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Natural History of the Vermont Mountains

Old Rock

The north/south-trending ridges of the Green Mountains roll across Vermont like great ocean swells frozen in time, cloaked in the verdant forests that give them their name. That analogy bears a grain of truth, for most of Vermont’s rocks were formed from sediments that collected under a tropical sea, brimming with the first evolutionary burst of multicellular life, at the edge of a lifeless continent. These rocks were then thrust up on to the edge of the continent like a breaking wave, in two mountain-building events that spanned the time that the first plants and animals emerged from the sea to live on land, between about 450 and 350 million years ago.

Most—but not all—of Vermont’s rocks can be traced to events that began more than 550 million years ago, when sediments were accumulating on a tropical continental shelf and slope—square miles of intertidal sands, subtidal limy mud, and deep water deposits of clay. Onshore stood the remains of an ancient mountain range, the rejuvenated, billion-year-old, deep roots of which now form the Adirondacks.

Erosion of these old mountains was the source of the sediment accumulating on the continental slope and shelf. There was no life onshore, and now-extinct life forms such as trilobites, crinoids, and ammonites crawled over and burrowed in the sands and muds of the submerged shelf. Their fossil remains can be found today in some of the rocks of the Champlain Valley.

About 450 million years ago, th is slow accumulation of sediments was interrupted by the first of two major mountain-building events, called orogenies. These major geologic upheavals involve folding, faulting, and physical and chemical changes in rocks, and are driven by plate tectonics, the movement of large sections of the Earth’s crust (plates) as they pull apart, collide, or grind past one another. Mountain ranges are formed where two plates converge, and the kind of mountains formed depends primarily on the kind of plates and their movement.

Geologists recognize two kinds of crust. Oceanic crust is thin and dense and contains high amounts of iron and magnesium, giving the minerals and rocks it forms generally dark colors. Continental crust is thicker and more buoyant, and the rocks are rich in silica, a compound of silicon and oxygen that is the most abundant substance in the outer crust of the earth, and makes lighter colored minerals and rocks. Like the first skin on a pool of candle wax, the plates that make up the outer crust of the Earth float on the mantle, a layer of molten rock that extends more than halfway to the solid core.

Where two plate edges converge or collide and both are made of oceanic crust, one edge rides over the other, and the crust in the lower plate melts as it descends into the mantle. Over the 200 million-year life cycle of oceanic crust, it becomes coated with layers of muddy sediment that originates from erosion of the continents and settles to the ocean bottom. The underlying, dense oceanic crust is destroyed and recycled in the mantle, but the lower density continental sediment melts and bubbles back to the surface to form a curved chain of volcanic islands like the Aleutian Islands in Alaska.

As the last of the sediments that would become Vermont rock accumulated, just such a chain of islands was forming in the proto-Atlantic ocean that separated Vermont from its nearest continental neighbor, the future Africa. At the same time, the ocean between Vermont and the islands was slowly being eaten up. The islands gradually approached and finally crashed into North America, beginning about 345 million years ago. This island-continent collision caused Vermont’s first mountain-building event, the Taconic orogeny. The heart of the Taconic Mountains remains in southwestern Vermont and adjacent New York and Massachusetts.

The Taconic orogeny was followed by a 50-million-year period of relative quiet, during which the newly formed Taconic Mountains were ground down by erosion. The sediments from the mountains formed sheets of new sedimentary rock, some of which are still found in New York State, mainly south and west of the Adirondacks.

But during this period, the ocean continued to close, with future Africa and North America approaching one another like behemoth ocean liners on a collision course. The continental crust of Africa was riding over the oceanic crust attached to North America. In this second type of plate convergence, involving continental and oceanic crust, volcanoes and folded mountains form on the edge of the continent, similar to today’s Andes Mountains on the western edge of South America.

Eventually all of the oceanic crust separating the two continents was destroyed, and the inevitable collision resulted in the much bigger Acadian orogeny, which lasted from 375 to 335 million years ago, and was actually part of a one-two punch that formed the entire Appalachian chain, including Vermont’s Green Mountains, as well as associated mountains in Great Britain and Scandinavia. (These European peaks were later separated from the Appalachians when the Eurasian, North American, and African plates tore apart 200 million years ago.) This last crash is the third type of plate convergence, where continental crust meets continental crust, and both plate edges are too buoyant to be carried downwards into the mantle, so they collide in a kind of geologic train wreck.

In the Taconic and Acadian orogenies, the sediments on the continental edge were compressed and piled up by the force of the collision -- imagine taking a sheet of clay 1 inch thick and 10 inches wide and squeezing it until it is 10 inches thick and 1 inch wide. The rocks folded and cracked along fault lines, and the squeezing generated intense pressure and high temperatures which "cooked" the rock, causing the minerals in the rock to partially melt and change into new minerals, a process known as metamorphosis.

The style of faulting, folding, and metamorphosis depended on how close to the plate edge and how deeply buried the rocks were. In western Vermont, in the Champlain Valley, the rocks were set back from the edge and close to the surface so that they were brittle and tore along long, jagged lines, forming horizontal slices that were then stacked up, a process known as thrust faulting. Although they have been altered slightly, these rocks are physically and chemically similar to the sediments that went into them, often with clearly recognizable sedimentary layers and fossil remains.

Farther east and in the heart of the Green Mountains, the more deeply buried and more plastic rocks responded to the temperature and pressure by folding, forming a series of wrinkles as in layers of cloth. In the Taconic Mountains, the rocks were so severely folded that a whole fold fell over to the west, then the whole mass slid further west along a thrust fault, forming an overturned fold or nappe.

