There is a birch tree planted about 10 from the front corner of our house. The last couple of years I've noticed it has sparse leaf production. All the leaves are healthy looking - no yellowing, all bright and nice green - but only about half the branches have leaves on them. It's about 16 years old.
Connected or co-incidence, I don't know - but last year the cherry laurels planted around the tree, near it's base (6 feet away), one by one quickly turned brown and died. I've never seen anything like it.