What Is An Invasive Plant?

What Is An Invasive Plant? What is an invasive plant? An invasive plant is a species that is not native to an area and causes harm to human health, the environment, or the economy. Invasive plants become a weed pest that grows rapidly. It spreads and displaces other plants. Invasive plants typically appear on disturbed ground but the most invasive ones can invade existing ecosystems. Invasive plants can be very expensive to control. What is a native plant? A native plant is one that occurs naturally in a particular place without human intervention. Species native to North America are generally recognized as those occurring on the continent prior to European settlement. What is an introduced plant? Introduced plants are mostly European or Asian species that have been accidentally transported or intentionally imported for their ornamental value or other characteristics, such as shade, windbreaks, or erosion control. Not all introduced species become invasive. What makes plants invasive? Fast growth rate Grow well in a wide range of soil and growing conditions Some have high seed production with seeds that easily disperse and sprout quickly Some have the ability to reproduce by roots or shoots, called suckering Why are invasive plants bad? Displace and reduce native plant species Destroy habitats that support native animals Change ecosystem processes so that they support aggressive and introduced plants, animals and diseases Are difficult to control, can escape from cultivation and can dominate whole areas Overall decrease in biodiversity of ecosystems. 1

Multiflora Rose Rosa multiflora Multiflora rose is an invasive species that is introduced from Japan and Korea and was introduced to the U.S. in the 1860s. It was originally planted as an ornamental shrub. In the 1930s conservation agencies began to promote it as a wildlife food and a cover plant for animal habitats. It was also used for erosion control and as living fences to confine livestock. Since its introduction, multiflora rose has spread rapidly from cultivation and readily invades open woodlands, forest edges, open fields, stream banks and other areas that have been subjected to land disturbance. Multiflora rose is spread by seeds and by suckering. Suckering occurs both when the tips of arching stems root where they contact the ground and also when roots sprout new growth. Birds eat and disperse the seeds which are the primary means by which the shrub moves to new areas. Reproduction by suckering allows the plant to form dense, impassable thickets. An average plant may produce a million seeds per year. These seeds may still sprout for up to 20 years. Multiflora rose has a wide tolerance for soil, moisture and light conditions allowing it to spread to many habitats. Regular mowing and repeated cutting in grassy areas inhibits seedling establishment. However, repeated cutting is often preferred to mowing because mowing will also damage native plants. Shrubs can be removed by digging and pulling. This is only effective when all of the roots are removed. Treatments with certain herbicides have also been effective at controlling the plant. Repeated treatments are needed because the seeds remain viable in the soil for many years. Also, two biological controls have been used successfully to manage the spread of multiflora rose. One is a native fungal pathogen (rose-rosette disease) this is spread by a tiny native mite. The second is a non-native seed-infesting wasp, the European rose chalcid. Common blackberry Flowering raspberry Pasture rose Swamp rose Witch hazel 2

Tree of Heaven Ailanthus altissima Tree of heaven is an invasive species that is introduced from central China. It was introduced to the U.S. in 1784 by a Philadelphia, PA gardener. By 1840 it was commonly available from nurseries. Since its introduction, tree of heaven has sprouted up just about anywhere including alleys, sidewalks, parking lots, streets as well as in fields, roadsides, fencerows, woodland edges and forest openings. Tree of heaven spreads by seeds and suckering. Suckering occurs when cut stumps and root fragments resprout. A single tree can produce up to 325,000 seeds per year. Once established, it grows dense stands that displace native plants. Tree of heaven also produces chemicals that kill or prevent other plants from growing near it. Seedlings can be pulled or dug up. Care must be taken to remove the entire plant including all roots and fragments to prevent resprouting. Several herbicides have also proven to be effective in controlling tree of heaven. Targeting the removal of large female trees is the best way to control the spread. Female trees are responsible for the seed production. Before any control measures are used, it is important to correctly identify the plant because some native species are often confused with tree of heaven. Box elder Smooth sumac Staghorn sumac Black walnut White ash Tulip tree 3

Princess Tree Paulownia tomentosa Princess tree is an invasive species that was introduced from China. The Dutch East India Company introduced it to Europe in the 1830 s and North America in the 1840 s, both times as an ornamental. It is currently grown in plantations for wood to export to Japan and as a quick growing ornamental. It has escaped from both uses and grows in forests, fields, and along roadsides. Princess tree spreads by seed or suckering. One tree can produce 20 million seeds per year. Seeds are lightweight and winged so they are spread easily by wind and water. Suckering occurs from buds or roots after fires, cutting, or even bulldozing. Small seedlings can be hand pulled or dug out. Make sure to remove all of the root system to prevent sprouting. Large trees can be cut and then the sprouts will have to be cut repeatedly. Large trees can be cut and the fresh stump can be painted with an herbicide to prevent sprouting. Small trees may be sprayed with an herbicide. Serviceberry Catalpa Redbud Flowering dogwood Sassafras Spicebush Red mulberry 4

Callery Pear Pyrus calleryana The callery pear is an invasive plant introduced from China, Japan, Korea, Taiwan, and Vietnam. It was introduced to the United States in 1917. In the 1950 s, the cultivar Bradford was developed and became popular for ornamental planting. This is also where it s other name, Bradford pear, originates. The callery pear spreads by seed. European starlings and American robins eat the small pears and spread the seeds. Each pear contains 2-6 seeds. The tree can also root sprout, if injured or cut. Complete removal of the tree is the best control. Large trees should be cut, with an immediate herbicide application to the stump. Seedlings can be pulled or dug out. serviceberry hawthorn redbud flowering dogwood 5

Norway Maple Acer platanoides Norway maple is an invasive species that was introduced from Eurasia, normally growing from southern Scandinavia to Iran. It was introduced in Philadelphia in 1776 by John Bartram, a botanist. It was frequently planted in neighborhoods during the 1950 s to replace native American elms that were killed by the Dutch elm disease. It spreads mostly by wind. The seeds (samaras) are spread by the wind. Norway maples out compete native maples even in shady conditions. Seedlings can be hand pulled when the ground is wet or dug. Larger trees can be cut close to the ground. Native alternatives Red maple American beech Sweet gum Black gum. 6

References: Culley, Theresa and Hardiman, Nicole. The beginning of a New Invasive Plant: A History of the Ornamental Callery Pear in the United States. BioScience Dec. 2007 vol. 57 No. 11. Doi:10.1641/B571108. Invasive Plants in Pennsylvania. PA Department of Conservation & Natural Resources. Published 4/2000. http://www.na.fs.fed.us/fhp/invasive_plans Weed of the week, Callery Pear Swearingen, J., B. Slattery, K. Reshetiloff, and S. Zwicker. 2010. Plant Invaders of Mid-Atlantic Natural Areas, 4 th edition. National Park Service and U.S. Fish & Wildlife Service. Washington, DC. 168pp. 7