Metamorphism was also much more intense in the Green and Taconic Mountains, so that they are now made mainly of "well-cooked," erosion-resistant rocks such as schists, like the shiny green chlorite schist that greets hikers on Camels Hump. The original sediments and layers in these rocks are no longer recognizable; scientists infer their origin as continental shelf and slope sedimentary rocks from their composition and geologic context.

Although they are also made of schist and similar rocks, parts of eastern Vermont close to the Connecticut River, along with a continuous band in western New Hampshire, belong to an entirely different geologic province. These are the compressed and altered remains of the volcanic islands that collided with the continent during the Taconic orogeny, now welded into the mix of rocks that make up the present day eastern edge of North America.

After the continental collision that created the Appalachian Mountains, North America and Africa were welded together as sections of the supercontinent of Pangaea, and remained so for over 100 million years, a time that saw the emergence of dinosaurs and extensive land-based ecosystems. About 200 million years ago, it all began to fall apart, beginning with the opening of an ocean basin between northern and southern supercontinents, then splitting each of these with the opening of the Atlantic Ocean, which continues to widen by a few inches a year today.

The events described thus far created most but not quite all of the rocks found in Vermont. One of the state’s most famous rocks is the granite that is quarried in Barre and used in buildings and cemeteries all over the country. Granite and similar kinds of plutonic rock are formed when pools or bodies of molten rock (plutons), often at the roots of volcanoes, cool slowly deep underground. The Barre granite and similar rocks in the western White Mountains of New Hampshire were formed at about the same time as the Acadian orogeny (350 million years ago) when there was extensive melting due to the high temperature and pressure caused by continental collision.

Vermont has been geologically quiet for about 125 million years, but the bedrock formed over the past 550 million years continues to shape both the coarse and fine details of Vermont’s natural history. The lay of Vermont’s land -- the mountain spine and the river veins -- is largely controlled by the bedrock type and structure. The original mountains created during the mountain-building events so long ago are gone, ground away by hundreds of millions of years of erosion. But where rock-forming and mountain-building processes have put hard rocks close to today’s surface, whether they form the summits of the Green Mountains or the low hills in the Champlain valley, these rocks have resisted erosion, and stand higher than the softer rocks around them.

The general north/south grain of the Green Mountains and of the hills and valleys of western Vermont, which shows up clearly on regional topographic maps and in satellite photographs, follows the grain of the bedrock, which runs perpendicular to the compressive forces of the great continental train wreck. Regional and local climate is very much affected by this topography, as are Vermont’s plant, animal, and human communities.

A second way that Vermont’s rocks affect local natural history is through their chemistry. Most rock types can be loosely classed as acid or limy, but the acidity is not so much in the rocks themselves as in the soils that develop on them. Limestone and similar rocks contain minerals, chiefly calcite (calcium carbonate), that dissolve in water and counter the acidifying effect of the organic matter that plants contribute to soils, keeping the soil nearly neutral on the pH scale. The higher pH of limestone soils results in greater nutrient availability, so that growing conditions in soils developed over limy rocks can be considerably richer than in soils formed over acid rocks. Many of Vermont’s rare plants, as well as our richest forest communities, are found in the limy lowland soils.

Because they are soft and dissolve slowly in water, limy rocks are also easily eroded. They are found mainly in the Champlain Valley and its southern extension, the Valley of Vermont, which separates the Taconic Mountains from the Green Mountains, lowland areas where erosion has scooped away the soft rock from between the harder rocks of the mountains. Some rock types in the Green Mountains contain intermediate amounts of limy minerals, enough to have some benefit for local soils and plant communities.

New England’s geologic history encompasses most of the different kinds of geologic events that can happen in the Earth’s crust, all of which are still occurring on different parts of the Earth today. They are all part of enormous cycles of continental movement and mountain building, which can take 500 million to 1 billion years to complete and operate over continent- and ocean-sized areas. Today the Atlantic Ocean is still opening, but we can anticipate a time in the far distant future when the sediments now accumulating east of Bangor and Boston will be shattered, wrinkled, and shot through with volcanoes to become New England’s next mountains.

Hard Water

If the geologic changes of the last 300 million years could be made into a two-hour feature film, the mighty alpine mountain range created by the Acadian orogeny would melt away like a parking lot snow bank on an April day. All it takes is gravity and running water, slowly turning hard rock to gravel, sand, and clay and transporting the sediments, first to some distant ocean on the fringes of Pangaea and later to the widening Atlantic Ocean.

Water and gravity are still at work in Vermont today, but the finishing touches over most of Vermont’s landscape were added by water in solid form, over only the last 2 million years or so. In the two-hour movie, the last ice age would be little more than a flicker of white in the last few seconds, but the continental ice sheets of the Pleistocene epoch have had an impact on Vermont’s natural history far out of proportion to their brief duration.

On a global scale and over geologic time, the temperature and climate of the Earth as a whole has fluctuated dramatically -- this last is not, by a long shot, the first ice age -- responding at least in part to the continual rearrangement of the continents resulting from plate tectonics, the wobble of the Earth as it moves around the sun, and other factors. Beginning about two million years ago, the imbalances that lead to ice ages were well at work, and ice began to accumulate and spread over northern North America in the first of several successive waves of glaciation. The most recent wave of glaciation began about 100,000 years ago.

With its center in the middle of the Quebec-Labrador peninsula, the Laurentide Ice Sheet buried all of Vermont under 1 to 2 miles of ice by 18,000 years ago. At its farthest advance, it spread like a great white ruffled apron across central Pennsylvania and Ohio, then bending northwestwards through Indiana, Illinois, and on to Wisconsin. The islands off of southern New England -- Long Island, Block Island, Nantucket, and Martha’s Vineyard -- are parts of the ice sheet’s terminal moraine, which marks its point of farthest advance. Because so much water was locked up in the ice sheet, sea level was more than 350 feet lower than today, and the North American shoreline was much farther east.

