Tree-of-heaven is an invasive, nonnative species that invades newly disturbed areas and forms large monospecific stands. It was surveyed from a vehicle along 5,175 km of roads in Virginia in 2004, 2005, 2010, and 2011. Fifty-eight percent of every 1.6-km road segment had at least one tree-of-heaven. Mean density of tree-of-heaven throughout the roads surveyed in Virginia was 39 km⁻¹. The interaction between road classification (interstate, primary, and secondary) and physiographic region (mountain, piedmont, and tidewater) was significant; consequently, the density of tree-of-heaven along the different road classifications depended on the effect of the physiographic region and vice versa. Tree-of-heaven was fairly evenly distributed throughout Virginia ranging from 39 to 78% of 1.6-km road segments infested, but had a greater variation in density. Current areas with low densities could increase in density in the future. The highest density of tree-of-heaven was along interstate highways in the mountains (85 km⁻¹), followed by the tidewater (63 km⁻¹), and piedmont (46 km⁻¹) regions. Primary roads had a moderate density of tree-of-heaven with a range of 24 to 36 km⁻¹. Secondary roads had lower densities with 12 km⁻¹ and 41 km⁻¹ in the tidewater and mountain regions, respectively. Tree-of-heaven spreads primarily by wind-dispersed seeds from female trees, and populations bordering roadsides could serve as seed sources for further local and landscape spread.

Nomenclature: Tree-of-heaven, Ailanthus altissima (P. Mill.) Swingle

Management Implications: The invasive nonnative tree-of-heaven invades newly disturbed areas and forms large monospecific stands. The mean density of tree-of-heaven throughout the 5,175 km of roads surveyed in Virginia was 39 km⁻¹ with mean infestation of 58% of 1.6-km road segments. Interstate highways had the highest tree-of-heaven densities and high infestation frequencies. Populations bordering the roads serve as seed sources for further dispersal along roads and into open and forested areas. Efforts to minimize the impact and spread of tree-of-heaven should be concentrated along the leading edge of infestations. Chemical applications and felling of mature female trees would reduce seed dispersal along roads and into adjacent forests. Reducing the amount of disturbed soil and quickly reseeding with native seeds would help in reducing new invasions of tree-of-heaven.