Oak decline is a gradual weakening of the tree over several years followed by death.
Outer branches die and leaves grow only near the trunk.
Oak decline is not well understood but is thought to be a complex mix of tree age, site, location, weather, soils, fungi and insect attacks. Oak decline is a normal part of ecosystem processes in aging upland hardwood forests. Dieback and death is an expected result when physiologically mature oaks come under stress. It is a normal function of root disease fungi like Armillaria mellea and insect pests like the two-lined chestnut borer to preferentially attack, kill and decompose weakened members of the tree canopy. As expected and natural as these results may be, many forest values including wildlife, timber and recreation will be influenced by oak decline.