Tree Structure: When to Provide Mechanical Support and When to say Goodbye.
I recently visited a couple of properties that had trees with significant structural defects, issues that could mean not only the mechanical failure of the tree, but also the probability of property damage or human injury.
In the first picture is a large Norway maple with advanced decay due to a canker. This decay is located in the main crotch of the tree, an area that the tree relies on for support and strength, and is the result of a sunken canker that never healed or compartmentalized. Norway maple is a species that is relatively weak and this tree had four codominant stems, meaning that the tree has a poor overall structure. My recommendation to the homeowner was to remove the tree. She really likes this tree, but safety has to be the top consideration as this urban tree overhangs two properties and the city sidewalk.
The second picture shows a significant split in a Bradford pear, another tree that is notorious for splitting limbs. The tree is in a high profile urban location in a courtyard and is greatly valued by the residents. Note the daylight visible through the 24″ diameter stem. Since this tree is otherwise healthy and is exhibiting wound wood formation (healing), the tree can be salvaged. The recommendation is for aggressive crown reduction pruning to reduce weight and to improve the structure, the installation of two through rods to brace the split, and two cables into the upper canopy to provide additional support to prevent further weight loading and splitting.
Knowing when a tree can be saved, and when the risk is unacceptable, is critical to making wise tree care decisions.