Part I: Ice Age Geology
Winter, 2000 (Vol. 27, no. 4)
An excursion into geology will seem far removed from your usual preoccupation with flowering plants. But it is necessary to an appreciation of what is now going on in the Connecticut landscape. There were no plants at all in this particular landscape for thousands of years until, that is, the last advance of the continental ice sheet — called the Wisconsin glaciation — stagnated in place, then rather abruptly melted back some 20,000 years ago. There were actually four advances and recessions of this continental ice sheet in the last two-and-one-half-million years. The latter half of this period is called the Pleistocene epoch. The details are still somewhat “iffy” because each advance obliterated most of the evidence of prior advances. Besides, fifty years is not a long time to clarify so complex a history.
Although Louis Agassiz first proposed the concept of a glacial age in 1837 from his studies of glaciers in the Alps, Glacial Geology is a new science, in the sense that someone living now might have known all the principals. Richard Foster Flint of Yale published the first textbook in 1947. Even college undergraduates, such as I was then, caught the excitement by joining in the annual field trips of Friends of the Pleistocene, where all the experts came to argue about interpretations on the ground. We saw how provisional particular interpretations were, and felt it might be fun to join the argument.
So, what have we learned about the causes of glaciation? Astronomers tell us that there are great cycles in the shape of the Earth’s elliptical orbit around the sun. For example, the ellipse itself varies over the millennia, the Earth’s axis tilts, and the equinoxes shift. These cycles, already identified as having 23-thousand, 41-thousand, and 1OO-thousand year durations, influence the warming we receive from the sun. The sun’s internal heat also varies, but our planet’s volcanic dust and greenhouse gases mask this effect. The large-scale timing of ice ages can therefore now be predicted reasonably, but not the incidence and extent of glaciation, thanks to the variables. The contemporary British biochemist, James Lovelock, who proposed the Gaia concept, calls this Earth’s relapsing fever. (The Gaia concept proposes that life on Earth not only made the atmosphere but regulates it.)
In the last half-century, also, geologists discovered that the continents wander (slide over and under) across the surface of the planet, a phenomenon called Plate Tectonics. Such movements are also likely to contract or expand oceans, and this disrupts the ocean currents that help redistribute the warm tropical waters that ameliorate climates at high latitudes. The dynamics of these currents are complex and sensitive, and thus precarious for us who have become adjusted to a particular climatic regime.
Add global warming by increased human emissions of carbon dioxide that accentuate normal greenhouse effects, and it is no wonder that positivists and ideologues among us can argue any climatic scenario they wish. Actually, because we are about half-way through an interglacial period, the long-term view calls for another cooling cycle. Ironically, the global warming our atmospheric emissions now foster may speed the transition by triggering feedback mechanisms that govern the extent of sea ice in the arctic. This may change regional humidity and temperature relations, lead to more snow accumulation over the short northern summer, and to the onset of another continental ice advance. There are thus two likely results: either, as newly potent geological agents, we extend the interglacial period, creating a sort of superinterglacial, or we speed the return of cold by unbalancing the natural processes. Either way, we probably won’t know until it happens to us. Those who know the most about these interrelationships are usually the most guarded in their predictions, but also often among the most concerned.
As you would suspect, tying up so much water in ice during a continental ice advance actually lowered sea level between 300 and 400 feet for a few thousand years. In the Northeast, this exposed the continental shelf. The shore was then over a hundred miles south of Long Island. When the climate warmed, the continental ice — which had extended beyond Cape Cod and Long Island — melted along its southern and eastern flanks, but was starved for snowfall on the north side. The term “glacial recession” is ambiguous because the ice sheet both stagnated in place, for lack of nourishment, and so melted back also.
Not only did sea level then rise with this new load of glacial melt waters, but the land which had been burdened by some 2000 feet or more of ice (as at New Haven) then rebounded. The “mile-thick” ice we often hear about remains problematic. That part of sea level change that can be credited to water volume is called eustatic; that part credited to the changing level of the land is called isostatic.
