Roadside Soils: A Corridor for Invasion of Xeric Shrub by Nonindigenous Plants
Invasion of ecosystems by nonindigenous species threatens native biodiversity by altering species compositi& and site chsracteristics, and by potentially impacting endangered species. We compared plant communities and soil charact&tics along clay, limerock, and unmodified sand roadsides, and in adjacent clearcuts in xeric Florida sand pine scrub to test our hypothesis that modified soils used in constructing roadways provide a roadside corridor for invasion by nonindigenous species and species that are uncharacteristic of xeric scrub. Clay and limerockroadsides had more clay and less sand than sand roadsides or clearcuts. Soil pH and levels of several nutrients differed significantly ip limerock roadsides relative to the other substrates. In general, sand roadsides and clearcuts had higher characteristic but lower uncharactistic and non indigenous plant cover and number of species than modified roadside substrates. This suggests that xeric scrub may be somewhat resistant to invasion where native soils are present, even if disturbed. However, ptesencc of nonindigenous species suggests that roadways facilitate the transport of source propagules to otherwise remote sites. Especially where roadside and native soil chamcteristicsdiffer markedly, conditions may be enhanced for invasion by nonindigenous and uncharacteristic plants.