UNIVERSITY PARK – Penn State’s College of Agricultural Sciences and the state Department of Conservation and Natural Resources have extended for 18 months a collaborative effort to stop the spread of invasive plant species in state parks.
Plants such as Japanese stiltgrass, mile-a-minute weed and multiflora rose have been taking over the ecosystems of many state parks in recent years, according to Art Gover, a research support associate in the university’s Department of Horticulture. He is on the Vegetation Management Project team funded by the $128,000 contract extension.
“To the untrained eye, Japanese stiltgrass creates a nice carpet of green in a forest understory, but that carpet of green also inhibits forest regeneration,” Gover said.
Invasive species are making parks less biologically diverse, explained Gover. “Losing plant diversity means losing the species-specific insects that eat those plants and in turn losing the birds that eat the insects,” he said. “Now, even though the forest looks healthy, a seemingly innocent shift in the plant population can have impacts on the food chain.”
The state parks project follows the model established by the Vegetation Management Project’s 24-year affiliation with the Pennsylvania Department of Transportation addressing invasive plants and problem vegetation along highways. Penn State provides training, operational demonstrations and research to the transportation department to deal with invasive plant species.
The joint project between Penn State and DCNR is aimed at assessing invasive species conditions and developing park-specific management plans. Under the contract, researchers select parks from different regions across the state for evaluation, target high-priority areas and train park staff in the most effective management techniques.
Four parks were included in the original $150,000, two-year contract: Ohiopyle in Fayette County, Kettle Creek in Clinton County, French Creek in Berks and Chester counties and Canoe Creek in Blair County. “We are not necessarily going to move into four new parks,” said Gover. “We are expanding our systemwide training efforts, and will continue developing a plan that parks can implement according to their needs and available resources, then move into new parks as the plans currently in place take shape.”
According to Gover, a candidate for the contract’s next series of parks is Bald Eagle, in Centre County. Also on the list is Neshaminy State Park in Bucks County, which is a priority because of its unique wetlands.
Gover explained that sensitive areas within parks get the most attention when it comes to invasive-plant control and removal. “Places that have particular natural value with unique native- plant communities get first priority,” he said. “Riparian corridors along a park’s water features are also valuable natural resources. In comparison, areas that are heavily trafficked are a lower priority.”
The success of invasive species is a matter of evolutionary advantage, Gover pointed out. “For thousands of years there have been collections of plants and animals that were coexisting and vying for space,” he said. “When a plant is introduced into a new environment, the system of evolutionary checks and balances that developed in its native habitat ceases to exist. Removed from the natural pressures of their historic cohorts, invasive species are equipped with an arsenal of weapons that their new plant neighbors are unprepared to deal with.”
Allelopathy is an example of these competitive weapons, Gover noted. The process of allelopathy involves plants exuding chemicals from their roots to inhibit competitors and defend themselves. This weapon can pose a major threat to unadapted species. “For example, garlic mustard is a common understory invasive that releases ‘allelochemicals’ that suppress mycorrhizal fungi in the soil critical to the regeneration of native trees.”
The extent of infestation is another criteria for prioritizing areas. “It’s easy to go onto a property, just throw your hands up and say, ‘They’re everywhere, we don’t have the resources,'” Gover said. “The largest threats to an area are species that have just appeared in a park, are on the leading edge of infestation or are documented nearby. Directing effort against new incursions is an effective use of limited resources,” Gover said.
Mile-a-minute weed is an example in parks such as Bald Eagle, where one primary infestation and several satellites were discovered this past fall. On top of monitoring and controlling areas within Bald Eagle, sites within the affected tributaries drainages will be closely monitored for new infestations. Mile-a-minute weed also has wreaked havoc in Sinnemahoning State Park, making Kettle Creek State Park, a watershed away, a major concern. “It is a situation where you monitor the most likely entry points. If you can find the really problematic species at their leading edge you have a much better chance of successfully managing them,” he explained.