Effects of terrestrial transport corridors and associated landscape context on invasion by forest plants

Abstract

The construction, use, and maintenance of terrestrial transport corridors [roads and railroads (TTCs)] facilitate the spread of invasive plants, but the distances at which plants typically spread away from TTCs, and how that process is mediated by landscape context, is not well understood. We compiled data on the number of invasive plant species per ~ 672 m2 plot (= invasive richness) from 44,000 + forest inventory plots in the eastern USA. Using a generalized linear model framework, we investigated how invasive richness is influenced by distance from the nearest TTC, surrounding land use type, and ecological province. Invasive richness in forests decreased as distance from the nearest TTC increased. Directly adjacent to TTCs, there were an estimated 1.4 ± 0.01 SE invasive plant species per plot compared to 0.8 ± 0.01 and 0.2 ± 0.01 species at 1 and 3 km, respectively, away from the nearest TTC. Invasive richness was highest on plots associated with a combination of agriculture/development (2.1 ± 0.03 species per plot) and in the Midwest Broadleaf Forest province (2.1 ± 0.06). Our macroscale analysis also demonstrated that rates of decay in invasive richness away from TTCs were mediated by the types of land use and ecological provinces within which plots were located. The influences of TTCs and associated activities (e.g., construction, travel) on invasive plant richness were widespread across forests of the eastern USA, but the relative importance of TTCs for facilitating spread appears to be highly context dependent.