Making Sense of the Whole

Thus far on American Voyages we have been from Atlantic to Pacific, down well into central Mexico, and up to the spruce wilderness of the Canadian Boreal forests.  While this is a good thing for people wanting to see environments and landscapes very different from their own, such a jumping around approach tends to get both the reader and the writer a bit lost.  At the same time, a strange image of a continental mosaic pops into mind, with a desert occupying on square, a forest the next, and then some huge lake after that.  In truth, our landscapes tend to merge together rather nicely, with some species of flora and fauna being found in places as seemingly different as the Ottawa Valley and the mountains of Oaxaca, and a species like Silver Maple (Acer Saccharinum) can be found growing next to either a boreal spruce or a subtropical palm tree.  That said, one will be hard pressed to fail to notice a difference between a cypress swamp in Mississippi and an open stretch of shortgrass prairie in Montana.  So, how about an overall picture?  I found an excellent mapping resource just last night at BONAP, the Biota of North America Project.

For now, they seem to be focused on the United States, but they intend to expand their mapping projects to Canada and (gasp!) Mexico.  They have absolutely wonderful maps when it comes to the art of documenting transitions between ecozones (known as tension zones), so let's take a look at two.

Map the first, Tension Zones Between North and South:

As you can see, the lines are not a continuous path from coast to coast, nor should they be.  Changes in scenery from Canada to Mexico and the Gulf tend to be dependent on elevation and proximity to the moderating effects of large bodies of water as much as latitude.  Where lines disappear, this is because there is a ton of overlap between existing regions, as is the case in eastern Oklahoma, where east meets west meets south meets northeast meets, etc. etc.  Some of the lines should make sense immediately:

South End of Lake Huron to northern Minnesota: Southern limit of Boreal species.  North of this line the eastern pines, spruces, and birches are common.

Central Kentucky to Tulsa, Oklahoma: A distinct edge of some of the interior South/subtropics.  South of this line, almost exactly in fact, you can find Baldcypress (Taxodium Distichum) and Water Tupelo (Nyssa Aquatica) as well as many other southern species.

Richmond, Virginia to Macon, Georgia: Another distinct edge of some of the coastal South/subtropics.  On the Atlantic side of this line, which roughly coincides with the "fall-line" on which the great cities of Richmond, Raleigh, and Columbia were built, you can find things like the southern pines, a good helping of broadleafed evergreens, and even some palms.

Also of note is that even though this is a latitude-oriented map, the lines bend significantly south when encountering mountain ranges, and the red gets really dense in those areas.  The sudden change in elevation can create conditions which contrast very sharply between mere miles, a contrast which is perhaps the sharpest in extreme southwestern Utah, where the Great Basin and its plentiful acres of sagebrush and junipers quickly give way to hot desert species, like Mesquites, Creosote (Larrea Tridentata) and Joshua Trees (Yucca Brevifolia), as well as the sudden appearance of cultivated palms.  Other good examples of sharp contrast include the Sierra Nevada range of California, where giant trees clash with lower elevation grasslands and deserts, as well as the southern Appalachians, where northern pines and spruces well south of their normal broad range grow in close proximity to southern pines and other trees.

Map number two shows us how Tension zones fall between east and west:

While it might seem obvious that lines would be drawn between the mountains, plains, and eastern forests, some of them might require a bit more explanation.

The line stretching from Manitoba to near Houston pretty much serves as an excellent line between east and west in general.  Though numerous guide books insist on dividing species at the base of the mountains (the line from Alberta to El Paso, Texas), the truth of the situation is that the open plains west of the tallgrass prairies are really a gateway to the west.  Yes, you can still find eastern species creeping out along the rivers, but the overall look and lack of water in the landscape is pretty effective at telling travelers that they have left behind the watered east.  The line to the west of this, the base of the Rockies, pretty much takes you away from the land of the maples and oaks and into the land of junipers, pines, and fun things like a diversity of cacti, yuccas, and more cottonwoods than you can handle.  The line to the east of this, from Minnesota to the Gulf, is pretty much the eastern boundary of open prairie, where the grass admits that it can allow the oaks and other trees to win the eternal struggle of dominance.  Again, these are not sharp lines.  Forests pretty much cover a ton of Arkansas, Missouri, and Oklahoma.

The line from British Columbia to southern California indicates the sharpest contrast of all.  On the eastern side lies deserts and the mountain forests which mock them from above.  To the west of the line, which roughly coincides with the Pacific Crest along the Cascades and Sierras, is an entirely different world of temperate rainforests, chaparral, towering redwoods, sequoias, firs, and Sugar Pines (Pinus Lambertiana). You know, the land that people tripped over themselves to get to when heading to make a new life out west.

If the last sentence seemed significant at all, that's because it probably is.  Cultural differences on this continent have a lot to do with differences between climate and ecosystems.  The sorts of crops one could grow in each region definitely birthed cultural differences, especially between North and South or Midwest, Nearwest, and Northeast (Corn vs. Cotton).  An open range created a new sort of rough and ready culture of the high plains and intermountain west.  Ontario is roughly divisible between its northern and southern parts, or between Shield and Carolinian forests.  The desert lands of northern Mexico can seem like a different world from the tropics of Oaxaca and Veracruz.  Southern California decidedly is on another planet.  Sometimes the differences in land and people are sharp, even as they are often less clear.