Exotic plant species invade hot spots of native plant diversity

Thomas J. Stohlgren, Dan Binkley, Geneva W. Chong, Mohammed A. Kalkhan, Lisa D. Schell, Kelly A. Bull, Yuka Otsuki, Gregory Newman, Michael Bashkin, Son Yowhan

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847 Citations (Scopus)


Some theories and experimental studies suggest that areas of low plant species richness may be invaded more easily than areas of high plant species richness. We gathered nested-scale vegetation data on plant species richness, foliar cover, and frequency from 200 1-m2 subplots (20 1000-m2 modified-Whittaker plots) in the Colorado Rockies (USA), and 160 1-m2 subplots (16 1000-m2 plots) in the Central Grasslands in Colorado, Wyoming, South Dakota, and Minnesota (USA) to test the generality of this paradigm. At the 1-m2 scale, the paradigm was supported in four prairie types in the Central Grasslands, where exotic species richness declined with increasing plant species richness and cover. At the 1-m2 scale, five forest and meadow vegetation types in the Colorado Rockies contradicted the paradigm; exotic species richness increased with native-plant species richness and foliar cover. At the 1000-m2 plot scale (among vegetation types), 83% of the variance in exotic species richness in the Central Grasslands was explained by the total percentage of nitrogen in the soil and the cover of native plant species. In the Colorado Rockies, 69% of the variance in exotic species richness in 1000-m2 plots was explained by the number of native plant species and the total percentage of soil carbon. At landscape and biome scales, exotic species primarily invaded areas of high species richness in the four Central Grasslands sites and in the five Colorado Rockies vegetation types. For the nine vegetation types in both biomes, exotic species cover was positively correlated with mean foliar cover, mean soil percentage N, and the total number of exotic species. These patterns of invasibility depend on spatial scale, biome and vegetation type, spatial autocorrelation effects, availability of resources, and species-specific responses to grazing and other disturbances. We conclude that: (1) sites high in herbaceous foliar cover and soil fertility, and hot spots of plant diversity (and biodiversity), are invasible in many landscapes; and (2) this pattern may be more closely related to the degree resources are available in native plant communities, independent of species richness. Exotic plant invasions in rare habitats and distinctive plant communities pose a significant challenge to land managers and conservation biologists.

Original languageEnglish
Pages (from-to)25-46
Number of pages22
JournalEcological Monographs
Issue number1
Publication statusPublished - 1999 Feb


  • Biodiversity
  • Central Grasslands (USA) plant diversity patterns
  • Exotic plant invasions
  • Exotic species richness
  • Native plant diversity
  • Rocky Mountains (USA) plant diversity patterns
  • Spatial autocorrelation
  • Species composition overlap
  • Species-specific responses
  • Vegetation sampling, multiscale

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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