These are results from the committee to assess the invasiveness of plants in New York State run by Marilyn Jordan of The Nature Conservancy on Long Island and Gerry Moore from the Brooklyn Botanic Garden.
The number of persisting non-native species in New York is 1405.
The number of persisting non-native species assessed as having a High or Very High invasive nature in New York as of January 2010 is 68.
So we can say that a minimum of ~5% of persisting non-native plant species in NYS are invasive.
Any increase in number of species assessed as invasive, or decrease in the number of non-native species thought to be persisting, would increase the calculated % invasive. It is possible (though probably less likely) that the number of non-native species assessed as invasive could decrease in the future, based on new information or interpretations of questions in the assessment form.
Marilyn J. Jordan, Ph.D.
Senior Conservation Scientist
The Nature Conservancy on Long Island