What causes "leaf clumping" on Garry Oaks
Hello - thanks for the photo. Those clumps of leaves along the trunks and branches are called epicormic shoots. They arise from dormant buds that become stimulated to sprout when there is either some stress on the tree, or sometimes, new exposure to light. We see oaks do this when surrounding taller trees are cut down, because there is more light hitting the dormant bud which stimulates it. Also, like in the case of the tree in the photo, they may arise from branches that have a dead or dying top - I see some branches that did not leaf out at their tips. It is one of the tree's mechanisms for survival and longevity - if the top of the limb dies, new sprouts beneath will help the tree produce energy and may eventually contribute to a new canopy forming. So, it's not a "problem" to be reversed; it's simply a tree responding to environmental cues.