Fall 2019 Conservationist

Extra Care for Oaks

by Tom Velat, Natural Resources

gray squirrel with an acorn in its mouth

Image Sandra Standbridge/Shutterstock.com

At Wayne Grove and West Chicago Prairie grow bur oaks that were mere seedlings when the Declaration of Independence was signed. Across several preserves most white oaks date back to the 1840s, 50s and 60s. (Not many are older because European settlers cut down oaks in large numbers in the late 1800s to build homes, barns and plank roads.)

These oaks put the “forest” in DuPage forest preserves, but there’s a problem. For oaks to continue to enrich the landscape (and support the squirrels, woodpeckers, owls and other native wild animals that rely on them) a new generation needs to fill the ecological shoes of today’s mature trees. But research shows this isn’t happening.

Oaks have grown here for centuries, so in biologically diverse natural areas they need no help from humans. But oaks need a fair amount of light, and in some habitats they’re no longer getting enough of it.

In many areas once suitable for oaks, fast-sprouting, shade-tolerant invasive trees have spread, even natives such as basswood, sugar maple, wild black cherry, ironwood, and American elm. Young oaks may be able to successfully compete for soil but are soon shaded out and stunted by the competition. As mature oaks get closer to the end of their natural lives, many arborists and restoration ecologists agree their struggling replacements may need some help.

Here at the Forest Preserve District, that help comes in many forms. Crews bring sunlight back to overgrown areas by removing the invasive competition, focusing on nonnatives like European buckthorn. Buckthorn creates dense shade and releases chemicals into the soil that prevent other plants from growing nearby.

Nursery-raised oaks in landscaping around picnic and other high-use areas, especially oaks from the Forest Preserve District’s own nursery, get extra care. Before performing a prescription burn, crews may mow around newly planted trees to create a buffer zone. Oaks evolved in ecosystems regularly visited by fire, so mature oaks have thick protective bark, but smaller ones may get scorched. Crews may also place protective screening around smaller oaks to keep them safe from hungry deer, eastern cottontails and small rodents. Trees can withstand some browsing, but too much can cause one to stop growing and eventually die. These extra steps not only give oaks a better chance of survival but also protect the investment of time and money it took to grow them.

The value of oaks doesn’t end at a forest preserve’s property line, though. The next time you drive past the edge of a wooded preserve, pay attention to the oaks growing across the street in neighborhood parks, backyards or corporate centers. In some cases, the leafy canopy is seamless. It may not have been a conscious decision, but over time public and private landowners have created an expanded oak community. As older trees die, both types of owners are needed to ensure oaks remain on the DuPage landscape for centuries to come.

Looking for your own way to do something for the mighty oak? If you have space, consider planting one in your yard. “Nuts About Oaks” in the fall 2018 Conservationist shows how to start from a single acorn, and the box below has tips for taking care of your tree over its first couple of years. You can also learn more (and spread the word!) about oaks by registering for our OAKtober programs. Join a walk. Paddle a kayak. Test your squirrel survival skills. Help out at a workday. Whatever you do, we guarantee you’ll end up caring even more about oaks!

Caring for Your New Oak

So you’ve decided to celebrate OAKtober by planting a tree. Fantastic! Below are some tips to give your oak a great head start.

Whether your oak is from a nursery or is one you raised from an acorn, the best time to plant it is spring or fall, when it’s coming out of or going into winter dormancy. You can plant in summer but will have to spend more time watering.

Before digging, select a spot with the proper moisture, light and space. To prevent future issues with roots and branches, it should be at least 8 feet from any sidewalk, structure, sewer line, or fence and clear of power lines.

The hole should be twice as deep as the container you’re transplanting from and deep enough for the tap root, the long white root that future roots will grow from.
Hold the tree with one hand so the tops of the roots are slightly below ground level. Use your other hand to fill the hole with loose soil. Pack the soil firmly around the roots to eliminate any air pockets.

Place a ring of 0.5-inch mesh hardware cloth around the oak so cottontails and other small mammals can’t chew on it. The ring should be at least twice as tall and wide as the tree so the leaves don’t touch it. Tie the ends together with zip ties, and use metal landscaping staples to secure it to the ground.

If you have deer in your area, cut a piece of hardware cloth to top off the ring like a lid. Deer can easily strip the top of your oak if it isn’t covered.

In winter, protect your tree from snow and ice with an overwintering cone or tent.
Water as needed. During long droughts, water regularly until the drought subsides or the tree is large enough to support itself, about 4 feet. Mulching around the tree can help keep the soil moist, but make sure the mulch slopes away from the tree and doesn’t touch the trunk.

Once your oak is 4 feet tall it should be able to withstand damage from animals, so you can remove the hardware cloth. If something’s still nibbling on it, pound three or four 6-foot-tall T-posts in the ground around the oak, and wrap aluminum fencing around the posts.