Wildflower is published quarterly by the Wildflower Center. Its content is national in scope with articles about the conservation and use of native plants as well as news from the Wildflower Center. A subscription is provided to Wildflower Center members as a benefit of membership.
Deer threaten woodland wildflowers
Story and Photos by Cece Fabbro
In mid-April, long-time Bedford, New York, resident Pat Keesee walks the woodlands there searching for some of the earliest-blooming wildflowers in the eastern deciduous forests. She hopes to find bright-yellow marsh marigolds, snow-white bloodroot, pale-blue Virginia bluebells and yellow-brown adder's tongue.
Disappointed at how few of these spring ephemerals she's able to find, Keesee shakes her head. "When I moved here 49 years ago, the woodland floor was carpeted with swaths of yellow, pink, blue and white. It was such a delight to step out after final frost and stumble upon these little gems; I just knew spring was on its way. All that has changed, however. Now, I only see a few here and a few there. My walks have become treasure hunts."
Spring ephemerals are a group of fleeting woodland wildflowers that must grow, bloom and set seed within a two-month period after last frost and before the trees' leaves block the sun. Many are long-lived, and their early appearance makes them a critical source of nectar for early-emerging insects, especially bumblebees. But spring ephemerals, like other woodland wildflowers, are in danger.
"There appear to be a number of factors contributing to their demise, including habitat destruction, aging forests, encroaching invasive species, air and water pollution, non-native worms, unrestrained collecting and especially rampant over-browsing by white-tailed deer," says Bill Cullina, nursery director and chief propagator at New England Wildflower Society (NEWFS).
Although scientific studies regarding the disappearance of ephemerals are few, one long-term study in Wisconsin addresses the impact that deer are having on woodland wildflowers in general. Dr. Tom Rooney, an assistant professor at Wright State University, has been studying changes in forest plant communities over the past 50 years. Using a baseline data set from a quantitative survey conducted in the 1950s, Rooney has resampled a number of sites originally surveyed. "The sites that we resurveyed in northern Wisconsin indicated an 18 percent decline in species richness from what was present around 1950," says Rooney. "In addition, we found that these sites were gaining in exotic species and becoming more similar to each other."
Sites where deer hunting was limited showed a greater loss of species than sites where the hunting was allowed - 65 percent compared with 12 percent. "We found that the deer population, which has been on the increase since the 1960s, was having a profound effect on wildflowers. Clearly, deer are a major force driving ecological change in our forests."
Another study begun in 2001 at the Mianus River Gorge Preserve outside of New York City evaluates similar effects on the 750-acre oasis of rich woodlands. Five deer exclosures of one-quarter acre each were erected at various locations on the preserve to learn what impact deer were having on wildflower populations and other native vegetation and to assess competition from invasive species if deer were absent.
"We used trillium as an indicator species because stands of the wildflower have disappeared from various sites on the preserve, and it's a species we know deer eat," says Rod Christie, executive director of the Preserve. "In 2001 we counted 7 mature trillium plants in one of the exclosures. In two years we counted 175 plants, and in 2006, 280 plants. In addition, we noticed dramatic increases in populations of other ephemerals, particularly bloodroot." From this the preserve implemented a deer management program that included selective culling to try and restore a balance between the native vegetation and the deer.
Until recently, the issues of herd reduction and selective culling have been controversial. However, public sentiment may be changing as an increasing number of deer invade suburban gardens, cause auto accidents and spread the deer tick that carries the bacterium known to cause Lyme disease.
Bill Cullina notes that while perception is that the deer problem is due to habitat loss, human-induced changes to habitat really are to blame. In fact, more deer exist today in the Northeast than in pre-colonial times because of habitat change.
"We have replaced the animals' native woodland habitat with a matrix of agricultural lands, suburban developments and woodlots - just the sort of varied landscape the deer really thrive on," says Cullina.
"We have planted lawns and gardens that become accessible, sustainable food for the deer once they have depleted the remaining wooded areas of native vegetation. Furthermore, we have eliminated the deer's natural predators and in some places even banned hunting. There are no more checks and balances to keep the population in check, and there is a vastly improved food supply to spur rapid reproduction."
"Deer control must be taken seriously," says Bill Brumback, Conservation Director of NEWFS, one of the oldest and most widely known plant conservation organizations in North America. "From a conservation perspective, deer over-browsing not only affects wildflowers, it also can change the entire vegetative composition of the forest. By browsing understory plants, which include wildflowers and tree saplings, the deer can create a void that may be filled by invasive species and other opportunistic plants. Many of these invasive plants are not palatable to deer, so they persist and may increase."
According to Brumback, NEWFS has formulated a plan for managing deer that includes deer fencing, deer repellants, controlled hunting and recreational hunting.
As the problem continues to grow throughout the East Coast, more and more preserves, parks, botanic gardens and even towns are wrestling with this issue and discussing appropriate options for deer reduction in their locales.
Last year Pound Ridge became one of the first towns in Westchester County, New York, to allow deer hunting on town-owned property. In doing so, town officials hope to address reports that five times as many deer as the environment could sustain were roaming the land.
A program at a Virginia park already has reaped results. Earl Hodnett, Fairfax County, Virginia's wildlife biologist, and Julia Kutruff, park operations superintendent of the Northern Virginia Regional Park Authority, point to Bull Run Regional Park as one of their successes. In 1998 a deer density survey indicated 419 deer per square mile in the park, when 15-20 deer per square mile was the optimal number. Over-browsing was evident throughout.
A program to cull select does and monitor deer herd populations was put into effect. Now, after years of monitoring and culling, spring ephemerals and other wildflowers are putting on a show for visitors again. "It's not just a one-time fix," cautions Hodnett. "It's an ongoing battle. We constantly are monitoring the deer population and culling when it begins to get out of hand."
A visit to River Bend Park in April is quite different than what Pat Keesee experiences in Bedford. Along the floodplain of the Potomac River lie acres and acres of Virginia bluebells, trillium, bloodroot, toothwort, Dutchman's breeches, spring beauty and trout lily. At this park, there is a conservation program with a deer-control component in place, for which wildflower lovers can be thankful.a
Cece Fabbro is a Westchester, New York-based nature writer and photographer. She is a long-time wildflower guide at Teatown Lake Reservation, an 834-acre preserve, and at the Native Plant Center ( a Wildflower Center affiliate), both in Westchester County, New York.