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Pathways of Invasive Plants - U.S. Fish and Wildlife Service

Pathways are the means and routes by which invasive species are introduced into new environments. Pathways can generally be classified as either natural or man-made.

Natural pathways (self introduction on their own) include wind, currents (including marine debris), and other forms of natural dispersal that can bring species to a new habitat.

Man-made (human assistance) pathways are those which are created or enhanced by human activity. These are characteristically of two types:

  • Intentional, which is the result of a deliberate movement of a species by humans outside of its natural range. Examples include the introduction of biological control organisms or the movement of species for the horticultural or pet trade. Intentional introductions as a whole should not be labeled as either good or bad. A specific intentional pathway can only be judged by the positive or negative impact of the specific organisms that are moving along that means.
  • Unintentional, which is the inadvertent or accidental movement of species as a byproduct of some other human activity. Examples of unintentional pathways are ballast water discharge (e.g. red-tide organisms), pests and diseases in imported plants, firewood, and other agricultural products (e.g. fire ants), the movement of recreational watercraft (e.g. zebra mussels), and the international movement of people (e.g. pathogens). In these and countless other unintentional pathways, the movement of non-native species is an indirect byproduct of human activities.

For our purposes, the term "vector" is viewed as a biological pathway for a disease or parasite (i.e. an organism that transmits pathogens to various hosts) and is not completely synonymous with the much broader definition of a pathway. The Asian citrus psyllid is an example of a vector of the serious citrus greening disease or Huanglongbing.

Examples of How Invasive Species are Spread


  • Balancing Act: A Policy Success Story in the Great Lakes

    • Feb 23, 2024
    • Michigan State University. Michigan Sea Grant.

    • The Great Lakes remain one of the most heavily invaded freshwater systems in the world. Ballast water from cargo ships crossing the ocean inadvertently brought in many aquatic invasive species (AIS), accounting for the introduction of 40% of all nonindigenous aquatic species in the Great Lakes. However, collaborative efforts have led to pioneering research and policy changes that have reduced this threat.

  • The Less Traveled Pathways for Species Introduction to the Great Lakes

    • Feb 23, 2024
    • Michigan State University. Michigan Sea Grant.

    • While ballast water has been a major way species have entered the Great Lakes, it hasn't been the only way.

  • Commercial Vessel Ballast Water Management (2020-2021): Report to Congress

    • Jul 7, 2024
    • Smithsonian Institution. Smithsonian Research Online; National Ballast Information Clearinghouse; United States Coast Guard.

    • The 2018 Vessel Incidental Discharge Act (VIDA) requires an annual report on the effectiveness of national ballast water management (BWM) requirements. This report provides analyses of (1) the patterns of ballast water (BW) delivery and management; (2) Coast Guard’s compliance and enforcement actions regarding BWM regulations; and (3) patterns of biological invasions by marine and estuarine aquatic nuisance species (ANS). It covers the two-year period from January 2020 through December 2021 to demonstrate the effectiveness of the Coast Guard’s statutorily mandated BWM regulatory program and validates that enforcement efforts continue to increase BWM and reduce the risk of introducing ANS into U.S. waters.

      Citation: National Ballast Information Clearinghouse and United States Coast Guard. 2023. Commercial Vessel Ballast Water Management (2020-2021): Report to Congress July 7, 2023. Washington, D.C.: United States Department of Homeland Security.

  • USGS Estimates Potential Spread of Invasive Species Carried by Hurricane-Induced Flooding

    • Jun 30, 2023
    • DOI. United States Geological Survey.

    • The high winds, heavy rains and storm tides caused by hurricanes and tropical storms can rapidly change the landscape of an area affected by a storm. Hurricane-related flooding can also result in a slow transformation of ecosystems found on land and in water, as floodwaters can carry invasive wildlife and plant species into new regions, accelerating their spread.

  • Antarctica: Invasive Species 'Hitchhiking' on Ships

    • Jan 10, 2022
    • BBC News.

    • Species from around the world that are "hitching a lift" on ships threaten Antarctica's pristine marine ecosystem.

  • Great Lakes Commission Shares Lessons Learned from Fight Against Internet Sales of Aquatic Invasive Species

    • Jul 12, 2022
    • Great Lakes Commission.

    • The Great Lakes Commission (GLC) released a report on the second phase of its work to stop internet sales of aquatic invasive species (AIS) in the Great Lakes region. The GLC initiative, known as the Great Lakes Detector of Invasive Aquatics in Trade (GLDIATR), demonstrated that “web crawling” applications can be used to track the online sale of priority AIS and support the work of AIS researchers, outreach coordinators, managers, and law enforcement officials across the Great Lakes basin.

  • Marine Plastic Pollution Could Contribute to the Introduction of Invasive Species

    • Mar 2, 2022
    • Institut de Ciències del Mar; University of Barcelona (Spain).

    • A new study led by the Institut de Ciències del Mar (ICM-CSIC) and the University of Barcelona (UB) has revealed that marine plastic pollution could contribute to the introduction and transport of non-native species that attach to these particles of anthropogenic origin.

