Islands are interesting habitats from an invasive species perspective - little chunks of land to which there are few vectors of introduction. States, provinces, even countries might act like they are islands, but their borders are virtually ignored by nonnative plants and animals.
This is one of the reasons why the Electronic Field Guide to the Invasive Plants of Nantucket is so interesting. On first glance, it reads like a who's who of invasive plant fact sheets. But it is worth a closer look, and not just because I am one of the authors of the project :-).
The 78 plant species currently listed were subject to a risk assessment modeled after the one completed by the state of Massachusetts (.pdf), but focused on Nantucket. One of the most interesting things, to me, is to compare the resulting list to the one compiled for the whole state. For example, there are species listed as invasive by the state of Massachusetts that have never been found on Nantucket Island, like glossy buckthorn (Frangula alnus) and lesser celandine (Ranunculus ficaria). Why are they not on Nantucket? Are conditions inhospitable or are there no vectors of introduction? Certainly special attention needs to be paid to prevent these known invaders from becoming established on the island.
There are also species categorized as invasive on Nantucket that are not considered a problem by the state of Massachusetts, like saltspray rose (Rosa rugosa) and white poplar (Populus alba). Also, we include pitch pine (Pinus rigida - likely a controversial listing since pitch pine is native to Massachusetts but not to Nantucket. Terms like "widespread" and "dense stands" can take on a different meaning when the area being evaluated is an island covering less than 50 square miles.
You can explore the guide on your own using the Search link on the website (left side of the page). Of course, the usual disclaimer must appear here: The plant list compiled for the Electronic Field Guide to the Invasive Plants of Nantucket has no legal status.