ROADSIDE SOILS - A CORRIDOR FOR INVASION OF XERIC SCRUB BY NONINDIGENOUS PLANTS

Invasion of ecosystems by nonindigenous species threatens native biodi versity by altering species composition and site characteristics, and by potentially impacting endangered species. We compared plant communi ties and soil characteristics along clay, limerock, and unmodified san d roadsides, and in adjacent clearcuts in xeric Florida sand pine scru b to test our hypothesis that modified soils used in constructing road ways provide a roadside corridor for invasion by nonindigenous species and species that are uncharacteristic of xeric scrub. Clay and limero ck roadsides had more clay and less sand than sand roadsides or clearc uts. Soil pH and levels of several nutrients differed significantly in limerock roadsides relative to the other substrates. In general, sand roadsides and clearcuts had higher characteristic but lower uncharact eristic and nonindigenous plant cover and number of species than modif ied roadside substrates. This suggests that xeric scrub may be somewha t resistant to invasion where native soils are present, even if distur bed. However, presence of nonindigenous species suggests that roadways facilitate the transport of source propagules to otherwise remote sit es. Especially where roadside and native soil characteristics differ m arkedly, conditions may be enhanced for invasion by nonindigenous and uncharacteristic plants.