The Spread of Exotic Plant Species at Mount St. Helens: The Roles of a Road, Disturbance Type, and Post-disturbance Management

  • Lindsey L. Karr
  • Charles M. Crisafulli
  • Jeffrey J. Gerwing


Mount St. Helens and the surrounding landscape were dramatically altered during and after the 18 May 1980 eruption, creating large expanses of disturbed land that could be susceptible to exotic plant invasion. We studied spatial patterns of exotic plant richness and abundance along a road and pedestrian trail that traverse a volcanic disturbance gradient with varying management prescriptions. In blast areas, exotic plant richness and abundance increased near the road, demonstrating the role that both roads and canopy cover play in the dispersal and establishment of exotic species. However, the overall richness and abundance of exotic plants were relatively low, and the pyroclastic-flow zone vegetation was dominated by native plants.


Plant communities Biological invasion Land management Volcanic disturbance Species richness Community composition Succession Invasive species 



Field data collection assistance was provided by Jessica Camp, Sara Copp, Abi Groskopf, and Kate Rhodes. Bill Becker, John Bishop, Sara Copp, Tim Elder, Ed Guerrant, Richard Halse (and the Oregon State University Herbarium), Dominic Maize, Ashley Smithers, Duncan Thomas, and Anthony Wenke provided assistance with plant identifications. We thank Sara Copp, Mat Dorfman, Yangdong Pan, and Jill VanWinkle for statistical consultation. We also thank Robert “Rocky” Pankratz for providing US Forest Service data regarding planting, thinning, and bough harvesting. LLK thanks the Mount St. Helens Institute for providing living arrangements while in the field. The USFS Pacific Northwest Research Station provided funding for CMC. This work was supported by the National Science Foundation. LTREB Program DEB-0614538 to CMC.


Blast pyroclastic density current

In the case of the Mount St. Helens 1980 eruption, failure of the volcano’s north flank unroofed pressurized magma and superheated water. Rapid exsolution of magmatic gases and conversion of superheated water to steam produced a laterally directed blast, which formed a density current that flowed across rugged topography. The current contained fragmented rock debris as well as shattered forest material.

Debris avalanche

A rapid granular flow of an unsaturated or partly saturated mixture of volcanic rock particles (± ice) and water, initiated by the gravitational collapse and disintegration of part of a volcanic edifice. Debris avalanches differ from debris flows in that they are not water-saturated. Although debris avalanches commonly occur in association with eruptions, they can also occur during periods when a volcano is dormant.


An Indonesian term for a rapid granular flow of a fully saturated mixture of volcanic rock particles (± ice), water, and commonly woody debris. A lahar that has ≥50% solids by volume is termed a debris flow; one that has roughly 10–50% solids by volume is termed a hyperconcentrated flow. Flow type can evolve with time and distance along a flow path as sediment is entrained or deposited.

Pyroclastic flow

Rapid flow of a dense, dry mixture of hot (commonly >700 °C) solid particles, gases, and air that moves across the ground surface, often following landscape typography. Flows are generally gravity driven but may be accelerated initially by impulsive lateral forces of directed volcanic explosions. Flows typically move at high velocity (up to several hundred km/h).


A rain of volcanic particles to the ground following ejection into the atmosphere by an explosive eruption. Tephra is a collective term for particles of any size, shape, or composition ejected in an explosive eruption.


