, Volume 167, Issue 2, pp 481–491 | Cite as

Plant community diversity and native plant abundance decline with increasing abundance of an exotic annual grass

  • Kirk W. DaviesEmail author
Community ecology - Original Paper


Exotic plants are generally considered a serious problem in wildlands around the globe. However, some argue that the impacts of exotic plants have been exaggerated and that biodiversity and other important plant community characteristics are commonly improved with invasion. Thus, disagreement exists among ecologists as to the relationship of exotic plants with biodiversity and native plant communities. A better understanding of the relationships between exotic plants and native plant communities is needed to improve funding allocation and legislation regarding exotic plants, and justify and prioritize invasion management. To evaluate these relationships, 65 shrub–bunchgrass plant communities with varying densities of an exotic annual grass, Taeniatherum caput-medusae (L.) Nevski (medusahead), were sampled across 160,000 ha in southeastern Oregon, United States. Environmental factors were generally not correlated with plant community characteristics when exotic annual grass density was included in models. Plant diversity and species richness were negatively correlated with exotic annual grass density. Exotic annual grass density explained 62% of the variation in plant diversity. All native plant functional groups, except annual forbs, exhibited a negative relationship with T. caput-medusae. The results of this study suggest that T. caput-medusae invasions probably have substantial negative impacts on biodiversity and native plant communities. The strength of the relationships between plant community characteristics and T. caput-medusae density suggests that some exotic plants are a major force of change in plant communities and subsequently threaten ecosystem functions and processes. However, experimental studies are needed to fully substantiate that annual grass invasion is the cause of these observed correlations.


Biodiversity Conservation Invasive plants Medusahead Species richness Sagebrush 



The author appreciated Dr. Bruce Mackey’s (Area Statistician) assistance with the statistical analyses. Data collection by Shawna Lang, Matthew Coffman, Josh Monson, Eric Hough, Julie Garner, Tate Walters, Elaine Cramer, Carrie Cimo, Ryan Morgan, Jen Trenary, and Aleta Nafus was greatly appreciated. The author also thanks the Burns and Vale Bureau of Land Management for allowing this research project to occur on lands they administer. Reviews of the manuscript by Jeremy James, Matt Rinella, Chad Boyd, Dustin Johnson, and Derek Allen were greatly appreciated. Thoughtful reviews and constructive criticisms by Dr. Bryan Foster and anonymous reviewers were greatly valued. The Eastern Oregon Agricultural Research Center is jointly funded by the USDA-Agricultural Research Service and Oregon State University. These experiments comply with the current laws of the country in which they were performed.


