The Douglas Fir tree in the left photo didn’t commit suicide. It was just “squeezed" off by the other poorly attached branches. This phenomena is called included bark – and occurs on defective V-shaped crotches in which the bark grows inward and on itself, causing a physical weakness when the co-dominant leaders meet. [Two vertical trunks about the same height.]
Notice the fallen branch was sharing the same area of the trunk with three other branches. This tree was topped during a wind storm some 40 to 60 years ago. The loss of the single leader [tallest, vertical shoot] caused four side limbs to compete to become the new leader. In the process, the interior tissue had to share increasingly smaller amounts of tissue. This lead to a structural weakness that allowed a slight wind to cause one of the limbs to jetison. The close up shows the darkened wood where the attachment was very weak.
The photo on the right is a Liquidambar tree [also known as a Sweet Gum tree in the Midwest] that exhibits the same problem – included bark. As mentioned above this happens when two shoots share the same location of growth. The trick to preventing this, as cabling is not an option, is to buy trees without two trunks attached at the same point. Or, prune off one of the leaders when the tree is young.
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