Like running water, glacial erosion responds to the different rock types and to the overall lay of the land created by mountain building. As it flowed in a generally northwest to southeast direction, the ice sheet piled up against the Green Mountains like a surging tide, and began to overflow first through low points on the mountain ridges, carving deep, U-shaped notches like Hazen’s and Smuggler’s Notches in Vermont, and numerous others in the Adirondack and White mountains. The glaciers also carved high mountain cirques, or bowl-shaped depressions high on the mountains’ sides. The most famous of these eastern cirques is Tuckerman Ravine in New Hampshire, but less dramatic examples may be found on the sides of Mount Mansfield.

Eventually the ice flowed right over the summits of the mountains, rounding off the summits and plucking at their flanks to create steep ledges and cliffs, like those on Camels Hump and Mount Mansfield. Glaciers erode rock by scouring and plucking. The scouring action is like sanding wood with sandpaper, with rocks embedded in the ice acting as the grit and the ice acting as paper. This scouring action is most evident in glacial striae, parallel grooves in the surface of eroded rocks that run in the direction that the ice flowed over the rock. The rocky summit ridge of Mount Mansfield is, in places, grooved like corduroy from this scraping, as are many other rock outcrops throughout the state.

In plucking, water finds its way into cracks in the rock and widens them as it freezes, so that blocks of rock are pulled loose and mix in the base of the glacier like raisins in bread dough -- providing grit for abrasion. Thus, sediment is mixed into the glacier ice and carried along with. This sediment can range from boulders the size of houses down to microscopic particles of silt, which has a floury texture when dry.

Glacier ice can carve rock, but it cannot destroy matter, so what is eroded in one place is deposited in another. When ice melts, all the sediment it carries is dropped as a chunky mixture of dirt, pebbles, rocks, and boulders called till. Most of Vermont’s upland areas are covered by a blanket of till ranging in thickness from a few to tens of feet, so it is till, rather than bare rock, that is the starting point for soil formation in these areas. Rock fragments in till are sharp-edged or angular because they haven’t been tumbled and smoothed by running water.

Melting ice also feeds streams and rivers that may flow over the surface of the ice, in tunnels under the ice, alongside ice lobes, or out of the glacier’s snout. These streams pick up till sediments, carry them a distance, and deposit them in new landforms. Streams tumble the sediment, knocking off the corners so that the particles are rounded like the gravel and cobbles in a streambed.

The energy of a stream allows it to sort sediment in layers of different particle sizes, because as the water speeds up or slows down, it tends to pick up or drop particles in different size ranges. The farther running water carries sediment, the more rounding and sorting there is. The kames, eskers, and deltas formed by these processes are the most important source of sand and gravel in the state, and some of the best places to see these sediments in profile are in quarries, ranging from big commercial operations like the one visible from VT 116 in Hinesburg, to small farm "borrow pits", sometimes found along local roads and trails.

Glacial geologists can read a landscape by looking at the kinds of deposits they find. Are the deposits a jumble of all different kinds of rocks with sharp edges? Then it’s till. Are they alternating layers of sand and rounded cobbles? Then the deposits were carried by water, and may be dumped as a delta into a glacial lake, like deposits found near Lake Mansfield outside of Stowe.

Glaciers do more than move dirt: they create lakes. Lake basins, especially smaller ones, are ephemeral in geologic time, because they are rapidly filled in by sediment carried in by streams and rivers. Lake Champlain, the Great Lakes, and various other large, deep lakes in the northern tier of the United States and Canada were all scoured by ice sheets where they encountered already low-lying, soft rock. Smaller lakes are created where glacial deposits act as dams on small streams or as flooded glacial kettles, where a mass of ice left by a retreating glacier is buried in outwash and leaves a pond-sized or smaller depression after it melts away. Spectacle Pond in Brighton State Park is one of the best-known examples of this kind of pond formation.

The retreating Laurentide Ice Sheet also created even shorter-lived lakes, some lasting only a few hundred to a thousand years, not long enough to be seen as even a flicker in the two-hour film but plenty long enough to have a lasting impact on local natural history. As the ice began to retreat through the Green Mountains, a lobe of ice in the Champlain Valley dammed the westward drainage of the Winooski, Lamoille, and Missisquoi Rivers, forming large lakes at elevations over 1,000 feet above present sea level in the upper reaches of these river valleys. These lakes drained as the ice retreated, but the gravel beaches and stream deltas that formed along their shorelines remain.

The Connecticut River was dammed by a glacial moraine in central Connecticut, forming 200-mile-long Lake Hitchcock, which extended nearly to the three-way border between Vermont, New Hampshire, and Quebec. There were also several smaller high-level, ice-dammed lakes on smaller streams in the Green Mountains and piedmont regions.

But the biggest lake by far formed in the Champlain Valley beginning about 13,000 years ago, when the glacier plugged the northward flow of water out of the valley and meltwater fed a water body geologists call Lake Vermont, which covered much of Chittenden and Addison counties with water. Later, as the ice retreated north across the St. Lawrence Seaway, the Champlain Valley was flooded by salt water, and for a few thousand years whales, seals, and numerous other saltwater and seashore species called Vermont home.

As with the high level lakes, the old shorelines of Lake Vermont and the Champlain Sea are marked by extensive beach and delta deposits. Some of these are the substrate for unique plant communities, like the pine barrens in the area around Burlington, which developed on a sandy delta deposited by the Winooski River as it flowed into the Champlain Sea.

