Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Photo of sun setting behind bare oak tree © DNR File Photo

Oaks are the foundation for many forests, woodlands and savannas in Wisconsin.
© DNR File Photo

June 2012

Reinforcing a foundation in oak

Why I sleep well at night.

Lisa Schulte Moore

". . .I hear the wind among the trees.
Playing the celestial symphonies;
I see the branches downward bent,
Like keys of some great instrument."
— Henry Wadsworth Longfellow

My dad and I like to debate politics, ethics, religion and science. There's no topic on which he won't try to get under my skin. The environment, though, is a common conversational theme given my professional pursuits in natural resource conservation and because my folks recently bought the farm my maternal grandfather grew up on.

I cite a report on the impacts of excessively high deer populations on understory flora; my dad sends me a picture, taken from the back window of his home in urban Eau Claire of the biggest buck he's ever seen.

I mention the importance of top predators such as red-tailed hawks, bobcats and wolves in food chains; he tells me a story about how his buddy's bird feeders were destroyed by a black bear the previous night.

I tell him how far the science of climate change has come in the last few years; he responds by sending me a 1971 paper from Science magazine warning of impending global cooling. It goes on.

But recently, rather than trying to rile me up, my dad asks if I'm doing okay. What am I doing to keep my balance? How do I stay positive? Do I get enough sleep?

As a scientist who studies the causes and consequences of changing landscapes, I consider human impacts on the biosphere on a daily basis. I work with data that document biodiversity declines due to loss of habitat, extensive top soil loss associated with common agricultural practices, and environmental and economic impacts of exotic pests and diseases introduced through global trade.

I understand how many small, seemingly inconsequential decisions, scale up to have large, sometimes global effects. And, I know all too well that the science will never be perfect, but the direction we must head is clear.

I do sleep well at night, though, because I also know that positive change begins with me. Change also begins with my dad, for that matter, because together we are taking steps to improve the environment for future generations by restoring oaks where we live and work.

The foundational role of oak trees

Why oak? Oak is a foundational species in Wisconsin and throughout much of eastern North America and portions of the Pacific West.

Foundational species are those that exert strong control on community dynamics and harmonize ecosystems. They influence the transfer or movement of energy, nutrients and water.

Most outdoorsy types are already familiar with the oak's foundational characteristics.

Acorns: this nut produced by oaks, in great abundance in some years, is a major food resource for many mammals, birds and insects. White-tailed deer, fox squirrel, gray squirrel, eastern chipmunk, wood duck, wild turkey, red-bellied woodpecker, tufted titmouse, white-breasted nuthatch and blue jay heavily rely on acorns for their fall and winter diets.

Furrowed bark: seeds get stuck in it and spiders and insects find ample habitat for hiding in the craggy oak tree bark. As such, oaks provide better foraging opportunities than smooth-barked tree species, such as maples and beeches, for many insectivorous birds, including brown creepers, whitebreasted nuthatches, black-capped chickadees and black-and-white warblers.

Leaves with short-petioles: a petiole is the stalk that connects a leaf to a branch, and the petioles on oaks are fairly short, at least compared to maples. This characteristic allows birds that feed on leaf-eating insects to remain perched on branches as they glean insects off the leaves. In terms of bird energetics, feeding from a perched position is much more efficient than aerial feeding. Maples have comparatively longer petioles, demanding energetically intensive aerial feeding from birds, resulting in a lower net caloric gain.

There are a few more reasons why oaks are preferable to maples:

  • Maples tend to have lower moth and butterfly larvae densities per leaf area compared to other hardwoods. This is important because moth and butterfly larvae comprise a key food resource for many birds, especially during migration. These larvae are packed with calories and are slow to move, making them easy prey.
  • Oak tree canopies let more light through to the forest floor, where it can be used by understory plants. For this reason, understory plant diversity and cover tend to be higher in oak forests.
  • The impacts of higher understory plant diversity and cover cascades through the ecosystem, translating to higher quality habitat for vertebrate and invertebrate communities. Lakes and streams benefit from a healthy understory because higher understory plant cover translates to less soil erosion, which yields higher quality habitat for fish and other aquatic creatures.

Many plants and animals have adapted to the unique environmental conditions that oaks provide. Ecologically speaking, oaks are the foundation for many forests, woodlands and savannas in Wisconsin.

Cause for concern

Oaks have been the dominant tree group throughout the eastern United States and portions of the Pacific West for millennia, and now we are losing them. While inventories from the Midwest today show that mature oaks still dominate the overstory of many forests, the next generation is missing from their understories. The reason why is tied to disturbance, and particularly the lack of it. As land use practices have changed, the characteristics that once provided oak trees with a competitive advantage now contribute to their potential replacement by other, later-successional tree species, especially maples.

Oaks are fire-adapted. They evolved in landscapes where fires were common and over time they developed characteristics allowing them to survive, and even thrive, with fire. Fires were historically common throughout much of North America, often because Native people actively burned to facilitate travel, enhance hunting and favor preferred plants, among other reasons.

