With spring settling in across the U.S. and days lengthening, many people are ready to spend more time outside. But after a walk outdoors, have you ever found seeds clinging to your clothes? Lodged in your socks and shoelaces? Perhaps tangled in your pet’s fur? While most of us don’t give these hitchhikers much thought, seeds and burrs may be the first signs of invasive plant spread.

Certain species of non-native invasive plants produce seeds designed to attach to unsuspecting animals or people. Once affixed, these sticky seeds can be carried long distances before they fall off in new environments. With favorable conditions, they can become established quickly and outcompete native plants.

Outdoor recreation has expanded at a record pace across the U.S. in recent years. Overcrowding in outdoor spaces has many harmful effects, from degrading trails to accelerating the introduction and spread of invasive plants.

As a recreation ecologist and an avid hiker, I study how people inadvertently spread invasive plants along trails. There are simple things that everyone can do before, during and after going outdoors to avoid picking up plant hitchhikers and help maintain trail systems for others to enjoy.

Invasive plants are non-native species that can harm the environment, human health and the economy when they are introduced into new areas. However, not all non-native plants are invasive.

Plants with invasive capabilities tend to grow quickly, adapt easily to many different environmental conditions, produce seeds in vast quantities and successfully disperse and germinate them. These characteristics enable the plants to spread efficiently to different areas. Many vectors help invasive plants disperse, including birds, animals, wind, water and humans, via clothing, shoes, pets, gear and vehicles.

Invasive plant seeds tend to be small in size, high in number and hardy. They can persist in soil for many years, remaining viable and ready to germinate when conditions are right.

These seeds will usually germinate earlier in spring than those of native plants and keep their leaves until late fall, crowding out and outcompeting native varieties. Each species produces seeds on a particular schedule – annual, biennial or perennial – and at a specific time. For example, invasive biennial garlic mustard releases seeds every two years in late spring.

Invasive plants have many harmful ecological impacts. One of the most familiar U.S. examples is kudzu, a climbing vine that has smothered trees across the Southeast.

Kudzu grows prolifically, outcompeting native vegetation. It also alters the nitrogen cycle by increasing soil nitrogen levels and releasing nitric oxide, a gas that reduces air quality and promotes ground-level ozone pollution.

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