  1. Abella, S.R., E.C. Engel, J.D. Springer, and W.W. Covington. 2012. Relationships of exotic plant communities with native vegetation, environmental factors, disturbance, and landscape ecosystems of Pinus ponderosa forests, USA. Forest Ecology and Management 271: 65–74.CrossRefGoogle Scholar
  2. Alignier, A., and M. Deconchat. 2013. Patterns of forest vegetation responses to edge effect as revealed by a continuous approach. Annals of Forest Science 70: 601–609.CrossRefGoogle Scholar
  3. Ansong, M., and C. Pickering. 2014. Weed seeds on clothing: A global review. Journal of Environmental Management 144: 203–211.CrossRefGoogle Scholar
  4. Antos, J.A., and D.B. Zobel. 2005. Plant responses in forests of the tephra-fall zone. In Ecological responses to the 1980 eruption of Mount St. Helens, ed. V.H. Dale, F.J. Swanson, and C.M. Crisafulli, 47–58. New York: Springer.CrossRefGoogle Scholar
  5. Bailey, J.D., C. Mayrsohn, P.S. Doescher, E.St. Pierre, and J.C. Tappeiner. 1998. Understory vegetation in old and young Douglas-fir forests of western Oregon. Forest Ecology and Management 112: 289–302.CrossRefGoogle Scholar
  6. Birdsall, J.L., W. McCaughey, and J.B. Runyon. 2012. Roads impact the distribution of noxious weeds more than restoration treatments in a lodgepole pine forest in Montana, U.S.A. Restoration Ecology 20: 517–523.CrossRefGoogle Scholar
  7. Braatne, J.H., and L.C. Bliss. 1999. Comparative physiological of lupines colonizing early successional habitats on Mount St. Helens. Ecology 80: 891–907.CrossRefGoogle Scholar
  8. Carlson, J.R., J.R. Stroh, J.A. Oyler, and F. Reckendorf. 1982. Erosion control revegetation on land damaged by the 1980 Mt. St. Helens eruption. In Proceedings: High-altitude revegetation workshop No. 5, Information Series No. 48, ed. R.L. Cuany and J. Etra, 174–189. Fort Collins: Colorado Water Resources Research Institute, Colorado State University.
  9. Chen, J., J.F. Franklin, and T.A. Spies. 1993. Contrasting microclimates among clearcut, edge, and interior of old-growth Douglas-fir forest. Agricultural and Forest Meteorology 63: 219–237.CrossRefGoogle Scholar
  10. ———. 1995. Growing season microclimatic gradients from clearcut edges into old-growth Douglas-fir forests. Ecological Applications 5: 74–86.CrossRefGoogle Scholar
  11. Christen, C.C., and G.R. Matlack. 2007. The habitat and conduit functions of roads of three invasive plant species. Biological Invasions 11: 453–465.CrossRefGoogle Scholar
  12. Clinton, W. 1999. U.S. presidential executive order 13112 re: Invasive species. February 3, 1999. Federal Register 64: 6183–6186.Google Scholar
  13. Cook, R. 1980. The biology of seeds in the soil. In Demography and evolution in plant populations, ed. O.T. Solbrig, 107–130. Berkeley: University of California Press.Google Scholar
  14. Dale, V.H. 1989. Wind dispersed seeds and plant recovery on the Mount St. Helens debris avalanche. Canadian Journal of Botany 67: 1434–1441.CrossRefGoogle Scholar
  15. ———. 1991. Revegetation of Mount St. Helens debris avalanche 10 years post eruption. National Geographic Research and Exploration 7: 328–341.Google Scholar
  16. Dale, V.H., and W.M. Adams. 2003. Plant reestablishment 15 years after the debris avalanche at Mount St. Helens, Washington. Science of the Total Environment 313 (1–3): 101–113.CrossRefGoogle Scholar
  17. Dale, V.H., C.M. Crisafulli, and F.J. Swanson. 2005. 25 years of ecological change at Mount St. Helens. Science 308: 961–962.CrossRefGoogle Scholar
  18. Davis, M.A., J.P. Grime, and K. Thompson. 2000. Fluctuating resources in plant communities: A general theory of invasibility. Journal of Ecology 88: 528–534.CrossRefGoogle Scholar
  19. del Moral, R., and L.C. Bliss. 1993. Mechanisms of primary succession: Insights resulting from the eruption of Mount St. Helens. Advances in Ecological Restoration 24: 1–66.CrossRefGoogle Scholar