With the final ebb of the brackish waters of the Champlain Sea, the overall lay of the land in Vermont came close to its modern form. But gravity never rests. The steep cliff faces created by glacial erosion are still under attack by frost and gravity, and Vermont’s streams and rivers are once again tirelessly excavating till and outwash, recycling the materials as modern floodplains and deltas. And life, ranging from diminutive peat mosses to 200-foot white pines, from beaver to deer to humans, continues to shape the landscape.

Abenaki, sheep, and potash

As the glaciers retreated from Vermont roughly 13,000 years ago, they left a barren landscape that looked more like northern Canada than Vermont. Tiny tundra plants colonized the rubble left by the glacier, followed by hardy willows and alders. Woolly mammoths, mastodons, and saber-toothed tigers roamed this rugged landscape.

No one knows for sure when people moved in, but it wouldn’t be too much of a stretch to imagine nomadic tribes venturing to the tundra in pursuit of arctic mammals, like the giant elk and caribou that lived on the glacier’s southern fringes. Archaeologists call these original Vermonters Paleoindians.

By about 11,000 years ago, archaeologists have good evidence of scattered settlements, suggesting low population densities of no more than 10 people per 100 square kilometers. Camps have been found on high cliffs that would have overlooked glacial Lake Vermont and the Champlain Sea. Blackened stones from campfires and knives and other utensils chipped out of chert are all that we know of these early inhabitants.

As Vermont’s climate warmed after the glaciers left, an army of trees slowly marched back into the Green Mountain State. First came spruce and balsam fir, the most cold-tolerant plants, which didn’t have so far to travel. Because they’re adapted to cold, these species inhabit the coldest, highest reaches of a mountain today; by the same token, when glaciers covered Vermont, these were the trees able to survive in closest proximity to the ice.

Less cold-tolerant trees, and those with heavy seeds, like oak, took longer to move north. By 12,000 to 11,500 years ago, however, scientists think that oak, birch, and maple trees found their way in small numbers to Vermont. By about 8,000 years ago, with maple, beech, and birch firmly established in the Green Mountains, bands of Abenaki people had taken up permanent residence throughout Vermont.

Water was their highway, so these settlers tended to concentrate along Lake Champlain and the Connecticut River Valley. Historians call this early period of Native American habitation the Archaic Period. These early Vermont residents lived lightly on the land, hunting deer, turkey, and bear and fishing the fresh cold streams and clear lakes for trout, landlocked salmon, and sturgeon. They made dugout canoes from trees, made or traded for beautiful cooking bowls crafted from soapstone, and had elaborate burial rituals, including cremating bodies and burying their remains with copper adzes and other tools.

Vermont’s recent geologic past had a very real effect on at least some of these tribes: they buried their dead in the mounds of gravel left as glacial kames, as did other Native Americans in the Great Lakes region. A gravel pit in Isle La Motte is the only known glacial kame burial site in New England and is about 3,000 years old.

From about 3,000 years ago until the time of the first European settlers, or about 300 years ago, Vermont’s native population made a major shift in technology. They used pottery instead of stoneware for cooking and began using the bow and arrow. Birchbark canoes replaced the heavier dugout canoes, and elaborate burial rituals were widespread. Historians call this culture the Woodland Period.

During this time, and up until about 1,500 years ago, Vermont’s climate was a few degrees warmer than it is today. Scientists call this warm period the Hypsithermal, and have found evidence for it throughout North America and Europe. In Vermont, at least some of that evidence is alive today. Some southern tree species made their way into the Green Mountains but weren’t able to survive in the subsequently cooler climate. In Vermont’s very warmest areas, typically in wetlands along Lake Champlain or the lower reaches of the Connecticut River, stands of black gum (Nyssa sylvatica) remain today as silent testimony to their peripatetic heritage.

While archaeologists generally consider Woodland people to be farmers as well as subsistence hunters, Vermont’s thin soils didn’t do much to encourage native Abenaki agricultural efforts. "It would seem that Vermont’s people were in no hurry to become farmers," wrote William Haviland and Marjorie Power in their book chronicling Vermont’s first inhabitants, "The Original Vermonters."

Instead, archaeological sites discovered on the lower reaches of the Winooski River suggest that residents continued to rely heavily on hunting, fishing, and gathering wild edibles, although at least one site from about 500 years ago shows that by then, native people were growing corn.

Native Americans who called Vermont home left fascinating artifacts the mountain explorer might be lucky enough to stumble upon. Green Mountain National Forest archaeologist David Lacy has found places along the Long Trail where Native Americans traveled, camped and made stone tools out of quartzite outcrops. Probably the biggest find was one area at about 2,000 feet along the southern section of the Long Trail where the Abenaki mined a particularly rich quartzite outcrop for more than a kilometer along the side of a small ridge.

Some camps and other sites are scattered along the mountain ridge between Killington and Pico peaks; a reroute of the Appalachian Trail in this area was shaped by Lacy’s finds, aided by the Abenaki, who worked with him to identify sacred sites. Still, the Abenaki and their forerunners didn’t make large-scale changes to Vermont’s landscape. That would come in the last 300 years of European settlement.

In 1609, when the French explorer Samuel de Champlain first sailed south with 24 canoes from the Richelieu River into Lake Champlain, he would have seen Lake Champlain’s shores populated with towering eastern white pines, some 6 feet in diameter or more. At the mouths of many rivers, including the Winooski, the native people had planted vast fields of corn to take advantage of the fertile floodplain soils, evidence by that time that the Abenaki had perfected the art of growing corn in Vermont’s short, harsh growing season.

And Champlain noted seeing a grove of chestnut trees (Castanea dentata) on the Vermont shore, a report that had botanical historians scrambling to find evidence of his observation two centuries later. Chestnuts, while once a common component of the southern New England forest, are heavy-seeded trees and were just finally making their way northward into southwestern Vermont when the entire population of the Northeast was wiped out by chestnut blight in the 1920s.