  • Recreational Craft and Invasive Species: How to Manage Biofouling to Stop the Spread

    • Oct 13, 2022
    • International Maritime Organization.

    • Invasive aquatic species are known to be one of the biggest drivers of biodiversity loss, and their management especially in marine environments is incredibly challenging. To tackle this issue, the GloFouling Partnerships, led by the International Maritime Organization (IMO) and in collaboration with the International Council of Marine Industry Associations (ICOMIA), World Sailing, and the International Union for Conservation of Nature (IUCN), has published a new Biofouling Management for Recreational Boating Report [PDF, 13.4 MB]. The aim of the report is to stop the spread of invasive aquatic species which can adhere to hulls and other areas of recreational craft by addressing how to manage biofouling.

  • Tracing the Source: How Did Invasive Northern Pike Arrive in the Columbia River Basin?

    • Nov 2022
    • USDA. FS. Rocky Mountain Research Station.

    • Northern pike are native to Alaska, Canada, and much of the central and eastern continental United States. Genetic evidence reveals the role of human transport in the spread of invasive northern pike in the Columbia River basin.

  • Firewood Transport as a Vector of Forest Pest Dispersal in North America: A Scoping Review

    • Feb 2021
    • Cornell University. New York Invasive Species Research Institute.

    • A cozy campfire for summer days, a warm fireplace for winter evenings– the use of firewood is an "established cultural norm". However, moving firewood from place to place can have devastating consequences, as it can spread forest pests that decimate forests to collectively cost an estimated $4.2 – $14.4 billion per year. In order to better address the problem of people moving firewood and vectoring forest pests, Solano and colleagues examined trends and gaps in the existing literature on firewood and human-mediated forest pest movement in North America. The existing literature demonstrates the risk of firewood movement, but fails to address the level of awareness the public has on such risks, or the level of effectiveness of firewood regulations to prevent forest pest spread.

  • Invasive Plants are Still for Sale as Garden Ornamentals, Research Shows

    • Aug 9, 2021
    • University of Massachusetts - Amherst.

    • UMass Amherst study finds that invasive species are widely available due to inconsistent regulation. Results of a new study by ecologists at the University of Massachusetts Amherst show that 1,330 nurseries, garden centers and online retailers are still offering hundreds of invasive plant species as ornamental garden plants. This includes 20 species that are illegal to grow or sell nationwide.

      The study, “Invaders for sale: the ongoing spread of invasive species by the plant trade industry,” published in Frontiers in Ecology and the Environment, shows that existing regulatory and ethical guidelines do not serve to limit the widespread introduction of invasive plants and that more than 60% of the 1,285 plants identified as invasive remain for sale.

  • Marine Debris as a Potential Pathway for Invasive Species

    • 2017
    • DOC. NOAA. Marine Debris Program.

    • There is mounting concern over the increase in debris in our ocean and the potential for that debris to assist in the spread of non-native species. While the pathways associated with global shipping draw the greatest amount of attention regarding marine invasives, the purpose of this paper is to consider the potential role that marine debris may play in introducing non-native species that may become invasive. This report reviews the scientific literature that exists on the subject and identifies areas where more research is needed.

  • Firewood

    • USDA. Animal and Plant and Health Inspection Service.

    • Whether used to heat your home or build a campfire, firewood is a must-have item for millions of Americans. However, firewood also presents a very real threat to the Nation's forests. Invasive species including the Asian longhorned beetle (ALB), the emerald ash borer (EAB), and spongy moth can be spread into new areas of the country on firewood.

  • Habitattitude - Animals and Plants in Classroom Education

    • Pet Industry Joint Advisory Council; DOI. Fish and Wildlife Service; DOC. National Oceanic and Atmospheric Administration.

    • Pets in K-12 school classrooms can be valuable teaching assets. Caring for companion animals helps students to relate to species in their natural habitats while fostering a sense of environmental ethics. Provides information for planning for classroom pets, caring the classroom pets after the school year, how to protect the environment, and additional resources.

Selected Resources

The section below contains highly relevant resources for this subject, organized by source.

Council or Task Force
  • Strategies Identified for Successful Outreach to Reduce the Spread of Forest Pests on Firewood

    • Aug 1, 2022
    • Nature Conservancy. Don't Move Firewood.

    • Collaborative study determines effective messengers, language choices, and modes of delivery for disseminating educational information on how firewood choices can impact forest health. A recent study done in collaboration between The Nature Conservancy’s Don’t Move Firewood campaign and researchers from Clemson University showed that most people in the U.S. don’t know firewood can harbor invasive forest insects and diseases, but when targeted education materials are used effectively, they can learn and are likely to change their behavior.

  • Neighborhood Watch: Early Detection and Rapid Response to Biological Invasion along U.S. Trade Pathways

    • 2009
    • International Union for Conservation of Nature.

    • This report offers recommendations to improve biosecurity measures at U.S. ports, as well as a possible funding mechanism based upon the polluter-pays principle.

