“Smell the flowering plant to your left. Isn’t it wonderful?”

Paula Sager, a tour guide at… “Smell the flowering plant to your left. Isn’t it wonderful?”

Paula Sager, a tour guide at Fallingwater, points to the Japanese Spiraea (Spiraea japonica) planted along the footpath to the house. The visitors agree the fragrance is lovely, but Sager’s face turns solemn.

“We are now being invaded by nonnatives.” The announcement to the tour group refers to the spread of invasive exotic species throughout the Fallingwater grounds.

When exotic species and, in this case, nonnatives such as English ivy, wisteria, burning brush and honeysuckle, grow freely in a foreign environment (Pennsylvania) without any natural controls, they overtake native species, causing an imbalance in the biological diversity of the area.

“All the nonnative plants will have to go,” says Sager. “Including [Spiraea] japonica.”

Frank Lloyd Wright designed Fallingwater in 1935 as a vacation home for the Edgar J. Kaufmann family of Pittsburgh. The house, located near Ohiopyle, rises more than 30 feet above a waterfall along Bear Run. Its design, some say, promotes harmony between man and nature.

The Western Pennsylvania Conservancy, the organization that preserves Fallingwater, realized that they needed to keep the spread of exotic plants under control before the plants destroy the native ecosystem.

According to Cara Armstrong, Fallingwater’s curator of buildings and collections, the WPC started planning a landscape masterplan in the mid- to late-’90s to control the various invasive species around Fallingwater.

Armstrong says that now, because of the growing problem, the WPC has begun implementing their landscape masterplan, which includes removing invasive species from the area surrounding Fallingwater and replacing them with native plants.

During the tour of the guest patio, Sager points out the Japanese white wisteria vine covering the canopy. She says that it will bloom beautiful white flowers around Mother’s Day, but the WPC will have to remove this nonnative species.

“I understand that this wisteria is going to get a pretty severe pruning,” Sager says.

Pitt senior Theresa Strazisar works in Dr. Susan Kalisz’s ecology lab, studying plant population biology of invasive species.

“Only 1 percent of exotic species are able to exist in an exotic environment,” says Strazisar.

“Our ecosystems should be stable, since they evolved over thousands of years ago. The functional space in an ecosystem should be filled with what is already there,” Strazisar said “and it is human induced disruption that causes a problem.”

“I’m not trying to say world travel is bad,” Strazisar says. “But how does a seed from Europe really get here?” Strazisar asks. “You can trace back a lot of the problems [with invasive species] to humans.”

“Humans create new disturbances in the ecosystem, giving invasive species new opportunities to grow. Plants have their own natural barriers, and do not grow invasively unless there is a disruption in their niche.”

Once exotic plants are established in an area, Strazisar adds, humans have control over their spread. Anything the WPC does at Fallingwater to preserve the area and control the invasive species is good, according to Strazisar. She says that the WPC can learn through trial and error how to control invasive species in the area.

Armstrong helped establish a volunteer project to remove exotic species around the Fallingwater house, which will begin on Earth Day, April 23, 2005.

“Students are welcome to help out,” Armstrong says, but she asks that they contact her first.