Skip to main content

The Invasive Species Assessment Protocol: A Tool for Creating Regional and National Lists of Invasive Nonnative Plants that Negatively Impact Biodiversity

  • John M. Randall (a1), Larry E. Morse (a2), Nancy Benton (a2), Ron Hiebert (a3), Stephanie Lu (a2) and Terri Killeffer (a2)...

We developed a protocol for categorizing nonnative plants according to their negative impacts on biodiversity in a large area such as a state, nation, or ecological region. Our objective was to provide a tool that makes the process of identifying, categorizing, and listing nonnative plants that cause negative impacts to biodiversity analytic, transparent, and equitable and that yields lists that are useful to researchers, land managers, regulators, consumers, and commercial interests such as the nursery industry. The protocol was designed to distinguish between species that cause high, medium, low, or insignificant negative impacts to native biodiversity within the state, region, or nation of interest. It consists of 20 multiple-choice questions grouped into four sections, which each address a major aspect of a species' total impact and when combined yield an overall “Invasive Species Impact Rank” or “I-Rank” (high, medium, low, or insignificant). The nonprofit organization NatureServe is now using this protocol to assess the estimated 3,500 nonnative vascular plant species that are established in the United States to create a national list prioritized by negative impact on biodiversity. The protocol and additional information are available on the Internet at, and over 500 completed species assessments are available through NatureServe Explorer (

Corresponding author
Corresponding author's email:
Hide All
Alien Plant Working Group 2005. Alien Plant Invaders of Natural Areas. Accessed: October 25, 2007.
Anonymous, , 1993. Florida's most invasive species. Palmetto Fall 67.
[APRS] Alien Plants Ranking System Implementation Team 2000. Alien Plants Ranking System. Version 5.1. Jamestown, ND Northern Prairie Wildlife Research Center Accessed December 4, 2007.
[APRS] Alien Plants Ranking System Implementation Team 2001. Alien Plants Ranking System. Version 7.1. Flagstaff, AZ Southwest Exotic Plant Information Clearinghouse Accessed December 4, 2007.
Australian National Parks and Wildlife Service 1991. Plant Invasions: The Incidence of Environmental Weeds in Australia. Kowari 2. Canberra, Australia Australian National Parks and Wildlife Service. Canberra. 188.
[AZ-WIPWG] Arizona Wildland Invasive Plant Working Group 2005. Invasive nonnative plants that threaten wildlands in Arizona. Flagstaff, AZ Arizona Wildland Invasive Plant Working Group. 23. Acessed: October 25, 2007.
Bailey, R. G. 1995. Description of the Ecoregions of the United States. Washington, DC U.S. Forest Service Miscellaneous Publication Number 1391. 108.
Belnap, J. and Phillips, S. L. 2001. Soil biotia in an ungrazed grassland: response to annual grass (Bromus tectorum) invasion. Ecol. Applications 11/5:12611275.
Biosecurity Australia 2003. The Weed Risk Assessment System. Accessed December 4, 2007.
Bowen, B. and Shea, A. 1996. Exotic pest plants in Tennessee: threats to our native ecosystems. Tennessee Exotic Pest Plant Council News. Fall (Special Insert) 14.
Bratton, S. P. 1982. The effects of exotic plant and animal species on nature preserves. Nat. Areas J. 2/3:313.
Brown, D., Reichenbacher, F., and Franson, S. 1998. A Classification of North American Biotic Communities. Salt Lake City, UT University of Utah Press. 141.
Brown, D. E. 1994. Biotic Communities: Southwestern United States and Northwestern Mexico. (Plus companion map, Biotic Communities of the Southwest.). Salt Lake City, UT University of Utah Press. 342.
[Cal-IPC] California Invasive Plant Council 2006. California Invasive Plant Inventory. Cal-IPC Publication 2006-02. Berkeley, California California Invasive Plant Council. 39. Accessed: October 25, 2007.
