Tuesday Talks with Dr. Patterson

February 24, 2015

Lions, Tigers and Bears, Oh My!

Dorothy, Tin Man, and Scarecrow chanted “lions, tigers and bears” with a sense of trepidation as they entered Haunted Forest in the famous movie “The Wizard of Oz,” nervously anticipating an encounter with these fierce beasts.  Today, we too face new threats to human health, the environment, and agricultural productivity in the form of invasive species.  And, these threats are no cowardly lion.  This week, beginning on February 23, marks the observance of National Invasive Species Awareness Week.

 Invasive species are defined as a species that is nonnative (or alien) to a particular ecosystem and whose introduction is likely to be harmful to the economy, the environment, or human health.  Invasive species can be plants, animals, or other organisms (e.g. bacteria, viruses, or fungi).  Once entering a new ecosystem these alien species often do not face the normal predators or controls they face in their native ecosystems and are able to proliferate rapidly, thereby threatening the new host ecosystem.  Images of very large snakes eating deer and alligators in the Everglades come to mind for many.  However, one can see numerous examples of invasive species in the Alabama landscape—kudzu, privet, honeysuckle, and Wisteria, to name a few plant species alone.  In fact, Alabama was ground zero for several now infamous invasive species.  Fire ants, which have spread through much of the southern United States entered through the Port of Mobile in the 1930s.  Cogongrass, the noxious weed, which was found to have no economic value as a forage crop and now disrupts forest operations, was first established first in Grand Bay, Alabama in 1912.  Also, Johnsongrass, a weed described as one of the world’s 10 worst was named after Alabamian Colonel William Johnson, who tried planting it as a forage crop in the 1840s.  It later proved to be of little value and is even potentially toxic to cattle.

 Over the past 200 years more than 50,000 foreign plant and animal species have become established in the United States with one in seven becoming invasive (Evans).  Furthermore, the number of invasive species entering the United States has increased as global trade has increased, particularly since the 1970s.  These invasive species are pushing out native plant and animal species, reducing biological diversity, killing forest trees, placing some species at increased risk of extinction, altering wildfire intensity and frequency, and damaging crops.  In addition to the cost associated with reduced crop yields or diminished livestock vitality or even livestock mortality, the presence of invasive species imposes other economic costs.  This includes the direct cost associated with attempting to control the invasive species, which may be incurred by government or private producers.  Foreign buyers may also ban the import of products from an infested area, as is allowed under World Trade Organization rules, further reducing producer returns.  Consumer demand for products may also be altered if they perceive a product to be unsafe.  Some invasive species can even cause human illness and will result in increased medical costs.  In some cases, invasive species could very well threaten the viability of an entire industry.  The annual economic cost of invasive species in the United States is estimated to exceed $100 billion (Pimental, et al).

 Invasive species arrive in new ecosystems in cargo containers and in travelers’ luggage.  There are cases of aquatic invasive species entering new environments in the ballasts of ships, which are flushed as they move towards ports in shallower inter-coastal waterways.  Boaters, hunters, and campers can also inadvertently move invasive species from one region to another, as they hitch a ride of boats, equipment, or clothing.  Some invasive species may move on ocean currents, storms spanning across continents, or with the movements of migratory wildlife.  Some invasive species are introduced when hobbyists irresponsibly release exotic pets into the environment.  As discussed above, some invasive species were introduced intentionally as ornamental plants (e.g. honeysuckle) or for agricultural and conservation purposes (e.g. kudzu).

 The U.S. government views the threat of invasive species very seriously.  In 1999, the National Invasive Species Council was formed with representatives from 13 agencies in an effort to coordinate procedures intended to prevent the introduction of new invasive species.  The council is co-chaired by the Secretaries of Agriculture, Commerce, and Interior.  The USDA leads efforts in inspections at U.S. ports of entry.  You can help limit the threat imposed by invasive species by being cognizant of the species you come in contact with as you travel and by not attempting to bring plant materials, foods, or animals into the United States from other countries.  Many horticulturalists now advocate for using only native or noninvasive plants in gardens and landscapes.  You too should be conscious of moving boats and other recreational equipment from one region to another.  Some recommend washing boats and equipment before moving them.  New research on control of these invasive species is needed, particularly for those invasive pests that threaten industries and for which no solution is currently known (e.g. citrus greening – see Tuesday Talk on January 20, 2015).

 The threat imposed by invasive species will grow over time, particularly with increased globalization, as travelers and products move freely around the world.  So, we too are entering our own form of the Haunted Forest.  Responding to this threat will require vigilant control and enforcement by government, conscientious behavior by individuals, and new research on control mechanisms. 


 Evans, E.A.  “Economic Dimensions of Invasive Species.”  Choices (2003).

 Pimentel, D.L., L. Lach, R. Zuniga, and D. Morrison.  “Environmental and Economic Costs of Nonindigenous Species in the United States.”  BioScience (2000)50:53-65.

 Dr. Paul Patterson is Associate Dean for Instruction for the College of Agriculture and Professor of Agricultural Economics.