  1. Adams SN, Engelhardt KAM (2009) Diversity declines in Microstegium vimineum (Japanese stiltgrass) patches. Biol Conserv 142:1003–1010CrossRefGoogle Scholar
  2. Aldridge CL, Nielsen SE, Beyer HL, Boyce MS, Connelly JW, Knick ST, Schroeder MA (2008) Range-wide patterns of greater sage-grouse persistence. Divers Distrib 14:983–994CrossRefGoogle Scholar
  3. Anderson EW, Borman MM, Krueger WC (1998) The ecological provinces of Oregon: a treatise on the basic ecological geography of the state. Oregon Agricultural Experiment Station, Corvallis, ORGoogle Scholar
  4. Belnap J (2003) Biological soil crusts in deserts: a short review of their role in soil fertility, stabilization, and water relations. Arch Hydrobiol 19:113–126Google Scholar
  5. Belnap J, Phillips SL (2001) Soil biota in an ungrazed grassland: response to annual grass (Bromus tectorum) invasion. Ecol Appl 11:1261–1275CrossRefGoogle Scholar
  6. Box GEP, Hunter JS, Hunter WG (2005) Statistics for experimenters: design, innovation, and discovery, 2nd edn. Wiley, Hoboken, NJGoogle Scholar
  7. Brewer S (2008) Declines in plant species richness and endemic plant species in longleaf pine savannas invaded by Imperata cylindrica. Biol Invasions 10:1257–1264CrossRefGoogle Scholar
  8. Brooks ML, D’Antonio CM, Richardson DM, Grace JB, Keeley J, DiTomaso JM, Hobbs RJ, Pellant M, Pyke D (2004) Effect of invasive alien plants on fire regimes. Bioscience 54:677–688CrossRefGoogle Scholar
  9. Canfield RH (1941) Application of the line interception methods in sampling range vegetation. J For 39:388–394Google Scholar
  10. Connelly JW, Braun CE (1997) Long-term changes in sage grouse Centrocercus urophasianus populations in western North America. Wildl Biol 3:229–234Google Scholar
  11. Connelly JW, Schroeder MA, Sands AR, Braun CE (2000) Guidelines to manage sage grouse populations and their habitats. Wildl Soc Bull 28:967–985Google Scholar
  12. Cronk CB, Fuller JL (1995) Plant invaders: the threat to natural ecosystems. Chapman and Hall, New YorkGoogle Scholar
  13. CS NR (1998) Precipitation maps. National Cartography & Geospatial Center, Fort WorthGoogle Scholar
  14. D’Antonio CM, Vitousek PM (1992) Biological invasions by exotic grasses, the grass/fire cycle, and global change. Annu Rev Ecol Syst 23:63–87Google Scholar
  15. D′Antonio C, Meyerson LA (2002) Exotic plant species as problems and solutions in ecological restoration: a synthesis. Restor Ecol 10:703–713CrossRefGoogle Scholar
  16. Davies KW (2008) Medusahead dispersal and establishment in sagebrush steppe plant communities. Range Ecol Manag 61:110–115CrossRefGoogle Scholar
  17. Davies KW, Bates JD (2010) Vegetation characteristics of mountain and Wyoming big sagebrush plant communities in the northern Great Basin. Range Ecol Manag 63:461–466CrossRefGoogle Scholar
  18. Davies KW, Johnson DD (2008) Managing medusahead in the Intermountain West is at a critical threshold. Rangelands 30:13–15CrossRefGoogle Scholar
  19. Davies KW, Sheley RL (2011) Promoting native vegetation and diversity in exotic annual grass infestations. Restor Ecol 19:159–165CrossRefGoogle Scholar
  20. Davies KW, Svejcar TJ (2008) Comparison of medusahead invaded and non-invaded Wyoming big sagebrush steppe in southeastern Oregon. Range Ecol Manag 61:623–629CrossRefGoogle Scholar
  21. Davies KW, Bates JD, Miller RF (2006) Vegetation characteristics across part of the Wyoming big sagebrush alliance. Range Ecol Manag 59:567–575CrossRefGoogle Scholar
  22. DiTomaso JM (2000) Invasive weeds in rangelands: species, impacts, and management. Weed Sci 48:255–265CrossRefGoogle Scholar
  23. Flory SL, Clay K (2010) Non-native grass invasion alters native plant composition in experimental communities. Biol Invasions 12:1285–1294CrossRefGoogle Scholar
  24. Gaertner M, Breeyen AD, Hui C, Richardson DM (2009) Impacts of alien plant invasions on species richness in Mediterranean-type ecosystems: a meta analysis. Prog Phys Geogr 33:319–338CrossRefGoogle Scholar
