25% of U.S. agricultural gross national product is lost to foreign plant invaders and the costs of controlling them. Exotic species have contributed to the decline of 42 percent of U.S. endangered and threatened species.
The chestnut blight fungus, which arrived in New York City in the late 19th century from Asia, spread in less than 50 years over 225 million acres of the eastern United States, destroying virtually every chestnut tree. Because chestnut had comprised a quarter or more of the canopy of tall trees in many forests, the effects on the entire ecosystem were staggering
Will cattle, sheep,goats, and horses have to be raised on feed lots in the future to prevent rangeland poisoning from invasive plants? (USDA 2011)
Poisonous plants are a major cause of economic loss to the livestock industry. Each year these plants adversely affect 3 to 5 percent of the cattle, sheep, goats, and horses that graze western ranges.
All too often the losses to individual livestock operations are large enough to threaten the viability of that ranch. Livestock losses can be heavy if animals:
- graze ranges infested with poisonous plants when plants are most toxic.
- are driven, trailed through, or unloaded from trucks onto range or pasture areas infested with poisonous plants. Animals are less selective in their grazing at these times of stress. • are not watered regularly.
- are allowed to become hungry. Such animals are more likely to eat lethal quantities of poi- sonous plants.
- are grazed on rangelands early in spring when there is no other green vegetation except poisonous plants.
- are stressed, such as when they are trucked, penned, or handled (branding, vaccination, etc.).
- are not limited on how much and how fast they consume the plants
Economic Impact of Poisonous Plants on Livestock Direct losses (effects on animals) include the following: • Deaths of livestock • Abortions • Birth defects • Weight loss (due to illness or decreased feed intake • Lengthened calving interval • Decreased fertility • Decreased immune response • Decreased function (due to damage to organs such as the nervous system, lungs, liver, etc. • Loss of breeding stock due to deaths, functional inefficiency, etc.
Indirect losses (management costs) include the following:
• Building and maintaining fences • Increased feed requirements • Increased medical treatments • Altered grazing programs • Decreased forage availability • Decreased land values • Opportunity costs • Lost time to management • Stress to management
Hundreds of plants are poisonous to livestock. Here are a few of the toxic plants or toxic plant categories in the West:
Bracken Fern (Western Bracken)
Colorado Rubberweed (Pingue)
False Hellebore (Veratrum)
Groundsel (Threadleaf and Riddell) and Houndstongue
Ponderosa Pine Needles
Snakeweed (Broom and Threadleaf)
Yellow Star Thistle and Russian Knapweed (invasive)
Other Poisonous Plants
Leafy spurge, an unpalatable European plant invading Western rangelands,andUnpalatable Eurasian plants-spotted knapweed infests 7 million acres in nine states and two Canadian provinces
Foreign weeds spread on Bureau of Land Management lands at over 2,300 acres per day and on all Western public lands at twice that rate.
The spread of fire-adapted exotic plants that burn easily increases the frequency and severity of fires, to the detriment of property, human safety, and native flora and fauna. In 1991, in the hills overlooking Oakland and Berkeley, California, a 1,700-acre fire propagated by Eucalyptus trees planted early in this century destroyed 3,400 houses and killed 23 people [including my home — now there is a group fighting removal of eucalyptus because they’re “pretty”]
Meleuca invasion in Florida: sawgrass dominates large regions of Florida Conservation Area marshes, providing habitat for unique Everglades wildlife. Although sawgrass may be more than 9 feet tall, introduced Australian melaleuca trees are typically 70 feet tall and outcompete marsh plants for sunlight. As melaleuca trees invade and form dense monospecific stands, soil elevations increase because of undecomposed leaf litter that forms tree islands and inhibits normal water flow. Wildlife associated with sawgrass marshes declines. The frequency and intensity of fires change, as do other critical ecosystem processes. The spread of melaleuca and other invasive exotic plants in southern Florida could undermine the $1.5-billion effort to return the Everglades to a more natural state
In parts of the southern Appalachians, two related insects, the hemlock woolly adelgid and the balsam woolly adelgid, defoliate and kill dominant native trees over vast tracts.
References & Recommended reading
B. N. McKnight, ed., Biological Pollution. The Control and Impact of Invasive Exotic Species. Indianapolis. Ind.: Indiana Academy of Sciences, 1993.
O. T. Sandlund, P. J. Schei, and A. Viken, eds., Proceedings of the Norway/UN Conference on Alien Species. Trondheim, Norway: Directorate for Nature Management and Norwegian Institute for Nature Research, 1996.
Don C. Schmitz. 9 July 1997. Biological Invasions: A Growing Threat. An army of invasive plant and animal species is overrunning the United States, causing incalcuable economic and ecological costs. issues in science and technology. National Academy of Sciences.
U.S. Congress, Office of Technology Assessment, Harmful Non-Indigenous Species in the United States. Washington, D.C.: U.S. Government Printing Office, 1993.
Williamson, M. 1996. Biological Invasions. London: Chapman & Hall, 1996.
USDA. April 2011. Plants Poisonous to Livestock in the Western States. United States Department of Agriculture, Agricultural Research Service Agriculture Information Bulletin Number 415