Carr, G. W., Yugovic, J. V., and Robinson, K. E. 1992. Environmental Weed Invasions in Victoria: Conservation and Management Implications. East Melbourne, Victoria, Australia Victoria Department of Conservation and Environment. 78.
Champion, P. D. and Clayton, J. S. 2001. A weed risk assessment model for aquatic weeds in New Zealand. Pages 194202. in Groves, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
Connecticut Invasive Plant Council Connecticut Invasive Plant List. 2004. January 2004. Accessed October 25, 2007.
Cronk, Q. C. B. and Fuller, J. L. 1995. Plant Invaders: The Threat to Natural Ecosystems. London Chapman and Hall. 241.
Deering, R. H. and Vankat, J. L. 1999. Forest colonization and developmental growth of the invasive shrub Lonicera maackii . American Midland Naturalist 141/1:4350.
Evans, R. D., Rimer, R., Sperry, L., and Belnap, J. 2001. Exotic plant invasion alters nitrogen dynamics in an arid grassland. Ecol. Appl. 11/5:13011310.
Florida Exotic Pest Plant Council Plant List Committee 2005. List of Florida's Invasive Species. Accessed: October 25, 2007.
Fox, A. M., Gordon, D. R., Dusky, J. A., Tyson, L., and Stocker, R. K. 2000. The story behind the IFAS assessment of nonnative plants in Florida's natural areas. Wildland Weeds 3/4:47.
Fox, A. M., Gordon, D. R., Dusky, J. A., Tyson, L., and Stocker, R. K. 2001. IFAS assessment of nonnative plants in Florida's natural areas. SS-AGR-79. Gainesville, FL Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. 25. Accessed: October 25, 2007.
Gerlach, J. D. Jr 1997. The introduction, dynamics of geographic range expansion, and ecosystem effects of yellow starthistle (Centaurea solstitialis). Proc. California Weed Sci. Soc. 49:136141.
Gordon, D. R. 1998. Effects of invasive, non-indigenous plant species on ecosystem processes: lessons from Florida. Ecol. Appl. 8/4:975989.
Gould, A. M. A. and Gorchov, D. L. 2000. Effects of the exotic invasive shrub Lonicera maackii on the survival and fecundity of three species of native annuals. Amer. Midl. Nat. 144:3650.
Gould, L. L. and Stuckey, I. H. 1992. Plants invasive in Rhode Island. Rhode Island Wild Plant Society Newsletter 6/2:17.
Grossman, D. H., Faber-Langendoen, D., Weakley, A. S., Anderson, M., Bourgeron, P., Crawford, R., Goodin, K., Landaal, S., Metzler, K., Patterson, K., Pyne, M., Reid, M., and Sneddon, L. 1998. International Classification of Ecological Communities: Terrestrial Vegetation of the United States, Volume I—The National Vegetation Classification System: Development, Status, and Applications. Arlington, VA The Nature Conservancy. 126.
Groves, C. R. 2003. Drafting a Conservation Blueprint. Washington, DC Island Press. 457.
Hartman, K. M. and McCarthy, B. C. 2007. A dendro-ecological study of forest overstory productivity following the invasion of the non-indigenous shrub Lonicera maackii . Appl. Veg. Sci. 10:314.
Heffernan, K. E., Coulling, P. P., Townsend, J. F., and Hutto, C. J. 2001. Ranking Invasive Exotic Plant Species in Virginia. Natural Heritage Technical Report 01-13. Richmond, VA Virginia Department of Conservation and Recreation, Division of Natural Heritage. 144. Accessed: October 25, 2007.
Henderson, L. 1995. Plant Invaders of Southern Africa. Plant Protection Research Institute Handbook No. 5. Pretoria, South Africa Plant Protection Research Institute–Agricultural Research Council. 177.
Hickman, J. C., ed. 1993. The Jepson Manual: Higher Plants of California. Berkeley, CA University of California Press. 1400.
