The importance of removing invasive plants

By Florrie Funk

 

An invasive plant is a non-native species capable of spreading aggressively and monopolizing essential habitat resources–

light, nutrients, water, and space, to the detriment of other species.

Our planet's life forms co-evolved over millions of years as complex, interdependent communities of organisms called ecosystems. Each species within an ecosystem depends on other species to provide nutrients, circumstances necessary for reproduction, and limits to its expansion.

Many plants rely on fungi and other soil organisms to decompose dead plants and animals, thereby releasing nitrogen and other nutrients into the soil. Specific plants often depend on specific insect species to pollinate their flowers so that they produce seeds, and they depend on other animals to help disperse those seeds. The community of organisms that make up an ecosystem includes of a variety of herbivores, predators, fungi, bacteria and other pathogens that help an ecosystem stay in balance by preventing one species from increasing to the point of extirpating others. When biodiversity (the number of different species) is reduced, this compromises the ability of an ecosystem to withstand drought, blights and other environmental stresses.

In our suburban communities, native species are being weakened by loss of biodiversity caused by habitat fragmentation. Ever-smaller natural areas are being separated by ever-wider highways and developments. Small, isolated populations of plants and animals, unable to exchange genes with other populations, become inbred and eventually die out.

The introduction of alien organisms has seriously compounded this problem. Some alien species were introduced intentionally by horticulturalists and others arrived by accident in soil or imported products. Some of these species do not survive; others persist as benign members of the community. But others grow and reproduce rapidly, displacing whole communities of native plants, sometimes causing rapid reductions in biodiversity and the extinction of other species.

Worldwide, invasive alien species are the second leading cause of species extinction. (The leading cause is habitat destruction.) More than 28% of the world’

s native species are threatened or endangered. There are 4000 non-native species grown outside of cultivation in the US (including 200 species in MA). The economic cost is estimated at $137 billion dollars annually (mostly from lost crops) and has led to a decline of 42% of endangered and threatened species nationwide.

In Newton, the worst offending invasive plants are species planted as ornamentals, such as Norway Maples, Japanese Barberry, Burning Bush, Oriental Bittersweet Vine, Japanese Knotweed (sometimes called “bamboo”

), Common and Glossy Buckthorn, Asian Shrub Honeysuckles, and Tree-of-Heaven.  Many of the characteristics that make a plant a good garden choice - rapid growth, disease resistance, easy propagation - increase the chances of its becoming invasive. These plants all produce seeds that are carried by birds or wind into natural areas, roadsides and vacant lots where they germinate, grow quickly and reproduce. This vegetation often looks at first glance like nature happily doing what it is supposed to do.  But dense patches of Japanese Knotweed or monoculture groves of Norway Maples are actually heartbreaking reminders of the many dozens of species that are now gone:  wildflowers, ferns, grasses, shrubs, trees, plus the insects, birds and other animals that depend on them.

In the past, conservation areas were purchased and left alone, and nature took care of itself.  No longer.  Due to the proliferation of invasive species most forests and conservation areas must now be actively managed.  If invasive species are not controlled, overall species diversity will decline, and the loss will be irreversible.

The MA Department of Agricultural Resources "Massachusetts Prohibited Plant List" designates 141 plants, including many popular ornamentals that are now prohibited from being imported, sold or propagated.  This ban may help reduce the spread of invasive species, but in many cases the horse is already out of the barn.

Promising research is being done on biological controls, such as a beetle species that eats Purple Loosestrife (a highly invasive plant found in wetlands throughout North America), but these methods are still experimental and may entail ecological risks. To learn what you can do to help to limit the spread of invasive species, visit: newfs.org (New England Wildflower Society), tncweeds.ucdavis.edu (Nature Conservancy), nps.gov/plants/alien (National Parks Service) and www.newtonconservators.org (Newton Conservators).

Florrie Funk, florriemfunk@aol.com, has taught interpretive nature study programs in CA, FL, MO and IL and assisted with ecological research and habitat restoration at the Chicago Botanic Garden and in Highland Park.