Historians located chestnut stumps in the nineteenth century that validated Champlain’s claim. The tree trunks were also evidence that the species had managed to migrate to northern Vermont during the warm Hypsithermal period 4,000 years ago. And the stumps, high on a hill in what is now Burlington, meant one important thing: Champlain also traveled up the Winooski River in his early exploration of the lake.

Champlain probably wasn’t too focused on the scenery, however. He was traveling with an escort of sixty Algonquin Indians, and at Ticonderoga New York, on Lake Champlain’s southern end, they were challenged by Iroquois. Champlain won the battle that ensued, which ensured that the Iroquois would be forever enemies of the French. That hatred set the stage for decades of fighting in at least four different wars; the last best known as the French and Indian War, or Seven Years’ War, in 1755-63.

Of course there was more to it than that, because both nations were fighting to control a valuable resource found in this new country -- beaver (Castor canadensis), whose pelts were made into men’s hats that were all the fashion in Europe. And the two nations were determined to control the future of Lake Champlain, because it was an important transportation corridor in those days, when the Green Mountains were a significant barricade to trade with the ports to the Southeast.

With the French aligned with the Algonquins and the British aligned with the Iroquois, Vermont became a kind of no-man’s-land in these years of fighting. Raiding parties from French-held Quebec traveled south to attack British settlements in western Massachusetts and eastern New York. Britain’s final decisive victory over the French in 1763 was a significant milestone for Vermont, because it meant settlers could brave Vermont’s harsh climate without the additional burden of worries about raiding soldiers.

The aftermath of the war would extend far beyond lucky Vermont settlers, however. The fortifications that were built as a result of the seven decades of warring - in particular, Fort Carillon, later renamed Fort Ticonderoga by the British - would play into the outcome of the American Revolution.

In 1763, historians estimate about 300 European settlers lived in the Green Mountain State. By 1791, when Vermont was officially accepted into the United States, about 85,000 settlers lived here. Their settlement choices mirrored those of the Native Americans who preceded them: since waterways were the preferred travel routes, areas along the Champlain Valley and the Connecticut River were first to be colonized.

Even before the end of the American Revolution, Vermont began to draw a flood of land-hungry settlers. It wasn’t Vermont’s climate that lured them northward, in fact, that was enough to keep most people away. It was money. Land was cheap, and in 1777, when Vermont declared itself an independent republic, settlers came to escape taxes.

At first the farms were subsistence farms, with families growing all they needed to survive. Hay, potatoes, and oats were early cash crops because they were more frost resistant than wheat. But the introduction of the merino sheep from Spain in 1809 and 1810 by William Jarvis, American consul in Lisbon and a Weathersfield, Vermont, farmer, had a profound impact on hill farming.

Sheep farming expanded the area of pastureland that farmers opened for their flocks, increasing the amount of cleared land to almost 90 percent. The cleared land was much more easily eroded. Some geologists estimate that the widespread clearing boosted erosion rates by a factor of 10, with heavy rains sending huge washes of gravel and soil down onto the bottomlands, in some cases burying cleared farmland in the valleys.

Merino sheep, with their long, soft fleece, were coveted for wool production, and Vermont’s climate and relatively cheap land made it a natural home for sheep production. Wool was an ideal cash crop, since pound for pound, it was more valuable than many food crops. Its value made it worthwhile to transport, and farmers didn’t have to worry about it spoiling. Historians estimate that there were as many as a million sheep in Vermont by 1836.

It’s almost impossible to hike up to the ridge of the Green Mountains without seeing some evidence of Vermont’s historic hill farms. Hillside farming, as it was known, made sense in Vermont because the valleys, while fertile, were areas where cold air collected. And narrow valleys tended to get darker earlier, a critical factor when combined with Vermont’s short growing season. Some historians estimate that virtually every mountain slope below about 1,800 feet in elevation was cleared at one time or another.

Some farms have become present-day homes, but many more have been returned to the forest. Attentive hikers and outdoors people can pick up traces of these old settlements by looking for old cellarholes, stone walls, family cemeteries, and wells. Vegetation can also give clues to the land’s past uses. If when hiking along, you find a big Eastern white pine (Pinus strobus) in the middle of the woods with thick branches on the lowest part of its bole, you can bet that it grew up in the middle of a field that is now grown over, because trees growing in the abundant light of open fields can grow outward as well us upward.

By about 1820, farmers were well enough established on the land that they had time to pay attention to their front yards: They planted paired sugar maples (Acer saccharum) at either end of the yard, sometimes called marriage trees as they were intended to grow with the married couple’s relationship. The thrifty Vermonters who settled these hills found another use for these plantings: since one tree was planted for the husband and one for the wife, these trees could be cut upon the death of the person it represented to be made into that person’s coffin.

Other plantings that are a sure sign of early settlement include clumps of lilacs (Syringa vulgaris) or a small apple (Malus pumila) orchard. Later, more exotic trees were planted, including black locusts (Robinia pseudoacacia) and Lombardy poplars (Populus nigra var. italica).

Sometimes the remnant vegetation isn’t the result of deliberate planting. Clumps of thistles (Cirsium spp.) and burdocks (Arctium minus) growing on large bumps on the ground are a sure sign of an old manure dump. Finding these clues in the middle of the forest is like finding ghosts of Vermont’s past and is a fascinating reminder of the state’s rich agricultural legacy.

Land above 2,000 feet may have been spared from the plow, but not from the ax. Even before the Revolution, there was money to be made from the forests. Burlington and Shelburne, with their strategic location on Lake Champlain, were centers of commerce where the trade was in lumber and other forest products like potash (wood ash extracts used in making soap and glass) and charcoal.

