In the United States, subtropical climates are pretty much kept south of the Ohio river, outside of the higher Appalachian mountains, and curve off in the ends southward into Oklahoma and northward into coastal Connecticut. That's right, technically speaking, New York City is subtropical. Yeah, it can snow and get pretty icy there, but I have noticed that even in the coldest years, the snow does not last nearly as long it does back upstate and in the southern Great Lakes (back when it did, anyway) and points north and west. If you manage to find some of the more natural spaces of New Jersey and Long Island, it will most likely be some pine barrens that will feature an odd conversation piece like a magnolia or two. Until you hit South Carolina, where palmettos will start to poke up in the underbrush, this scenery will change little along the drier parts of the coastal plain.
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| Magnolias, Baldcypress, Pines, and company at Jamestown National Historic Site. |
How about a bit further inland, past the Appalachians? Well, the changes will be a bit more subtle. Evergreen Rhododendrons and Azaleas will start showing up in the more rugged parts, and some of the coniferous trees will disappear until they are replaced by southern species in Tennessee. As would be the case with developed land on the east coast, though, one would be more likely to notice things like magnolias being planted in increasing frequency the further south one travels. To my knowledge, the first Southern Magnolia (Magnolia Grandiflora) one can encounter along the main travel routes is in Bowling Green, Kentucky at some hotel parking lot. Back a few years ago, it stuck out like a sore thumb in a cold March landscape. Apparently people in Cincinnati have started growing palms in their yards, so the transition zone could be noticeable even further north.
Naturally speaking, a fine indicator of the edge of subtropical land would be the presence of Baldcypress stands along the major rivers. The furthest northern ones can be found in Indiana and Delaware. In Arkansas and Virginia they start getting draped with Spanish Moss. This is probably where the tropical part of subtropical starts making more sense, but again, same-elevation climate transitions are not usually as plain as a line drawn on the map. In North America, this is especially true.
You see, we have no major east-west mountain ranges here that can block Arctic winter cold fronts. The fact that warmer weather can even persist so far north at all is largely due to the Gulf of Mexico, which is a sauna that keeps sending heat and humidity north. In contrast, we also have Hudson Bay, which not only can fight back against the Gulf rather well, but is responsible for maintaining the world's southernmost tundra on our northern half of the planet, right along the coast in Ontario. About ten thousand years ago and earlier, it was also responsible for maintaining the continental ice sheet across much of Canada and the northern United States. These days, the Gulf seems to be winning the tug of war, but now and then even during our recent mild years, the frigid north can send hard freezes as far south as Miami and Tampico. In fact, chilly nights in the lower forties have even been reported in Cuba and Veracruz, places that are definitely well within the limits of true tropical.
Perhaps the northern edge of the subtropical world gets noticed a bit more by someone from northern Ontario. Heck, I was shocked when I moved to Detroit and first ran into "southern" trees like Tulip trees and hot and steamy Ash tree swamps. In any event, the next time you take a car trip, you might notice the same subtle changes as you head toward Dixie.
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