Mapping Invasions: Examining the spread of purple loosestrife in the St. Lawrence River Valley

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Jessica Rogers, Environmental Studies, SUNY Potsdam, Potsdam, NY, Kamal Humagain, Geographic Information Science, SUNY Potsdam, Potsdam, NY and Adam J Pearson, Geology, SUNY Potsdam, Potsdam, NY

Background/Question/Methods
Purple loosestrife (Lythrum salicaria) is an herbaceous plant, frequently found in wetlands, and often found along roadsides. Its effects on wetlands has resulted in management with biological controls in parts of its range, including central New York, Ontario and Quebec. The goal of this study was to map infestations along roadsides in northern New York State with the intention of improving management. We were trying to answer several questions: What is the level of infestation along roadsides? Does mowing contribute to the spread? What other factors influence spread in our area? Between mid-July and mid-August in 2017-2019, we mapped all infestations along 93 miles of state highway north of the Adirondack Park and south of the St. Lawrence Rivers using the ESRI Collector app. In addition to the size and locations of infestations, we collected information on the plants within 1m, recording over 100 additional species. In addition, we recorded the presence and absence of herbivory to understand whether a biological control, Galerucella sp. had spread throughout our region.
Results/Conclusions
Our preliminary analysis revealed significant increase in plants over the study time (P<.001), including several hundred more infestations than had previously been recorded. The results of examining spread indicated no statistical or spatially clear evidence of spread by mowing over the scale of the study. This is likely causing smaller scale spreading than we captured and more years of data collecting may indicate a clearer connection or merely connecting from wetland to wetland. We did find, expectedly, larger infestations in wetlands along the highways (P <.003 in 2019) than along the highway in other water sources. During the study we noticed that culverts, tunnels underneath the highway carrying water, frequently had purple loosestrife on both sides of the road. We mapped all 223 culverts along our route and compared them to 223 randomly generated points along the route. The presence of purple loosestrife on both sides of the road was more likely at culverts than randomly generated areas (P<0.01). We assumed culverts were found where wetlands intersected with the route, but only 15 of 223 culverts intersected with wetlands. This suggests the strong contribution of culverts to the spread, particularly across roads, which is unlikely based on the plant’s ability to spread. We will work with local landowners and the department of transportation to contain the spread, and continue to propagate and spread the biological control.