Do invasive plant species follow human activity into remote rangelands? If so, how far does that change extend?

An article published in the current issue of Rangeland Ecology & Management evaluates how invasive species follow human development across southwestern Wyoming. The authors associated the number and spread of introduced plants with environmental factors and then looked at the distance between heavily invaded areas and human-built features.

They began with the idea that as people develop a rural area, their actions encourage exotic plant species to move in. People change the original habitat by introducing foreign species and spreading them throughout the area, sometimes unintentionally. These changes stress native plants, making it easier for already aggressive invaders to put down strong roots and further stress native species into a downward-spiraling cycle. This cycle increases the challenge of managing rural lands.

The current study covered 3 million hectares of northern sagebrush steppe in southwestern Wyoming. The authors targeted infrastructure such as roads, oil and gas well pads, pipelines, and power lines and then created 1,000-m-long sample sites extending outward from these man-made features. They chose sites that reflected climate, soil, geology, topography, and dominant vegetation variations in the region. They then considered both these environmental factors and the distance from man-made features as they sampled invasive plants across the sites.

The authors expected that invasive species would be densest within 50 to 100 m of man-made features and drop steeply as the sample site became less disturbed. This pattern did appear in some cases. However, it was the extent of indirect human influence that most surprised the authors. Instead of finding fewer introduced plants 100 m or more from a road or well pad, they often did not see a decline until 500 or even 700 m out.

More invasive plant species lined informal roads than other human-built features, but all roads, well pads, and pipelines were surrounded by more invasive species compared with semiremote reference sites. In some cases, these exotic plants spread from man-made features so that the greater the distance, the greater the number of invasive plants in the sample site.

The occurrence and area occupied by invasive species in response to human development found in this study can help local managers better target their management activities. The authors also suggest that researchers may need to broaden their study areas around human structures to include the total area of invasive species and to exclude reference sites from this area.

Full text of the article “Human infrastructure and invasive plant occurrence across rangelands of southwestern Wyoming, USA,” Rangeland Ecology & Management, Vol. 67, No. 2, 2014, is now available.