Four years have passed since we built our three-acre deer exclosure, and already the changes are noticeable. Tree seedlings have sprouted and grown, and new wildflower species have appeared. Slowly the deer browse line has softened and filled in.
We chose to put the exclosure in a mature patch of deciduous forest so the changes are not as dramatic as they would be if the area had been cut and then fenced. Still, month by month, season after season, I chart the changes in what my husband Bruce named the Turtle Woods Wildflower Sanctuary (see my column in May 2002).
In spring, I search for the first emerging leaves of wildflowers. Last spring false Solomon’s seal Smilacina racemosa (or Solomon’s plume as the late Lemont, PA, botanist George Beatty more poetically called it) and Solomon’s-seal (Polygonatum biflorum) bloomed for the first time. Beds of violets–common blue (Viola papilionacea) and downy yellow (V. pubescens)–covered the wet corner of the exclosure. The mayapple (Podophyllum peltatum) or mandrake colony continued to spread, but not one flower has appeared yet. Pink lady’s slipper (Cypripedium acaule), also known as moccasin flower, bloomed here and there, and a small patch of Canada mayflower (Maianthemum canadense) sent up their first blossoms.
In summer, when the woods are dark and deep, fewer wildflowers appear. The downy rattlesnake-plantain (Goodyera pubescens) that I discovered right after the fence went up produced 31 flowers two years later. The third year there were only five blossoms and last year none. Still, the attractive evergreen, white and dark green leaves continue to multiply, and I look forward to more flowers from this orchid in the future.
Not so the single spotted wintergreen plant I found after the fence was built in the spring of 2001. That year the wintergreen’s single bud disappeared. The following summer, on July 6, a nodding, waxy, white flower that looked as if it was made of fine porcelain dangled from the top of the stem. Luckily Bruce photographed it because that was the last year I found any trace of it. Since then I have repeatedly searched the exclosure for more spotted wintergreen plants, but so far I have found none.
Spotted wintergreen (Chimaphila maculata), also called striped wintergreen, is a member of the Pyrola family and lives in dry woods from New England to the southern United States. I have seen it growing as a ground cover in the forests of Connecticut and North Carolina. The Plants of Pennsylvania by Ann Fowler Rhoads and Timothy A. Block calls it “common in wooded areas; throughout except in the northernmost counties,” yet on our mountain in southcentral Pennsylvania the spotted wintergreen in the exclosure was the first one I’ve recorded in the 33 years we have lived here.
A far more common wildflower in midsummer, both inside and outside the exclosure, is the Indian-pipe (Monotropa uniflora). Last summer it did especially well because of all the rain. Inside the exclosure in one small corner alone I counted over 100 plants, far more than I found in any similar habitat outside the exclosure. Yet I’ve never seen any sign of deer herbivory on Indian-pipe.
Its close relative pinesap (Monotropa hypopithys) is relished by white-tailed deer so I was pleased when it appeared in the exclosure for the first time late last summer. Thirteen large, healthy, red and gold plants bloomed amid the blackened, uplifted pipes and stems of the pollinated Indian-pipes. The few pinesaps I found outside the exclosure were quickly browsed to the ground.
Another summer beauty–black Cohosh (Cimifuga racemosa)–blossomed first inside the exclosure in 2003. It also grows along our access road in the hollow above the stream, the same place where horse-balm (Collinsonia canadensis) thrives. Both species suffer some deer browsing, but horse-balm is especially hard hit. Still, I didn’t expect the dozens of horse-balm plants growing waist high that now blanket the moist corner of the exclosure in mid-summer. Horse-balm or richweed is a member of the Mint family, and its light yellow, lemon-scented flowers retain their odor even after they have dried on their stems.
Clearweed or coolwort (Pilea pumila) also grows in the moist corner of our exclosure. A member of the Nettle family, it sports undistinguished, branching clusters of greenish or whitish flowers in late summer.
By then white snakeroot (Eupatorium rugosum) is flourishing both inside and outside the exclosure but especially outside. This is one wildflower that our deer never touch, unlike its close relative spotted Joe-Pye weed (Eupatorium maculatum) that is mowed down almost as quickly as it germinates in our wet meadow.