  20. del Moral, R., and C.A. Clampitt. 1985. Growth of native plant species on recent volcanic substrates form Mount St. Helens. American Midland Naturalist 114: 374–383.CrossRefGoogle Scholar
  21. del Moral, R., and D.M. Wood. 1993. Early primary succession on a barren volcanic plain at Mount St. Helens, Washington. American Journal of Botany 80: 981–991.CrossRefGoogle Scholar
  22. Delgado, J.D., N.L. Arroyo, J.R. Arevalo, and J.M. Fernandez-Palacios. 2007. Edge effects of roads on temperature, light, canopy cover, and canopy height in laurel and pine forests (Tenerife, Canary Islands). Landscape and Urban Planning 81: 328–340.CrossRefGoogle Scholar
  23. Flory, S.L., and K. Clay. 2009. Effects of roads and forest successional age on experimental plant invasions. Biological Conservation 142: 2531–2537.CrossRefGoogle Scholar
  24. Forman, R.T.T., D. Sperling, J.A. Bissonette, A.P. Clevenger, C.D. Cutshall, V.H. Dale, L. Fahrig, R. France, C.R. Goldman, K. Heanue, J.A. Jones, F.J. Swanson, T. Turrentine, and T.C. Winter. 2003. Road ecology: Science and solutions. Washington, DC: Island Press.Google Scholar
  25. Foster, D.R., D.H. Knight, and J.F. Franklin. 1998. Landscape patterns and legacies resulting from large, infrequent forest disturbances. Ecosystems 1: 497–510.CrossRefGoogle Scholar
  26. Fuller, R.N., and R. del Moral. 2003. The role of refugia and dispersal in primary succession on Mount St. Helens, Washington. Journal of Vegetation Science 14: 637–644.CrossRefGoogle Scholar
  27. Gilkey, H.M., and L.J. Dennis. 2001. Handbook of Northwestern plants. Corvallis: Oregon State University Press.Google Scholar
  28. Gray, A.N. 2005. Eight nonnative plants in western Oregon forests: Associations with environment and management. Environmental Monitoring and Assessments 100: 109–127.CrossRefGoogle Scholar
  29. Gray, A. 2007. Distribution and abundance of invasive plants in Pacific Northwest forests. In Meeting the challenge: Invasive plants in Pacific Northwest ecosystems. General Technical Report PNW-GTR-694, ed. T.B. Harrington and S.H. Reichard, 143–148. Portland: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station.Google Scholar
  30. Grime, J.P. 1979. Plant strategies and vegetation processes. New York: Wiley.Google Scholar
  31. Halpern, C.B., P.M. Frenzen, J.E. Means, and J.F. Franklin. 1990. Plant succession in areas of scorched and blown-down forest after the 1980 eruption of Mount St. Helens, Washington. Journal of Vegetation Science 1: 181–194.CrossRefGoogle Scholar
  32. Halvorson, J.J., J.L. Smith, and E.H. Franz. 1991. Lupine influence on soil carbon, nitrogen and microbial activity in developing ecosystems at Mount St. Helens. Oecologia 87: 162–170.CrossRefGoogle Scholar
  33. Hansen, M.J., and A.P. Clevenger. 2005. The influence of disturbance and habitat on the presence of non-native plant species along transport corridors. Biological Conservation 125: 249–259.CrossRefGoogle Scholar
  34. Harper, K.A., S.E. Macdonald, P.J. Burton, J.Q. Chen, K.D. Brosofske, S.C. Saunders, E.S. Euskirchen, D. Roberts, M.S. Jaiteh, and P.A. Esseen. 2005. Edge influence on forest structure and composition in fragmented landscapes. Conservation Biology 19: 768–782.CrossRefGoogle Scholar
  35. Hitchcock, C.L., and A. Cronquist. 1973. Flora of the Pacific Northwest. Seattle: University of Washington Press.Google Scholar
  36. Holm, L., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: Natural histories and distribution. New York: Wiley.Google Scholar
  37. Johnston, F.M., and S.W. Johnston. 2004. Impacts of road disturbance on soil properties and on exotic plant occurrence in subalpine areas of the Australian Alps. Arctic Antarctic and Alpine Research 36: 201–207.CrossRefGoogle Scholar
