Oak Decline and the Future of Missouri’s Forests
become vulnerable due to old age. Harvest mature trees and allow seedlings and sprouts to re-stock the site.
Remember that "old age" varies by site condition and tree species. For example, trees growing in fertile, deep, well-drained soils on north-facing slopes can remain vigorous at much older ages than trees of the same species growing in thin, rocky soils on south-facing slopes. White oaks and post oaks grow slower and live longer than black and scarlet oaks. Under very good growing conditions, white oaks may live up to 600 years, while black oaks may live up to 150 or 200 years. Their life spans under most Missouri conditions, however, are typically much shorter.
Given the composition of many of our forests, oak decline seems inevitable. With it, we'll see reduced mast (acorn) production, degraded timber value and a higher risk of wildfires, as well as increased danger from toppling trees.
On the other hand, the dying trees will create openings in the forest canopy that may encourage a different and hardier composition of tree species to grow. Forest stands that were predominantly oak, for example, may change to mixed pine and oak, or even all pine, a species which once dominated many of these sites.
That's not to suggest that we should just let this "natural" phenomenon take its course.
Active management plans that restore and maintain the appropriate species on appropriate sites will improve forest health and reduce the need for drastic management intervention in the future.
Why Oak Decline Occurs
Trees most vulnerable to decline have one or more of the following characteristics:
- tree age (70 to 90-plus years)
- shallow, rocky soils
- south- and west-facing slopes
- Conditions that have further stressed Missouri's oaks:
- short-term, severe drought
- repeated insect defoliation
- damage by frost, ice, or wind
Diseases and insects that are taking advantage of the weakened state of our red oaks:
- Armillaria fungus
- Hypoxylon fungus
- red oak borer
- two-lined chestnut borer
- leaf-feeding insects
Preventing Oak Decline
- Maintain a diversity of tree species, ages and sizes. A good rule-of-thumb for larger stands of trees is the "Four Quarters Rule": No more than 25 percent of tree stocking should be in any one species. Count scarlet and black oaks together as one species. For example, you could have 25 percent in shortleaf pine, 25 percent in scarlet/black oaks, 25 percent in white oak and 25 percent in other mixed species of maples, hickories, etc.
- Match tree species to the sites where they grow best. In the Missouri Ozarks, shortleaf pine is often better suited