5. PART-2.Pdf

Part Two Biophysical Regions of Vermont Biophysical Regions of Vermont ne of the most rewarding parts of studying a landscape and its natural communities is appreciating all the factors that work together to cause Ovariation within that landscape. When we study the landscape of the world, we look to climate to explain most of the broad patterns of geographic variation. As we look more closely, say at the North American continent, climate is still the overrid- ing feature that causes variation, but we begin to see influences from other factors such as geological history. As we look even more closely, for example at the state of Vermont, we begin to see that landforms and soils, along with human history, influence variations as well. The biophysical regions of Vermont presented in Figure 2 help organize the landscape into smaller units that share features of climate, geology, topography, soils, natural communities, and human history. Although each region has variation within it, all are widely recognized as units that are more similar than they are different. Figure 2 was developed by analyzing existing land classification maps and by assessing biological and physical data with new analytical techniques (Girton 1997). The map was created so that land managers from all state and federal land managing agencies, as well as private land managers, could have a single map of biophysical regions to work with as a way of organizing their planning and thinking about natural communities in Vermont. Although our map shows Vermont only, the regions have no political boundaries, and they do not end at Vermont’s border. The Taconic Mountains occur mostly outside Vermont, in eastern New York. The Vermont Valley extends into Massachu- setts and Connecticut, though its name changes. The Southern Green Mountains become the Berkshires in Massachusetts. The Champlain Valley extends across the lake into New York, and north to the Saint Lawrence River. The Northern Vermont Piedmont extends northward into Québec and east into New Hampshire at least a bit, and the Northeastern Highlands share geology, climate, and vegetation with adjacent northern New Hampshire. The U.S. Forest Service is leading the effort to join the biophysical regions of all the states and the Canadian Provinces. Our work is a part of that effort. Nevertheless, we describe these eight biophysical regions with their Vermont characteristics. The eight regions are all distinct, and they all have variety within them. We describe their climates, geology, soils, landforms, topography, water resources, human history, natural vegetation, and animals in a general way here. At the end of each biophysical region section, we list the characteristic natural communities of that region, including its matrix* communities, communities that are best expressed there, and communities that are restricted to that region in Vermont. The best way to understand the variety of Vermont’s eight biophysical regions is to spend time in each one, hiking its hills, walking its wetlands, and exploring its natural history. *Matrix communities are those that dominate the landscape and form the background in which other smaller scale communities occur. See further discussion in Part Three. 22 / Wetland, Woodland, Wildland Figure 2: Biophysical Regions of Vermont CV NH NM Burlington NP Montpelier • SP Rutland White River Junction • • TM CV: Champlain Valley SM TM: Taconic Mountains VV: Vermont Valley NM: Northern Green Mountains SM: Southern Green Mountains NP: Northern Vermont Piedmont SP: Southern Vermont Piedmont NH: Northeastern Highlands VV • Brattleboro Adapted from Girton, 1998. Biophysical Regions of Vermont / 23 Champlain Valley AIN LW E C M ARIEN D he Champlain Valley is low, warm, and comparatively dry — Vermonters refer to the region as the “banana belt.” Clay soils deposited by post-glacial Tlakes and seas, sands from post-glacial rivers, and outcrops of limestone and other Ordovician rocks form the raw materials for soil development here and provide excellent agricultural soils. If one were to extend the boundaries of this region beyond Vermont, it would go north and east to the St. Lawrence River. Westward, it would encompass the lowlands of eastern New York and perhaps even wrap around the Adirondacks to meet the Great Lakes. In fact, the soils, climate, and vegetation of the Champlain Valley have more in common with the lowlands surrounding the Great Lakes than with the closer Adirondacks or Green Mountains. Climate The growing season in the Champlain Valley ranges from about 130 days in the foothills to over 150 days in the lowest places near Lake Champlain. It is similar to the growing season in parts of the southern Connecticut River Valley but is in sharp contrast to the coldest parts of the Northeastern Highlands, where the growing season is only 90 days or