I’m standing in a northern Wisconsin forest with botanist Sarah Johnson, an associate professor of natural resources and biology at Northland College, where I work. She has been checking text messages from her student researchers, who are working on Outer Island—one of the twenty-two Apostle Islands on Lake Superior that are located roughly thirty miles from where we stand. The wind has picked up and the National Park Service boat may not be able to get to them tonight. “I tell them to pack extra clothes and food, just in case,” she says.
Johnson is one of the hardest-working professors I know. She teaches September through May; then, in summer, she’s out in the field. She and her students chiefly focus on the islands, conducting plant and field studies. Johnson is particularly interested in the effects of deer on the forest understory. The islands offer a unique view of a northern forest with little deer pressure.
Johnson is walking in the woods with me on a Friday afternoon in June for two reasons. First, because I asked her if she would show me the impacts of high-density “deer browse” on the landscape. Second, because further down this road is a thirty-acre, fenced “exclosure,” built to keep deer out. County foresters want to see the difference between deer and no deer on a new forest. Johnson is interested in scouting the exclosure as a teaching tool for her students in the fall. Exclosures permit the scientific community to study the impacts of deer and to preserve plant species. They are also becoming a necessity among foresters and timber-industry professionals for tree regeneration. To read the full issue.
White-tailed deer are plant-eating machines—and, in some places, there are more of them than ever due to milder winters, hunters that lobby for letting them multiply, and land-management policies that favor them. They consume seven pounds of vegetation daily—tree saplings, adult branches, shrubs, flowers, sedges, and anything else in their vicinity. Their impact is so severe that biologists use terms that could have been coined by Dr. Seuss to describe what they’re seeing: “sandwich” trees (where deer have eaten out the tree’s middle), “lollipop” trees (where deer leave only a rounded crown, pruning like bonsai masters), deer “candy” (the edibles deer prefer), and the “molar zone”—the region from Johnson’s calf to just above her head that is in reach of munching deer.
Johnson has found that plant communities on sites with long-term deer pressure are becoming increasingly different from those on sites that have never had deer. Before European settlement, scientists estimate there were about eight deer per square mile in Wisconsin. Now there can be as many as seventy-two per square mile.
To the untrained eye—my eye—the forest Johnson and I are standing in seems fine. The trees are about thirty years old, and there is a mixture of birch, aspen, and conifers. The forest floor is carpeted in Pennsylvania sedge – an inviting grassy green perennial – and I can see for a distance through the trees. It feels neat and, well, parklike. Comfortable.
What’s missing, Johnson tells me, is what the UW-Madison limnologist John Magnuson called the “invisible present.” It refers to changes that happen so slowly that most of us don’t notice what is changing and therefore don’t recognize what’s missing. In this case, a lot is missing: bush cherries, sumac, blackberries, saplings, bluebead lily, and Canada yew—basically, the preferred plant species that live within the “molar zone.”
This is a forest of the invisible present—mostly trees and Pennsylvania sedge, a species that tolerates grazing by deer by regrowing from buried meristems, just as mowed grass in a lawn does. Forests are essentially a four-layer cake of ground flora, shrubs and saplings, subcanopy (younger trees), and canopy. And yet in this random but fairly typical northern forest, we’re missing diversity in the ground flora, shrubs, saplings, and subcanopy – three of the four layers.
Johnson tells me that the changes in the landscape are not only due to plants gone missing but also to invasive species, like garlic mustard, filling in the gaps while plants that belong get smaller. Johnson provided testimony in 2009 at a Wisconsin state legislative hearing regarding placing a moratorium on the Wisconsin Department of Natural Resources’ “earn-a-buck” program—one of the most immediate and useful methods for controlling deer populations, according to Johnson. This program, which many state botanists and foresters supported, required that hunters shoot a doe before shooting
a buck to keep the deer population in check.
In giving testimony, Johnson listed trillium—a popular and showy white-to-pink flower that appears in the Wisconsin woods in early summer – as one of the impacted understory species. She said a hunter testified after her, stating that he had lots of trillium in his woods. “I have trillium in my woods too,” Johnson said. “The difference is in the size.” Trillium has become smaller as deer prune out the biggest and most obvious plants.
