The number of invasive exotic plant species establishing in the United States is continuing to rise. When prevention
of exotic species from entering into a country fails at the national level and the species establishes, reproduces,
spreads, and becomes invasive, the most successful action at a local level is early detection followed eradication.
We have developed a simple geographic information system (GIS) analysis for developing watch lists for early
detection of invasive exotic plants that relies upon currently available species distribution data coupled with
environmental data to aid in describing coarse-scale potential distributions. This GIS analysis tool develops
environmental envelopes for species based upon the known distribution of a species thought to be invasive and
represents the first approximation of its potential habitat while the necessary data are collected to perform more in-depth analyses. To validate this method we looked at a time series of species distributions for 66 species in Pacific
Northwest, and northern Rocky Mountain counties. The time series analysis presented here did select counties that
the invasive exotic weeds invaded in subsequent years, showing that this technique could be useful in developing
watch lists for the spread of particular exotic species. We applied this same habitat-matching model based upon
bioclimaric envelopes to 100 invasive exotics with various levels of known distributions within continental U.S.
counties. For species with climatically limited distributions, county watch lists describe county-specific vulnerability
to invasion. Species with matching habitats in a county would be added to that county's list. These watch lists can
influence management decisions for early warning, control prioritization, and targeted research to determine specific
locations within vulnerable counties. This tool provides useful information for rapid assessment of the potential
distribution based upon climate envelopes of current distributions for new invasive exotic species.