An Attractive Problem; 

 A Growing Concern 



DIANE E. YORKE 



Plants that wreck havoc where they grow. We call 

 them invasives, non-natives, exotics, aliens, nox- 

 ious weeds, and biological pollution. Some are 

 attractive to the horticultural community because they 

 mature early, are disease-free, and offer profuse flower- 

 ing. Most are hardy, grow aggressively, produce large 

 quantities of seeds, reproduce vegetatively, and are free 

 from any predators that limit their reproduction and 

 spread. These collective common traits are what make 

 some plants such serious competitors when released in 

 a new environment. Pretty as they may be, many in- 

 troduced plant species are causing problems and have 

 become a growing concern. 



How they got here is nothing new. Thousands of 

 plants have been brought to the United States for 

 food, fodder, windbreaks, and other reasons. But oth- 

 ers arrive accidentally in the ballast of ships, in prod- 

 ucts, on people, and through a variety of transporta- 

 tion. Though the majority blend in and cause no 

 problem, others become invasive and spread across the 

 landscape, leaving irreparable damage in their wake. 



Invasives are especially problematic in disturbed ar- 

 eas, suggesting a relationship between disturbance and 

 invasion. However, no habitat is exempt. They grow 

 in forests, wilderness areas, lakes, rivers, wildlife ref- 

 uges, wetlands, and urban spaces, infesting over 100 

 million acres nationwide. Thousands are established, 

 across the country, with 94 listed as Federal Noxious 

 Weeds, and 1,400 scientifically recognized as pests. 

 Once established, they reduce and degrade plant com- 

 munities, degrade riparian areas, create fire hazards, 

 reduce land values, and interfere with recreational and 

 harvesting opportunities. The economic cost is up- 

 wards of $20 billion annually. 



Some think invasives are the second greatest threat 

 to biodiversity after habitat destruction. They compete 

 with native plants for sun, water, and nutrients and 

 alter hydrology and soil chemistry. Over time, they af- 

 fect entire communities and ecosystems as they alter 

 environmental conditions and processes. Of particular 

 concern is the risk posed to fully two-thirds of all 

 threatened and endangered species and their habitats 



by invasives. Determining the ecological cost is impos- 

 sible, as there's no price that can be placed on losing 

 valuable habitats and native species. 



Examples are everywhere. Least damaging, but clos- 

 est to home, are the invasives that appear out of no- 

 where, such as the dandelion introduced in the early 

 1600s as a salad green. Another common backyard 

 nuisance is oriental bittersweet, the twining vine. 

 Though embraced for its decorative yellow-and-red fall 

 fruits, it invades even undisturbed forest areas, where 

 it overtakes and kills many of the plants it entwines. 

 Then there are the wildlife enthusiasts among us who 

 planted an autumn olive or two in our back forty, 

 only to find them now an impenetrable spreading 

 thicket, and appearing along roadsides, fields, and for- 

 est edges. 



New Hampshire's greatest threat is purple loos- 

 estrife. It has received national attention as over 1.5 

 million acres of wetlands have been consumed nation- 

 wide. Though it may have arrived accidentally, it was 

 also brought over from Europe in the early 1800s as 

 both an ornamental and medicinal plant. It is still val- 

 ued today for its showy flowers and for the copious 

 amounts of rich nectar honeybees seem to favor. 

 Though it's most abundant in New England, it is 

 present in 40 states. A single plant can produce almost 

 three million seeds, and it can spread vegetatively as 

 well. In its native habitat, it grows in individual 

 stands or in small groups of a few hundred plants. 

 Without natural predators, it can grow in monotypic 

 stands with upwards of two million plants. In spite of 

 its beauty, it is particularly damaging as it replaces na- 

 tive cattails, grasses and sedges, and some rare, threat- 

 ened, and endangered species. 



Garlic mustard, Japanese barberry, common reed, 

 Eurasian milfoil, goutweed . . . the list of examples 

 goes on. It varies from state to state and even from 

 organization to organization, depending upon the cri- 

 teria used in classifying a plant as "invasive." How- 

 ever, despite the lists and the known impacts of many 

 invasives, they continue to be sold in wildflower seed 

 mixes, promoted as ornamentals and wildlife plants, 



FEBRLARY/MAKail999 



