For as long as anyone can remember, wild orchids have rewarded sharp-eyed hikers in Maryland's Catoctin Mountains with pink, yellow and white blooms peeping from the forest floor.
But these "secret beauties," as one researcher dubbed them, are vanishing at an alarming rate, likely devoured by a horde of deer feeding on every leaf and shoot they can reach, according to a new study.
"Deer are like lawnmowers when they get going in a forest," said J. Mel Poole, the superintendent of Catoctin Mountain Park in Thurmont. "They especially like things like orchids."
The study, based on 41 years' worth of data, shows precipitous declines in the number and variety of orchids in the Catoctins in Frederick County, with three species vanishing altogether from spots where they had been seen year after year. Seven other species have dwindled by more than 90 percent, while nine shrank by between 51 percent and 87 percent. Only two orchid species gained or held their own.
The findings, published online last month in the journal Biodiversity and Conservation, document the drastic changes that white-tailed deer are wreaking on one of Maryland's showiest wildflowers.
"I think it comes as a surprise to people that there are even any native orchids in Maryland," said Kirsten Johnson, president of the Maryland Native Plant Society.
Orchids, especially those that grow in the tropics, are prized for their delicacy and rarity. Maryland has been home to 51 species, though many are considered rare, threatened or endangered in the state, and a handful have been declared "extirpated," meaning they are no longer found here. Twenty-one are — or were — growing in the Catoctins, according to the study.
While the loss of such remarkable flowers is hard to take, Johnson said grazing deer are taking a similar toll on a lot of less charismatic vegetation, altering the natural landscape by consuming plants, shrubs and tree seedlings.
Previous studies have found that deer are having major effects on flora, said Wesley Knapp, a botanist with the Maryland Department of Natural Resources and the study's lead author. But by following one set of plants in one area for so long, Knapp said, the data "really shows how things have changed over time."
Knapp said the findings are the life's work of his co-author, Richard Wiegand, a state ecologist who tracked the Catoctin orchids from the 1960s until his retirement four years ago,
Wiegand, 67, said he was out hunting snakes in the forest one day when he noticed an orchid blooming beneath a hemlock.
"It was just like a Chinese lantern lit up from the inside, the way the light hit it," he recalled. "I had not known we had orchids in the area."
From then on, Wiegand said, the exotic-looking flowers became his passion, and year after year he logged the number and species that he found, often on his own time. An article he wrote in 2008 called them "Maryland's secret beauties."
For many years, he didn't really analyze the data he was collecting. It wasn't until the early 1990s, he said, "that I actually became conscious we were losing our orchids."
Ultimately, Wiegand and Knapp pulled together four decades' worth of data, in which 21 species of orchids had been inventoried annually across the 300-square-mile mountain range running from the Potomac River north to Pennsylvania. Much of the land was protected, including the federal Catoctin Mountain Park near Thurmont, Camp David, and Cunningham Falls and Gambrill state parks.
In that time, they found that three species, including the greater yellow lady's slipper and the lesser round-leaved orchid, had disappeared from the 167 sites checked each year. Others seemed headed that way, such as the Adam and Eve orchid, the summer coralroot and northern slender lady's tresses.
Orchids are known to be fickle, dying back one year only to rebound, Wiegand said. But this study ruled out such annual fluctuations, finding severe and widespread declines across the mountain range.
While it's possible that some of the orchids that vanished from survey sites are growing elsewhere in the Catoctins, Knapp said, their future there is in doubt.
"We have so many sites, the trend is obvious," he said.
The researchers considered a variety of possible causes but soon focused on the profusion of deer roaming the forests. There were no reliable long-term tallies of the animals' abundance to match the orchid data, so the researchers looked instead at how many deer were reported killed by hunters every year. The number of deer shot increased 12-fold from 1980 to 2000, they found, suggesting that the harvest grew because the deer population did.