Roads and Transmission Corridors Aid Plant Invasions

By Garry Rogers

Roads and Transmission Corridors

Any type of construction destroys vegetation and disturbs the surrounding area.  Roads and transmission corridors do even more.

New Pipeline in Central Arizona.  Native chaparral removed, heavily grazed, constant traffic.

New Pipeline in Central Arizona. Native chaparral removed, heavily grazed, constant traffic.

Throughout human history roads and trails have been the principal routes for long-distance weed dispersal (Cousens and Mortimer 1995).  During the past century, power lines and pipelines have spread across the land.  Their construction removes vascular plants (Vasek et al. 1975a, 1975b), BSCs (Belnap 2001), and AMFs, and prepares the soil for colonizing weeds.  New lines often do not follow existing roads and corridors.  Instead, they take direct routes that allow weeds to disperse to areas they would not reach using their own dispersal mechanisms (e.g., Tyser and Worley 1992, Wein et al. 1992, Zink et al. 1995).

Weeds spread with surprising speed along roads and transmission corridors (Macfarlane 1997, Trombulak and Frissell 2000, Pauchard and Alaback 2004, Brisson et al. 2009, Mortensen et al. 2009).  The primary dispersal vectors are wind, inspection vehicles, livestock grazing, and recreation vehicles. 

Recreational vehicles are the major dispersal vector along corridors near large cities.  Bob Frenkel (1970) analyzed the sediment traps in car washes and found that cars carried seeds and viable roots and joints of hundreds of weed species.

Fire Tolerant Weeds Replacing Native Shrubs

Fire Tolerant Weeds Replacing Native Shrubs on Black Mesa

Roads are the most common origin for human-caused fires.  Small fires accidentally ignited beside roads and railroads provide many opportunities for invasive weeds to establish an outpost from which to spread into adjacent vegetation.  The loss of native species on Black Mesa mentioned in my earlier post, occurred because the invasive species tolerated frequent human-caused fires better than the natives.

Road maintenance, mowing, and herbicides create constant turmoil on roadsides.  Along fenced roadways, native vegetation sometimes survives in ungrazed strips just beyond the reach of road maintenance.  To me, the strips often appear as tarnished relics of the natural past.  Tarnished, because they are narrow islands besieged on one side by invasive species and human impacts beside the roads, and on the other side by the cloud of seeds from the invasive species in the livestock region beyond the fence.

There will be no end to new roads and transmission corridors.  Land managers can place short-term limits on invasive species by implementing a few basic requirements for roads and transmission routes:

  • Preliminary analyses of potential weed introductions, damage to biological soil crusts, and fire occurrence
  • Weed prevention (Singleton 2003:  9, Radosevich et al. 2007:  290)
  • Restoration of native plants, BSCs, and AMF (AISAC 2008:  90, Blumenthal et al. 2003, Clewell et al. 2005, Society for Ecological Restoration)

My home state of Arizona has some requirements, but they are often ignored by public agencies and large contractors.  The state’s major public power agency was recently found guilty of ignoring laws that required preservation of native cacti.  The penalties were insignificant, and they did not include restoration of lost species.

Recognizing the role that roads play in spreading weeds, land managers should not allow road construction in high-priority areas such as wilderness areas, national monuments, and national parks.  They should close or fence existing roads.

Education is important.  Many wilderness and backcountry road users might help with weed prevention if they knew how much their activities disturbed soils, disrupted animal life and spread habitat-destroying invasive species.

Road and Transmission Corridors References

AISAC.  2008.  Arizona Invasive Species Management Plan.  Arizona Invasive Species Advisory Council.  145 p.

Belnap, J., J. H. Kaltenecker, R. Rosentreter, J. Williams, S. Leonard, and D. Eldridge.  2001.  Biological soil crusts:  Ecology and management.  USDI BLM Tech Ref 1730-2.  111 p.

