Effects of reduced mowing on invasive species management in roadside ecosystems
Roadside ecosystems represent a significant portion of the remaining semi-natural environment, comprising six billion acres in the United States. Of Rhode Island’s 13,510 miles of roads, 2,924 are state owned. With an average of four acres of mowed roadside per mile, the state of Rhode Island is responsible for managing 11,696 acres of roadside. These highly disturbed habitats support both invasive and rare native plant species and are buffers zones between highway stormwater runoff and natural areas. Because of this, roadside ecosystems are of great concern to land managers and transportation agencies. The Federal Highway Association has proposed reducing mowing to encourage native plant growth in roadsides and medians. Recently, the Rhode Island Department of Transportation (RIDOT) initiated a reduced mowing maintenance regime which decreased or eliminated mowing in some regions, but little monitoring of the effects of this change has occurred. This research assesses native versus invasive plant establishment in roadsides transitioning from heavily mowed to infrequently or never mowed ecosystems. We used Modified Whitaker vegetation surveys to calculate species richness and percent cover of native, introduced, and invasive plants to compare community composition under different management practices: Fully Mowed, Reduce Mowed, and Never Mowed (n=5).
Roadside sites that were never mowed by RIDOT and are secondary deciduous forests have a significantly higher native species richness (p=0.03) and average native plant percent cover (p<9.36-5) than sites that were frequently mowed. Additionally, sites that were not historically mowed have a significantly lower average introduced percent vegetation cover than frequently mowed and reduce mowed sites (p<7.59-5). We found no significant differences between frequently mowed and reduce mowed site community composition. Based on these results, we recommend that RIDOT cease mowing roadsides where vehicular safety will not be impaired and allow these areas go through natural succession and return to forest ecosystems. We will use this research to help RIDOT create a mowing policy which benefits both public interest and ecological services.