Question
We have several sycamore trees in our yard, at least 20 years old about 30-40 feet high.  We just lost one, the only symptom was the upper layer of bark peeling revealing black.  We cut the tree down and I can peel off the black revealing normal looking wood. It doesn't look powdery; it just looks like the under layer of bark is turning black.  Now I have another one (still alive) that is doing the same thing.  The leaves look normal, perhaps the leaving out is a bit thinner than normal.  We live in Texas and have had dryer weather than normal the last 18 months.  Help!

Answer
Although I am not completely certain on the cause of your tree's problem, it sounds to me that it is a fungal problem. Many times a fungal issue will reveal itself beneath the bark where the vascular system of the tree is located and usually looks like black striping. Some types of fungus can grow runners to surrounding trees to infect them as well.  The thinner leaf canopy and abnormally dry weather shows that this tree is under stress. If you contact your extension office for your county, they should have a lab where they can test a sample of this bark and tell you exactly what is causing it. Your local garden center should have the information as to where your county's extension service is located if you do not know.