East Coast: Where the Trees Don't Lose Their Leaves

I've always wondered where the leaves stay green throughout the year - on the East Coast. Why does this matter? West Coast natives will never understand this, how the combination of the East Coast mentality and continental climate can make you feel trapped by the climate. During a road trip from Philly to Florida at spring break one year, the sun came up right about as we were crossing from South Carolina into Georgia, and seeing the green forest around us, I felt like we'd escaped - like we had cheated the world. It's not even the temperature that can be grueling about a temperate zone winter - it's the colorlessness, the gray clouds and especially the brown trees. A friend from Georgia referred to the Pennsylvania winter's wan sun, clouds and dead trees as the Dead Land. I had the same experience when I moved to California, and drove across the country in December as I descended the Sierras and came into the foothills and Sacramento's eastern suburbs, again there was green. Again I felt like I had come back to life, and I was home.

So I had always wondered: where do the trees stay green?

I started to think I was going to have to learn to program somewhat, and find satellite images from August and February of the East Coast, and then (if I was being rigorous) look at the color value of each pixel and try to correlate that with vegetation. But these maps are already available. (I couldn't find them the last time I did this search.) The first map is from databasin.org. Although weather moves west to east (hence the East Coast being much less moderate), there is still an under-emphasized maritime moderation effect near the coast - for example, the robins don't migrate for the winter in suburban Philadelphia, but one county away in Berks, they do (they come back early February though.) So this map shows how the coastal deciduous zone ends right near the Virginia-North Carolina line, and then hugs the coast, a bit downhill of the Fall Line, maybe 100 miles from the ocean. The pattern continues as it bends around the Gulf Coast, trends a bit north in Louisiana, and then much to my surprise, bends back toward the coast to include Houston. West of that, the mountains and/or dryness of the climate dictate vegetation more than temperature. I can confirm - having flown into Houston at Christmas, I was quite surprised that the trees were brown. (Corpus Christi was still green.) What surprises me most is I think I expected the 40th parallel to dominate more over coastal effects (as the typical dividing line between temperate and subtropical) but this is not the case.

And speaking of the southeast - while you're social-distancing, don't all hike on the same trails! It happened in both California and now Georgia. Come on outdoorsy types. We're smarter than this. And I want more of us to stay alive!



It also confirms what I suspected about Virginia: it's really just Pennsylvania with nastier summers.

Below is a map of the Fall Line from gallivance.net, where the first hills begin. There's nothing like this on the West Coast, where instead of being a passive margin where the land just kind of "gives up" to the ocean, the mountains come right up to the water, sometimes a mile high within a few miles as in California's Central Coast. The Fall Line corresponds to agricultural development historically, the Black Belt, and where the mills were. Almost all of Pennsylvania is uphill from the Fall Line - it's already at the Falls Bridge/Schuylkill Aqueduct, and the Twin Bridges (ie, Roosevelt Boulevard - before Manayunk even!), which is why large vessels don't go upriver past Philly. (Imagine a parallel universe where they dock in Reading. With cruise ships as carriers of disease - norovirus for many years and now COVID-19 - that's probably a good thing.)




Above: from Wiki, the Falls Bridge, aka the Reading Railroad Bridge, and the Twin Bridges at the Fall Line on the Schuylkill in Philly. Below, a typical cruise ship (from Signal Horizon.)



Of course a lot of the non-deciduous forest in the Carolinas is pine forest. This map shows that the vegetation you'll see along I-95 heading south transitions from Loblolly pine to mangroves along the river and patches of chestnut oak.