by Jennifer Mahar
Editor’s note: If you have been anywhere near the Horticultural center in the past few weeks you must have noticed all the work going on in the park and the trees being cut down. The Casual Park goer probably pays little attention to the specific types of trees or other plant life found in Fairmount Park. Most of us simply see the ‘woods’ in the park they love and take for granted that they will always be there. However, that’s not guaranteed. Our Park lands take care and nurturing to preserve for future generations. The following article emphasizes why we must now take a more ‘hands on’ approach regarding plant life in our parks. It details what is being done to meet the critical challenge of ensuring the continued survival of a healthy, diverse forests in our city’s parks.
Philadelphia Parks & Recreation (PPR) and the Fairmount Park Conservancy selected the forests surrounding The Horticulture Center, one of the jewels of the Philadelphia park system, as the focal point for a major restoration effort. The Horticulture Center facility and grounds, which include an arboretum, are historic and provide the setting for horticultural excellence in our park system. The facility features a conference center, indoor gardens and greenhouses, and is a destination for ceremonies, including weddings, corporate events and holiday celebrations. Unfortunately, the native forests surrounding the site are being lost. The forest canopy is dominated by a large number of invasive tree species and portions of the canopy are over-run by invasive woody vines, which are tearing the forest apart. The understory is dominated by a limited number of non-native species of saplings and shrubs, and the native herbaceous layer (wildflowers, ferns and grasses) has disappeared. This forest is on a trajectory to become dominated by a limited number of invasive trees, shrubs, and vines, with little aesthetic appeal, diminished wildlife habitat and minimal diversity. Without intervention, the future forest will provide an unfortunate example of neglect and lost potential.
The Horticulture Center Forest Restoration and Protection project includes three distinct Project Areas, identified as Lansdowne Glen ( 12.8 acres); Montgomery Creek ( 10.7 acres) and Michaux Grove (5.9 acres), totaling approximately 29.4 acres in size. The project sites each abut the Horticulture Center and grounds. The current project will demonstrate to our many visitors that carefully planned restoration can transform a degraded forest into a diverse and functional ecosystem.
Urban forests are subject to a wide range of stressors that do not commonly afflict non-urban or “wildland” forests. The cumulative effect of these stresses is too slow to be observed, but over time, the impacts become obvious. The native trees and shrubs are replaced by non-natives, rampant woody vines tear off limbs and encroach into the canopy; regeneration (i.e. seedlings and saplings) disappear, diversity diminishes, and eventually the forest is lost.
One of the most significant stressors, surprisingly, is an over-population of white-tailed deer. Deer are a native animal; however, the abnormally high population that roams our park system takes a huge toll on the native forest. These herbivores selectively and continuously consume almost every native tree or shrub seedling growing within the forest floor. The “carrying capacity,” or ability of our native forest to provide sufficient food for the deer herd, has been overwhelmed. In addition, these same deer also prefer to consume the native plants rather than the non-native or invasive plant species, which have become increasingly common throughout Philadelphia’s forests. This is because that over the millennia, our native deer co-evolved with our native plants and as a result find the native plants far more palatable and nutritious than the non-natives. In addition to herbivory by deer, our forests have become overrun with non-native plants. The Philadelphia region has a high diversity and abundance of invasive plants due to our rich history of botanical introductions and horticultural plant promotion. These two factors – deer browse and invasive plants – will, over time, result in the replacement of our native forest with a degraded landscape dominated by a few species of non-native trees, shrubs and vines. Unlike most wildland forests, urban forests must be maintained and stewarded if they are to survive.
The goal of this forest restoration project is focused on the removal of nonnative species of plants (trees, shrubs and vines) using traditional forestry equipment in order to prepare the sites for planting and to promote the regeneration and establishment of native plants.
Following the removal of the undesirable vegetation, each of the sites will receive targeted herbicide treatment and then be protected with eight foot (8′) height deer exclusion fencing. Deer fencing is visually unobtrusive and the fence will include multiple pedestrian gates so as not to impede access by park users. A new walking trail for education and passive recreation will be constructed within the Lansdowne Glen project area. While performing clearing, the contractor will be “topping” a number of the undesirable trees that are being removed as part of this project. Standing dead trees are referred to as “snags,” which provide valuable wildlife nesting and feeding opportunities. The contractors will also leave large logs or “habitat logs” laying onsite. These provide habitat and help return nutrients back to the soil as they decay. In fall 2019, PPR and the Fairmount Park Conservancy will plant the site with thousands of native trees and shrubs. Some of these plants will be purchased from local native plant nurseries; however, many will be grown from locally-sourced seed at PPR’s Greenland Nursery (off of Ford Rd. near the Organic Recycling Center).
The project should result in the restoration to a regionally-native forest along with a significant increase in plant diversity. Plant diversity is closely correlated with wildlife diversity, so the project should provide improved nesting and breeding opportunities for resident and migratory wildlife. This effort will reset the trajectory of this urban forest and provide an example of ecological restoration that can be used to teach students and practitioners alike.