A Northwoods Almanac for Nov. 11-24, 2022 by John Bates
Deer Browse
Nearly eighty years have passed since “The Slaughter of ’43,” when, for the first time in the history of Wisconsin deer hunting, young bucks and does were harvested. Aldo Leopold, then a board member of the Wisconsin Conservation Commission (later to become the DNR), strongly advocated for the hunt and was vilified for his heresy until his death in 1949. Leopold’s sin was that he understood landscape ecology and dared to speak out against single-species management for the benefit of single-user groups, in this case, the deer hunters of Wisconsin.
Leopold had seen firsthand the dramatic long-term impacts of high deer populations in Germany, the American Southwest, and areas of the eastern and midwestern United States. In his essay, Thinking Like a Mountain, he is most remembered for his depiction of shooting wolves in Arizona, but the essay is every bit as much about over-populations of deer:
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 anemic desuetude, and then to death.
Leopold’s admonitions were written a long time ago, and while Wisconsin’s landscape differs dramatically from Arizona’s, the lessons regarding deer are equally poignant today. Wisconsin deer numbers have profoundly increased in the last 30 years. Depending on the year, we now average over 1.5 million deer in the state, and while annual deer harvest totals now range between 300,000 and 400,000, we rarely have been able to knock the population back far enough to make a difference for the forest vegetation of Wisconsin.
The saddest part may be that some of the beauty and grace of white-tailed deer has been lost in their commonness. Indeed, familiarity breeds contempt. Our prodigal deer numbers are such that just the reported traffic collisions total around 19,000 cars annually. The number of deer crashes as a percentage of all yearly car crashes averages around 15%. Deer are the third most-commonly struck object in Wisconsin traffic crashes, after other vehicles and fixed objects. The state of Wisconsin is now at number 5 in the United States for deer vs. car accidents, according to an annual study done by State Farm Insurance.
So, it has come to this: in their appetite for agricultural crops, gardens, and ornamental plants, deer are discussed in the same vein as common thieves, with endless discussions on how to fence them out, repel them, or plant what they won’t eat. Deer have become like Canada geese, a native species that has exploded in population so dramatically that it has lost its favored status in many people’s hearts. Too much of anything is a bad thing, whether it’s ice cream, CO2, geese, or deer.
Unlike geese and ice cream, however, deer vitally impact the integrity of whole ecosystems. Called a “keystone” herbivore, like beaver (and humans), deer have the
ability to restructure whole ecological communities. Deer graze mostly on herbaceous plants in the summer and early fall, but in winter, they switch their diet to woody browse, eating an estimated five pounds of buds a day. In effect, deer eat cereal four months of the year, and the box the other eight months.
In the woods, native orchids and lilies, white cedars, eastern hemlock, and Canada yew are the greatest casualties in this floral warfare, but a host of other species are eaten, often resulting in a profound change in the species composition and diversity of a forest. One study found that 98 species of threatened and endangered plants in the eastern U.S. are in jeopardy from white-tailed deer browsing. And while many woody species can often recover quickly from browsing, herbaceous species like spring wildflowers may require decades to recover fully, if ever.
Changing forest plant composition and diversity also changes the structure of the woods, reducing or eliminating the ground and shrub layers of the forest. Change forest structure, and the microclimate changes as well. By taking away understory and shrubby plants, the soil gets more sunlight, and thus warms up and dries more rapidly. Altering the physical architecture of the woods changes a whole array of animal/plant interactions. For example, as the plant layer thins, avian predation increases on small mammals because vision along the ground is improved. And, tit for tat, larger mammal predation (chipmunks, squirrels, weasels, etc.) of bird nests increases, too.
With the loss, or inhibition, of so many groundlayer and shrublayer plants, a “trophic cascade” occurs, a term used by ecologists to describe the waterfall of indirect effects that deer create through their voracious appetites. Grazing and browsing include the consumption of stems, flowers, leaves, buds, twigs, and fruits, all of which are physical sites on plants where other vertebrates and invertebrates feed, seek cover, lay eggs, mate, etc. Birds that nest from the ground up to 23 feet decline where understory vegetation has declined. They also find it more difficult to successfully nest, find cover, and find food where there’s limited plant life. Twelve species of warblers nest on the ground in northern Wisconsin forests, and ornithologists legitimately fear what their future may look like.
It’s not just nesting birds that suffer from excessive deer browsing. The loss of vertical complexity—the layering of a forest from herbaceous species to shrubs to small trees to large trees—has resulted in a reduction in the density of migrating birds as well. A migrating songbird needs food and cover after a long flight, and a depauperate understory of plants offers neither.
A significant proportion of invertebrate species may also decline in distribution and abundance due to chronic deer browsing. Whether through direct food competition, or indirectly by changing species composition or modifying the physical structure of the woodland habit, species like woodland butterflies have lost habitat.
