Environmental consequences and economic costs of alien species - Invasive Plants: Ecological and Agricultural Aspects - page 246

In US forests, more than 20 non-indigenous species of plant pathogens
attack woody plants [13]. Approximately 9% or a total of $7 billion per year
of forest products are lost due to plant pathogens [3, 14]. Assuming that the
proportion of alien plant pathogens in forests is similar to that of introduced
insects or about 30%, then approximately $2.1 billion in forest products are
lost each year to non-indigenous plant pathogens in the United States (Tab. 3).
Livestock pests
Microbes and other parasites were introduced when various species of live-
stock were brought into the six nations (see introduction). In addition to the
hundreds of pest microbes and parasites that have already been introduced,
there are more than 60 additional microbes and parasites that could easily
invade the United States and become serious pests to US livestock [15]. A con-
servative estimate of the losses to US livestock from alien microbes and para-
sites is approximately $14 billion per year (Tab. 3).
The current threat of bioterrorism has brought a call from the American
Association of Veterinary Laboratory Diagnosticians to establish an Animal
Disease Diagnostic Network that would link local, state and federal (USDA)
in a communication system to enhance quick response to natural and or inten-
tional contamination of livestock. The proposed start up cost of this network is
estimated to be $85 million with yearly additional costs of $22 million [16].
Conclusion
More than 50,000 non-indigenous species of plants, animals, and microbes
have invaded the United States. An estimated 20-30% of the introduced spe-
cies are pests and cause major environmental problems [17]. Although rela-
tively few of these species become serious pests, some species inflict signifi-
cant damage to natural and managed ecosystems and cause public health prob-
lems. There is a complex of ecological factors that allow alien species to
become abundant and emerge as ecological threats in their new ecosystem.
These include: alien plant or animal species introduced without their natural
enemies (e.g., purple loosestrife); the development of new associations
between alien parasite and host (e.g, AIDS virus and humans); effective pred-
ators in new ecosystem (e.g., feral cats); artificial and/or disturbed habitats that
provide favorable ecosystems for the invasive aliens (e.g., weeds in crop and
lawn habitats); and invasion by some highly adaptable and successful alien
species (e.g., water hyacinth and zebra mussel).
This study documents that economic damages associated with non-indige-
nous species invasions in the United States to be $120 billion per year (Tab. 3).
Precise economic costs associated with some of the most ecologically dam-
aging alien species are not available. Cats and feral pigs, for example, have