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Invasive plant and tree species pose a serious threat to the ecosystem balance of Pennsylvania. Invasives usually out-compete native plants in the same environmental conditions. This is mostly because the natural controls that keep the invasive species in check in their native ranges are not present in our environment. They also often have wide-ranging effects over simply crowding out native plants. Invasive species “green up“ earlier than native species and also hold leaves and fruit longer in the growing season, making them highly competitive to natives. Many invasive plants are also unpalatable to native species that need to eat plants, notably white-tailed deer.
Invasive plants are categorized by the potential threat they pose to the native species or agriculture. Invasive plants that pose a significant economic impact to farmers, in cropland or forest, are placed higher than those that have yet to become “naturalized” (meaning they have not been found to spread widely on their own and are less aggressive in displacing desirable species). Some of these plants may only spread in recently disturbed areas (such as timber harvests, tilled land, or recent construction) and are placed lower on this index. With a changing climate, some invasive plants that present a problem in surrounding states may find new regions more habitable and will expand their range. While they have yet to become widespread problems in Pennsylvania, they are watched carefully, and active measures can be taken to ensure they do not become established here.
Many species of invasive plants were not always considered a problem, and some were even introduced for erosion control or landscaping. Most, however, escaped gardens or their original cultivation. Often a plant gets its start through human activities. These vectors can be as benign as European settlers wanting their homes to resemble those they left, or for purposeful reasons such as using the plant for erosion control or living fences.
While these plants served their initial purposes well, often to great acclaim by their original introducers, over time their impact on our native plant communities and ecosystems has been negative. The native plants that evolved with multitudes of native pollinators, birds, and other cute-and-cuddlies face extreme competition with the aggressive newcomers. Other invasives can alter the soil composition - either through actively introducing inhibiting chemicals or absorbing more nutrients and leaving the soil unsuitable for other plants.