Invasive species in Pennsylvania are destroying cropland, disturbing wetlands, hurting timber production, making parks less accessible and exacerbating flooding problems. And that doesn’t include a variety of impacts on native wildlife and ecosystems.
Those are some of the findings from a survey of more than 1,000 residents, including individuals from every single county, conducted by the Pennsylvania Governor’s Invasive Species Council last fall.
The survey aims to help the council better understand the impact of invasive species on residents, as well attract attention and funding. The council believes the state should create funding for regional invasive species programs that would be better able to respond to local ecosystems and increase local participation.
“If there's one thing that this survey showed, this is how many people really care about this topic, how many people are affected by the topic,” according to Fred Strathmeyer, who chairs the invasive species council as the Deputy Secretary for Plant Industry and Consumer Protection in the state Department of Agriculture.
But right now many of those people say they feel like they are tackling the issue alone or with insufficient resources and time. Strathmeyer believes that a more regional approach would allow the state to make more progress. For example, he said, McKean County in northern Pennsylvania has been struggling to contain knotweed in one of its watersheds. But knotweed isn’t a big issue in southeastern Pennsylvania, he said.
“What happens in Erie may or may not happen in Philadelphia,” he said. “Or what happens in Washington County may not be the same thing that happens in Scranton.”
Strathmeyer said that New York has already adopted a regional model funded by a local real estate tax that allows it to better respond to local invasive species. And he said there are already existing organizations – like conservation districts or conservancies – that could spearhead regional task forces.
This issue is only going to become more important as the climate changes, he said, pointing to the unusually warm winter this year. “The one thing we know about invasives, insects, plant material, they're all reliant on the weather,” he said. “And so if we end up with milder winters, we end up with opportunities for these plants or these invasive insects to become more prevalent because the natural course that they may have run up against is no longer there.”
Southwestern Pennsylvania
The challenge with planting native trees in Southwestern Pennsylvania isn’t just the three prominent invasive trees crowding them out – Tree of Heaven, Norway Maple and Bradford Pear – according to Joe Stavish, the education director of Tree Pittsburgh, which grows and plants a variety of native trees in the region.
The problem is the ground cover has also often been taken over by invasive plants, such as dense stands of Japanese knotweed, rampant honeysuckle and porcelain berry vines, not to mention the overgrowth of grape vines that, though native to the area, have overtaken many hillsides.
“So, it's very challenging to go in and work in those areas because you have such a thick, dense cover of grapevines shading out the entire lower canopy of the forest,” he said.
And invasive insects like the emerald ash borer and, more recently, the spotted lanternfly have been tearing through local tree populations. Not to mention the crazy jumping worms from the Korean Peninsula that devour leaves, creating hillside erosion and making it difficult for native trees to root.
Once you have a thicket of invasive trees, Stavish said, it gets even harder to remove them. Deer don’t eat invasive trees, so native trees are increasingly winnowed away. Many hillsides have also come to depend on invasive trees to maintain their stability. “And if we clear all those [invasives], we sometimes see other issues with erosion and sedimentation and air pollution increase,” he said.
Stavish agrees that any approach to tackling invasive species can’t be done without thinking about the broader impacts on the local ecosystems. “Just coming in and removing stuff isn't always the best idea,” he said.
Tree Pittsburgh doesn’t even always plant native trees, Stavish said. It’s often difficult for native trees to grow along the edges of roads or in parking lots, not to mention in salty, compacted soil, with high urban temperatures and little growing space. And some trees like the loblolly pine, which are native in the southern U.S., are becoming increasingly attractive here because they may do better several decades into the future as the climate continues to warm.
“So, we have to be creative about the types of trees we're putting in and where they go,” he said.
The key distinction isn’t so much whether a tree is native to the region, he said, so much as whether or not the trees will take over after they are planted. For example, he said, many people like to plant fruit trees that aren’t native to the area but most of them are not then crowding out trees that are.
Perhaps the most damaging invasive species of all, Stavish said, isn’t one we typically even consider: humans. Developers have been destroying old trees across the area, while homeowners cut them down out of fear of what they might do. Allegheny County alone lost 10,000 acres of tree cover between 2011 and 2015.
But one of the unique advantages of invasive humans, Stavish said, is they can change their behavior. “And that's probably the best recipe for success when you're looking at tree canopy,” he said. “Just getting people involved with tree planting today because those trees take years to become established in the landscape.”