Blumenthal, D. M. N. R. Jordan, and E. L. Svenson.  2003.  Weed control as a rationale for restoration:  the example of tallgrass prairie.  Conservation Ecology 7:6. Online:

Brisson, J., S. deBlois, and C. Lavoie.  2009.  Roadsides as invasion pathway for common reed (Phragmites australis).  Invasive Plant Science and Management:  Ahead of Print.

Clewell, A., J. Rieger, and J. Munro.  2005.  Society for Ecological Restoration International, Tucson, AZ .  16 p.  Online:

Cousens, R. and M. Mortimer.  1995.  Dynamics of weed populations.  Cambridge University Press, New York.  337 p.

Frenkel, Robert E. 1970. Ruderal vegetation along some California roadsides. University of California Publications in Geography. University of California Press. Berkeley, CA.  V. 20. 140 p.

Macfarlane, G.  1997.  Roads and weeds:  Partners in crime.  Road RIPorter 2:6-7.

Mack, R. N.  1981.  Invasion of Bromus tectorum L. into western North America:  An ecological chronicle.  Agro-Ecosystems 7:145-165.

Marcus W. A., G. Milner, and B. D. Maxwell.  1998.  Spotted knapweed distribution in stock camps and trails of the Selway-Bitteroot wilderness. Great Basin Naturalist 58:156–166.

Maxwell, B. D., L. J. Rew, and R. Aspinall.  2003.  Exotic plant survey and monitoring: methods to discover distribution with low frequency occurrence. in T. Philippi and R. Doren, eds.  Proceedings of Detecting Invasive Exotic Plants, Workshop and Conference.  Florida International University, Miami, FL.

Mortensen, D. A., E. S. J. Rauschert, A. N. Nord, and B. P. Jones.  2009.  Forest roads facilitate the spread of invasive plants.  Invasive Plant Science and Management 2:191-199.

Parendes, L. A., and J. A. Jones.  2000.  Role of light availability and dispersal in exotic plant invasion along roads and streams in the H.J. Andrews Experimental Forest, Oregon. Conservation Biology 14:64–75.

Parks, C. G., S. R. Radosevich, B. A. Endress, B. J. Naylor, D. Anzinger, L. J. Rew, B. D. Maxwell, and K. A. Dwire.  2005a.  Natural and land-use history of the northwest mountain regions (U. S.A) in relation to patterns of plant invasion.  Perspectives on Plant Ecology and Systematics 7:137-158.

Pauchard, A.,  and P. B. Alaback.  2004.  Influence of elevation, land use, and landscape context on patterns of alien plant invasions along roadsides in protected areas of south-central Chile. Conservation Biology 18:238–251.

Radosevich, S. R., J. S. Holt, and C. Ghersa.   2007.  Weed ecology: implications for management‎.  589 p.

Singleton, S. R.  2003.  Integrated weed management plan, Missoula Field Office.  Bureau of Land Management, Missoula Field Office, Missoula, MT.  33 p.

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

Tyser,  R. W., and C. 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.

Vasek, F. C., H. B. Johnson, and D. H. Eslinger.  1975a.  Effects of pipeline construction on creosote bush scrub vegetation of the Mojave Desert.  Madroño 23:1-13.

Vasek, F. C., H. B. Johnson, and G. D. Brum.  1975b.  Effecs of power transmission lines on vegetation of the Mojave Desert.  Madroño 23:114-131.

Wein, R. W., G. Wein, S. Bahret, and W.J. Cody.  1992.  Northward invading non-native vascular plant species in and adjacent to Wood Buffalo National Park, Canada. Canadian Field Naturalist 106:216-224.

Zink, T. A., M. F. Allen, B. Heindl-Tenburen, and E. B. Allen.  1995.  The effect of a disturbance corridor on an ecological reserve.  Restoration Ecology 3:304-310.

4 thoughts on “Roads and Transmission Corridors Aid Plant Invasions

  1. Pingback: Just One Road Can Destroy a Forest | GarryRogers Nature Conservation


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