less. No actual banana plantations exist in the Champlain Valley, but warm-climate crops like peaches can be grown successfully here. In summer, temperatures in the Champlain Valley are higher than in most of the state. The average July temperature exceeds 70°F. In winter, the valley is warmer than much of the state, with average January temperatures between 18°F and 20°F. There are small warm spots in Vermont’s southeast and southwest corners, where temperatures are higher than this. In contrast, Canaan, in the far northeast corner, has average January temperatures between 12°F and 14°F. The Champlain Valley is warm in summer because of its elevation: it is the lowest part of Vermont, with an elevation of only 95 feet above sea level next to Lake Champlain. The lake itself has a modifying effect on the climate in the valley, too, storing heat during the summer and radiating it well into the fall, keeping adjacent areas warm and frost-free. In the winter, however, latitude takes over as the control- ling factor in temperature. Hence, Bennington is often warmer than Burlington in the winter. 24 / Wetland, Woodland, Wildland The Champlain Valley is not only warm, but it is also dry. Average annual precipitation in the Champlain Valley ranges from 28 inches closest to the lake to 38 inches or more at the higher elevations in the foothills. The highest parts of the Green Mountains, on the other hand, get over 70 inches of precipitation in an average year. Commuters traveling from Burlington to Montpelier often feel this effect, encountering unexpected weather as they travel from the Champlain Valley into the Green Mountains. Geology and Soils The Champlain Valley with its Ordovician limestones, dolomites, and shales has some of the oldest rocks in the northeast. Some of these rocks are filled with fossil trilobites, snails, corals and algae, reminding us of their marine origin. These rocks and the processes that shaped them give the region much of its character. Natural communities that thrive on calcareous soils are common here, and the cliffs and steep slopes associated with the thrust faults created during the Taconic Orogeny provide specialized habitats such as cliffs, outcrops, and talus. In very recent times, at least geologically speaking, glaciers transformed the valley, as they did all of northern North America. Following the retreat of the glaciers from Vermont, which was more or less complete by 13,500 years ago, the valley was first filled with fresh water (Glacial Lake Vermont) and then with sea water (Champlain Sea). All the streams and rivers that fed these bodies of water carried huge loads of sediment. These sediments, gravels, sands and fine silts, and clays, were left behind in the lake or sea bottom. As a river travels down its own valley to a large body of water (a lake or bay or ocean), it drops its load of sediments in accordance with its speed. If it is moving very fast, it can carry heavy particles such as rocks and large cobbles. As it slows, the heavy particles drop out and only the finest remain in suspension. For example, as the ancient Winooski approached Lake Vermont, it dropped its heavy cobbles on bends all along its length. Most of the sand particles were carried all the way downstream, but the sudden slowing of the water as it entered the lake caused most of the sand to settle out near the mouth of the river, in a fan-shaped delta. Some sand was carried by water and wind to other places and formed beaches. The finest particles were carried out into the lake where they dropped to the bottom very slowly. After the Champlain Sea entered the basin via the Saint Lawrence valley, the same phenonemon continued, but since the sea was smaller than the lake, the sand deltas were lower in relative elevation and the deposition of clay at the sea bottom covered a smaller area. The flooding of the basin by lake and sea, and the movement of sediment into the basin, had more effect on the soils of the Champlain Valley than any other factor. Stop in a graveyard in the Burlington area, and you are probably on an old Champlain Sea delta, where the sand makes for easy digging. Old dunes and beach ridges can be found throughout the valley, well above where the lakeshore is today. Biophysical Regions of Vermont / 25 Ask the farmers in Addison or Panton about sand, though, and they’ll wonder what you’re talking about. This area got the fine stuff, the tiniest particles of sediment, the famous Addison County clay. Sticky, wet, hard to plow in spring, and very productive, this is the soil that characterizes the lowest elevations in the Valley. The hills of the Champlain Valley were spared the direct flooding effects of Lake Vermont and the Champlain Sea. But they were scoured by the glaciers and blanketed with a layer of till as the glaciers retreated.

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