Hiebert, R. D. 1997. Prioritizing invasive plants and planning for management. Pages 195212. in Luken, J., Theiret, J., eds. Assessment and Management of Plant Invasions. New York Springer.
Hiebert, R. and Klick, K. 1988. Exotic plant species ranking system. Nat. Areas J. 8/2:121.
Hiebert, R. D. and Stubbendieck, J. 1993. Handbook for Ranking Exotic Plants for Management and Control. U.S. National Park Service Natural Resources Report NPS/NRMWRO/NRR – 93/08. 29 p.
Hiebert, R. D. and Stubbendieck, J. 2007. Alien Plants Ranking System Version 5.1. Accessed: October 25, 2007.
Hobbs, R. J. and Mooney, H. A. 1998. Broadening the extinction debate: population deletions and additions in California and Western Australia. Conserv. Biol. 12/2:271283.
Humphries, S. E., Groves, R. H., and Mitchell, D. S. 1991. Plant invasions of Australian ecosystems: a status review and management directions. Pages 1134. in Walton, D. W., Reville, B., George, A. Jr., Just, J., Forbes, M., Fagg, M., and Longmore, R. (eds.). Kowari 2, Part I. Canberra, Australia Australian National Parks and Wildlife Service.
Huston, M. A. 1994. Biological Diversity: The Coexistence of Species on Changing Landscapes. Cambridge, UK Cambridge University Press. 681.
Hutchinson, T. F. and Vankat, J. L. 1997. Invasibility and effects of Amur honeysuckle in southwestern Ohio forests. Conserv. Biol. 11/5:11171124.
Kartesz, J. T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. 1st ed. in Kartesz, J.T., Meacham, C.A., eds. Synthesis of the North American Flora. Version 1.0. Chapel Hill, NC North Carolina Botanical Garden.
Luken, J. O. and Goessling, N. 1994. Seedling distribution and the potential persistence of the exotic shrub Lonicera maackii in fragmented forests. Am. Midl. Nat. 133:124130.
Luken, J. O. and Mattimiro, D. T. 1991. Habitat-specific resilience of the invasive shrub Amur honeysuckle (Lonicera maackii) during repeated clipping. Ecol. Appl. 1:104109.
Maddox, D. M., Mayfield, A., and Poritz, N. H. 1985. Distribution of yellow starthistle (Centaurea solstitialis) and Russian knapweed (Centaurea repens). Weed Sci. 33/3:315327.
Mehrhoff, L. J., Metzler, K. J., and Corrigan, E. E. 2003. Nonnative and Potentially Invasive Vascular Plants in Connecticut. Storrs, CT Center for Conservation and Biodiversity, University of Connecticut, Storrs Accessed December 4, 2007.
Melgoza, G., Nowak, R. S., and Tausch, R. J. 1990. Soil water exploitation after fire: competition between Bromus tectorum (cheatgrass) and two native species. Oecologia 83:713.
Morse, L. E., Swearingen, J. M., and Randall, J. M. 1999. Defining a native plant. Pages 1214. in. Roadside Use of Native Plants. Washington, DC Federal Highway Administration, publ. FHWA-EP-99-014.
Morse, L. E., Randall, J. M., Benton, N., Hiebert, R., and Lu, S. 2004. An Invasive Species Assessment Protocol: Evaluating Nonnative Plants for their Impact on Biodiversity. Version 1. Arlington, VA NatureServe. 40.
National Invasive Species Council 2001. Meeting the Invasive Species Challenge: National Invasive Species Management Plan. Accessed October 25, 2007.
Olson, D. M., Dinerstein, E., Wikramanayake, E. D., Burgess, N. D., Powell, G. V. N., Underwood, E. C., D'Amico, J. A., Itoua, I., Strand, H. E., Morrison, J. C., Loucks, C. J., Allnutt, T. F., Ricketts, T. H., Kura, Y., Lamoureaux, J. F., Wettengel, W. W., Hedao, P., and Kassem, K. R. 2001. Terrestrial ecoregions of the world: a new map of life on earth. BioScience 51:933938.
