Urban Renewal

by | Nov 1, 2006 | Conservation

ALONG THE WOODED BANKS of the San Antonio River in south-central Texas’ Goliad State Park, bald cypress, sycamore, black walnut and box elder trees vie for sunlight with hackberry and mesquite bushes. Hawks circle overhead, and herons stalk the shallows, while bluegills, bowfins and bass hitch rides on the fast-moving downstream current. This remote park represents just one of several sites Wildflower Center ecologist Mark Simmons and Kevin Conner of landscape architecture firm Carter & Burgess are examining to gain a sense of what types of native plants should be used in restoring a more urban and heavily degraded stretch of the same river 100 miles to the northwest. The land being restored is in downtown San Antonio in an area known as Mission Reach, named for its proximity to the four 18th-century Spanish missions that laid the foundation for modern-day San Antonio.

Nearly 1,800 miles to the east, in Brooklyn, and more than 2,000 miles to the west, in Seattle, others can relate. Ed Toth was just starting out in his career at Brooklyn, New York’s, Olmsted-designed Prospect Park when in the early ’90s he urged its administrators to restore a suffering 13-acre gorge-like ravine with native woodland plants. At about the same time, Seattle homeowner Cheryl Klinker helped mobilize community volunteers who would restore to its natural glory Seattle’s largest watershed, Thornton Creek, by replacing invasive plants with site-appropriate natives. Today, urban landscape restoration projects that emphasize native plants can be found across North America, but this wasn’t always the case. In fact, less than two decades ago, before many land managers understood their benefits, most urban landscaping projects were making extensive use of non-native ornamental plants, some of which aggressively invaded once-pristine natural areas.

Slowly but surely, however, native plants are making their way into varied landscaping and gardening projects. Having evolved with the land forms, climate conditions and wildlife of a particular place, indigenous plants and wildflowers simply are better suited for many places than non-native plants, and their beauty as well as the habitat and food they offer wildlife are among the reasons they are being chosen.

Perhaps the most compelling reason to use native plants in urban restoration projects is to bring nature back into America’s cities, where 80 percent of the population lives. Indeed, the proliferation of development in America’s urban areas during the 20th century has meant that city dwellers have little if any contact these days with the natural world, save for the occasional weekend getaway to the country or summer vacation in a national park. A new wave of concerned citizens, urban planners and landscape architects are hoping to change that by bringing native plants back into our cities to affirm a regional sense of place, encourage enjoyment of the outdoors, and restore the health and diversity of ecosystems long traumatized by pavement and pollutants.

Restoring ecological health to an area is not without its challenges, and no two urban areas are alike. In the case of the San Antonio Mission Reach project, since the 1920s engineers have worked to speed the river past the city to keep floodwaters out of the densely populated metropolitan area. While this approach has been effective at reducing the volume of floodwater on the city’s downtown streets, it tore apart what must have long ago been an ecologically healthy – and beautiful – landscape.

These days the river channel along the Mission Reach is lined with concrete, and a few non-native, invasive plants prevail. The city of San Antonio and the U.S. Army Corps of Engineers contracted with Carter & Burgess and the Wildflower Center last year to oversee what has turned into a multi-year, $140 million restoration effort to rehabilitate the river channel and increase riparian and aquatic habitat potential while improving recreational and scenic opportunities for the public. The project, for which construction is scheduled to begin next summer, seeks to do so while maintaining hydrologic flood control features. It should be completed by 2011.

There are plans to install more than 24,000 individual native trees, 56 acres of native grasses, 113 acres of aquatic habitat and 320 acres of riparian habitat along the eight-mile stretch of the San Antonio River.

Conner, a project manager with Carter & Burgess, says it’s easy to see why native plants are figuring prominently in the design solution. “It was a base assumption from day one,” he says. “There was never a discussion of doing anything else.”

Simmons agrees that if San Antonio wants a restored riparian ecosystem with vibrant wildlife habitat, using native plants would be the only way to go. “By having a diverse suite of native plant species, you increase the value, not only in terms of habitat but also in terms of food sources for wildlife,” he says. “For instance, if you put some [native] hackberries in there, the birds will have plenty to eat for a good portion of the year as well as a greater choice of nesting sites.”

To Kern Ewing, a plant ecology professor at the University of Washington’s Center for Urban Horticulture, this alone is a reason to bring natives to city projects.

“There are some native species all the way down the food chain, from nematodes to invertebrates to mammals to birds, that have a high degree of association with native plants,” says Ewing. “So it makes sense if you want to keep a native floral or faunal biodiversity that you want some native plants in a city.”