A final bit of introductory geology should record that Connecticut was host to two very large proglacial lakes (i.e., at the front of the ice) during the retreating phase, each of them a product of impounded glacial meltwater. When the ice front retreated to roughly the present-day Connecticut shoreline — about 18,000 years ago — sea level was still some 250 feet below its present stand. Long Island was built from glacial outwash deposits during this recession, and its coarser deposits (especially the more northern Harbor Hill Moraine) enclosed both the east and west ends of a long intervening depression that lay between Connecticut and Long Island. This closed basin then filled with meltwater to create what has been called Glacial Lake Connecticut. About 11,000 years ago this lake overflowed its constraining moraines, eroded them, and was drained. Not until 8000 years ago did sea level rise enough to begin refilling the old lake basin, slowly creating present-day Long Island Sound. Continuing field studies will modify the dates, but this version is drawn from “A Movable Shore,” an attractive and readable 1992 book by Peter C. Patton and James M. Kent.
Meanwhile, as the ice retreated to what is now Massachusetts, about 15,000 years ago, southward drainage of meltwaters in the Central Valley was blocked by sand and buried ice at Middletown. This impounded Glacial Lake Hitchcock which gradually extended northward to the Vermont border and persisted for a thousand years or so. When the lake overflowed its Middletown “dam,” it cut a new channel southeastward to Old Lyme, instead of to New Haven.
Part II: The Plant Migrations
Fall, 200 (Vol. 28, no. 2 & 3)
When the time is ripe, the imagination of one individual may set the stage for years of effort by others who catch the spark. This appears to be true for most human activities, and may even be true for most of the animal kingdom, since mimicry is widespread. To lead is to educate by showing the way.
Such a timely, imaginative individual was the biologist, G. Evelyn Hutchinson (1903-1991), who became a world-class ecologist at Yale University, where he taught and did research from 1928 to 1971. That mid-century was such a “ripe time” — what the Greeks and the New Testament authors called a kairos — seems evident because, then, all the sciences rather suddenly started to cross-fertilize one another.
Hutchinson’s observations on the biochemistry of Linsley Pond in North Branford, where he lived, generated a long series of stimulating commentaries on ecosystem interactions, and led to the publication of a three-volume opus, “Treatise on Limnology,” in 1975.
His work attracted talented students for a generation. Edwin S. Deevey, Margaret B. Davis, Estella Leopold, and Lucinda McWeeney fit this pattern for the history of vegetation in Connecticut.
Hutchinson taught Deevey, who then stayed at Yale from 1938 to 1962. Deevey taught Leopold (Ph.D. 1955), whose father Aldo had gotten a Master’s degree there in 1909. Deevey also worked with Davis, who came as a research associate in 1960 and 1961. In 1994 Leopold encouraged McWeeney to complete her doctoral work at Yale.
Deevey, Davis, and Leopold did the pioneering work in analyzing pollen deposits in Connecticut lakes and bogs.
Deevey’s early work was at Linsley Pond, Lydflyt Pond, Totoket Bog, Lake Quonnipaug, and Job’s Pond Kettle, all in New Haven County. Leopold worked at Totoket Bog and Durham Meadows. Davis worked at Roger’s Lake, in Old Lyme. McWeeney, currently herbarium assistant at Yale, carries on this work, and has made investigations at Pequot Cedar Swamp on the Mashantucket Reservation, and in the glacial Lake Hitchcock Basin, along with a growing number of Willimantic Basin archeological sites. She focuses on plant fossils other than pollen, the so-called macrofossils. It may be added that Peter Patton of Wesleyan University in MiddIetown, and the late William Niering of Connecticut College in New London, along with others, have studied and dated salt marshes, which are a sort of hinge point in assessing vegetation and its history in this State.
Recall that when the ice was at its maximum, about 20,000 years B.P. (before present), it extended slightly beyond present-day Cape Cod and Long Island. At that time sea level was lower and the continental shelf was exposed. We must not make the facile assumption that the advancing ice sheet simply “pushed” the vegetation southward. There was indeed no plant life where you now sit in Connecticut during the ice advance, but the exposed coastal plain beyond the ice (east and south) served as a refugium for plants and animals.
Ice caps, because they chill their surroundings, generate a quasi-permanent high-pressure area over themseIves, and are circled by strong anticyclonic (clockwise) winds. For our region, at the southeastern sector of the ice sheet, this meant strong easterlies and northeasterlies much of the time. These conditions created a periglacial climate, with permanently frozen ground (permafrost) and a great deal of frostheaving, resulting in patterned ground and rock fragmentation. Those society members who botanized Mount Washington in June, 1999, saw such frost polygons, one of which had seventeen inches of cIay at its center, and whose annual churning prevents colonization by plants.