Thus, while park-like understories make for great hiking and may appear aesthetically pleasing, they broach hard on the shores of sterility. The term “ecological desert” is usually reserved for poorly thinned red pine plantations in Wisconsin, but fairly applies to forests when deer reach unsustainable populations.
The oft-cited, most extreme example of too many deer is Sharon Woods Metro Park in Ohio, where 150 plant species were lost when the unmanaged white-tailed deer population reached densities over 110 animals per square kilometer. Unhunted parks and private properties that are posted “No Hunting” suffer the deepest botanical wounds, as deer come to understand the safety of a refuge and concentrate in numbers far exceeding the land’s carrying capacity.
Various studies have measured as high as a 60 to 80 percent loss of native species in old-growth stands with high populations of deer. Those remnant old- growth stands too small to prevent the mobile deer herds from invading have been termed “forests of the living dead” because of their lack of seedling reproduction.
As the old trees finally all come down, the new forest that comes up will look quite different from its predecessor. Sugar maple will replace the hemlock, and white cedar will be little more than a memory, while Canada yew will continue its role as the vegetative equivalent of the buffalo, a comparative ghost species on the landscape. There is some yew scattered out there, but too little ever to remotely exert the ecosystem influence they once had.
The winners have been those species that are unpalatable to deer, or those less vulnerable to their chronic browsing. Forests with long-term chronic browsing have changed from herb- and shrub-dominated understories to simpler communities now dominated by the grasses, sedges, and ferns least preferred by deer.
The losers have been those favored by deer taste buds, and those intolerant of chronic browsing. Consider trilliums, a genus universally known and loved by people throughout the Midwest. Several seasons of browsing have been shown to reduce trilliums in large numbers, and the surviving population is skewed towards smaller plants.
In the very few forests where deer are exiled, the plant communities look very different. Canada yew thrives in astonishing abundance on islands in the Apostle Islands National Lakeshore that have no deer. Yew covers 60 to 70 percent of the ground surface in many areas, growing to over 8 feet tall.
Bringing deer numbers down appears nearly impossible if forestry practices remain as they are. Some have suggested wolves could do the job, but will bringing back more wolves turn the tide? The simple math says no. Wolf biologists universally agree that individual wolves eat on average somewhere in the range of 20 deer a year. Given that our wolf population is around 1,100, wolves will only take around 22,000 deer, a pittance in the estimated 400,000-plus deer in the Northwoods herd.
In all of pre-Euro-settlement Wisconsin, ecologists estimate deer were present on the order of five to 10 per square mile, totaling perhaps around 200,000 in number. Even then, habitat was the limiting factor of deer populations, not wolves. Young forests support large numbers of deer. Older forests support fewer deer. Harsher winters in the 1800s thinned the herd out even further, whereas warmer winters in the late 1990s and the twenty-first century are providing optimal conditions for deer survival.
Recent studies indicate that Wisconsin’s higher wolf population has helped
increase understory herb and shrub populations primarily by moving deer around rather than allowing semi-domesticated herds to stay in one place and devour the understory. In fact, there’s evidence that a trophic cascade of benefits may be occurring from Wisconsin’s higher wolf population.
However, wolves will never pull down enough deer in Wisconsin to bring deer browsing fully into balance. And with Wisconsin’s legislatively introduced wolf hunting season soon to return, numbers of wolves will be suppressed in order to increase the number of deer, the biological reverse of what our ecosystem management should entail.
In the meantime, an aging hunter population and low recruitment of new hunters bodes ill for hunting to continue as the prime management tool. Areas without deer hunting experience plant species losses four times greater than elsewhere.
Leopold wrote, “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.”
What to do? Change forestry practices from a hyper-focus on early-successional species like aspen to later-successional species like sugar maple, yellow birch, and white pine. By managing for older forests, forest communities will be repopulated by a diversity of native species. Build it, and the deer will come more into balance, as will the surrounding forest.
Celestial Events
Look later in the evening tonight, 11/11, for Mars a couple of degrees below the waning gibbous moon.
The peak North Taurid Meteor Shower occurs from midnight to before dawn on 11/12. It’s a modest shower, averaging about 10 meteors per hour, but the shower sometimes produces fireballs, which might make their cyclical reappearance in 2022.
The peak Leonid Meteor Shower occurs on the evening of 11/17, averaging about 15 meteors per hour.
Thought for the Week
“The universe is a unity, an interacting, evolving, and genetically related community of beings bound together in an inseparable relationship in space and time. Our responsibilities to each other, to the planet, and to all of creation are implicit in this unity, and each of us is profoundly implicated in the functioning and fate of every other being on the planet.” – Chet Raymo
Please share your outdoor sightings and thoughts: e-mail me at manitowish@centurytel.net, call 715-476-2828, snail-mail at 4245N State Highway 47, Mercer, WI, or see my blog at www.manitowishriver.blogspot.com.
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