Dominance of invasive Johnsongrass in roadside vegetation of Serbia

Roads, railways and watercourses represent major terrestrial invasion corridors, which enable long-distance dispersal and transport of invasive alien plants between previously isolated regions. Johnsongrass (Sorghum halepense (L.) Pers.) is a highly invasive perennial weed species of cosmopolitan distribution. It forms dense, monodominant stands, which can crowd out native vegetation. Given its importance in agricultural production, especially in light of its multiple herbicide resistance, and the recognition of roads as major non-agricultural areas for Johnsongrass spread, our aim was to evaluate the role of roads as linear corridors facilitating its spread in Serbia. Field research was carried out in July-September of 2018-2020, at a total of 205 field sites. These field sites were distributed along highways and major state roads in Serbia, with 100 m 2 belt transects set up parallel to the road, in every section of the roadside terrain. Cover values of the roadside vegetation were expressed in % of the transect area. Correlation between the Johnsongrass invasion (presence and cover) and selected characteristics of the field site were analyzed using linear regression analysis in Statistica software. Johnosongrass was recorded at 57% of field sites (55% of relevés). In the majority of field sites (64%), its cover ranged between 5% and 50% of the transect. However, more than 10% of transects contained dense stands: 15 with 51–75% cover and five fully dominated (>75%). Records of its presence and dominance were concentrated in the northern, low-lying part of Serbia, where at two field sites it formed nearly monodominant stands (>90% cover). While its presence and cover were negatively correlated with altitude of the field site, both were positively correlated with the number of other aliens plants in the transect.