  25. Gee GW, Bauder JW (1986) Particle-size analysis. In: Klute A (ed) Methods of soil analysis, part 1. Physical and mineralogical methods. American Society of Agronomy and Soil Science Society of America, Madison, pp 383–411Google Scholar
  26. Gerber E, Krebs C, Murrell C, Moretti M, Rocklin R, Schaffner U (2008) Exotic invasive knotweeds (Fallopia spp.) negatively affect native plant and invertebrate assemblages in European riparian habitats. Biol Conserv 141:646–654CrossRefGoogle Scholar
  27. Harniss RO, Murray RB (1973) 30 years of vegetal change following burning of sagebrush-grass range. J Range Manag 26:322–325CrossRefGoogle Scholar
  28. Hironaka M (1994) Medusahead: natural successor to the cheatgrass type in the northern Great Basin. p 89–91. In: Monsen SB, Kitchen SG (comps.) Proceedings—ecology and management of annual rangelands. Boise, ID. May 18–21, 1992. United States Department of Agriculture, Forest Service, Intermountain Research Station. General Technical Report INT-GTR-313. Ogden, UTGoogle Scholar
  29. Hironaka M, Sindelar BW (1975) Growth characteristics of squirreltail seedlings in competition with medusahead. J Range Manag 28:283–285CrossRefGoogle Scholar
  30. Hobbs RJ, Atkins L (1988) Effect of disturbance and nutrient addition on communities in the Western Australian wheatbelt. Aust J Ecol 13:171–179CrossRefGoogle Scholar
  31. Hobbs RJ, Atkins L (1990) Fire related dynamics of a Banksia woodland in south-western Australia. Aust J Bot 38:97–110CrossRefGoogle Scholar
  32. Hooper DU, Vitousek PM (1998) Effects of plant composition and diversity on nutrient cycling. Ecol Monogr 68:121–149CrossRefGoogle Scholar
  33. Hughes F, Vitousek PM, Tunison T (1991) Alien grass invasion and fire in the seasonal submontane zone of Hawaii. Ecology 72:743–746CrossRefGoogle Scholar
  34. Humphrey LD (1984) Patterns and mechanisms of plant succession after fire on Artemisia-grass sites in southeastern Idaho. Vegetatio 57:91–101CrossRefGoogle Scholar
  35. James JJ, Davies KW, Sheley RL, Aanderud ZT (2008) Linking nitrogen partitioning and species abundance to invasion resistance in the Great Basin. Oecologia 156:637–648PubMedCrossRefGoogle Scholar
  36. Krebs CJ (1998) Ecological methodology, 2nd edn. Benjamin Cummings, Menlo Park, CAGoogle Scholar
  37. Lacey JR, Olson BE (1991) Economic and resource impacts of noxious range weeds. In: James LF, Evans JO, Ralphs MH, Child RD (eds) Noxious range weeds. Westview Press, Boulder, pp 5–16Google Scholar
  38. Lauenroth WK, Dodd JL, Sims PL (1978) The effects of water- and nitrogen-induced stresses on plant community structure in a semiarid grassland. Oecologia 36:211–222CrossRefGoogle Scholar
  39. Lepš J (2004) What do the biodiversity experiments tell us about consequences of plant species loss in the real world? Basic Appl Ecol 5:529–534CrossRefGoogle Scholar
  40. Levine JM (2000) Species diversity and biological invasions: relating local processes to community patterns. Science 288:852–854PubMedCrossRefGoogle Scholar
  41. Liu J, Dong M, Miao SL, Li ZY, Song MH, Wang RQ (2006) Invasive alien plants in China: role of clonality and geographical origin. Biol Invasions 8:1461–1470CrossRefGoogle Scholar
  42. Mack RN (1981) Invasion of Bromus tectorum L. into western North America: an ecological chronicle. Agro-Ecosystems 7:145–165CrossRefGoogle Scholar
  43. Mack RN, Simberloff D, Lonsdale WM, Evans H, Clout M, Bazzaz FA (2000) Biotic invasions: causes, epidemiology, global consequences, and control. Ecol Appl 10:689–710CrossRefGoogle Scholar
  44. Maron J, Marler M (2007) Native plant diversity resists invasion at both low and high resource levels. Ecology 88:2651–2661PubMedCrossRefGoogle Scholar
  45. Maron JL, Marler M (2008) Field-based competitive impacts between invaders and natives at varying resource supply. J Ecol 96:1187–1197CrossRefGoogle Scholar