Ewing says this biodiversity engenders a connection to the natural world that many city dwellers may never experience otherwise, and he points to Thornton Creek as an example.

The 18-mile creek drains run-off from the northeastern section of Seattle into Lake Washington and eventually into the Pacific Ocean via Puget Sound. Once a salmon stream teeming with wildlife, Thornton Creek was degraded over a 50-year period by development encroaching all around it. Like most of Seattle’s streams, parts of Thornton Creek were channeled into underground tunnels to facilitate building directly above.

In 1992, however, a small group of enlightened homeowners in the area decided to take matters into their own hands and began removing invasive species and planting natives along small sections of Thornton Creek. Their enthusiasm was contagious, and eventually hundreds of volunteers were coming out to various work parties to help restore different parts of the creek’s ecosystem. Today, after a decade and a half of volunteer restoration work, four species of wild Pacific salmon, other fish and a plethora of birds, mammals, amphibians and insects are once again thriving in Thornton Creek.

“For me, the most exciting result of removing invasive plant species and restoring the native plants to re-create critical habitat areas is the quick response by wildlife to move back into the city,” says Klinker. “We feel that as members of this stream-related ecosystem we need a diversity of life to sustain us and to retain a connection to the earth for a healthier and happier life,” she says. “Otherwise our neighborhoods would become depressing, dense, concrete environments that feel devoid of life.”

In Brooklyn, Toth felt it was important to maintain that sense of connection to the wild. Back then, a capital campaign undertaken by New York City’s parks department had generated millions of dollars to restore Brooklyn’s landmark Prospect Park, which had been suffering from decades of overuse and neglect.

Toth says that the park’s ravine surrounded by 150 acres of woodland was “devoid of understory, and there was no regeneration of overstory trees. The soil was severely eroded and compacted, and the overstory trees were suffering accordingly.” As a result of the erosion on the slopes, the watercourse through the ravine was almost completely silted-in, resembling a murky backwater more than a sparkling stream. Meanwhile, invasive tree species were beginning to dominate portions of the woodlands, especially where larger native overstory trees had been lost.

Toth, who had been trained as a botanist, was surprised to learn that the emerging restoration plan called for planting non-native plants in the ravine and surrounding woodlands for the sake of staying true to Olmsted’s century-old vision that included decorating the landscape with a wide variety of mostly non-natives. Toth wondered if the ravine area’s destruction was partly attributable to the original plant choices made by Olmsted, who sought exotic flora from all over the world for the project. When Toth discovered that Olmsted had no written planting plans for the ravine, he decided the time was right to start lobbying to restore the area with native plants, regardless of historical accuracy.

While Toth’s main reason for advocating native plants was the ecological health of the ravine and woodland, he knew the decision-makers at city hall would listen to arguments based on cost. “If you were to try to do such a project using traditional non-native horticultural plants, as was originally intended, you would have acres and acres of gardens to maintain and not the staff or money to maintain them,” says Toth. “I advocated for an approach more akin to natural resource management: Manage these as woodlands so they’ll be more self-sustaining.”

Toth’s viewpoint won out, and he was put in charge of planning and overseeing the native restoration of the ravine accordingly. From 1996 to 1998, he and his crew worked feverishly to remove thousands of invasive trees and shrubs, dredged tons of silt out of the watercourse, constructed barriers to hold back freshly augmented soil, and grew and planted as many as half a million native plants to be placed in the park’s quickly changing ravine.

Over the course of Prospect Park’s woodland restoration, park horticulture crews have planted 65,000 trees, 47,000 shrubs and 463,000 herbaceous plants. Looking at the ravine and surrounding woodlands today, it’s obvious that native plants have improved the health of the ecosystem significantly. Herbaceous understory plants have been successful in holding back the soil, ensuring that the watercourse remains clear of silt. Invasive overstory trees have been removed and replaced with native saplings, which are already starting to fill in any remaining gaps in the canopy. And wildlife has flocked to the area in droves, with the Brooklyn Bird Club anecdotally reporting a doubling of species sighted in the park since the restoration work began.

Perhaps it is the very success of projects like the Prospect Park ravine restoration that have made using native plants in restoring degraded urban lands standard operating procedure these days. The fact that such thinking was not always commonplace shows just how far urban land managers have come in less than 20 years. The results in Seattle, Brooklyn, San Antonio and dozens of other cities across the country show that using native plants in urban landscapes just makes economic, aesthetic and environmental sense.