Thursday, February 9, 2017

Oak Tales

The dead white oak stood along a seldom-traveled township road where it had caught the eye of someone with a chainsaw who needed firewood. The first time I saw the tree it had been felled and all that remained was the stump and the smaller branches.

Whoever cut the tree was pretty good with a chainsaw so the stump was quite smooth. The tree’s annual rings, formed each year as the tree grows in diameter, spoke of its life. Oak trees in temperate areas like northcentral Pennsylvania form annual rings that can usually be seen clearly. The wood that is formed in spring consists of large-diameter vessels that are easily seen with the naked eye; wood formed in the summer consists of vessels of much smaller diameter.

The width of annual rings depends on the many things that impact the tree’s vigor: on the availability of water and nutrients, competition from neighboring trees, defoliation by insects or disease, damage from ice storms or logging, root damage from flooding or soil compaction – or a host of other factors.  

Looking at the annual rings on this stump, it was obvious that there was a great range in the width of the tree’s annual rings –

The outer inch of wood, the tree’s sapwood, was deteriorated due to decay, but the heartwood was sound and undecayed (the heartwood of white oak is decay resistant because the vessels are blocked by deposits, called tyloses, that block fungi).

The age of the tree at the time it died can be determined by counting the annual rings. Although a few of the annual rings were difficult to distinguish, it appears that the tree was 112 or 113 years old when it died. The annual rings became markedly narrower during the last 25 years of its life, probably due to competition from surrounding trees. 
Much more interesting is the tree’s remarkably slow growth from age 45 to age 62. What happened to put a brake on its growth in 1949 and then suddenly speed the growth up in 1966? It could be any one or a combination of quite a few things that stressed the tree, reduced its vigor and slowed its growth.

Many years ago I was visiting a landowner whose family had kept meticulous records of activities in their woodland; he showed me a stump that had a very similar pattern in its annual rings. He’d counted the rings in the stump and realized that the sudden jump in the annual rings' width occurred nine years after his grandfather had sold timber thereby removing some of the competition from adjacent trees that had been cut.

The nine year delay was apparently the time it took for that tree to add leaf surface to its crown following the logging and then begin growing more rapidly. Perhaps that’s what happened with this tree as well – which still doesn’t explain a sudden tremendous spurt in growth rather than a slow acceleration as the leaf surface gradually expanded year by year.   

Unfortunately, although this stump has a story to tell there’s no way to interpret the tale without a detailed history of the weather, insect defoliation, and logging that could tell us more about the life of this tree.

1 comment:

  1. Very interesting post. Reminded me of a classic story from Aldo Leopold! I have a slice of a Cedar grown on bedrock, and a Spruce grown in deep sand. Same size, but one is 121 years old; other is 55 years old.


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