From Seed to Seed:
Plant Science for K-8 Educators

What's the problem?

Why can't we simply enjoy these beautiful exotics? In some cases, the presence of invasive plants enhances natural landscapes. For example, purple loosestrife growing in a wetland adds a vibrant purple color to this ecosystem.

Unfortunately, the problems associated with invasive plants far outweigh the pleasure that we receive from their beauty. Early on, relatively few plants were being moved between continents. After the Industrial Revolution and with the advent of modern transportation technology, however, humans began to travel at an increased pace and range. This resulted in increased plant introductions-of not only non-native plants, but also invasive plants. Soon it was too much for native ecosystems to handle. The aliens began taking over!

The biggest problem with the introduction of invasive plants is the resultant reduction in native biodiversity. The term biodiversity describes the number of different species-of plants or animals-in an area. Invasive plants not only alter the structure of a plant community, but they also have the ability to out-compete native plants for sunlight, nutrients, and space. For one thing, invasive plants frequently have extensive underground systems composed of roots and sometimes rhizomes. This enables them to spread rapidly and discourage other plants from growing in an area. Secondly, since they are lacking their native predators-who got left behind in the move-invasive plants are able to grow unchecked in their new habitats. Often a single species of invasive plant will take over an entire habitat. As a result, the number of native plants declines.

This reduction in biodiversity because of the presence of invasive plants is the second-leading cause of the loss of biodiversity in the world! (The leading cause is habitat destruction.) Not only is this a loss on a global scale-the ultimate result being the homogenization of the world's flora-but it is a loss at the local scale. Native animals, especially birds, are rapidly losing their sources of food and their homes!

There are also other problems...

Not all plants are introduced into terrestrial ecosystems. There are several examples of plants that are invasive in aquatic ecosystems. Examples include water chestnut (Trappa natans) and Eurasian watermilfoil (Myriophyllum spicatum). Aquatic invasive plants such as these take over wetlands, interfere with hydroelectric power production, and clog waterways. In many regions of the world, clogged waterways prevent proper drainage, resulting in the flooding of large tracts of land. This displaces not only native animals, but humans.