I have 2 trees with very dark brown rings around the trunk. Why!?

Question

Do my trees have a disease?

Answer 1

You have to specify the kind of tree and symptoms in detail to find out answers. Usually dark brown rings occure in some trees because of Fungi like bracket fungi and in later stages the fruiting bodies of fungi appear on trunk . In case of bacterial diseases spots, blight etc may appear atleast on leaves. See if leaves are shed in large quanities, or leaves are yellowing, or root is rotting etc.

Answer 2

I'd say it is definitely some sort of disease, bacterial wetwood maybe,