Effects of terrestrial transport corridors and associated landscape context on invasion by forest plants
The construction, use, and maintenance ofterrestrial transport corridors [roads and railroads(TTCs)] facilitate the spread of invasive plants, butthe distances at which plants typically spread awayfrom TTCs, and how that process is mediated bylandscape context, is not well understood. We com-piled data on the number of invasive plant speciesper*672 m2plot (= invasive richness) from44,000?forest inventory plots in the eastern USA.Using a generalized linear model framework, weinvestigated how invasive richness is influenced bydistance from the nearest TTC, surrounding land usetype, and ecological province. Invasive richness inforests decreased as distance from the nearest TTCincreased. Directly adjacent to TTCs, there were anestimated 1.4±0.01 SE invasive plant species perplot compared to 0.8±0.01 and 0.2±0.01 species at1 and 3 km, respectively, away from the nearest TTC.Invasive richness was highest on plots associated witha combination of agriculture/development(2.1±0.03 species per plot) and in the MidwestBroadleaf Forest province (2.1±0.06). Our macro-scale analysis also demonstrated that rates of decay ininvasive richness away from TTCs were mediated bythe types of land use and ecological provinces withinwhich plots were located. The influences of TTCs andassociated activities (e.g., construction, travel) oninvasive plant richness were widespread across forestsof the eastern USA, but the relative importance ofTTCs for facilitating spread appears to be highlycontext dependent.