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Garden With Natives

Invasive Species

An invasive plant is a non-native plant that has escaped cultivation and proliferates aggressively in the ecosystem in which it was introduced, overwhelming and out-competing the native plants that should be found there.

According to the National Invasive Species Council of the USDA, an invasive species (plant, animal or pathogen) is “non-native (or alien) to the ecosystem under consideration; and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”

Why are Invasive Plants Found in our Area?

Many invasive plants were first introduced into North America intentionally by humans, usually because they were considered to have ornamental value in our landscapes. Humans introduced others inadvertently when their seeds, rhizomes or roots piggybacked onto shipments of goods and/or livestock.

Usually the invasive nature of a given species was unknown before it was introduced, and it may have existed here for many years before it was discovered that the species had spread beyond its original planting through aggressive proliferation. In many cases this has occurred because of the absence of the diseases, pests or environmental conditions that would have kept the plant in check in areas where they are naturally found.

In contrast, there are many other non-native species that have been introduced to our landscapes from somewhere else, either intentionally or unintentionally, that have also become established here. These are called naturalized species, and as long as they do not threaten economic, environmental or human health, they would not be considered invasive species.

In many areas such as Bucks County, the spread of invasive species has been facilitated by habitat loss due to development and the fragmentation of natural areas. Invasive plants seem to prefer areas where there has been soil disturbance. Many are particularly good at outcompeting their native rivals for resources such as water and soil nutrients, especially in the early successional stages of disturbed soils.

Unfortunately, many species that are now listed as “invasive” in a given state or region are still propagated and sold in the commercial nursery trade.

What Threats Do Invasive Plants Pose to Our Native Plant Communities?

  • Invasives reproduce aggressively and out compete native plants, thereby reducing biodiversity and the health of the ecosystem
  • Invasives may hybridize with native species, altering their genetic makeup
  • Invasives may support other non-native plants, animals and pathogens
  • Invasives change fundamental ecosystem processes, such as the frequency of wildfires, availability of water and nutrients and the rate of soil erosion
  • Invasives are a nuisance, degrade habitat and are difficult to eradicate.

What Can I Do to Prevent the Spread of Invasive Plants?

  • Learn to identify the invasive species that have been listed for your state or region and their eradication methods
  • Remove invasives from your landscape, especially those that are spreading rapidly to natural areas in or beyond your property. Be vigilant. Deal with them early while their population density is still low.
  • Prevent new invasions by minimizing soil disturbance and bare soil on your property
  • Plant more native species, especially in bare areas, before an invasive takes hold
  • Assist with volunteer efforts to remove invasives in natural areas, such as BHWP
  • Join local land stewardship and conservation organizations.