Revitalizing the Arboretum’s East Woods
If you walk along the Heritage Trail in the East Woods of The Morton Arboretum, you may come across areas where many trees have been cut down.
These areas are being restored through a restoration effort aimed at revitalizing the Midwest’s native oak woodlands and securing their future. It uses what foresters call the shelterwood method. Its goal is to create open, sunny areas where oak trees can naturally grow from acorns and mature into trees.
Other trees that hamper the growth of oaks—such as invasive species, those that create too much shade, and species that can tolerate more shade than oaks can—have been thoughtfully removed between large, mature oak trees that will produce plenty of acorns and provide shelter for oak seedlings. This creates open, sun-filled areas where the acorns can sprout and where tiny seedlings are far more likely to survive long enough to become established trees that grow into tomorrow’s magnificent oaks.
New oaks needed
The Arboretum’s shelterwood project is addressing a major problem for the oak-dominated woodlands of the Chicago region: Although many great oak trees still stand after a century or more, new oaks are not growing to replace them when they eventually reach the end of their natural lifespan. Oak seedlings, which need abundant sun to grow, die because they are shaded and out-competed by more shade-tolerant species such as sugar maples. Unless ways can be found to foster new generations of oak trees, the Arboretum’s East Woods and other forests in the Chicago region will gradually lose their oaks, one by one.
Oaks are at the center of many forest ecosystems around the world. In the Chicago region, hundreds of species of animals and other plants depend on oaks for food and habitat.
Before Illinois became heavily settled, Arboretum scientists have found, the forest was kept in balance by frequent fires that cleared competing species and kept woodlands open and sunny, favoring oak seedlings. After settlement, the fires were suppressed to protect nearby farms and towns. As a result, the woods have become much more dense and shady, making it nearly impossible for young oaks to thrive without help.
In 2010, the first Chicago Region Tree Census identified the lack of young oaks as a major problem for natural areas, leading to the establishment of the Oak Ecosystems Recovery Project. The project is led by the Chicago Region Trees Initiative, managed by the Arboretum.
The shelterwood process
In commercial forestry, shelterwood cutting is a proven method of making sure that valuable kinds of new trees will grow up to replace trees that have been logged. The technique has been successfully adapted for restoration of natural oak woodlands in the East, but the Arboretum’s shelterwood project is the first of its kind in the Chicago region.
It is part of the Arboretum’s ongoing work to restore and maintain its natural areas and ecosystems. For example, every fall and spring, the staff conducts carefully controlled prescribed burns. However, previous oak regeneration projects that created smaller openings in the woods were not sufficient to foster the trees’ regrowth, so the Arboretum has turned to shelterwood cutting.
The process can take more than a decade before young oak trees are successfully launched toward the sky. At the Arboretum, the shelterwood method was first tried on a five-acre plot in the East Woods beginning in 2014. In 2018, it was expanded to 28 plots. Some of these areas can be seen from the Heritage Trail, which can be reached from the Big Rock Visitor Station.
First, the mature trees that will be kept to provide acorns and shelter for future oaks are chosen. Then the unwanted trees are removed. The work is done in winter when the ground is frozen. Over the next several years, oak seedlings sprout abundantly, but so do many trees of other species whose seeds were in the soil. About five to eight years after the first cutting, the plot is cut again to eliminate young trees and shrubs that are competing with the oak seedlings. To thin the canopy overhead and reduce shade, trees are removed. This allows the young oak trees the space and sun they need to firmly establish themselves for the long term.
The Arboretum’s shelterwood project is being carefully monitored to assess its prospects as a tool for restoring oak ecosystems. Since trees grow slowly, it will take researchers many years to fully judge the success of the effort.
