Also last month, New York bought several hundred trees and shrubs for the restoration of the 200-acre Inwood Park, the only native forest left in Manhattan, said Jane E. Shachat, director of the North Manhattan Park System.
Temple's Ambler nursery is one of a few that exclusively grow plants native to the region for landscape architecture, restoration and gardening, said Caroline Friede, staff horticulturist and nursery manager.
The focus is symbolic of a larger movement toward a more natural approach in horticulture, Friede said. Traditional landscaping - vast expanses of grass and gardens of exotic plants - harms the regional ecology because it requires chemical herbicides, pesticides and fertilizers that ruin water and air quality, she said.
Using native plants to restore areas such as corporate campuses, farmland, and abandoned golf courses can re-establish the ecological balance, Friede said.
The plants are well adapted to the region - they are robust and require less maintenance than exotic species do, said David S. Froehlich, executive director of the Wissahickon Valley Watershed Association, which has bought plants from Temple's Ambler nursery.
"This is plant material which, over thousands and thousands of years, has developed well to the ecosystem here. It supports the wildlife that evolved along with it," Froehlich said. "These things have a place in the ecosystem."
New York's Operation Green Thumb uses plants grown at Temple for its city gardening program - including 350 plants bought last month. The federally funded agency helps community groups turn vacant lots into gardens.
Most of its 800 gardens are in the inner city, a harsh environment for anything but the hardiest plants, which are most often native ones, said Ramesh Ahmadi, Operation Green Thumb's horticulture coordinator.
Native plants "are well-adapted to the area, they're bound to do well here, and they don't need a lot of special care or adjustments made in the soil," Ahmadi said.
The new focus on cultivating native plants stems from their dwindling numbers, Friede said.
Years ago, gardeners and farmers introduced exotic and invasive plants from China and Europe into the region. Plants such as the multiflora rose, touted as "the living fence," were introduced by farmers, who used it as a hedgerow to keep cattle in. But the prodigious multiflora quickly took over the landscape, overgrowing abandoned fields and farmland. Native plants couldn't compete, and were quickly crowded out.
Native plants "have been neglected in the craze for the exotic and the unusual. They should be the backbone of the planted landscape," said John F. Collins, chairman of Temple's department of landscape architecture and horticulture.
The Norway maple, one of the leading trees sold in commercial nurseries, is a good example of a problem exotic plant, Friede and others said. The tree, originally from northern Europe, each year produces leaves earlier and keeps them longer than most trees. Its broad leaves form a dense canopy that blocks the sun, preventing other plants from growing beneath it in the forest. In addition, its roots send chemicals into the soil that discourage other plants
from growing, Friede said.
"Once you start introducing these exotic invasive plants, they tend to disrupt the native plant community and be aggressive in the landscape, (reducing) the diversity of plant species," she said. "The ecosystem is compromised and can't support wildlife. The food chain is disrupted."
Other plants disruptive to the ecosystem include the ailanthus, or "Tree of Heaven," which is often found growing in cracks in sidewalks; the mulberry, brought from China to feed silkworms; and the Japanese honeysuckle and the Oriental bittersweet, both invasive vines.
Because so many nonnative species are growing uncontrollably, horticulturists say, the regional landscape has changed dramatically in the last 20 years.
The sugar maples, white oaks, and swamp white oaks that once predominated have decreased in number significantly.
Paul Lindell, landscape architect for the Smithsonian, which will pick up its saplings next week, cautioned that the greater use of native plants in horticulture - like any trend - could be taken too far. For example, he said, some "arch-purists" support using only plants that were here before Columbus set foot on the shores of the New World.
"I think it's good and bad, depending on how far the pendulum swings," Lindell said. "I think it's good to cultivate them and use them, but I don't think many horticulturists agree that the straight back-to-native (approach) is best. No matter who you're talking to, you'll get a different answer."
Native plants can be difficult to transplant, and some might not survive well out of their native woodlands, he said.
The Ambler nursery grows about 65 native species, including common persimmon; sassafras, which has a complex system of underground stems well- suited for controlling erosion; witch hazel; maple leaf viburnum; shag bark hickory; and a variety of oaks.
"We grow most of our plants from seed," Friede said. "That ensures genetic division so that the plants are less vulnerable to pests and diseases. Often, nursery stock is grown from the same parent stock material - from cuttings. They're all genetically identical. We're trying to keep the gene pool diverse and large to mimic a wild community.
"When you grow things from seed, you don't know what you're going to get - a pink flower from a typically white-flowering plant, a great fragrance, a particularly fast-growing plant, large blossoms."
The nursery also offers hands-on experience to students in the university's landscape architecture and horticulture department. The staff and students also conduct research on propagating and growing native plants.
"Our philosophy is in understanding the ecology of the natural landscape and how man fits into it," Collins said.