By the end of the nineteenth century, this frenzy of moneymaking had made some of the profoundest changes on the Vermont landscape since the passage of the glacier. Vermont, once so heavily forested that early settlers reckoned squirrels could travel the state from one end to the other without ever having to touch the ground, lost more than 75 percent of its forest cover. Making charcoal was a kind of cottage industry, and in some places in what is now the Green Mountain National Forest, observant hikers can see the pimple like mounded remains of primitive charcoal kilns.

Changes in trade practices, improvements in transportation and the westward migration ended the profitability of sheep farming in Vermont just before the Civil War. It was replaced by dairy farming, which was able to exploit nearby markets for a profit. That heritage as a dairy state continues today. But the last century has seen an inexorable, piecemeal invasion of trees, reclaiming lost ground, so that now the state is 80 percent forested, and can once again live up to its nickname, the Green Mountain State.

Sidebar: Stone walls and barbed wire

Sometimes the landscape holds subtle clues to its former inhabitants. None are so permanent as a stone wall or as evocative as the tatters of a barbed wire fence. Stumbling upon this hint of open fields and pastures in the middle of an 80-year-old forest opens a door on a tantalizing mystery: who lived here, and when?

While it’s difficult to date stone walls, it’s possible to tell from their construction where the wall might have been constructed and for what purpose.

It wasn’t until fields were plowed that stone walls began to sprout on cleared Vermont land. Farmers built single thickness stone walls with large stones for pastures. Double thickness walls were only built for extremely stony or cultivated fields. A double thickness wall is just what it sounds like: two walls built with a gap in between where smaller stones were tossed.

Barbed wire arrived in Vermont in the mid- to late 19th century. It didn’t necessarily take the place of stone walls - farmers still needed places to pile all those rocks - but sometimes was used on top of stone walls. The pattern of barbs can help with the wire’s approximate date of use. For example, "Crandal’s zigzag," a pattern of teeth that juts from either side of the central strand, came into use in 1879. "Allis’ buckthorn" was another pattern where the central strand was flattened in an oblong shape, with points all along the oblong; that came into use around 1881.

A mantle of green

In his classic 1969 work on Vermont’s flora, Frank Conklin Seymour calculates the state’s flora has five times more variety per acre than New England’s as a whole. Vermont’s 1,400 native species of trees, shrubs, and other plants comprise about 60 percent of the total number of species found in the 6 New England states combined.

Think of Vermont as a kind of crossroads, a place where plants from north, south, east, and west mix together to form different plant communities. Ecologists recognize in Vermont more than 70 community types, or unique plant assemblages. In the southern part of the state, and along the shores of Lake Champlain where the huge thermal mass of the lake helps moderate Vermont’s chilly winters, look for red and white oaks (Quercus rubra and Q. alba) and shagbark hickory (Carya ovata), southern species you ordinarily wouldn’t expect to find this far north. In the cold northeastern highlands, Canadian immigrants abound: white spruce (Picea glauca), tamarack (Larix laricina) and Labrador tea (Ledum groenlandicum) are but three of about a dozen northern migrants. And while Vermont’s flora includes most of the species found to the east in New Hampshire and Maine, it also includes some midwestern species, such as Northern prickly-ash (Xanthoxylum americanum) that are at the eastern edge of their range.

Add to those crossroads conditions the overlay of the past land use itself. Virtually all of Vermont’s 4.5 million acres of forest have been completely cut at least once in the past two centuries of European settlement. Whether the land was plowed or logged or used for pasture, the trees that reestablish themselves give subtle clues to the past. Eastern white pines (Pinus strobus) and grey birch (Betula populifolia) are two classic colonists in old abandoned fields, for example.

The corrugated landscape adds a final dimension of complexity. For every 1,000 feet of elevation gain, the average temperature drops 3.6 degrees Fahrenheit, a temperature change that has a profound effect on the vegetation. Traveling to the barren summit of Mount Mansfield is like visiting the arctic. The miniature landscape of tiny arctic plants such as crowberry (Empetrum nigrum) and mountain cranberry (Vaccinium vitis-idaea) and dwarfed balsam fir (Abies balsamea) or black spruce (Picea mariana) are remnants of Vermont’s glacial past. And then you can drop down 3,500 feet and find beautiful bogs peppered with tiny translucent orchids and weird insect-eating plants, like the northern pitcher plant (Sarracenia purpurea). It’s a landscape that’s fascinating to explore, and the purpose of the rest of the book is to allow you to do that.

But before you venture into the Vermont woods, it’s helpful to be familiar with the state’s two most common vegetation types.

Maple-beech-birch forest

On the flanks of the Green Mountains below about 2,400 feet, expect to find the Vermont state tree, the sugar maple (Acer saccharum) blending with yellow birch (Betula alleghanienesis) and American beech (Fagus grandifolia). This is the northern hardwood forest that dominates the Vermont landscape and turns flaming colors of red, orange, and gold in the fall. Walking through a rich northern hardwood forest can feel exactly like traveling through a long green tunnel. This trio of trees is often joined in lesser numbers by white ash (Fraxinus americana), hemlock (Tsuga canadensis), black cherry (Prunus serotina). American basswood (Tilia americana) is the most common of several tree species that show up on more nutrient-rich sites, while red oak (Quercus rubra) joins in on warmer sites at lower elevations.

