Abstract
Purple loosestrife (Lythrum salicaria L.) is an invasive herbaceous plant, frequently found in wetlands and along roadsides throughout northern New York State. Its propensity to create monoculture stands in wetlands has resulted in intensive management in parts of its range, including central New York and Ontario and Quebec. The goal of this study was identifying the extent of infestations and to determine factors that promote the spread of purple loosestrife in order to determine best land use practices to reduce the spread of this highly invasive wetland plant." We attempted to answer several questions: What is the level of infestation along roadsides? Does mowing contribute to the spread? How do culverts under roadways influence the spread? Between mid-July and mid-August in 2017–2019, we mapped all infestations along 150 km (93 miles) of state highway north of the Adirondack Park and south of the St. Lawrence River using the Environmental Systems Research Institute (ESRI) Collector app. We mapped the size and locations of infestations, in addition to collecting information on the plants within 1 m, recording over 100 additional species. The results of our preliminary analysis revealed significant increase in the number of plants over the study time (P < 0.001), including several hundred more infestations than had previously been recorded. We did not find any evidence that mowing promotes the spread of loosestrife. There were many more individual infestations in ditches along highways, but much larger and denser infestations in wetlands (P = 0.003 in 2019). We observed that culverts, drainage conduits under roadways, frequently had purple loosestrife on both sides of the road. We also found that culverts appear to serve as corridors that promote the spread of purple loosestrife from one side of the road to the other. We recommend working with the local landowners and NYS Department of Transportation to contain the spread and continue to propagate and spread the biological control.
Mapping the Purple Menace: Spatiotemporal Distribution of Purple Loosestrife (Lythrum Salicaria) Along Roadsides in Northern New York State