I've got an Ash tree in my back yard, a really nice tree for climbing. One day, from the ground, I noticed what looked like a split at a major fork, about 30 feet up.

I climbed up and took some pics, this one is the best look at it.

The really strange thing is there is no sign of a split on the other side of the fork. You talk about disappointing. Not only do I lose a good climbing tree, but I could lose a good portion of a tree.

How is it it can have such a split on one side and no sign of a split on the other?

Click here to see the split
The split

Watcha got there is a classic codominant inclusion. On the other side of the crotch you'll probably see a vertical "lump" extending from the crotch downward. It's not unusual to see one side with built up structure and a split on the other.

Not a great climber. If you want to keep the tree I think you could have it cabled by an arborist to keep it going for many years to come. Consult with an arborist, I'm no expert.
-moss