  • Denying Entry: Opportunities to Build Capacity to Prevent the Introduction of Invasive Species and Improve Biosecurity at US Ports

    • 2007
    • International Union for Conservation of Nature.

    • The aim of this report was to identify the resources, strategies, and policies necessary to create, maintain, and make accessible one or more commodity/invasive species databases that EPA and other relevant agencies can apply to trade policy decision-making in a timely and scientifically-based manner.

  • AIM - How Invasions Happen

    • Aquatic Invaders in the Marketplace.

    • The AIM campaign that focuses on providing information and best practices to manage The Organisms in Trade (OIT) pathway. The OIT pathway is one of the main avenues by which non-native aquatic species become established in waterways. Many of the aquatic plants and animals available in the marketplace can negatively impact ecosystems, economies, and public health when introduced to new freshwater habitats. AIM was developed by a collaboration of researchers and outreach specialists led by Illinois-Indiana Sea Grant and the Illinois Natural History Survey.

  • Don't Move Firewood - Emerald Ash Borer Awareness Week Toolkit

    • Nature Conservancy.

    •  Emerald Ash Borer Awareness Week is in May each year. Provides outreach materials for EAB EAB Awareness Week.

  • Don't Move Firewood - Toolbox

  • Great Lakes Detector of Invasive Species in Trade (GLDIATR)

    • Great Lakes Commission.

    • The Great Lakes Detector of Invasive Aquatics in Trade (GLDIATR) is an innovative approach developed by the Great Lakes Commission that uses advanced technology to search the internet for sites where aquatic invasive species can be purchased and shipped to the Great Lakes region. This information can be used by invasive species managers to inform and help target a variety of activities including outreach and education, risk assessment, monitoring and surveillance, and enforcement.

  • - Pathways

    • Ontario's Invading Species Awareness Program (Canada).

  • Local Government Aquatic Invasive Species Toolkit

    • Pacific States Marine Fisheries Commission. Western Aquatic Invasive Species Resource Center.

    • The purpose of this toolkit is to assist local governments with navigating the regulatory framework associated with high-risk priority aquatic invasive species (AIS).
      Note: In 2020, the National Sea Grant Law Center and project partner, Creative Resources Strategies, LLC, received funding from the U.S. Fish and Wildlife Service to conduct research on the role of municipalities in aquatic invasive species (AIS) prevention efforts. This project resulted in the development of an online toolkit to help local governments navigate the regulatory framework associated with high-risk priority AIS.

  • National Plant Board Firewood Working Group Guidelines

    • National Plant Board.

    • In an attempt to limit the transfer of pests across state lines in firewood, these guidelines provide information on the process of drafting new or revising current state-based regulations pertaining to firewood, share case studies of states that have already approached firewood quarantines, provide examples of strategies beyond regulation that could enhance a state’s overall response to the firewood pathway, and give selected recommendations or examples within these strategies.

Federal Government
International Government
  • Invasive Alien Species in Ireland - Pathway Action Plans

    • National Biodiversity Data Centre (Ireland).

    • With increased movement of people and goods around the world, there is an increased introduction of alien (non-native) species to new areas where they can become invasive. Key to this, is knowing how the invasive species are likely to be introduced and acting to prevent further introductions through those pathways. The purpose Pathway Action Plans is to raise public awareness as well as to prevent unintentional introductions by minimizing the contamination of goods, commodities, vehicles and equipment by IAS, and ensuring appropriate checks at EU Union borders.

State and Local Government
  • The States of Invasion: How Does a Nonnative Species Transition to an Invader?

    • Jul 2022
    • University of Florida. Institute of Food and Agricultural Sciences Extension.

    • Learn how to prevent introductions. This publication is written for the general public and describes why invasive species are an important issue in Florida and how nonnative species become invasive by moving through five stages of human-aided biological invasion (1) transport, (2) introduction, (3) establishment, (4) spread, and (5) negative impacts. The article also connects these stages to examples in Florida.
      Electronic Data Information Source Publication #SS-AGR-464

  • Firewood as a Vector in Invasive Pest Dispersal

    • North Carolina State University. Cooperative Extension.

  • Tourism, Recreation and Biological Invasions (requires login 🔒)

    • 2022
    • CABI Digital Library.

    • The first section of the book includes information about how tourism-related infrastructure and activities promote biological invasions, including key pathways for non-native invasive species introductions. This section provides case studies of different organisms that are known to be introduced and/or promoted by tourism in different ecosystems or regions. The second section elaborates on known and potential impacts of invasive species on tourism and recreation, including how they may affect, positively or negatively, the economic revenue from tourism, tourist access, recreation, aesthetic values and tourists’ perceptions. The last section focuses on management and policy, covering aspects of how visitors perceive invasive species and their willingness to manage them, biosecurity measures to prevent invasion related to tourism, as well as potential policy options moving forward. The book draws on a number of examples across multiple taxa, landscapes and regions of the world.

      Citation: Barros, A., Shackleton, R., Rew, L. J., Pizarro, C., Pauchard, A. (Eds.). (2022). Tourism, Recreation and Biological Invasions. CABI.