Bureau of Land Management Learning Landscapes

What's Wrong With This Picture?

Invasive Weeds: A Growing Pain

Many weeds have pretty flowers but they are a growing pain. They crowd out native plants, harm animal habitats and increase erosion.

Native or non-native?

In this activity, students explore local plant communities and research the history of plants they find. Students living in urban areas without access to parkland might focus their collection on tree leaves or vegetation growing in undeveloped lots.

Begin by checking the rules for collecting plant specimens from public lands or parks and ask for permission from owners of any private lands you'd like to explore. (As an alternative to collecting plants, you might bring along plant identification guides and photograph or sketch and measure specimens.) Next contact a local agricultural or land managing agency, a university natural resources or botany department, or a museum to learn if there are any rare or endangered plants that students should not collect. Explain the proper procedures for collecting plant specimens. Take care not to trample vegetation and take only the minimum necessary to make an identification (one sprig with leaves and flower for woody plants; for others, you might need the whole plant, but uproot a plant only if there are at least 20 others nearby). Be careful to avoid spreading the seeds of uprooted plants. Go over guidelines to avoid spreading weed seeds to new areas.

Have each student collect up to six different plant specimens during their walk. Back in the classroom, students should press the plants between layers of newspaper in a press or under a heavy book. When the plants are dry, they can be mounted on cardstock with diluted white glue. Students should then refer to plant guides to label each plant with its common and scientific name, and divide the plants into native and non-native categories. Have students research their plants in both local historical accounts and in plant guides. For native plants, students should try to discover the following:

• What is the plant's place in the food web?
• What animals use the plant for food and shelter?
• What do humans do with the plant?
• What might they do with it in the future?
• Is the plant species increasing or decreasing in number in your area, and why?
• Are there threats to the plant's existence?
• What can people do to ensure the plants survival?

For non-native plants, students should investigate the following:

• When, why and how was the species introduced locally?
• What are the drawbacks and benefits of its presence?
• Is it an invasive weed?
• What animals use the plant for food and shelter? Are these animals native or introduced species?
• What natural balancing mechanism kept the plant in check in its place of origin?

Does this plant threaten native plant communities? If so, how?

What can people do to ensure that this plant does not damage native plant communities?

Your county extension agent, a local botanist, land management agency, or local nature center may be able to assist with this project.

---

Last Updated: June 2006