This P&G brings you to a very interesting tree. Half of the tree has been devastated by the "Emerald Ash Borer." An insect that has been devastating the Ash Tree Population in Southern Ontario. When I found this tree, there was a sign to inform people about the affects of the Ash Borer, taped around it. That's how the cache got its name.
The most significant damage to a tree by the emerald ash borer takes place when the insect is in its larval stage. In an infestation, bore holes and serpentine feeding galleries of the larvae essentially disrupt the flow of nutrients as they rise up the trunk from the roots to the crown, just under the bark. This eventually results in the death of the tree. This can take place over a number of years, and the first noticeable sign is usually some die back in the crown of the tree. The tree will usually be dead by the following year or soon after. In areas where the insect is invasive and has no natural predators, it can and usually does have a devastating effect on the local ash tree population. You will notice some holes in the side of the tree, that's where you should look for the cache.
Good Luck and Happy Caching!