  38. Kozloff, E.N. 2005. Plants of Western Oregon, Washington and British Columbia. Portland: Timber Press.Google Scholar
  39. Lipman, P.W., and D.R. Mullineaux, eds. 1981. The 1980 Eruptions of Mount St. Helens, Washington. Professional Paper 1250. Washington, DC: U.S. Geological Survey.Google Scholar
  40. Lockwood, J.L., M.F. Hoopes, and M.P. Marchetti. 2007. Invasion ecology. Malden: Blackwell Publishing.Google Scholar
  41. Lonsdale, W.M. 1999. Global patterns of plant Invasions and the concept of invasibility. Ecology 80: 1552–1536.CrossRefGoogle Scholar
  42. Lonsdale, W.M., and A.M. Lane. 1993. Tourist vehicles as vectors of weed seeds in Kakadu National Park, Northern Australia. Biological Conservation 69: 277–283.CrossRefGoogle Scholar
  43. Lozon, J.D., and H.J. MacIsaac. 1997. Biological invasions: Are they dependent on disturbance? Environmental Review 5: 131–141.CrossRefGoogle Scholar
  44. Mack, R.N., D. Simberloff, W.M. Lonsdale, H. Evans, M. Clout, and F.A. Bazzaz. 2000. Biotic invasions: Causes, epidemiology, global consequences and control. Ecological Applications 10: 689–710.CrossRefGoogle Scholar
  45. McEvoy, P.B., and C.S. Cox. 1987. Wind dispersal distances in dimorphic achenes of ragwort, Senecio jacobaea. Ecology 68: 2006–2015.Google Scholar
  46. Michalcov, D., S. Lvoncik, M. Chytry, and O. Hajek. 2011. Bias in vegetation databases? A comparison of stratified-random and preferential sampling. Journal of Vegetation Science 22: 281–291.CrossRefGoogle Scholar
  47. Moody, M.E., and R.N. Mack. 1988. Controlling the spread of plant invasions: The importance of nascent foci. Journal of Applied Ecology 25: 1009–1021.CrossRefGoogle Scholar
  48. Mooney, H.A., and J.A. Drake. 1989. Biological invasions: A SCOPE program overview. In Biological invasions: A global perspective, ed. J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, 491–506. Chicheser: Wiley.Google Scholar
  49. Mortensen, D.A., E.S.J. Rauschert, A.N. Nord, and B.P. Jones. 2009. Forest roads facilitate the spread of invasive plants. Invasive Plant Science and Management 2: 191–199.CrossRefGoogle Scholar
  50. Nelson, C.R., C.B. Halpern, and J.K. Agee. 2008. Thinning and burning result in low-level invasion by nonnative plants but neutral effect on natives. Ecological Applications 18: 762–770.CrossRefGoogle Scholar
  51. Newsome, A.E., and I.R. Noble. 1986. Ecological and physiological characters of invading species. In Ecology of biological invasions, ed. R.H. Groves and J.J. Burton, 1–20. Cambridge: Cambridge University Press.Google Scholar
  52. Ortiz, M.Â., K. Tremetsberger, A. Terrab, T.F. Stuessy, J.L. García-Castaño, E. Urtubey, C.M. Baeza, C.F. Ruas, P.E. Gibbs, and S. Talavera. 2008. Phylogeography of the invasive weed Hypochaeris radicata (Asteraceae): From Moroccan origin to worldwide introduced populations. Molecular Ecology 17: 3654–3667.CrossRefGoogle Scholar
  53. Parendes, L.A. 1997. Spatial patterns of invasion by exotic plants in a forested landscape. Doctoral dissertation. Corvallis: Oregon State University.Google Scholar
  54. Parendes, L.A., and J.A. Jones. 2000. Role of light availability and dispersal in exotic plant invasion along roads and streams in the H. J. Andrews Experimental Forest, Oregon. Conservation Biology 14: 64–75.CrossRefGoogle Scholar
  55. Parks, C.G., S.R. Radosevich, B.A. Endress, B.J. Naylor, D. Anzinger, L.J. Rew, B.D. Maxwell, and K.A. Dwire. 2005. Natural and land-use history of the northwest mountain regions (USA) in relation to patterns of plant invasions. Perspectives in Plant Ecology Systems 7: 137–158.CrossRefGoogle Scholar
  56. Pickering, C., and A. Mount. 2010. Do tourists disperse weed seed? A global review of unintentional human-mediated terrestrial seed dispersal on clothing, vehicles and horses. Journal of Sustainable Tourism 18: 239–256.CrossRefGoogle Scholar
