conditions over the life of the tree.   For more information on counting tree rings to determine the age of a tree, use the blog search engine to find the post of June 7, 2013.  Also, The International Society of arboriculture has published average age to diameter statistics for a number of tree species.  Finally, read "Good Oak," an essay by environmentalist Aldo Leopold.