So, about twenty thousand years ago, Cape Cod, where I am sitting in Cottage #5 right now, was covered by ice. A mile or so thick, it flowed and ground along imperceptibly, grabbing anything at all loose and hauling it at least for short distances. Anything that had been growing and living in its path was pretty much doomed unless somehow a spot of ground was preserved in a little refugium, a place that for some reason the ice flowed around instead of over. They have those little refuges in Hawaii, too, places a flow of lava has missed, thus sparing from fire the plants and maybe animals that live on it. But mostly the land here on the Cape was scraped to nude.
Geology in New England is complicated. But suffice it to say that when the great glaciers began to recede, perhaps fifteen thousand years ago, a little of the Cape’s land (which is mostly glacial debris), and all of its attached continental shelf (now under the sea you know) was dry. This was because the still-receding glaciers continued to hold a lot of the world’s water as ice, and thus sea-level was much lower than now. It seems there were mammoths and other great creatures living on this exposed land.
Yes, there were mammoths wandering around on the continental shelf! Naturally they had to eat something, the big fellows, and since they were herbivorous, we know there were lots of plants to supply them. But those are all gone of course, flooded by rising seas. Mammoth plant-grinding teeth have been dredged up from what’s now the sea floor, on the now-flooded continental shelf. Awesome.
But here on the Cape proper (where I am sitting), very little was able to grow at that time. Not much soil was left, and of course it was cold, and the drying salt-filled wind howled over it. A tough life for a plant. However, Nature is inexorably determined, and at length lichen came.
Yes, the coming of the Lichen! Lichen is a marvelous thing, a partnership between an alga (which photosynthesizes) and a fungus (which lends structure to the enterprise). There are three forms of lichen, and the kind which really lays low (in all that wind, on rocks) is called crustose, which looks just like what you would think. You have seen it on rocks—black, white, green, even orange.
Lichen does a great thing: if it finds itself growing on a bare rock, eventually over its very long life, it can turn the rock surface where it is growing into soil, miniscule amounts of soil. It does this both by the persistent action of its structure against the rock, and also chemically, interacting with the rock. Thus a tiny bit of dirt is made.
So fast forward then, and some other tough plants appeared, low-growing, drought-and-wind tolerant plants, making their difficult living on the debris left by the retreated glaciers, and doubtless using a bit of the soil made by lichens. Many of these plants are what are called, after the landscape they inhabit, heath plants. There’s bearberry and broom crowberry and poverty grass. They hug the ground and the wind blows right over them.
But the land would have looked pretty barren. Here on the Cape there are still heathlands, and today they are a globally-endangered landscape. We took a walk among one of the largest stands of heathland plants in the country. You can see from the picture that there are no trees—too much wind and salt for trees. This is probably not too different from the way it looked after the glaciers retreated and there was finally enough dirt for stuff to make a living.
Away from the shore, though, inland, trees wanted to grow. Conditions were easier—not so much wind, and not much of that irritant, salt spray, and the climate was warming up, too. Tree seeds arrived, by wind from the east and south, by bird or mammal maybe, via the eat-and-poop strategy. A few managed to find a place to sprout, and in due course, after thousands of years, forest began to appear on the Cape.
Enter Humans, Stage Left.
Indians first, and then Europeans, with some overlap (the last Nauset Indian died only in 1901…).
In low swampy places left by chunks of glacial ice, white cedars had found a home, and eventually red maples too. On higher ground grew pitch pine and white pine, various kinds of black and white oaks, tupelo, beech, and by Colonial days, even ash and walnut. There were some really big trees here. The Cape was beautiful with trees.
Oh great, thought the Colonials. Look at these big trees! Boy, can we use all this wood or what!
They used the wood for houses, and for heating and cooking in the houses, and for everything in the houses to sit on and lie on and eat from, and to store things in. They used the wood for fences to enclose their livestock and farming fields, fields from which they had to clear the trees, naturally. They used the wood for tools. For carts and wheels, and for boats from which to fish.
You can see where this is going. By about 1800, all that great forest, that had sprung over millennia from lichen, as it were, in post-glacial times, was gone. Henry David Thoreau, visiting the Cape in mid-century, observed “…an exceedingly barren and desolate country, of a character which I can find no name for; such a surface, perhaps, as the bottom of the sea made dry land day before yesterday. It was covered with poverty-grass (so-called because it grew where nothing else would), and there was hardly a tree in sight…”
Well, having cleared the Cape of its wood, and anyhow there were new, modern materials at hand, the Colonials spread to other places, and the forests made a fresh start. Nowadays, a lot of trees grow on the Cape—locusts (brought here from away, and fast-growing), pitch pines again, red maples and cedars in the wet places, black and white oaks, most of them short and scrubby. Nobody cuts these trees down anymore unless they are sick unto death. So they are free to flourish.
There are a few remnants of forest left from the glory days. We went walking in one of them, a lush forest of beeches. Shade-tolerant plants filled in below. A pair of redback salamanders was found under a log. Red squirrels stared at us briefly and darted away. Some irritated blue jays yelled at us from the beech canopy. Beeches can sprout and grow in their own shade, so this forest is, for this landscape, a so-called climax forest, which supposedly will not be replaced by other plants.
Unless, of course, there is a violent storm, or a fire, which might take out some of the beeches, and thus open a patch to sunlight, in which a light-loving plant, such as a white pine, might make an attempt, and succeed.
Well, so it’s all set now, right? You’ve got the heathlands on the wind-swept east side of the Cape, and the current forest, your oaks and pines and locusts, and those little old-time deep-forest remnants that the Park Service now protects. You’ve got the glorious beaches with their grasses and such.
I mean, we have global warming and all, but that isn’t going to affect anything here on the Cape for ages yet, right? No glaciers in sight, no Colonials cutting down everything…yes, quite permanent a set of landscapes, probably.
Hmm. The other day we were over on the ocean side of the Cape, facing the Atlantic. In a high sand bank below the parking lot was a row of holes, dug by bank swallows, now flown off in migration to South America or Africa. And sifting down between the holes, from the bank above, runnels of sand. Agitated by the moderate wind, this sand bank was eroding right in front of us. On the bank above, trees, shrubs. Their ground being cut out from beneath them.
No climax communities here, or any other place. All is change, everywhere.