  57. Pimentel, D., R. Zuniga, and D. Morrison. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics 52: 273–288.CrossRefGoogle Scholar
  58. Rejmanek, M., and D.M. Richardson. 1996. What attributes make some plant species more invasive? Ecology 77: 1655–1661.CrossRefGoogle Scholar
  59. Reynolds, G.D., and L.C. Bliss. 1986. Microenvironmental investigations of tephra covered surfaces at Mount St. Helens. In Mount St. Helens: Five years later, ed. S.A.C. Keller, 147–152. Cheney: Eastern Washington University.Google Scholar
  60. Schoenfelder, A.C., J.G. Bishop, H.M. Martinson, and W.F. Fagan. 2010. Resource use efficiency and community effects of invasive Hypochaeris radicata (Asteraceae) during primary succession. American Journal of Botany 97: 1772–1779.CrossRefGoogle Scholar
  61. Swanson, F.J., and J.J. Major. 2005. Physical events, environments, and geological-ecological interactions at Mount St. Helens: March 1980–2004. In Ecological responses to the 1980 eruption of Mount St. Helens, ed. V.H. Dale, F.J. Swanson, and C.M. Crisafulli, 27–44. New York: Springer.CrossRefGoogle Scholar
  62. Taylor, K., T. Brummer, M.L. Taper, A. Wing, and L.J. Rew. 2012. Human-mediated long-distance dispersal: An empirical evaluation of seed dispersal by vehicles. Biodiversity Research 18: 942–951.Google Scholar
  63. Titus, J.H., and E. Householder. 2007. Salvage logging and replanting reduce understory cover and richness compared to unsalvaged-unplanted sites at Mount St. Helens, Washington. Western North American Naturalist 67: 219–231.CrossRefGoogle Scholar
  64. Titus, J.H., S. Moore, M. Arnot, and P. Titus. 1998. Inventory of the vascular flora of the blast zone, Mount St. Helens, Washington. Madroño 45: 146–161.Google Scholar
  65. Trombulak, S.C., and C.A. Frissell. 2000. Review of ecological effects of roads on terrestrial and aquatic communities. Conservation Biology 14: 18–30.CrossRefGoogle Scholar
  66. Tsuyuzaki, S., J.H. Titus, and R. del Moral. 1997. Seedling establishment patterns on the Pumice Plain, Mount St. Helens, Washington. Journal of Vegetation Science 8: 727–734.CrossRefGoogle Scholar
  67. Tyser, R.W. 1992. Alien flora in grasslands adjacent to road and trail corridors in Glacier National Park, Montana (U.S.A.). Conservation Biology 6: 253–262.CrossRefGoogle Scholar
  68. U.S. Department of Agriculture (USDA). 2013. Mount St. Helens National Volcanic Monument. Accessed 14 May 2013.
  69. Usher, M.B. 1988. Biological invasions of nature reserves: A search for generalisations. Biological Conservation 44: 119–135.CrossRefGoogle Scholar
  70. Vitousek, P.M., C.M. D’Antonio, L.L. Loope, M. Rejmanek, and R. Westbrooks. 1997. Introduced species: A significant component of human-caused global change. New Zealand Journal of Ecology 21: 1–16.Google Scholar
  71. Walker, L.R., and R. del Moral. 2003. Primary succession and ecosystem rehabilitation. Cambridge: Cambridge University Press.CrossRefGoogle Scholar
  72. Wilson, E.O. 1992. The diversity of life. Cambridge, MA: Belknap Press.Google Scholar
  73. Wood, D.M., and R. del Moral. 1987. Mechanisms of early primary succession in subalpine habitats on Mount St. Helens. Ecology 68: 780–790.CrossRefGoogle Scholar
  74. ———. 1988. Colonizing plants on the Pumice Plains, Mount St. Helens, Washington. American Journal of Botany 75: 1228–1237.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media LLC 2018

Authors and Affiliations

  • Lindsey L. Karr
    • 1
  • Charles M. Crisafulli
    • 2
  • Jeffrey J. Gerwing
    • 1
  1. 1.Environmental Sciences and ManagementPortland State UniversityPortlandUSA
  2. 2.U.S. Department of Agriculture, Forest Service, Pacific Northwest Research StationMount St. Helens National Volcanic MonumentAmboyUSA

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