Busse Woods was among the first natural areas to be set aside as an Illinois nature preserve. The 440-acre hardwood forest, which is part of the Ned Brown Forest Preserve in Elk Grove Village, was also cited in the early 60s by the federal government as a uniquely diverse remnant of the native landscape. Only one other place in Illinois–Volo Bog–has received such recognition.
Busse Woods was famous for its spring wildflower display. In May the ground was carpeted with Dutchman’s-breeches, spring beauty, red trillium, and large-flowered trillium. Rare orchids such as purple twayblade and the purple-fringed orchid added their delicate beauty to the scene. But by the late 70s the richness of this display was declining rapidly. The cause was an overabundance of white-tailed deer, which were eating many kinds of plants to extinction.
In 1983 scientists from the Illinois Natural History Survey began a systematic study of the effects of heavy deer populations on Busse Woods. At the same time they began removing deer from the preserve in an attempt to bring the population down to a level that would be within the carrying capacity of the land. Some of the deer were transported to new homes near Joliet, but most were killed with shotguns or netted and then killed by lethal injection.
A survey of the plants of Busse Woods conducted in 1983 revealed that 26 species that had grown there in the early 60s had disappeared. The famous spring wildflower display was almost completely gone. But now, after eight years of deer population control, there are some encouraging signs of regeneration. Dutchman’s-breeches were rediscovered last year, and large-flowered trillium–which had hung on here and there in the shelter of downed logs–is appearing again out in the open.
But according to Chris Anchor, a wildlife biologist with the Cook County Forest Preserve District, “regeneration has been painfully slow. The deer abundance continued for so many years that many plants were extirpated.” The wildflowers of a woodland spring are perennials. Each year a bulb or other underground structure sends up new green shoots and new flowers. The bulbs live for many years, and they can survive a few years of having their leaves clipped by browsing deer. But if the clipping continues for six or eight years, the bulbs die.
The sad story of Busse Woods is unfortunately being repeated at other preserves throughout the area. The Lake County Forest Preserve District has had to set up a deer-control program to protect the biological diversity of the Ryerson Preserve, the magnificent old-growth forest on the Des Plaines River near Deerfield. This winter the Cook County Forest Preserve District will be taking similar actions in its portion of the Des Plaines River valley and in the Palos preserves around Camp Sagawau.
Just a few decades ago the spring wildflower display around the River Trails Nature Center, which is along the Des Plaines River between Lake Avenue and Willow Road, was as fine as anything at Ryerson. But then came the boom in deer numbers. They started on the trilliums, and when those were gone they switched to plants such as false Solomon’s-seal, which deer avoid unless they are very hungry.
The spring display at River Trails is now nothing but a few trout lilies and spring beauties. The situation elsewhere along the river is even worse. Around Dam Number One at the northern edge of Cook County, according to Chris Anchor, nothing grows in the forest understory except garlic mustard, buckthorn, and white vervain. The first two of these are aliens, the last is a native–but all three are regarded by deer as extremely unpalatable.
So over the next few months sharpshooters licensed by the Illinois Department of Conservation will be working along the Des Plaines and in Palos to reduce the deer populations. Nets will also be used, and the deer captured in the nets will be killed using methods approved by the American Veterinary Association.
A fundamental question for all those involved in controlling the deer herd is how many deer are enough? The answer needs to be tailored to the individual site. A good healthy woodland can support about 18 deer per square mile. In the Des Plaines River valley, where years of heavy deer browsing have seriously degraded the woods, five to seven animals per square mile would be an appropriate density. The preserves around Crabtree Nature Center near Barrington could sustain as many as 25 to 30 animals per square mile because there are still cornfields in the area to supply food.
Other portions of the Cook County forest-preserve system will soon need deer-control measures too, including the preserves along the North Branch of the Chicago River. These preserves have received a lot of attention in recent years as volunteers from the North Branch Prairie Project have worked to restore the native prairie and savanna vegetation. Now increasing evidence shows that heavy deer populations are undercutting our efforts to increase the biological diversity of the preserves.
I spend a lot of time at Somme Woods, the northernmost of the North Branch preserves, studying the nesting birds, and my unscientific impression is that there are a hell of a lot of deer around. I have seen as many as 11 animals in a one-hour stroll around the 60 or 70 acres that lie between Waukegan Road and the Milwaukee Road railroad tracks. I am very cautious in counting the animals I see, since it is easy to flush the same deer more than once, so that figure of 11 could be too low.
The best scientific estimate, derived from an aerial census, shows that Somme Woods is currently home to about 54 deer per square mile, three times the ideal figure of 18 per square mile.
All those hungry animals are having a noticeable effect on the vegetation. Steve Packard of the Nature Conservancy offered me a litany of distressing details when I asked him for some specifics on what the deer have eaten.
Among the rarities sheltered at Somme were two milkweeds. One of these has disappeared completely; the other, which is not known to grow anywhere else in the state, is dwindling. An annual called maple-leaved goosefoot that grew under the oaks of the savanna has vanished completely. There may still be seeds in the ground that will sprout next year, but we don’t know if this one will come back. Of course if it does grow next year, the deer will probably eat it all again.
The cream gentian, a lovely savanna wildflower, grew at Somme in great abundance a few years ago. The plants are still there, but they have set no seed in the past few years because the deer eat the tops and prevent them from setting seed. The small white lady’s slipper is an endangered orchid that was moved into Somme Woods from a site in Buffalo Grove that was about to be bulldozed. It did well initially, but now its numbers are declining.
The Canada milk vetch, a rare legume, is being eaten right down to the roots. Established plots that are censused every year are showing consistent drops in species such as woodland joe-pye weed, bottlebrush grass, and cow parsnip, all of which were planted in the Somme savanna as part of the restoration work. Places that used to support large numbers of trilliums and woodland phlox are now completely devoid of these spring flowers.
Chris Anchor says that at this point he does not have enough hard empirical data about Somme to support an application to the state to carry out a deer-control program. The hope is that enough such information can be gathered this year to make deer control possible next winter. Packard points out that there is good reason to concentrate efforts in places where the damage is not yet major. It may be too late along the Des Plaines, but moving quickly on the North Branch may deal with the problem before species have been extirpated.
We can expect deer-control measures to be a part of forest-preserve management for years to come. Deer herds all over the midwest are at historic highs. Mild winters, the absence of predators, and low levels of disease and parasites are all contributing to this abundance.
Busse Woods is also showing us that controlling deer numbers can work. In addition to the return of some of the woodland plants, reduced numbers are producing larger, healthier deer. The whole ecosystem is benefiting from the control of the white-tails.