Dr. Alex Shigo

Part 1 | Part 2 | Part 3 | Part 4 | Part 5

Canadian Hemlock

CANADIAN HEMLOCK , Tsuga canadensis, about 40 years old, with a dead branch.

1. The pith of the branch was infected and darkly discolored.

2. Both arrows show the branch protection zone that formed after the branch died.

3. The branch bark ridge.

4. Note the invaginated increments indicating included bark to this point. Note also the dark color of the wood from the arrow downward toward the trunk. This indicates that the increments were squeezing together to the point of cell death.

5. For some reason, the increments began to form normally at this point. A much narrower growth increment formed at this time, suggesting a possible injury.

6. A different type of checking pattern can be seen where the normal branch-trunk collars began to form. Compare area 6 to area 4.

7. A crack formed after the branch died. The branch died about 12 years before the tree was cut.

8. There was a sudden decrease in growth rate at this time. Note both arrows 8. The number of growth increments above the branch are equal to those below the branch from arrows 8 to the bark.

9. Compression wood began to form here.

Dr. Alex Shigo is a noted authority in the field of modern arboriculture. An author, lecturer and consultant, he is the owner of Shigo, Trees & Associates in Durham, New Hampshire.

Reproduced with permission of Tree Care Industry and Dr. Alex L. Shigo.
The article was published in Volume VII, Number 6 -June 1996 of TCI.

Part 1 - Reading the Tree's Log
Part 2 - Red Oak
Part 3 - Red Spruce
Part 4 - American Beech
Part 5 - Canadian Hemlock

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