Sustain Our Nation's Forests and Grasslands

Discerning the role of roads in driving forest plant invasions

Researchers found that land use within ‘road effect zones’ is an important predictor of forest plant invasions. Photo courtesy of Larry Korhnak, InterfaceSouth.

NORTH CAROLINA – Roads provide a means for moving people and products, but they can also allow hitchhiking organisms to spread. Some exotic invasive plants thrive on the disturbance created by road construction that displaces native plants.

A new study led by Kurt Riitters, USDA Forest Service research ecologist with the SRS Eastern Forest Environmental Threat Assessment Center, found that the presence of a road may be less important than the presence of farms and other human activities.

“In the eastern U.S., a third of all forested areas are within 650 feet of a road, and invasive plants are found on half of the plots monitored by the Forest Inventory and Analysis program,” says Riitters. “While there is little doubt that roads are linked to forest plant invasions at local scales, effective resource conservation at regional scales requires an understanding of other factors linked to both roads and invasions across the larger landscape.”

To gain this understanding, researchers developed a series of models that allowed them to see the incremental influences of land use (including agriculture and development), forest fragmentation, local site conditions and regional ecosystem characteristics in comparison to road proximity effects in eastern U.S. forest plant invasions.

Their results were published in the journal Diversity and Distributions. The team used FIA data collected on more than 23,000 forested plots, excluding urban and residential forests, between 2001 and 2011. The data indicated the presence or absence of invasive plants and classified plots as high, medium, or low productivity sites.

Results of the study demonstrate the value of the modern FIA program for answering non-traditional forest inventory questions. Managers can use the findings to develop regional strategies to control or eradicate invasive plants. Scientists monitoring forests and developing risk assessments can also apply the model results.

“Because roads and human activities surrounding them are so pervasive in the East, we should be thinking of ‘human impact zones’ instead of ‘road effect zones,’” adds Riitters. “The risk of forest plant invasions cannot be evaluated only on the basis of distance from a road. The context of the road is key.”

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