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Impacts of Non Native Invasives

Invasive plants have negative resources in a myriad of areas ranging from natural resources to human health. Please review the topical area below for more detailed information and examples of impacts.

1. Natural Resources

  • Declines in wildlife habitat and timber availability: Chestnut blight is a disease of American chestnut caused by a non-native fungal pathogen that was introduced into eastern North America  around 1910.  The disease eliminated the American chestnut from eastern deciduous forests thereby decreasing timber harvests and wildlife that depended upon the American chestnut for habitat (USDAAPHIS/FS 2000). European gypsy moth defoliates trees on millions of acres of northeastern and mid-western forests.  It  currently is found in 19 states causing an estimated $3.9 billion in tree losses and also decreased  wildlife habitat (USDA-APHIS/FS 2000).
     
  • Decreased soil stabilization and interrupted forest succession: White pine blister rust is a disease  of white pine species caused by the non-native fungal pathogen Cronartium ribicola.  It was introduced  into eastern North America around 1900 and western North America in 1920.  It spread rapidly, killing  off native white, whitebark, and limber pines, whose  seeds are an important food source for birds,  rodents and bears.  Elimination of these trees caused by this pathogen alters forest ecosystems,  eliminates wildlife forage, and decreases the soil stabilization effects of these trees, snowmelt  regulation, and forest succession (Krakowski et al. 2003).
     
  • Changes in wildfire frequency and intensity: Cheatgrass decreases the interval between the occurrences of wildfires in the Great Basin region from once every 70 to 100 years to every 3 to 5 years because it forms dense stands of fine fuel annually.  The decrease in interval between wildlfires causes increased risk to human life and property and also places at risk established communities of plants and animals that we consider desirable (Knapp 1996; Pimentel et al. 2000; USFWS 2003; Whisenant 1990).
     
  • Excessive use of resources: Tamarisk in the desert southwest use more than twice as much water annually as all the cities in southern California, which places this invasive weed in direct competition  with humans for the most limiting resource in the southwestern U.S. (Friederici 1995; Johnson 1986).
     
  • Suppressors: Russian knapweed exudes toxins from its tissues that inhibit the growth of surrounding  plants or eliminates them.  Desirable plant communities are placed at risk from  Russian knapweed invasion, which may result in decreased numbers of wildlife species or livestock that the invaded land otherwise could support.  Russian knapweed also is very toxic to horses (Stevens 1986; Young et al. 1970a and 1970b).  
     
  • Decreased carrying capacity for wildlife and livestock: Expansion of  leafy spurge, yellow starthistle, or other unpalatable invasive weeds displace desirable forage plants and may allow fewer grazing animals to survive in infested areas (DiTomaso 2001; Lym and Messersmith 1985; Lym and Kirby 1987).
     
  • Altered ecosystems and recreational opportunities: The submersed aquatic plant hydrilla, forms dense canopies at the water surface that raise surface water temperatures, change pH, exclude light, and consume oxygen, resulting in native plant displacement and stunted sport fish populations.  This example of an altered aquatic ecosystem caused by an invasive aquatic weed also negatively affects recreation and businesses that depend upon that human activity (Colle et al. 1987).

2. Human Health: 

Exposure to the sap of  Tree-of-heaven/Chinese sumac tree has caused
inflammation of the heart muscle (myocarditis) in workers charged to clear infested areas.  Afflicted  personnel experienced fever/chills, chest pain that radiated down both arms, and shortness of breath.   Exposure occurred when sap from tree-of-heaven contacted broken skin.  Such exposure has caused  hospitalization, medical expense, and lost productivity due to absence from work (Bisognano et al.
2005).

Giant  hogweed Heracleum mantegazzianum  is another invasive with human health imppacts. This invasive dangerous plant and is designated as a federal noxious weed due to its toxic sap that causes skin sensitivity to UV radiation and leads to blistering and severe burns.

3. Economic

  • Decreased property values: Emerald ash borers were first detected in the U.S. in 2002.  They currently are found in Michigan, Ohio, and Indiana.  Emerald ash borer larvae tunnel under bark of ash trees and could eliminate ash as a  street, shade, and forest tree throughout the U.S.  Estimated replacement cost in six Michigan counties  is $11 billion and an additional $2 million in lost nursery sales (Chornesky et al. 2005).

    Dutch elm disease was first introduced into the U.S. in 1927 and occurs in most states.  Dutch elm disease has killed more than 60% of elms in urban settings and decreased the value of urban and suburban properties (Brasier and Buck 2001).

    Spotted knapweed and  leafy spurge expansion in the western U.S. have displaced desirable forage plants thereby decreasing the value and sales price of grazingland in the western U.S. (Maddox 1979;  Weiser 1998).
     
  • Decreased tourism income
    Eurasian watermilfoil was introduced into the U.S in the 1940s and has since spread throughout much of the country. This submersed aquatic plant can form dense mats at the water surface limiting access, recreation, and aesthetics and thus, has decreased the values of shoreline properties in New Hampshire, the Midwest and elsewhere (Halstead et al. 2003).

    Non-native algae introduced into the Hawaiian Islands costs Maui alone about $20,000,000 annually due to algae fouling the beaches and subsequent lost tourism (Carroll 2004; Keeney 2004; Univ. Hawaii 2006).

 

Source: National Invasive Species Council. Invasive Species Definition Clarification and Guidance White Paper. April 2006.