The understory plants have evolved to take advantage of the low light, often by growing enormous leaves to act like big solar collectors. Hobblebush (Viburnum alnifolium) and moose maple (Acer pensylvanicum), common understory shrubs, both have been known to grow leaves the size of dinner plates. The low light levels also explain why spring flowers are so plentiful and beautiful: spring is the only time during the growing season when there’s enough sunlight for the plants to grow, because the hardwoods aren’t fully leafed out. Some of these understory plants, like squirrel corn (Dicentra canadensis) and bloodroot (Sanguinaria canadensis), have taken their low-light adaptation to the extreme: once they’ve flowered and had leaves for a short while, the leaves shrivel up and disappear, leaving the plant to save its energy in a bulb or corm for the following spring.

The bounty of the northern hardwood forest attracts a variety of birds, mammals, reptiles, and amphibians, and at least some of these creatures leave record of their passage. Strange, round, dime-sized marks that scar some beech trees are a sign that black bear (Ursus americanus) have been feeding on the trees’ nuts.

Vermont’s hard winters mean that most of the state’s roughly 150 bird species migrate south to spend the winter. But come springtime, the woods are alive with the calls of mating songbirds. What’s most interesting about this immigration is how different returning species of birds manage to share the same habitat by feeding in distinct parts of the canopy, shrub, and ground layers. Ecologists use the word niche to describe this partitioning of habitat.

Some birds, like wood thrushes (Hylocichla mustelina) and veerys (Catharus fuscescens) forage on the ground and fill the early morning air with their ethereal songs. Black-throated blue warblers (Dendroica caerulescens) and red-eyed vireos (Vireo olivaceus) feed in the lower or mid-level tree branches. The black-and-white warbler (Mniotilta varia) creeps up and down tree trunks, gleaning insects from the bark.

The northern hardwood forest’s thick layer of decaying leaves, plentiful streams, and tiny vernal pools provide rich habitat for six species of salamanders and seven toads and frogs. Like birds, these creatures share the forest by limiting their foraging to a specific kind of habitat. Gray treefrogs (Hyla versicolor) spend most of their time in rotted logs, under loose bark, and on the moss or lichen that covers the bark of older trees. In contrast, spring peepers (Hyla crucifer), while breeding in vernal pools, spend most of their summer on the ground or burrowed in the soil. In winter these frogs avoid freezing by wintering in the mud at the bottom of ponds, but wood frogs (Rana sylvatica) hibernate by burrowing into the upper soil layers, freeze solid as ice forms in the soil, and thaw out early enough to be the first frog species to begin breeding activity in the spring.

Probably the most well known inhabitants of Vermont’s northern hardwood forest are white-tailed deer that now number about 250,000. They weren’t always so abundant. Early settlers hunted them to near extinction, and those that weren’t killed for meat found their habitat gobbled up by Vermont’s early deforestation. So serious was their decline that the first laws to protect them were enacted in 1741, even before Vermont was a state. By 1779, the independent territory of Vermont had a closed season on deer, prohibiting hunting from January to June. But it was too little, too late.

By 1800, they were virtually extinct, and it became illegal to hunt deer in Vermont. In 1878, 17 deer were imported to Vermont in an attempt to reestablish their numbers. As today’s numbers show, the effort was a success. Today’s patchwork of mature forest and successional communities provides both winter cover and abundant summer browse, and deer may well be more abundant in Vermont than they were 300 years ago.

Spruce-fir forest:

Spruce-fir forest grows on the mountain slopes and ridges above about 2,500 feet and continues up to treeline, which in Vermont can dip as low as 4,000 feet. Confined as it is to the hills, it covers only about a quarter as much of Vermont as northern hardwood forest, but these are the forests that hikers will come to know best.

A hiker traveling from valley bottom to mountaintop would travel first through the northern hardwood forests up until about 2,000 feet. Then, in a transition to the spruce-fir forest, paper birch (Betula papyrifera) and red spruce (Picea rubens) begin to interfinger with the maples, beeches, and yellow birches.

Continuing the climb, balsam fir (Abies balsamea) and mountain ash (Sorbus americana) begin to appear, first in the cold drainages, but then more and more as the dominant trees in the canopy, until the hardwoods have dropped out. Spruce-fir forests have their beauty, but their typically high elevation locations, with associated cool temperatures and acidic soils don’t make for such a hospitable place for understory plants. Look for club moss (Lycopodium sp.) or small flowering plants like bunchberry (Cornus canadensis), starflower (Trientalis borealis), wood sorrel (Oxalis acetosella) and goldthread (Coptis trifolia), so named because its roots are golden yellow.

Black-capped chickadees (Parus atricapillus) winter in these forests, but it is the summer breeding birds that capture most visitors’ imagination. More than a dozen species of warblers either nest here or make stops here on their way north. Blackburnian warblers (Dendroica fusca), blackpoll warblers (Dendroica striata), and northern parula warblers (Parula americana) forage in the forest canopy’s uppermost reaches. Ruby-crowned kinglets (Regulus calendula) use their fine tiny bills to pick insects and insect eggs off twigs and needles. Dark-eyed juncos (Junco hyemalis) flit about on the ground, searching for seeds and insects. But the biggest treat may be from the calls of the Swainson’s thrush (Catharus ustulatus) or the gray-cheeked thrush (Catharus minimus), both high elevation inhabitants and each with their own distinctive flutelike songs.

As in the hardwood forest, warblers have found separate feeding and nesting niches in spruce-fir forest. For example, the parula warbler builds one of the forest’s most distinctive nests out of the long green threads of old-man’s beard (Usnea spp.)., a lichen that grows on conifer branches. The Nashville warbler (Vermivora ruficapilla) invariably builds its nest on the ground, in well-hidden depressions in the sphagnum moss that often grows in the understory. And the magnolia warbler (Dendroica magnolia) builds a more traditional looking nest right in the branches of a spruce or fir, using fine twigs and weed stalks. The use of different materials in nest construction limits competition for nesting supplies and increases the amount of time the birds have to forage and raise their young.

