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Dr. Alex Shigo
1. The tree started to grow at an even rate. After six years, it began to lean slightly to the left.
2. After 13 years, it began to lean slightly to the right. Note the larger and darker bands of compression wood.
3. At this time, the tree was injured. Note the sudden decrease in growth rate.
4. Spruce trees have very few resin ducts in healthy wood. The wood is a non-resinous type. However, when the tree is injured, resin ducts, called traumatic ducts, often form. The ducts appear as dark spots in the wood. Even though the wound is not shown in the photo, you can be sure there was a wound nearby on the tree.
5. A very narrow ring shake or separation indicates a small wound near where this specimen was cut. Note also the sudden decrease in growth rate to the left of the arrow.
6. The wound penetrated one growth increment. A very strong "CODIT wall 2" resisted deeper spread into the tree. Note the dark and of fiber tracheids at the arrow point. The wood was altered chemically as a protection wood after wounding.
7. Note both arrows showing the barrier zone that formed after wounding. When trees are wounded during the growing period, it is possible to date the wound to within a week of when it was inflicted. The barrier zone is slightly beyond the middle of the growth increment indicating that the wound was inflicted about four to five weeks after new needles began to form. Under normal conditions, it takes about six to eight weeks after needle or leaf formation before the growth increment is fully formed. This tree was wounded around the third week of June in New Hampshire.
8. Thick woundwood ribs began to close the wound.
9. The wound was closed in four years.
10. The tree was cut about a week after new tracheids began to form. It was cut the third week of May, and therefore the wound was six years and about four weeks old.