Fungus at the base of mature oak tree
Is this fungus at the base of my oak tree dangerous to this tree and the others around it? Our landscaper removed a dead branch from the tree and I see where others were removed in the past. We bought this property last December and love the large oaks in the yard and want to help them to be healthy.
What your second photo shows is a fungal growth called Inonotus dryadeus.
Unfortunately it is not a good sign. It is an indicator of significant decay within the tree.
This can lead to a tree which is structurally unsound.
If the tree's fall were to threaten people or property, we'd suggest having it evaluated by a tree health expert (certified arborist) credentialed by the International Society of Arboriculture. You can search for one at www.treesaregood.org
Mature oaks are having a hard time right now and many are failing due to a variety of factors.
Oaks are dying all over the region, unfortunately. There is no one cause. For such a situation to occur over many species of oaks and a wide area, it is probably an environmental problem-- multiple years of drought and higher summer temperatures are a possibility. Also, white oaks are intolerant of water-logged soils. Last year's excessively wet weather may have contributed to the problem. Root stress can lead to early fall coloration, browning, and leaf drop. When trees are stressed by unfavorable environmental conditions, they become more susceptible to pest and disease issues as well.
Some oaks are dying of bacterial leaf scorch, but this is not common on white oaks. Oak wilt is not active in Maryland generally. Here is more about those diseases: https://extension.umd.edu/hgic/why-oak-trees-are-declining
Take a look at this publication about oak decline. https://extension.tennessee.edu/publications/Documents/SP675.pdf