The earn-a-buck program was unpopular with a vocal and politicized segment of Wisconsin hunters, who argued they did not want to shoot antlerless deer and potentially pass up trophy kills. And in 2011, Governor Scott Walker signed a law repealing the earn-a-buck, thereby barring the Department of Natural Resources from using their most effective management tool.
Don Waller—a plant ecologist, a professor at UW-Madison, and an expert on high-density deer damage to forest ecosystems – says that the forests are at a crossroads, facing deer destruction and other threats, such as invasive species and overlogging. Now more than ever, the scientific community needs to monitor and manage forests with care.
“We have the tools and the capability,” he says. “Instead, politicians are cutting science while increasing logging and eliminating protection of wolves that act—at least, locally—to reduce browsing impact.”
The twentieth-century conservationist Aldo Leopold—a wildlife biologist and professor at UW-Madison who wrote A Sand County Almanac —was the first to observe that we can change landscapes to favor certain species and that species can, in turn, affect the land. He noticed that deer and grouse, for instance, prefer open, younger forests to old growth. In the early twentieth century, when Leopold observed this, deer were nearly gone from Wisconsin.
By the 1940s Leopold had traveled to Europe and walked in German forests devoid of diversity. In Wisconsin, where deer had rebounded, Leopold began to warn of overabundance and the impact that high deer density could have on the landscape. In one of his most famous essays, “Thinking Like a Mountain,” he describes shooting at a pack of wolves in the days when that’s what young men did and then watching an old wolf fade, the “fierce green fire dying in her eyes.”
In his final paragraphs, Leopold warns of an ecosystem out of balance:
Since then I have lived to see state after state extirpate its wolves. I have watched the face of many a newly wolfless mountain, and seen the south-facing slopes wrinkle with a maze of new deer trails. I have seen every edible bush and seedling browsed, first to anaemic desuetude, and then to death. I have seen every edible tree defoliated to the height of a saddlehorn. Such a mountain looks as if someone had given God new pruning shears, and forbidden Him all other exercise. In the end the starved bones of the hoped-for deer herd, dead of its own too-much, bleach with the bones of the dead sage, or molder under the high-lined junipers.
I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer. And perhaps with better cause, for while a buck pulled down by wolves can be replaced in two or three years, a range pulled down by too many deer may fail of replacement in as many decades.
Leopold died in 1948. Although Sand County Almanac remains a classic, in the decades following his death, his home state of Wisconsin has largely forgotten the lessons he imparted. This seemed odd to Waller, who only became aware of deer impacts in the 1980s, when his colleague and student Bill Alverson alerted him to the fact that deer threatened several plant species, including some of the state’s rarest plants. They were both startled to learn that no one was researching or monitoring these impacts. “I did not plan to pursue this so much,” Waller admits. “But I kept expecting someone else to do more about deer impacts, and no one was.”
Waller’s group started to document the deer impacts in Wisconsin’s forests and found them to be surprising in both their number and variety. By the 1990s deer densities started to match, then exceed, the high densities of the 1940s that had so alarmed Leopold—and they have not slowed. The group has published more than a dozen articles documenting in detail the impacts deer are having – on seedlings of eastern hemlock and northern white cedar; on the size, flowering, and fruiting of understory herbs; and on plant diversity over the past half-century.
Their latest study drew on the careful baseline studies of the Wisconsin plant ecologist John Curtis, who surveyed the vegetation of Wisconsin with his students in the 1950s. It was telling that three state parks in northern Wisconsin had lost the most diversity—more than half of their original species: all these parks had also prohibited deer hunting for decades.
Waller and his team identified species that have increased or decreased over the past fifty years, creating a winners-and-losers list. Winners included grasses, sedges, invasive exotics, and several tough or toxic species that resist or tolerate deer herbivory. The big losers included pretty wildflowers like trillium, bluebead lily, and rosy twisted stalk, all of which have declined by more than 50 percent. “These changes parallel many differences we see between in and outside the fences of exclosures,” Waller notes.
Waller and Johnson continue to research how deer affect plant communities in the Apostle Islands and elsewhere, treating unrestricted areas as natural experiments that complement the exclosures they have built. They are also busy trying to design and test simple methods to measure deer impacts. “We want to find a method that is easy, cheap, and quick to apply,” Waller says. “The method could then be shared with foresters, wildlife biologists, and citizen scientists to build a network for monitoring deer impacts over space and time.”
