gin data recorded in trail register books to spatial cadastral data (Federal Information Processing Standards, FIPS). If the origin information and the FIPS data could not be matched, we examined the entry to determine if the reported origin was part of a larger town (e.g., boroughs of NYC) or a misspelling. If we could not determine the exact location of a visitor, we removed this entry.

ields include group size, length of stay, and user days (defined as group size multiplied by the length of stay), as well as visitor origin information (location of residence). Only entries with valid origin data and those orginating from the states of Connecticut (CT), Massachusetts (MA), Maine (ME), New Hampshire (NH), New Jersey (NJ), New York (NY), Pennsylvania (PA), Rhode Island (RI), and Vermont (VT) are included in this dataset.

osystem Health 2019), and (3) iMapInvasives (NatureServe 2019). Each entry was updated with the currently-accepted and previously-accepted scientific names based from ITIS (2019). Previously-accepted scientific names were retained in the case that an invasive plant record was collected using that name. All common names were also retained. We selected only observations made prior to 2012 from states of CT, MA, ME, NH, NJ, NY, PA, RI, VT.

the group size in origin data by town and trail register. Using these data, we computed a trail-town exposure score: the amount of potential exposure per species to each trailhead per town. We computed this score by multiplying the species’ total number of observations per town and the number of visitors per town. From these values, we computed a raw total exposure potential per species per trailhead by summing the trail-town exposure score across all towns. We log-transformed the raw total exposure score due to its skewed distribution and then normalized these values based on a pooled distribution of the scores across all trailheads. This resulted in transfer risk potential score per species per trailhead. It can be interpreted as the relative risk of that invasive plant species being inadvertently transported to that location.