A Survey of Non-Native Plants Along Roadsides in the Central and Western States

Kathryn A. Yurkonis^1,2*, Janice M. Coons^1,3, Scott J. Meiners¹ and Susan E. Lewis².

 ¹Department of Biological Sciences, Eastern Illinois University, Charleston, IL

  ²Department of Biological Sciences, Carroll College, Waukesha, WI

  ³Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL

Abstract

Roadways serve as a dispersal corridor for non-native species. This study identified common non-native species along 100 mile interstate transects and 10 mile two-lane roadway transects in national protected areas throughout the north central and western states. For each transect, species frequency was calculated and analyzed using a Principle Components Analysis (PCA). Comparisons of non-native species for transects pooled across ecoregions indicated roadway type as a determinant of roadway vegetation. In grasslands, however, there were no significant differences in vegetation between roadway types, suggesting that interstate and two-lane roadways have similar vegetation impacts on a regional scale.

Introduction

Over 3.6 million km of roadways cover 8.1 million hectares (Forman, 1995).

Vehicles are a seed dispersal mechanism.

Roadway Vegetation:

Typically edge and generalist species (Forman, 1995).

Roadways contribute to spread of non-native plants (Trombulak & Frissell, 2000).

Intensity of corridor use is associated non-native species richness (Tyser & Worley, 1992; Parendes & Jones, 2000).

Objectives 

(1) What are common non-native roadside plant species? 

(2) Does roadside vegetation composition vary with roadway type across all ecoregions? Within ecoregions?

Methods

June 2002 recorded non-native species presence/absence on right roadway edge along ten 100 mile interstate transects (Figure 1) sampling every other mile to fencerow.  And eight 10 mile two-lane roadway transects (Figure 1) in national protected areas sampling every other tenth mile to 10m from the roadway edge.

Figure 1.

Species Identification:

Selected species easily visible from the roadside (i.e. forbs and flowering species).

Photo documentation and specimen collections (where applicable) were taken for unknown species.

For pooled transects and grassland transects:

Frequency of observed species/transect (0-50) was calculated for each sample location.

Principle Components Analysis (PCA) identified common floristic components.

Bivariate correlation identified species significantly correlated with PCA components.

Mann-Whitney test compared positions of interstate and two-lane roadway transects along PCA components.

Results 

Non-native roadside vegetation: 

26 non-native plants/genera were identified (Table 1) 

Most frequently observed species: 

Melilotus officinalis (Yellow sweet clover) 

Trogopogon dubius (Goatsbeard) 

Elaeagnus angustifolia (Russian Olive) 

Bromus sp. (Japanese Brome, Smooth Brome, Cheatgrass) 

Non-native roadside vegetation across ecoregions: 

Analysis included all roadway transects. Significant differences occur in non-native vegetation between interstates and two-lane roadways (P= 0.003) (Figure 2)

Figure 2.

Non-native roadside vegetation in grasslands:

Compared species frequency data along interstate (n=8) and national protected area (n=3) grassland transects.  No significant differences occurred in species distributions between interstate and national protected area transects (Figure 3).

Figure 3.

Discussion

26 non-native species or species groups identified along interstate and two-lane roadways.  Results may vary by time as well as a result of seasonal conditions (i.e. western droughts).

Significant differences occur in roadside vegetation composition between roadway types.

Additional sampling is needed for Midwestern national protected area roadways.

Non-native species for which significant differences occur between roadway types typically planted along interstate roadways.

No significant differences between interstate and national protected roadway vegetation.

Non-native vegetation along roadways in the north central and western states related to ecoregion.

References

Forman, Richard T. T. 1995. Land Mosaics: The Ecology of Landscapes and Regions. Cambridge University Press, New York.

Tyser, Robin W. and Christopher A. Worley. 1992. Alien Flora in Grasslands Adjacent to Road and Trail Corridors in Glacier National Park, Montana (U.S.A.). Conservation Biology. 6: 253-262.

Trombulak, Stephen C. and Christopher A. Frissell. 2000. Review of ecological effects of roads on terrestrial and aquatic communities. Conservation Biology. 14: 18-30.

Acknowledgements

Ann Clarbout, Shannon Beach and Eric Janssen.

National Science Foundation- Research Experience for Undergraduates program at Eastern Illinois University.

University of Illinois at Urbana-Champaign Natural Resources and Environmental Science Department and Special Undergraduate Research on the Environment program.