Once such a standardized method is applied widely, it provides forestland owners and the Department of Natural Resources with a tool they can use to manage deer. Waller points out that the practice of relying on imprecise estimates of deer density has been contentious with hunters while also failing to identify thresholds where deer impacts become unsustainable. He adds: “I predict continuing conflicts and forest degradation until we can figure out how to use our science and concern to reform forest and wildlife management. This was Leopold’s vision.”
Jim Meeker, a former botany professor at Northland College, studied with Waller and taught Johnson when she was an undergraduate; he subsequently worked in collaboration with her when she returned as a professor. Meeker, now deceased, moved from Madison to northern Wisconsin in 1990 and built a house there with his wife, the biologist Joan Elias.
When Meeker moved north, Canada yew, a low-growing evergreen shrub with bowl-shaped red arils, was in decline. According to early reports, the shrub was historically a dominant understory plant in many northern forests across the Great Lakes region. Meeker got to work almost immediately installing a dozen fenced squares in patches of Canada yew.
A week after my trek with Johnson, Elias and I go for a hike to look at the exclosures and get a visual read on the ecosystems in and outside them. She and Meeker built trails through their mixed-age northern forest of birch, hemlock, cedar, oak, and maple. As Elias and I walk past the exclosures protecting Canada yew and other deer favorites like bluebead lily, we talk about the botanists who have built upon the work of their predecessors—Aldo Leopold, John Curtis, Don Waller, Jim Meeker, Sarah Johnson, and others. “They have a sense of the long-term and see the value in each other’s work,” she says.
We walk off the trail to the first fenced-in area. A Canada yew, which looks like Christmas wreath material, grows in an eight-foot-by-eight-foot square inside the fencing—the smallness of the fenced square is so that deer are not tempted to jump inside, Elias tells me. Outside of the exclosure, there is no longer any sign of Canada yew. Anywhere. It is night and day. Even this untrained eye gets it. Very little Canada yew persists at all in northern forests, except as a small, scattered shrub primarily present along ravine faces or around rock outcrops.
Johnson and her students have been documenting the presence of Canada yew in the Apostle Islands, comparing it to baseline data collected in the 1990s. Her surveys show a dramatic decline on islands that have recently had deer.
“In short, Canada yew and deer are not compatible,” she says. Not only is there a rate of decline but the plant does not return even when deer are out of the picture.
For example, Rocky Island had deer in the 1940s, but even though the herd declined, the Canada yew that once flourished there had not returned by the 1990s and still hasn’t today. In contrast, she has seen Canada yew as tall as she is on North Twin Island, where there is no deer activity. “There’s a lot of factors that go into the differences—but we know Canada yew does best where you have old-growth features of a moist, shady forest with small light gaps and few deer.”
As Elias points to features in her forest (new discoveries, trees fallen, vanishing groundcover), she tells me about the one-two punching going on in the woods – deer being the first punch and non-native earthworms the second. The worms eat the leafy duff layer, which means seedlings have a harder time taking hold. She also shows me the damage from flooding last year. I tell her about how I learned that the timber industry is starting to adapt by erecting large-scale exclosures to grow high-end timber. Elias explains that birds are also big losers in this story. Without the forest structure—the ground flora and the shrubs—they have no nesting habitat.
It occurs to me later that I am walking through a museum, filled with relics of the past, and I wonder about the future of the northern forest. I later ask Johnson her thoughts on this. She says she suspects that future generations will wonder why we didn’t do more to stop the spread of deer impacts—chronic wasting disease, tick-borne illnesses, and decimation of understory plants. But she’s hopeful they’ll look back and be thankful for the land that has been protected and the plants that remain.
“When I take my students into the woods,” she says, “we focus on what’s here now, we look for evidence of legacies of past land use, and I push students to look for clues to consider the trajectory of change and the future of the forest.” To the trained eye, she explains, the decisions of those who have come before are still legible, and our actions—or inactions —will be interpreted and judged as well: “Future generations of conservationists will be building narratives around our influence on these forests.”
Julie Buckles is the director of communications at Northland College. This article was written on a freelance contract for Site/Lines, a publication of the Foundation for Landscape Studies.