The vegetation of such sites is called tundra, it is dominated by sedges, rushes, and low heaths. For years, then, “off-shore” Connecticut had a broad strip of tundra. When the ice melted back, and before sea-level had risen much, this coastal strip was apparently a highway for the northward invasion of more southern species that today occur only in protected sites along this ancient corridor. The small cactus, Opuntia, is such a “relict”. Finally, also during the melting phase, the materials carried by the ice and redeposited by meltwater as broad outwash plains had their fine particles picked up by the strong periglacial winds and redeposited as loess in sheltered places. This accounts for the scattered deposits of fine-sandy loam so valued now for agriculture.
Naturally, therefore, the first vegetation to recolonize the Connecticut mainIand when the ice retreated was tundra from the coastal refugium. It is this progress of vegetative types with climatic amelioration that Deevey and his paleontologists were tracking. First tundra, then taiga (Spruce-Fir-Larch), then a transition forest of Pine-HemIock-Northern hardwoods, and, eventually, the central hardwoods (Oak-Hickory, Chestnut, etc.), all from more southern refugia of their own, and each “migrating” at its own rate, so that the species arrived before the forest, as it were.
This of course only means that the composition of a stand of trees is time dependent. Despite the appealing, early-century presumptions of Frederick E. Clements and Lucy Braun, there is no “climatic climax” because the climate continues to change and every species responds individually. Plant “migration” is an abstraction. Plants prosper or die in place. It is the seed … wind-blown or carried by animals, or dropped nearby … that accounts for new colonizations, and these will vary with the method of dispersal, the condition of the new site, including climate, disturbances, etc.
Commanding as he was in his eclectic accomplishments, Evelyn Hutchinson yet had the humility to point out that one’s good luck in entering a tradition at the right time has much to do with one’s stature. Those who enter later, when the exciting outlines have been sketched in, will appear less remarkable. Deevey and Davis are the notable post-glacial vegetationists on the East Coast, and Leopold on the West Coast. McWeeney, though she is revising their early reports, has yet to capture Yale’s interest in a professorship to continue the local research.
It turned out that there are serious problems in interpreting pollen deposits in lake and bog sediments. Pollen is wind-blown, so its presence is only a clue to the proximity of the plants that released it. Whence did the wind blow, and how far away the releasers? Besides, cutting sections from a core where a half-inch accumulation may represent a century or more does not yield robust results. And prior to 1950 or so, researchers had no means of “dating” the pollen, such as Carbon-14 analysis now permits.
Nowadays, analysis of oxygen isotopes trapped in the GreenIand ice cap provides an increasingly reliable proxy climate record. And those who analyze deep ocean sediment cores tell us that there were probably several more glaciations during the Pleistocene than land explorations have so far revealed. This is why the macro-fossil people like chaffed plant remains. The source of the charcoal grew there. So did anaerobically preserved remains of seeds, needles, bark, and other plant fragments.
McWeeney’s current reconstruction of these events suggests that southeastern Connecticut had a periglacial climate from 15,200 to 12,500 years ago, and was therefore in tundra. It also confirms that Spruce-Fir-Larch and White Pine arrived by 12,000 B.P.; and that Red Oak, Black Ash, and Maple were present 10,000 or more years ago. This is a couple of thousand years earlier than the pollen record had suggested.
Finally, Patton showed that present-day salt marshes … some of them now with fifteen feet of peat … could not have accumulated until less than 3000 years ago, when rising sea level at last stabilized enough to permit this. What a perspective!
Part III: Global Warming or Precessional Cooling?
Winter, 2001 (Vol. 28, no. 4)
If global warming has set in, as is very likely, the Northeast will become even more a mosaic of vegetation types than it now is.
There is nothing uniform about such change, nor is it an averaging-out. The die is probably already cast. Nature has its own habits, and the changes we impose may take years to fully express themselves.
