One that is definitely doing it and not getting a lot of attention is Eupatorium serotinum, late boneset.
This is a perennial with wind-dispersed seeds. It is abundant in the midwest and south, and until European settlement was probably not found in the northeast, not even in PA or NJ. It has now expanded as far north as eastern NY state and coastal Massachussets, and has also expanded north into Wisconsin and northwest into Minnesota.
It takes advantage of railroads and roadways; it grows well in the cleared areas along them. It can sometimes even grow in cracks in roads. Humans have thus created habitat for it along which it can spread.
Interestingly, I’m seeing no negative effects of it. Because the areas it is expanding into have close relatives, especially E. perfoliatum, which is widespread and extends much farther north, and to a lesser degree E. altissimum, which extends slightly farther north (and is also expanding in this fashion), there are plenty of insects that eat it, so it supports the food web a lot. And it is most common in human-altered habitats. Nor does it usually dominate or form monocultures.
It’s gotten to where I basically treat this species as native when doing ecological restoration work even if it’s not locally native.
Probably not. It didn’t spread as far as it is distributed now, when only Native Americans were living here. It was probably mainly the building of roads and railroads in modern Western society that led to its spread, at least from what I’ve read about it.
One bird I haven’t seen mentioned is the Anna’s Hummingbird (Calypte anna), historically it’s breeding range was restricted to Southern California and the northern Baja California Peninsula, in the past century it’s range has expanded north into BC, east into southern New Mexico , and is now colonizing southern Alaska. The expansion is generally associated with ornamental plants in residential.
The Rufous/Allen’s Hummingbird ( Selasphorus rufous/sasin) has also become more and more abundant as a winter visitor in the east, as for the reason for this expansion, the main agreement is that the Gulf and East coasts are becoming warmer, making the region more suitable as winter freezes become less common and less severe. A secondary reason is that more flowers are blooming in the winter, again due to the milder winters.
The Buff-bellied Hummingbird was once very rare north of the Rio Grande river, but is now being recorded in greater and greater numbers in the Gulf Coast for the same reasons listed above
Like the Anna’s Hummingbird, the Channel Island Allen Hummingbird (Selasphorus sasin sedentarius) has expanded greatly from a relatively small breeding range. They first appeared in around the late 1960s, in the Palos Verdes peninsula. Since then, they have expand south into San Diego Co, east into Riverside Co, and may have reached Ventura or Santa Barbra Co. They appear to be predominate in cities, likely because the presence of ornamental plants, which seems to be the same reason they made the move in the first place.