Orr, R. 2003. Generic nonindigenous aquatic organisms risk analysis review process. Pages 415438. in Ruiz, G.M., Carlton, J.M., eds. Invasive Species: Vectors and Management Strategies. London Island Press.
Orr, R. L., Cohen, S. D., and Griffin, R. L. 1993. Generic nonindigenous pest risk assessment process (for estimating pest risk associated with the introduction of nonindigenous organisms). Riverdale, MD U.S. Department of Agriculture, Animal and Plant Health Inspection Service (internal report).
Owen, S. J. 1996. Ecological weeds on conservation land in New Zealand: a database. Accessed: October 25, 2007.
Panetta, F. D., Mackey, A. P., Virtue, J. G., and Groves, R. H. 2001. Weed risk assessment: core issues and future directions. Pages 231240. in Groves, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
Parker, I. M., Simberloff, D., Lonsdale, W. M., Goodell, K., Wonham, M., Kareiva, P. M., Williamson, M. H., Bon Holle, B., Moyle, P. B., Byers, J. E., and Goldwasser, L. 1999. Impact: toward a framework for understanding the ecological effects of invaders. Biol. Invasions 1:319.
Pheloung, P. C. 1995. Determining Weed Potential of New Plant Introductions to Australia. A Report on the Development of a Weed Risk Assessment System Commissioned and Endorsed by the Australian Weeds Committee and the Plant Industries Committee. Perth, Western Australia, Australia Agricultural Protection Board.
Pheloung, P. C., Williams, P. A., and Halloy, S. R. 1999. A weed risk assessment model for use as a biosecurity tool evaluating plant introductions. J. Environ. Manag. 57:239251.
Pitcairn, M. J., O'Connell, R. A., and Gendron, J. M. 1998. Yellow starthistle: survey of statewide distribution. Pages 6466. in Woods, D.M., ed. Biological Control Program Annual Summary, 1997. Sacramento, CA California Department of Food and Agriculture, Plant Health and Pest Prevention Services.
Randall, J. M. 1993. Exotic weeds in North American and Hawaiian natural areas: The Nature Conservancy's plan of attack. Pages 159172. in McKnight, B.N., ed. Biological Pollution: The Control and Impact of Invasive Exotic Species. Indianapolis, IN Indiana Academy of Science.
Randall, J. M. 1996. Weed control for the preservation of biodiversity. Weed Technol. 10:370383.
Randall, J. M. 1997. Defining weeds of natural areas. Pages 1825. in Luken, J., Theiret, J., eds. Assessment and Management of Plant Invasions. New York Springer.
Randall, J. M., Benton, N., and Morse, L. E. 2001. Categorizing invasive plants: the challenge of rating the weeds already in California. Pages 203216. in Groves, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
Randall, J. M., Morse, L. E., Thunhorst, G. A., and Benton, N. 1996. Criteria for ranking invasive natural area weeds objectively. in. Abstracts 23rd Annual Natural Areas Conference. St. Charles, IL 78.
Randall, J. M., Rejmánek, M., and Hunter, J. C. 1998. Characteristics of the exotic flora of California. Fremontia 26/4:312.
Redford, K. H. 1994. Science and The Nature Conservancy. Nature Conservancy 44/1:15.
Reichard, S., Schuller, R., Isaacson, D., Whiteaker, L., Kruckeburg, A., Kagan, J., Chappell, C., and Old, R. 1997. Nonnative Pest Plants of Greatest Concern in Oregon and Washington as of August 1997. Redmond, OR Pacific Northwest Exotic Pest Plant Council. 7.
Reichard, S. H. 2001. The search for patterns that enable prediction of invasion. Pages 1019. in Groves, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
Reichard, S. H. and Hamilton, C. W. 1997. Predicting invasions of woody plants introduced into North America. Conserv. Biol. 11:193203.