While colder temperatures and fewer pools and ponds on the mountain slopes limits the numbers of reptiles and amphibians at higher elevations, it’s still possible to find breeding populations of wood frogs (Rana sylvatica), spring peepers (Hyla crucifer), American toads (Bufo americanus), and a number of different salamanders. In one study of the distribution of amphibian populations along a transect up Vermont’s highest peak, Mount Mansfield, researchers found 13 species at 1,200 feet, and seven species at Lake of the Clouds, a high-elevation pond at 3,930 feet. Because amphibians have moist, sensitive skin, some researchers think that acid rain and other airborne pollutants, like ozone, may also limit amphibian numbers and diversity at higher elevations, where pollutant doses are higher because the mountains intercept air masses coming from the midwestern states.

Acid rain has also been implicated in the widespread dieback of red spruce throughout the northern Appalachians and Adirondacks. The next chapter in Vermont’s natural history will likely involve, once again, human impacts on the land and its inhabitants, working not only tree by tree or acre by acre as in the past, but through the regional and global effects of air pollution and climate change. Still, in view of the last 500 million years of upheaval and invasion, Vermonters and their guests can step into the twenty-first century with some confidence that the mountains of Vermont will remain green.

Sidebar: Wood Sorrel

Wood sorrel (Oxalis acetosella) is a perennial herb that is abundant in acid forest soils, especially mid-elevation transition forests. Its leaves are anatomically and physiologically adapted to take advantage of the low, diffused light of the forest floor—so much so that direct light can potentially damage the leaves by overloading the photosynthetic system. Within a few minutes of exposure to direct sunlight, the three heart-shaped leaflets fold neatly down against the main leaf stalk, a process that involves an upward crease along the midrib of the leaflet as well as downward bending of the short stalk at its base. This minimizes light interception and allows the leaves to survive brief exposure to direct sunlight as occurs in sun flecks that reach the forest floor. The young leaves make a nice addition to a salad, in moderation; the tart flavor comes from oxalic acid, which could cause an upset stomach if leaves are eaten by the handful. As with many wild edibles, be certain of your plant identification before you eat the plant, or you run the risk of confusing it with other species that could cause poisoning.

The Lay of the Land

Geographers generally describe five distinct physiographic regions in Vermont, each recognized by a suite of geologic, climatic, and ecological characteristics. Mountain building and the invasions of ice, trees, animals, and people have all worked together to create these regions and their distinctive character.

The Champlain Valley and Valley of Vermont

The Champlain Valley encompasses the low-lying area around Lake Champlain, and sends a finger south between the Taconic and Green mountains to form the Valley of Vermont. The bedrock is a complex mix of slightly altered Paleozoic sedimentary rocks that were only slightly "cooked" or metamorphosed during mountain building, including shale, quartzite, limestone, and dolostone. These rocks are sliced by a series of thrust faults, resulting in the formation of klippen like Snake Mountain and Mount Philo. In the Champlain Valley, low-lying areas are blanketed by lake bottom clays, bordered along the uplands by delta and other shoreline deposits. Otter Creek, Vermont’s longest river, has built an extensive floodplain in the Valley of Vermont, with glacial deposits and carbonate rocks along its upland edges. The carbonate rocks, varied surficial deposits, and lowland topography, combined with the relatively warm and dry valley climate, support a rich array of plant communities, ranging from lowland swamps and bogs to oak-hickory and other rich hardwood forests in the uplands.

The Taconic Mountains

The Taconic Mountains in the southwestern corner of the state are a single, large, overturned klippe composed of folded slates, quartzites, and phyllites, with locally limy layers, and a moderate degree of metamorphism. The klippe forms a steep-sided mountain range with summits up to 3,800 feet at Mount Equinox, which supports a variety of hardwood and coniferous forest types, including rich hardwoods at the lowest elevations and spruce-fir forest at the highest.

The Green Mountains

The Green Mountains form a series of long ridges that run north/south through the center of the state, with summits near or over 4000 feet in elevation, from Jay Peak in the north to Killington Peak in the south. In the north, the Green Mountains are formed of strongly folded and moderately metamorphosed Paleozoic rocks of marine sedimentary origin. The southern end of the range is a high, hilly plateau formed of ancient Precambrian metamorphic and plutonic rocks. The high elevation makes for Vermont’s coldest, wettest climates, with well over 100 inches of annual average snowfall on the mountain tops. At lower elevations, northern hardwood forests grade upward into spruce-fir forests. At the highest elevations, small areas of alpine tundra grow over exposed bedrock ridges and ledges. Steep ledges and cliffs carved by glacier ice and lowland lakes and wetlands add to the diversity of this region.

The Vermont Piedmont

The Piedmont forms a narrow band of low hills along the Connecticut River from Brattleboro to White River, then flares northward toward the Northeast Kingdom of Vermont. In the north, medium- to high-grade marine schists are interrupted by a large masses of granite around Barre. Deep soils made from glacially deposited till support northern hardwood forests in the southern part of the province and lower elevations of the north, while northern hilltops favor spruce-fir forest.

The Northeast Kingdom

Except that it is on the wrong side of the Connecticut River, the extreme northeastern corner of Vermont may well have a lot more in common with the White Mountains of New Hampshire than the rest of the Green Mountain State. Geographers call this part of Vermont the Northeastern Highlands, but Vermonters call it the Northeast Kingdom. It is pocked by bodies of granite that rise to over 3,000 feet, forming an upland that rises above the Piedmont to support extensive boreal forests similar to those found further north in Canada. The relatively low Victory Basin harbors extensive wetlands, including an isolated black spruce bog.

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