ACADIA NATIONAL PARK — Out with the orchids, in with the deadly nightshade.

The profile of plants found in Acadia National Park has been shifting over the past century, with some species declining and others on the rise, and researchers believe climate change is mainly to blame.

Some of the plants that are becoming more common in the park are considered invasive species, according to park officials. Purple loosestrife, glossy buckthorn and barberry are among the invasive species that have become a common sight on Mount Desert Island over the decades, while native flower species such as orchids, asters and lilies have decreased in quantity.

Other native species, such as blueberries, continue to do well, despite the earlier spring thaws and heavier precipitation, according to Abe Miller-Rushing, science coordinator for Acadia National Park.

“Conditions in the park are changing,” Miller-Rushing said this week. “The last thaw in spring is earlier [in the year] now. We’re a lot wetter and warmer than we were” 100 years ago.

Caitlin McDonough MacKenzie, a doctoral degree candidate at Boston University, is one of a group of graduate students who have been examining the shifting prevalence of plant species in the national park, which bars development on 47,000 acres on and around MDI.

She said that, after consulting with a field guide on MDI’s plant species written in 1894, researchers have determined that a significant number of wildflower species that were listed in the catalog no longer are found on the island.

Of the 500 or so wildflower species listed in the 1894 guide, written by Henry Rand and John Redfield, 20 percent of them have declined in abundance. Almost as many are gone altogether, she added.

“We had this huge percentage of species that had just disappeared from Rand and Redfield’s time,” MacKenzie said. “Eighteen and a half percent of those [500 wildflower species], 91 species, have disappeared from the island.”

MacKenzie said researchers looked into several possible factors in MDI’s changing plant profile. The decline of farming and the regrowth of woodlands was considered, she said, as was the great fire of 1947, which burned more than 17,000 acres of spruce and fir forests and developed land on the eastern side of the island.

Park officials have long known that birch and aspen trees, which thrive in direct sunlight, proliferated after the fire but, as the forests have grown back in and as the competition for sunlight has intensified, those types of trees recently have been on the wane.

What researchers found, MacKenzie said, was that plant species have disappeared from all types of habitat on MDI, be it wetlands, open grassland or dense forest, which suggests that a common factor is to blame.

Development has been blamed for species loss in Massachusetts, she said, and for the spread of invasive species in parts of Maine and elsewhere such as lupine, Japanese knotweed, giant hogweed and deadly nightshade. Those invasive species have been found in Acadia, but MacKenzie said the impact of development on the park is considered to be fairly minor and not a primary factor in the shifting plant profile.

MacKenzie said evidence shows that earlier thaws caused by climate change are behind the species shift in the park. Plants that are more responsive to temperature changes tend to grow and leaf out sooner each spring than plants that are less responsive to temperature change.

So as thaws come earlier in the year, she said, temperature-sensitive plants are getting an earlier start and are slowly squeezing out plants that bud the same time each year regardless of how warm it is.

And, she said, many of the species that respond more quickly each spring to increasing temperatures happen to be considered invasive.

“The ones that seem to be most successful are taking advantage of this adaptation to respond to early spring temperatures,” MacKenzie said. “They must be getting some kind of competitive edge over the native species. We’re definitely getting an increasing non-native population.”

According to Miller-Rushing, the park’s staff does what it can to prevent and control the spread of invasive species in the park. He said that the National Park Service is charged with trying to protect the integrity of native species in national parks and, if feasible, to restore native species that have disappeared. Keeping out all invasive species, he said, would be “an impossible task.”

Acadia has two vegetation restoration projects planned, near Sieur de Monts Spring and at the summit of Cadillac Mountain. The park has not determined which species it will plant in the restoration areas, Miller-Rushing said, but will consider reintroducing native species that have disappeared, though he acknowledged conditions in the park are probably “not ideal” for some of them.

Acadia staff will consider which native species will have the best chance of surviving in a warmer, wetter climate when making those selections, he said.

“We will focus our efforts on those species that have the best chance of doing well in the park today and in the future,” Miller-Rushing said.