Rejmánek, M. 1996. A theory of seed plant invasiveness: the first sketch. Biol. Conserv. 78:171181.
Rejmánek, M. and Richardson, D. M. 1996. What attributes make some plant species more invasive? Ecology 77:16551661.
Rejmánek, M., Richardson, D. M., Barbour, M. G., Crawley, M. J., Hrusa, G. F., Moyle, P. B., Randall, J. M., Simberloff, D., and Williamson, M. 2002. Biological invasions: politics and the discontinuity of ecological terminology. Bull. Ecol. Soc. Am. 83:131133.
Ricciardi, A. and Cohen, J. 2007. The invasiveness of an introduced species does not predict its impact. Biol. Invasions 9:309315.
Richardson, D. M., Pysek, P., Rejmánek, M., Barbour, M. G., Panetta, F. D., and West, C. J. 2000. Naturalization and invasion of alien plants: concepts and definitions. Divers. Distrib. 6:93107.
Robertson, M. P., Villet, M. H., Fairbanks, D. H. K., Henderson, L., Higgins, S. I., Hoffman, J. H., LeMaitre, D. C., Palmer, A. R., Riggs, I., Shackleton, C. M., and Zimmerman, H. G. 2003. A proposed prioritization system for the management of invasive plants in South Africa. S. Afr. J. Sci. 99:3743.
Schmidt, K. A. and Whelan, C. J. 1999. Effects of exotic Lonicera and Rhamnus on songbird nest predation. Conserv. Biol. 13/6:15021506.
Schwegman, J. 1994. Exotics of Illinois forests. Erigenia 13:6567.
Standish, R. J., Robertson, A. W., and Williams, P. A. 2001. The impact of an invasive weed Tradescantia fluminensis on native forest regeneration. J. Appl. Ecol. 38/6:12531263.
Strayer, D. L., Eviner, V. T., Jeschke, J. M., and Pace, M. L. 2006. Understanding the long-term effects of species invasions. Trends Ecol. Evol. 21:645651.
Swarbrick, J. T. and Skarratt, D. B. 1992. The Bushweed Database of Environmental Weeds in Australia. 1st ed. Lawes, Queensland, Australia University of Queensland and Gatton College.
Swearingen, J., Reshetiloff, K., Slattery, B., and Zwicker, S. 2002. Plant Invaders of Mid-Atlantic Natural Areas. Washington, DC National Park Service and U.S. Fish and Wildlife Service. 82.
Thorp, J. R. and Lynch, R. 2000. The determination of weeds of national significance. Accessed October 25, 2007.
Timmins, S. M. and Owen, S. J. 2001. Scary species, superlative sites: assessing weed risk in New Zealand's protected natural areas. Pages 217227. in Grove, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
[USDA APHIS] U.S. Department of Agriculture Animal and Plant Health Inspection Service 2004. Weed-Initiated Pest Risk Assessment: Guidelines for Qualitative Assessments. Accessed: October 25, 2007.
[USDA NRCS] U.S. Department of Agriculture Natural Resources Conservation Service 2000. National Plant Materials Manual. 3rd Edition. Title 190. Accessed: October 25, 2007.
Virginia Department of Conservation and Recreation and Virginia Native Plant Society 2003. Invasive Alien Plant Species of Virginia. Accessed: October 25, 2007.
Virtue, J., Cunningham, D., Hanson, C., Hosking, J., Miller, I., Panetta, D., Pheloung, P., Randall, R., Timmins, S., Walton, C., Weiss, J., and Williams, P. 2006. National Post-Border Weed Risk Management Protocol. HB 294: 2006. Sydneyand Wellington, AustraliaNew Zealand Standards Australia and Standards New Zealand.