  46. Masters RA, Sheley RL (2001) Principles and practices for managing rangeland invasive plants. J Range Manag 54:502–517CrossRefGoogle Scholar
  47. Meffin R, Miller AL, Hulme PE, Duncan RP (2010) Experimental introduction of the alien plant Hieracium lepidulum reveals no significant impact on montane plant communities in New Zealand. Divers Distrib 16:804–815CrossRefGoogle Scholar
  48. Milton S (2004) Grasses as invasive alien plants in South Africa. S Afr J Sci 100:69–75Google Scholar
  49. Moroń D, Lenda M, Skórka P, Szentgyörgyi H, Settele J, Woyciechowski M (2009) Wind pollinator communities are negatively affected by invasion of alien goldenrods in grassland landscapes. Biol Conserv 142:1322–1332CrossRefGoogle Scholar
  50. Naeem S, Knops JMH, Tilman D, Howe KM, Kennedy T, Gale S (2000) Plant diversity increases resistance to invasion in the absence of covarying extrinsic factors. Oikos 91:97–108CrossRefGoogle Scholar
  51. Olson BE (1999) Impacts of noxious weeds on ecologic and economic systems. In: Sheley RL, Petroff JK (eds) Biology and management of noxious rangeland weeds. Oregon State University Press, Corvallis, pp 4–18Google Scholar
  52. Oregon Climatic Service (2009) URL: Accessed 1 Sept 2009
  53. Pawson SM, McCarthy JK, Ledgard NJ, Didham RK (2010) Density-dependent impacts of exotic conifer invasion on grassland invertebrate assemblages. J Appl Ecol 47:1053–1062CrossRefGoogle Scholar
  54. Ponzetti JM, McCune BP (2001) Biotic soil crusts of Oregon’s shrub steppe: community composition in relation to soil chemistry, climate, and livestock activity. Bryologist 104:212–225CrossRefGoogle Scholar
  55. Purdie RW, Slatyer RO (1976) Vegetation succession after fire in sclerophyll woodland communities in south-eastern Australia. Aust J Ecol 1:223–236CrossRefGoogle Scholar
  56. Sagoff M (2005) Do non-native species threaten the natural environment? J Agric Environ Ethics 18:215–236CrossRefGoogle Scholar
  57. Sax DF, Gaines SD (2003) Species diversity: from global decreases to local increases. Trends Ecol Evol 18:561–566CrossRefGoogle Scholar
  58. Simberloff D (2005) Non-native species do threaten the natural environment. J Agric Environ Ethics 18:595–607CrossRefGoogle Scholar
  59. Tilman D (1999) The ecological consequences of changes in biodiversity: a search for general principles. Ecology 80:1455–1474Google Scholar
  60. Tilman D, Lehman CL, Thomson KT (1997) Plant diversity and ecosystem productivity: theoretical considerations. Proc Natl Acad Sci USA 94:1857–1861PubMedCrossRefGoogle Scholar
  61. Torell PJ, Erickson LC, Haas RH (1961) The medusahead problem in Idaho. Weeds 9:124–131CrossRefGoogle Scholar
  62. Wallestad R, Peterson JG, Eng RL (1975) Foods of adult sage grouse in central Montana. J Wildl Manag 39:628–630CrossRefGoogle Scholar
  63. Wambolt CL, Walhof KS, Frisina MR (2001) Recovery of big sagebrush communities after burning in south-western Montana. J Environ Manag 61:243–252CrossRefGoogle Scholar
  64. Whisenant SG (1990) Changing fire frequencies on Idaho’s Snake River Plains: ecological and management implications. In: McArthur ED, Romney EM, Smith SD, Tueller PT (eds) Cheatgrass invasion, shrub die-off, and other aspects of shrub biology and management(comps). Las Vegas, Nevada, pp 4–10Google Scholar
  65. Young JA (1992) Ecology and management of medusahead (Taeniatherum caput-medusae ssp. asperum [SIMK.] Melderis). Great Basin Nat 52:245–252Google Scholar
  66. Young K, Mangold J (2008) Medusahead outperforms squirreltail through interference and growth rate. Invasive Plant Sci Manag 1:73–81CrossRefGoogle Scholar

Copyright information

© Springer-Verlag(outside the USA) 2011

Authors and Affiliations

  1. 1.United States Department of Agriculture, Agricultural Research ServiceEastern Oregon Agricultural Research CenterBurnsUSA

Personalised recommendations