Indian-tobacco (Lobelia inflata) is another wildflower our deer seem to dislike. It too grows within and without the exclosure. So do blue-stemmed or wreath goldenrod (Solidago caesia) and white wood aster (Aster divaricatus). Still, both of those species are more abundant inside the exclosure than on our road bank where they also appear.
Native shrubs have also been disappearing in our woods. Yet inside the exclosure they are thriving. In the wetland corner, nine new common elderberries, a red elderberry, and a couple spicebushes have sprung up. New sprouts of wild azalea have appeared in the drier woodland area of the exclosure.
But the shrub that is filling in the understory most rapidly is witch-hazel. Back in 1952 research forester A.B. Mickalitis called witch-hazel “the most common shrub native to Pennsylvania,” according to Charles Fergus in his informative book Trees of Pennsylvania and the Northeast. Although we’ve always had a scattering of witch-hazel in our forest, inside the exclosure the witch-hazel sprouts have formed a green ground cover, and along the trunks of the older shrubs new green leaves have emerged.
A few greenbriers, a hawthorn, many huckleberry shrubs, some blackberry canes, and a spreading wild black raspberry patch are our other understory species in addition to mountain laurel. Even the ubiquitous mountain laurel shows more sprouting and leaves inside the exclosure and may also be adversely affected by too many deer.
Dr. Ed Levri of the Altoona College of Penn State and his botanist wife Dr. Maureen Levri, have been studying the effect of deer herbivory on the mating system of mountain laurel in our forest for four years. With the help of students, they have labeled and numbered dozens of shrubs both inside and outside the exclosure as they carry on their research from year to year. They suspect that deer herbivory reduces the mountain laurel’s ability to produce the more desirable self-fertilized offspring.
But what of tree species? Those large trees, most between 100 and 200 years old, that we originally recorded throughout the exclosure–red maple, black and yellow birch, pignut hickory, white ash, black gum, white pine, black cherry, American elm, and white, chestnut, red, and black oak–are mostly flourishing. The pignut hickory did fall across the fence in July 2002, but already new hickory seedlings have sprouted. New white pine saplings are thriving, and all the oak species have produced many seedlings. Even a few American chestnuts have germinated. Most surprising of all has been the regeneration of black gum. Many are already shoulder-high saplings. Yet outside the exclosure, where the mix of trees and shade are the same, no tree seedlings of any species survive.
Those less desirable, even, in some cases, invasive natives, are only a small portion of the overall species’ numbers in our exclosure. For instance, with all the rampant undergrowth, only a small patch of hay-scented fern survives, yet one study, back in 1989, found that as much as 30% of Pennsylvania’s forest understories are blanketed in hay-scented and New York ferns. Striped and red maple seedlings, in many forests the only tree species that are regenerating, are far outnumbered in our exclosure by oak and black gum. All of the wildflowers inside the exclosure are natives. So too are the native Virginia creeper and wild grape vines. The only non-natives in the exclosure are a multiflora rose and a couple Japanese barberry shrubs. Because this is an experimental plot, we are not removing them. We want to see what happens to them as the natives continue to spread.
In a recent study by researchers at the USDA Forest Service’s Northeastern Research Station in Warren (PA), which tested the effects of various numbers of deer on the Allegheny National Forest, they discovered “that deer affected the abundance and density of all plants; the horizontal and vertical structure of the forest; species abundance of wildflowers, shrubs, and birds; species composition and biodiversity of the forest understory and resilient versus deer-preferred foods,” according to Forest Science Review.
“We think we know our forests,” says one of the researchers Dr. Susan Stout. “But in Pennsylvania and many other parts of the Northeast, deer abundance has changed our forest so much and for so long that we truly don’t know how our forests would look without too many deer.”
Certainly having our exclosure has made us acutely aware of what is not growing outside the fence as well as what is growing inside. It also shows us how quickly some plants recover, such as the black gum, and how slowly, if at all, other plants come back. Every year there are more surprises.