Virtue, J. G., Groves, R. H., and Panetta, F. D. 2001. Towards a system to determine the national significance of weeds in Australia. Pages 124152. in Grove, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
Vitousek, P. M. 1986. Biological invasions and ecosystem properties: can species make a difference? 163176. in Mooney, H.A., Drake, J.A., eds. Ecology of Biological Invasions of North America and Hawaii. New York Springer-Verlag.
Wagner, W. L., Herbst, D. R., and Sohmer, S. H. 1990. Manual of the Flowering Plants of Hawai'i. 2 Volumes. Honolulu, HI University of Hawaii Press and Bishop Museum Press. 1853.
Wainger, L. A. and King, D. M. 2001. Priorities for weed risk assessment: using a landscape context to assess indicators of functions, services, and values. Pages 3451. in Grove, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
Warner, P. J., Bossard, C. C., Brooks, M. L., DiTomaso, J. M., Hall, J. A., Howald, A. M., Johnson, D. W., Randall, J. M., Roye, C. L., Ryan, M. M., and Stanton, A. E. 2003. Criteria for categorizing invasive nonnative plants that threaten wildlands. Accessed: October 25, 2007.
Webb, C. J., Sykes, W. R., and Garnock-Jones, P. J. 1988. Flora of New Zealand: Naturalised Dicots, Gymnosperms, Ferns and Fern Allies. Christchurch, New Zealand: Balogh Scientific Books. 1365.
Weiss, J. 1999. Assessment for Invasive Potential of Victoria's State Prohibited, Priority, and Regional Priority Weeds. Pest Plant Assessment Project. Frankston, Vicotria, Australia Agriculture Victoria. 24.
Western Australia Department of Agriculture 2005. Declared Plants List. Accessed December 4, 2007.
Whisenant, S. G. 1990. Changing fire frequencies on Idaho's Snake River Plains: ecological and management implications. Pages 410. in McArthur, E.D., Romney, E.V., Smith, S.D., Tueller, P.T., eds. Proceedings: Symposium on Cheatgrass Invasion, Shrub Die-off, and Other Aspects of Shrub Biology and Management. Washington, DC USDA Forest Service Intermountain Research Station General Technical Report INT-276.
White, D. J., Haber, E., and Keddy, C. 1993. Invasive Plants of Natural Habitats in Canada: An Integrated Review of Wetland and Upland Species and Legislation Governing Their Control. Ottawa, Canada Canadian Wildlife Service, Environment Canada, and Canadian Museum of Nature.
Williams, P. A., Nicol, E., and Newfield, M. 2001. Assessing the risk to indigenous biota of plant taxa new to New Zealand. Pages 100116. in Grove, R.H., Panetta, F.D., Virtue, J.G., eds. Weed Risk Assessment. Collingwood, Victoria, Australia CSIRO.
Wilson, E. O. 1988. The current state of biological diversity. Pages 318. in Wilson, E.O., Peter, F.M., eds. Biodiversity. Washington, DC National Academy.
Wilson, E. O. 1992. The Diversity of Life. Cambridge, MA Belknap Press. 424.
Wilcove, D. S., Rothstein, D., Dubow, J., Phillips, A., and Losos, E. 2000. Leading threats to biodiversity. Pages 239254. in Stein, B.A., Kutner, L.S., Adams, J.S., eds. Precious Heritage: The status of Biodiversity in the United States. New York Oxford University Press.
Wunderlin, R. P. 1998. Guide to the Vascular Plants of Florida. Gainesville, FL University Press of Florida. 806.
Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Invasive Plant Science and Management
  • ISSN: 1939-7291
  • EISSN: 1939-747X
  • URL: /core/journals/invasive-plant-science-and-management
Please enter your name
Please enter a valid email address
Who would you like to send this to? *



Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 2 *
Loading metrics...

Abstract views

Total abstract views: 147 *
Loading metrics...

* Views captured on Cambridge Core between 20th January 2017 - 21st March 2018. This data will be updated every 24 hours.