How to Interpret Invasive Species Distribution Maps
The gardening public might note that a distribution map does show that an invasive plant occurs in their county, or even their state, and conclude that it is not a concern where they live. However, this is not necessarily the case. Although many invasive species can tolerate a wide range of climates, it is unlikely that a species only known to be invasive in Southern Florida poses a threat in Saint Louis. However, species that are invasive in climatically similar regions such as parts of the Midwest, Mid-South, and Mid-Atlantic are also capable of invading our region.
Invasive species distribution maps underestimate the true distribution of species, since each county record must be formally documented and confirmed by an expert. An invasive species may actually be common in a particular county, but the distribution will only show a record for that county if this data has been properly reported. For instance, the distribution map for Japanese Wineberry (Rubus phoenicolasius) would suggest that it does not occur in Missouri, but it has actually been collected in the past two decades from seven Missouri counties, with vouchers in the Garden herbarium that have not yet been incorporated into the distribution map below (EDDMapS). Despite the shortcomings of this distribution map, the invasion of Japanese wineberry to the east of Saint Louis indicates that this species is capable of invading our region. The distribution map for wintercreeper (Euonymus fortunei) includes every single county in Indiana, but only several scattered counties in Missouri and Illinois. In reality, wintercreeper is one of the worst invasive plants in much of Illinois and Missouri; the distribution has simply been documented more comprehensively in Indiana.
Distribution maps