Freeways as Corridors for Plant Dispersal: A Case Study from Central Arizona

General ecological thought pertaining to plant biology, conservation, and urban areas has rested on two potentially contradictory underlying assumptions. The first is that non-native plants can spread easily from human developments to “pristine” areas. The second is that native plants cannot disperse through developed area. Both assume anthropogenic changes to ecosystems create conditions that favor non-native plants and hinder native species. However, it is just as likely that conditions in developed habitats will favor certain groups of plant species with similar functional traits, whether native or not. The function of corridors as conduit for plant movement has long been suggested, but the actual mechanisms at work in the process have only recently begun to be studied. Functional traits of species determine which are the most successful at each of the stages of invasion or range enlargement. The author studied the traits that allow both native and non-native plant species to disperse into freeway corridors, germinate, establish, reproduce, and then disperse along those corridors in Phoenix, Arizona. Sampling sites were selected along freeways throughout the Phoenix metro area, on both gravel-landscaped and non-landscaped road verges. Field methods included measurements of soil nitrogen content, seed bank sample collection and germination, vegetation surveys, and seed trapping. Some uncommon native species were found on the roadsides. More seeds were trapped at the gravel-landscaped sites, which also had greater average daily traffic loads than the non-landscaped sites. The seed bank study showed the opposite pattern, with higher numbers of seeds germinating in the samples from the non-landscaped sites. The majority of the seeds trapped in developed areas had adaptations for wind dispersal; the proportion was much smaller at the desert sites. Near the urbanized area there was little evidence of use of the freeway verges by birds or other animals. Currently, plants with weedy traits are the most likely to move along highways in the Arizona desert. The seed trapping data show that wind plays a large role in seed dispersal along the highways in developed areas. While both landscape design and maintenance choices play a large role in determining the initial roadside conditions and species assemblage, it appears that ongoing maintenance regimes and dry nitrogen deposition influence species composition and distribution along highways over the long term. This study adapted methods to gain insight into the functional traits of plants that are able to survive and potentially migrate along highways. Studying roadside plants using a functional trait approach will allow road ecologists to move toward assessing the ecological roles of design and maintenance practices. Eventually, it may be possible to manipulate design and maintenance processes to achieve goals in preventing or promoting migration of different groups of plants along roadways. This could result in benefits ranging from decreasing maintenance costs, to more effectively managing invasive species, and potentially to integrating larger ecological goals, such as promoting migration of species under changing climate conditions, into transportation system planning and maintenance.

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  • Supplemental Notes:
    • Abstract used with permission from the International Conference on Ecology and Transportation, organized by the Center for Transportation and the Environment, Institute for Transportation Research and Education, North Carolina State University.
  • Corporate Authors:

    North Carolina State University, Raleigh

    Center for Transportation and the Environment
    Raleigh, NC  United States  27695-8601
  • Authors:
    • Gade, Kristin J
  • Conference:
  • Publication Date: 2013


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References; Tables;
  • Pagination: 19p
  • Monograph Title: Proceedings of the 2013 International Conference on Ecology and Transportation (ICOET 2013)

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Filing Info

  • Accession Number: 01558280
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 30 2015 9:36AM