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Alien Plant Invasion in Mixed-grass Prairie: Effects
of Vegetation Type and Anthropogenic Disturbance

Diane L. Larson, Patrick J. Anderson, and Wesley Newton

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Abstract: The ability of alien plant species to invade a region depends not only on attributes of the plant, but on characteristics of the habitat being invaded. Here, we examine characteristics that may influence the success of alien plant invasion in mixed-grass prairie at Theodore Roosevelt National Park, in western North Dakota, USA. The park consists of two geographically separate units with similar vegetation types and management history, which allowed us to examine the effects of native vegetation type, anthropogenic disturbance, and the separate park units on the invasion of native plant communities by alien plant species common to counties surrounding both park units. If matters of chance related to availability of propagules and transient establishment opportunities determine the success of invasion, park unit and anthropogenic disturbance should better explain the variation in alien plant frequency. If invasibility is more strongly related to biotic or physical characteristics of the native plant communities, models of alien plant occurrence should include vegetation type as an explanatory variable. We examined >1300 transects across all vegetation types in both units of the park. Akaike's Information Criterion (AIC) indicated that the fully parameterized model, including the interaction among vegetation type, disturbance, and park unit, best described the distribution of both total number of alien plants per transect and frequency of alien plants on transects where they occurred. Although all vegetation types were invaded by alien plants, mesic communities had both greater numbers and higher frequencies of alien plants than did drier communities. A strong element of stochasticity, reflected in differences in frequencies of individual species between the two park units, suggests that prediction of risk of invasion will always involve uncertainty. In addition, despite well-documented associations between anthropogenic disturbance and alien plant invasion, five of the six most abundant alien species at Theodore Roosevelt National Park had distributions unrelated to disturbance. We recommend that vegetation type be explicitly taken into account when designing monitoring plans for alien species in natural areas.

Key words: Akaike's Information Criterion; alien plants; anthropogenic disturbance; Great Plains; mixed-grass prairie; native vegetation type; Theodore Roosevelt National Park, North Dakota (USA).

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This resource is based on the following source (Northern Prairie Publication 1119):

Larson, Diane L., Patrick J. Anderson, and Wesley Newton.  2001.  Alien 
     plant invasion in mixed-grass prairie: effects of vegetation type and 
     anthropogenic disturbance.  Ecological Applications 11(1):128-141.

This resource should be cited as:

Larson, Diane L., Patrick J. Anderson, and Wesley Newton.  2001.  Alien 
     plant invasion in mixed-grass prairie: effects of vegetation type and 
     anthropogenic disturbance.  Ecological Applications 11(1):128-141.
     Jamestown, ND: Northern Prairie Wildlife Research Center Online.  
     http://www.npwrc.usgs.gov/resource/plants/apinvas/index.htm  
     (Version 01OCT2001).

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Table of Contents

• Introduction
• Methods
  • Sampling
  • Data Analysis
• Results
  • Number and frequency of alien species
  • Presence of individual alien species on transects
• Discussion
• Management Implications
• Acknowledgements
• Literature Cited
• Appendix

Tables and Figures

• Table 1 -- Properties of vegetation in the north and south units of Theodore Roosevelt National Park, North Dakota, U.S.A.
• Table 2 -- Variables included in the three best models of vegetation structure, as determined by Akaike's Information Criterion (AIC).

• Figure 1 -- Akaike's Information Criterion identified the fully parameterized model, including the vegetation type × park unit × disturbance interaction, as the best model for both (a) mean number of alien species on transects and (b) mean frequency of alien plants on occupied transects.
• Figure 2 -- Proportion of transects on which Salsola iberica and Tragopogon dubius were found in 11 vegetation types at TRNP.
• Figure 3 -- Proportion of transects on which alien species were found in 11 vegetation types, by park unit.
• Figure 4 -- Proportion of transects occupied by species for which the best model contained park unit and/or disturbance.
• Figure 5 -- Proportion of transects occupied by Bromus inermis, for which the best model contained the interaction between vegetation type and disturbance.

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Diane L. Larson, USGS, Northern Prairie Wildlife Research Center, Minnesota Project Office, 100 Ecology Building, 1987 Upper Buford Circle, University of Minnesota, St. Paul, Minnesota 55108 USA. E-mail: dlarson@biosci.umn.edu
Patrick J. Anderson, USGS, Northern Prairie Wildlife Research Center, 8711 37th St. SE, Jamestown, North Dakota 58401 USA. Current address: USGS, 4512 McMurry Avenue, Fort Collins, Colorado 80525 USA.
Wesley Newton, USGS, Northern Prairie Wildlife Research Center, 8711 37th St. SE, Jamestown, North Dakota 58401 USA.

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