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Invasive Plants

Invasive plants are those that:

  • Are not native to an area
  • Spread quickly
  • Cause economic or environmental harm, or harm to human health

They can be:

  • Trees
  • Shrubs
  • Vines
  • Grasses
  • Flowers

Invasive plants have been brought into areas, and this can happen accidentally or on purpose. They are often referred to as "exotic," "alien," "introduced," or "non-native" species.

In their natural range, these plants are limited by factors that keep them in balance including pests, herbivores, or diseases. However, when introduced into an area where these limitations are absent, some species can become invasive.

Impact of Invasive Plants

Invasive plants reduce habitat for native wildlife. Invasive plants out-compete natives and “take over” native plants’ habitats.

They often emerge earlier in the spring and push natives out through fast reproduction. This limits habitat available for native wildlife and disrupts the food chain.

One example is the invasive plant, garlic mustard. Native butterflies lay eggs on garlic mustard, and they either die or the caterpillars don’t properly grow.

Other ecological impacts include:

  • Changes in availability of water, light, and nutrients
  • Disruption of native plant-pollinator relationships
  • Serving as host reservoirs for plant pathogens
  • Replacing nutritious native plant foods with lower quality sources
  • Killing trees and shrubs through girdling
  • Changes in the rate of soil erosion
  • Changes to natural ecological processes, such as plant community succession

Invasives also cost money. According to the U.S. Fish and Wildlife Service (PDF), the U.S. spends more than $120 billion on invasive species each year. Farmers spend money on insect pests and invasive plant control such as bindweed. Waterfront property homes can be reduced in value on lakes invested with Eurasian watermilfoil. 

What Makes a Non-Native Plant Invasive?

While the species may differ, invasive plants have some things in common that make them aggressive and difficult to control:

  • Ability to grow in many conditions
  • Rapid growth
  • Ability to exploit and colonize disturbed ground
  • Ability to thrive in high nutrient conditions (i.e. excess fertilizers)
  • Reproduce rapidly by roots and shoots. If spread by seed, produce numerous seeds that disperse and sprout easily
  • Having roots and rhizomes with large food reserves
  • Ability to survive and reproduce under adverse conditions
  • Having high photosynthetic rates -- "greening up" earlier in the spring than natives gives these plants an competitive advantage
  • Lack of natural predators, pathogens, and parasites

What Can I Do?

Learning to identify invasive plants is the first step in understanding and combatting the problem. They can be difficult to control. But by taking some steps at home and in the wild, you can help limit the spread of these troublesome plants.

  • Plant natives. The key to controlling invasives is to promote healthy native plant communities. By keeping a native healthy ecosystem on your property, invasives will have less opportunity to invade. Planting native species, using local nurseries that provide native alternatives, and choosing the right species for the site can all help limit invasives. Learn more about planting with natives.
  • Minimize ground disturbance. Invasive plants thrive on bare soil when native plants have been displaced. By limiting ground disturbance on your property, you can minimize invasives spreading to your area. Also, make sure any fill material you use (rocks, soil, mulch, etc.) is free from weed seeds. This can be a source of invasives on a property.
  • Use fertilizers wisely. How much fertilizer do you need? You might be giving invasives an advantage by over-fertilizing. First, start with a soil test before applying fertilizer. Instead of chemical fertilizer, try using organic, slow-decomposing compost and mulches. Better yet, make your own compost by saving vegetable peels and table scraps. This saves waste and creates healthy soil.
  • Know your property. Check your property often, know what is “normal” and what isn’t. Scouting and monitoring can help find problem species before they take hold. When you notice a problem species, take action.
  • Act fast. It is most effective to treat invasive populations when they are still small and easily controllable. For instance, do not let invasive plants go to seed. Mechanical removal through digging or cutting is preferred. Large populations of invasives may need to be stopped chemically with spot applications of herbicide by trained individuals or by homeowners carefully following label instructions.
  • Have a plan. It makes sense when designing a property to plan for future maintenance. Lawns are maintained by weekly mowing, while gardens are often hand-weeded. Meadows in Pennsylvania may need to be mowed every year. Woodlands are probably the lowest-maintenance landscape, but they too will need to be monitored and invasive plants removed. A service forester (PDF) or extension service personnel can help you.
  • Clean your boots and equipment. When you’re out and about, be aware that you may be transporting hitch-hikers. Seeds, roots, and plant parts can stick to your boots or clothing. Aquatic plant parts or animal larvae can be transported on boats, fishing equipment, or waders.

What is DCNR Doing?

DCNR manages 2.2 million acres of state forest land and 120 state parks in Pennsylvania. That is a lot of land with the potential for invasive plant problems. DCNR has developed some management tools to combat invasives on our land and to teach others:

  • Trainings and Outreach. Education is the first step toward combatting any issue. DCNR conducts trainings on invasive plant identification and control, both field and classroom settings. We train our foresters and park personnel as well as the public.
  • Early Detection and Rapid Response. DCNR has begun using this method, adapted from the U.S. Forest Service, to quickly assess an area and treat prioritized species. Smaller populations of high-priority species are given treatment. This saves time and money in treatment later.
  • Pennsylvania Invasive Species Management Plan. DCNR participated in the development of the Pennsylvania Invasive Species Management Plan in May 2009, developed by the Pennsylvania Invasive Species Council, an inter-agency state-wide group. This plan introduced the issue and set a framework for response for state agencies. It addresses both plant and animal invaders. The plan is being revised by the council. 
  • DCNR Invasive Species Plan. This plan was a collaboration between all bureaus in DCNR. It was developed in 2011 and addressed plant and animal invaders on DCNR lands. This plan explains DCNR’s role, prevention, survey and detection, control and restoration on DCNR lands. In addition, challenges, education, and outreach were also addressed. This plan will be revised soon to reflect updates in technology and understanding.