If you have ever noticed acorns so numerous that you could not take a step without crushing several, you may be asking the question, “why are there so many acorns?” Some answers to this question can be found in the physiology and ecology of trees and their relationship to wildlife. Oaks and several other tree species occasionally produce enormous crops of seed. This is called “masting” or “mast events”. These events are periodic. In the case of many oak species, a large mast event may happen every two to five years, depending on the species of oak and several other factors. Masting events may be preceded and followed by small or moderate acorn crops, or complete crop failures in some cases. Why does this irregular seed production happen? These events may be tied to several aspects of the life of oaks.
First, the production of a huge volume of a large seed like an acorn requires a lot of resources from the tree. This level of production may not be possible for the tree every year. Trees allocate energy to several different functions, so committing large amounts of energy to one area could mean deficits in others. This may mean there are advantages for the tree to produce occasional, rather than annual, mastings.
Second, weather does not always cooperate to provide the conditions for a bumper acorn crop. Unfavorable weather during pollination and seed development periods can result in reduced production of acorns. Late spring freezes, extremely high temperatures, summer droughts and other weather stresses can reduce acorn pollination and production.
Third, predation by seed-eaters like squirrels, deer, turkey and even weevil larvae can greatly reduce the number of viable acorns. It may take a very large acorn crop to have many acorns escape from the numerous species that depend on acorns for food.
This irregular cycle of large crops can be beneficial for the oaks by overwhelming the seed eaters. Populations of wildlife that depend on acorns may eat most of the seed during normal seed crops, but may not be able to utilize all the seed produced during a masting. This surplus seed is available produce the next generation of oak seedlings.
However, some species will produce copious amounts of the mast if the developmental age of the tree is favorable, regardless of conditions.
Acorn production can vary by species and individual trees across the oak family, but masting is a way this important group of trees can continue to be a part or our Midwestern landscape.
Woodland Management Moment: Direct Seeding, Purdue Extension – Forestry and Natural Resources (FNR) YouTube Channel
Ask an Expert: Tree Selection and Planting, Purdue Extension – Forestry and Natural Resources (FNR) YouTube Channel
Forest Improvement Handbook, The Education Store, Purdue Extension resource center
Native Trees of the Midwest, The Education Store
Investing in Indiana Woodlands, The Education Store
Tree Pruning Essentials, The Education Store
Lenny Farlee, Sustaining Hardwood Extension Specialist
Purdue University Department of Forestry and Natural Resources
Lindsey Purcell, Chapter Executive Director and Certificate Liaison
Indiana Arborist Association