Photo of controlled burn. © DNR File Photo
The openness of oak savanna is maintained by fire; oaks are uniquely fire-adapted..
© DNR File Photo

As Europeans and their descendents settled the United States, they heavily logged wooded areas, contributed to a proliferation of forest fires and widely used woodlands for grazing. Because young oak trees can readily sprout from their stumps, the combined effects of this harvesting, fire and grazing perpetuated oak dominance in many regions, including much of southern and western Wisconsin.

The lack of fire in Wisconsin landscapes today has allowed maples and other mesophytic tree species (those that do well under moist, shady conditions such as ash, elm and ironwood) to flourish in the understory of mature oak forests. These species are not fire-adapted and are prolific seeders. Without fire, they out-compete the oaks.

In addition, the predominant approaches to forest management today are to either do nothing ("hands off") or to only remove a few trees here and there (selective harvesting). In either case, light levels within the forest understory are inadequate for oak seedlings to become established.

Other reasons for oak decline include:

  • Competition with non-native invasive shrubs, such as common buckthorn. In the forest understory, these shrubs win out over oak seedlings in battles for light and nutrients.
  • Widespread browsing by white-tailed deer, which often prefer oak seedlings and saplings to other tree species.
  • Forest pests and diseases including oak wilt, oak tatters and gypsy moth.

The sum of these factors points toward future widespread loss of oak trees. Because oaks provide a vital foundation for biodiversity, there is a strong potential for subsequent declines in the populations of associated plants, insects, fish, birds and mammals. We are at a critical juncture for oaks.

What can you do?

The good news is we still have mature oaks in the canopies of many of our forests and these trees can provide seeds for the next generation of oak forests. The bad news is that the conditions in the understories of our current forests are generally not conducive to germinating those seeds and nurturing them into trees.

But you can create the fertile conditions oak need by taking a few small steps.

First, adjust your attitude. There's a widespread perception that the best thing to do for biodiversity is to leave it alone – la "nature knows best." But in the case of oak and oak-dependent species, well-executed management activities, including prescribed fire, mechanical shrub removal (brushing) and/or harvesting, can do a lot to improve habitat for biodiversity.

When properly executed, prescribed burning is especially effective because many oaks are highly fire-adapted and their competitors such as ironwood and buckthorn are not.

Brushing and harvesting are useful in locations not suited to prescribed fire. Although these techniques do not perfectly mimic the fires, they are the only option in many places, because of the lay of the land, ownership boundaries, liability and financial resources.

Work locally and support local land stewardship organizations and group activities. Cut buckthorn and plant trees. Cage seedlings to protect them from deer. Volunteer on a prescribed burn. If you can't do these activities yourself, consider donating to organizations employing summer field crews of student interns to do this important work.

Support conservation policies at federal, state and local levels. Reward landowners for providing environmental benefits, including oak forests and quality habitat, clean water and scenic views as well as producing marketable goods such as timber, corn and soybeans.

Show your love and appreciation for wildlife by maintaining the habitat they depend on. This includes hunting or supporting hunters. When there are too many animals of any species, they outstrip their habitat and starve causing a decrease in the population's health as a whole.

And, finally, talk to your neighbors. If you own forestland, find out whether you share similar interests and goals for your land. Ask them what they have learned from their past management efforts: Have they worked with a forester? Who would they recommend? Have they tried thinning? To what stocking level (number of trees remaining per acre of land)? What was the result? How about planting? Where did they get their seedlings? What about prescribed burning as an option?

Managing for oak goes beyond a onetime event and future collaboration may be needed to see progress and regeneration. Oak forests don't end at property lines. Tackling the issue of oak conservation can't end there either.

Full circle

Now, back to me and my dad. What's our latest debate? We've been arguing about how many oaks to plant and where to plant them.

As I mentioned, several years ago my folks purchased the farm my maternal grandfather grew up on in Wisconsin's Driftless Area. My ancestors purchased the land and built there in 1869 at a time when the land was covered by prairie, oak savanna and marsh.

Photo of Lisa Schulte Moore. © Bob Elbert, Iowa State University
The author, Lisa Schulte Moore.
© Bob Elbert, Iowa State University

When my folks bought the farm, almost all of the 60 acres were row cropped, despite the land's proclivity toward severe erosion. Today, 28 of the most sensitive acres are enrolled in either the Conservation Reserve Program (CRP) or a local prairie restoration program.

On all of the CRP acres, except those that are too wet, my folks have planted trees – predominantly oaks. Although these 20 acres do not look like much right now, the trees will provide many benefits as they grow.

They will stabilize the soil on this highly erodible land. They will capture excess fertilizer running off surrounding cropland, keeping it from entering the stream down slope. They will soak up and transpire water, contributing to flood control within the stream. They will help maintain a stable climate by capturing carbon dioxide from the atmosphere and trapping it in their roots, stems and leaves. They will provide acorn crops and habitat for wildlife long into the future. And, someday, they will provide a hearty source of income for my sons, niece and nephew.

My dad and I sleep easy because we know that positive change begins with us.

It also begins with you. Plant an oak tree and watch it grow. Take time to stop and listen to the wind in its leaves, birds building nests in its branches and squirrels scurrying to collect its acorns. Embrace the annual cycles of the sap run, flowering, leaf out, growth, seed set and leaf off. A simple, but boundless beauty. A service to society. A service to you.

Lisa Schulte Moore is an associate professor at Iowa State University.