Tree species we have come to think of as typical of our region will falter. Others, now subordinate, will prosper, and the composition of the stands will change over the generations. Depending upon locale, temperature changes may be expressed as hotter, drier summers, warmer nights, or colder winters. The seasons will shift a week or two, or more. Water temperatures will lag, but they too will change. Water tables will fall. Then forestry, agriculture, fisheries, and the migratory schedules of birds, fish, and insects and the phenology of flowering and fruiting will have to adjust. Perhaps not drastically at first, though we cannot be sure. But significantly enough to make a real difference to those habituated to the existing schedule of events. Much of this we can adapt to in our generation, and the next, but the price may be high in some areas.
Ironically, the warming we are imposing may simply extend the interglacial period we now enjoy. In the long run, that is, in a few tens of thousands of years – again we can’t be sure – we are due for another cooling cycle, thus another Ice Age. We thus gamble with cycles we barely understand.
Perhaps a better title for this third, and final, contribution on the history of Connecticut’s recent post-glacial greening might be, “Who and Where are We?”
The new knowledge about our planet’s functionings acquired in just the last fifty years strains credulity. It reveals that the natural systems we have only just begun to understand a bit have an impetus of their own. It is our first glimpse into the deep history of our planet, an awakening for those who are listening. Unfortunately, not many have heard. The “noise” out there is deafening, a diversion funded by those who want only to sell us something.
The new vision suggests that our inherited notions of “special creation” for ourselves were a provincialism. That, rather, as so many other races have thought, the Earth is our mother. Our lives are short, so our biographies are mere snapshots. We must ask how, really, things came to be as they are. What processes rule history? Only then can we assess our impacts and their consequences.
It is, for example, a twentieth century revelation that humankind has a four-billion-year history. That evolution has produced other kingdoms, only to see them fall victim to extinctions generated by physical or biological forces that otherwise help build the diversities of life. That, as our numbers and cleverness have grown, we have become geological agents in our own right. That, consequently, it matters what we do, brief, as our potencies seem.
Consider the three million acres we call Connecticut. Only a small northwestern segment, west of Cameron’s Line – that great suture which runs from Greenwich to Barkhamsted – was part of proto-North America 450,000,000 years ago. Since then, thanks to plate tectonics, that original continent (craton) has traveled to Africa and collided with it. The collision erected the Appalachian chain. All that was “in the beginning.” North America then “returned” to its present geographic coordinates, taking part of Africa with it (the lower Connecticut River Valley, for our part), and accreting several slices of intervening terrain (now called terranes). All this, of course, prior the Ice Age, whose ice advances and retreats reshaped the old surfaces in the last million years and more. The final stages created the contemporary coast, that movable shore with which we have a love-hate relationship.
Freed of ice, the land rebounded somewhat and its surface was re-vegetated as outlined in Part II of this article (Fall 2000 issue). Early hunter-gatherers crossed from Asia to North America on the temporarily exposed land bridge called Beringia over 12,000 years ago, and reached New England about 7000 years ago. About 400 years ago Europeans invaded in turn, and cleared the forests to grow crops to feed the growing white population. They even imported black Africans, Chinese, and others to speed development. We (they are us) then moved most of the agriculture westward and mechanized it, thus creating today’s urban-suburban population.
This recent land-use reversal of course allowed forest to re-colonize the abandoned farmland – thirteen million acres of them in the Northeast – so that, in little more than a century, Connecticut has gone from sixty percent open land to over sixty percent wooded. This raises questions of forest policy we have been slow to ask. And the new awareness of global processes we have outlined is a challenge to a more inclusive conservation policy for the entire Connecticut landscape.
Aware, at last, that cultural change overrides biological evolution for us, we ought to inquire more closely into the nature of the political economy that dominates our lives. Conservation doctrine has been a genteel tradition. Since our world is changing faster than ever, it would pay to revisit it.
A first, impeccably conservative step, much neglected for two centuries or more, would be to insist on “least social cost” methods for all subsequent development. This was propounded by landscape architect Ian McHarg in a 1969 book, Design with Nature. Our public officials must be asked to do this, since it has become everyone’s duty to do so. Otherwise, the rape of the land will continue.
Secondly, we can foster more of the kind of land conservation The Nature Conservancy has pioneered. This takes land of the market, expressing a social preference. Privately and publicly, we should avowedly do this so as to foster the reconstruction of the cities, because this is where civilization flourishes is we make the necessary allocation of resources. No one who prospers in the richest nation the world has ever known should be condoned in saying that “We can’t afford it.”