Find out why oaks are endangered and how to help preserve them
The oak tree was once hailed as king of the forest. People called it magnificent, majestic and mighty.
But that was then. Now, the oak no longer reigns supreme. As a group, oaks are in serious decline. As ecological communities, oak woodlands are imperiled.
"But I see oaks every day," you may say. It's true, there are oaks in Kane County. But we've lost close to 90 percent of our oaks since 1837, according to Ben Haberthur, restoration ecologist with the Forest Preserve District of Kane County.
"For every 10 trees that were seen by the first European settlers of Kane County, nine are gone," he said. And, for those that remain, there are few young oaks to take their place when they fall.
Members of the old guard still stand along roadsides and in suburban yards. Often, you can only see the tops of these oaks straining for sunlight above a dense thicket of shrubs and trees. Or, in a landscaped setting, the grass under the trees is closely cropped by constant mowing.
In either situation, there are scant few acorns sprouting. Those that make it to seedling stage soon die. When the centenarians fall, there are no recruits to take their place. Put another way, what you see is what you get. And your kids may not see oak woodlands when they grow up.
Passing of the guard
Oaks were dominant trees in the great wilderness of the American frontier. The forest covered a million square miles of North America east of the Mississippi River at the time of European settlement. White oak, bur oak, and red oak were among the 20 species of oaks in Illinois. They typically grew with hickory trees, and today we refer to "oak-hickory woodlands" as a plant community type.
As the United States expanded westward in the 1800s, the great forests were cleared for their abundant (and seemingly inexhaustible) resources. By the turn of the century, the majority of the "old growth" forest in Illinois had been logged. Much of the original forest land was converted to towns, cities, and agriculture. "Second growth" forest grew on the leftover land.
The American chestnut was another great tree that grew alongside oaks. A disease known as chestnut blight erased the American chestnut from the forest by the early 1900s. Oak and hickory trees held their ground, albeit precariously. The pre-settlement landscape of Illinois had been completely transformed.
Quest for fire
The transformation of the land came with some specific changes. One that has greatly affected oak trees is fire -- the lack of it.
Oaks evolved with periodic burning over thousands of years. Woodland fires, less volatile than prairie fires, crept slowly across the forest floor. The flames were low -- not at all like the dramatic crown fires that consume the western forests. Oaks with thick bark and deep root systems adapted over thousands of years to survive this type of fire.
Oak trees are not only resistant to fire, they are dependent on it. Native Americans set fires to keep the woodlands open, thereby enhancing game. Such deliberate burning of forests flies in the face of Smokey the Bear, to be sure. It's taken a century of fire suppression for newcomers to realize what indigenous people knew long ago: oak woodlands must be burned to remain healthy. Without fire, they rapidly decline.
What's the secret? Sunlight. Oak seedlings thrive in open, sunny conditions. They cannot grow in shade. Fire keeps woodlands open by preventing the growth of invasive brush and heavy shade-producing species. An open canopy above allows dappled sunlight to reach the forest floor -- and oak seedlings -- below.
Another change came hand in hand with the lack of fire: invasion by aliens. Alien plants, that is. Two of the most pernicious nonnative plants in Kane County are buckthorn and honeysuckle.
Both of these species were brought to the United States with the best of intentions. They were imported for use in landscaping.
Both species are woody -- buckthorn is a shrubby tree; honeysuckle a large shrub. Both bear prolific berries that are devoured by birds and distributed far and wide. Thus, buckthorn and honeysuckle made their escape from cultivation, and the renegade species now dominate former oak-hickory woodlands.
Oak seedlings are doomed when buckthorn and honeysuckle move in. The invasive species take up space, absorb nutrients, and produce lots of shade. Recent research suggests that buckthorn also engages in chemical warfare, as its roots and leaves contain a chemical deterrent that inhibits the growth of other plants.
Oak seedlings have a slim chance of survival in the dense shade and adverse chemical environment caused by these invasive plants. To make matters worse, both honeysuckle and buckthorn re-sprout vigorously when cut down. So, if you go out to your back woods with a saw to cut them back, they will return with a vengeance. In their presence, an oak seedling will get nary a sunbeam.
Enter the herbivore
The scene grows more complicated when plant eaters come onstage. A key herbivore is the white-tailed deer. The deer is an edge species, living where forests meet fields, woodlots meet crops, and gardens meet lawns.
The fragmented habitat of the modern landscape -- small parcels of wooded land in suburbia -- is ideal for the hooved herbivores. Unfortunately, as deer populations have increased in the past 50 years, oak regeneration has decreased.
White-tailed deer are selective herbivores. In other words, they're picky eaters. They favor certain plant species in the botanical smorgasbord of the landscape. They're particularly fond of oak seedlings. Forest preserve districts and conservation districts region wide are concerned about the effects of deer browse and oak regeneration.
Research conducted by numerous agencies has shown that high-density deer populations lead to high oak seedling mortality.
This triple-whammy -- fire suppression, invasive plants, and hungry herbivores -- has led to the "virtual cessation of oak regeneration," as Marc D. Abrams explained in his article, "Where Has All the White Oak Gone?" published in the journal Biocience.
What can we do?
But Haberthur is not one to give up. He and his crew in the district's Natural Resources Department work on oak restoration projects throughout the county.
"The district plants thousands of oak trees each spring and fall," he said. "We plant anywhere between 2,000 and 8,000 whips (seedling oaks) with our tree planter annually, and between 1,500 and 2,000 larger potted oaks at our volunteer events."
Prime examples of oak restoration can be seen at Big Rock Forest Preserve, the Dick Young Forest Preserve, Burnidge Forest Preserve, and Fitchie Creek.
Our native oaks have a storied history and an uncertain future. Oak communities are degraded, dying, or missing altogether. Restoration of these majestic trees in their ecological communities is, as Haberthur stated, "increasingly urgent."
Look for an oak tree today. You may see a grand old specimen rooted in 200 years of history. Perhaps it's a tree your grandfather saw as a seedling. It could be a tree that your grandchild will see some day. Pick up an acorn, and you will hold both history and the future in your hand.
You can help preserve and restore these magnificent trees by joining any of the district's volunteer work days at preserves throughout the county. For a list of these opportunities, see kaneforest.com/volunteer/restorationWorkdays.pdf.
• Valerie Blaine is a naturalist with the Forest Preserve of Kane County. You can contact her by emailing firstname.lastname@example.org.