Colonial Ecology, Atlantic Economy. Strother E. Roberts
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Название: Colonial Ecology, Atlantic Economy
Автор: Strother E. Roberts
Издательство: Ingram
Жанр: Историческая литература
Серия: Early American Studies
isbn: 9780812296143
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The approximately eleven thousand square miles of the Connecticut drainage basin likely supported upward of half a million beaver prior to the fur trade. The ponds sequestered behind the dams built by these half million beaver—maybe as many as one hundred thousand individual impoundments—would have varied in size from a few square feet to hundreds of acres. These beaver colonies formed a dense mosaic of nearly contiguous ponds and wetlands stretching along the length of most rivers and streams. One of the early settlers of Massachusetts provided a glimpse of these vast interior wetlands, writing in the 1630s of “swamps, some be ten, some twenty, some thirty miles long.”16 Taken together, beaver ponds may have engulfed up to 40 percent of the length of each of the Connecticut’s tributaries.17 While not quite on the scale of Ktsi Amiskw’s engineering handiwork, early seventeenth-century beaver ponds likely covered hundreds of thousands of acres within the basin—perhaps as much as nine hundred thousand acres, approximately 12 percent of the total Connecticut watershed.18
Beaver not only lived within the natural landscape of the Connecticut Valley, to an appreciable extent they created it. Long-term beaver occupation engineered much of the fertile bottomlands lining the Connecticut and its many tributaries, the very lands that first attracted English settlers to the valley in the 1630s. In the absence of beaver ponds, swiftly flowing streams would have gradually eaten away their beds and banks. The valleys of the watershed would have grown deeper and their banks steeper. Beaver dams slackened the flow of waters both within the ponds they impounded and in downstream stretches of river, decreasing stream bank erosion.
Indeed, the engineering skills of beaver actually reversed the process of stream bank erosion. Over time, beaver habitation built up rich meadowlands along the banks of tributary waterways.19 Rain and snowmelt runoff from the mountains, hills, and uplands of the watershed carried gravel, sand, silt, and soil into the streams of the region. As these waterways entered beaver ponds and their flow slowed, suspended sediment settled to the bottom of the pond. Individual beaver dams remain in operation for decades, sustaining multiple generations of a beaver colony and multiplying the effects of sediment retention over time.20 Deposited sediment gradually raised the floor of these ponds, until grasses and swampland brush could take root and the pond site became too shallow to house a beaver lodge. When this happened, the beaver would move on in search of a new dam site. Abandoned by its engineers, the old dam would decay, and the last shallow waters impounded behind it would drain away to reveal a lush meadow. Given sufficient time—the several millennia beaver thrived in New England following the last Ice Age—the aggregate action of beaver colonies throughout the Connecticut watershed resulted in the painstakingly gradual aggradation of valley floors.
Beaver ponds played an important role in determining the species composition of the woodlands that, at least in part, came to cover these newly formed valley lands. The presence of beaver ponds raises the water table in a landscape. In the long term, those trees poorly adapted to life in wet soils—primarily pines and firs—slowly lose out to trees more tolerant of higher water tables. Most notable among these latter are aspens and birches, the two species most preferred by beaver for construction material and food. The cumulative effect of the hundreds of thousands of acres of beaver-engineered wetlands in pre–fur trade New England meant that birch and aspen stands would have been far more common than they are today.21 In essence, the beaver could be said to have farmed their own preferred tree species.
By engineering new ponds and wetlands, beaver also created habitat for numerous other species. Beaver ponds and the semisubmerged wetlands that often lay along their edges support a biomass that ranges from two to five times greater than comparable undammed stretches of stream. Species that call beaver ponds home tend to be extremely rare or nonexistent in other stretches of a watershed. Fish, bird, amphibian, reptile, mammal, aquatic invertebrate, and aquatic plant species that require ponded or slow moving waters to grow, breed, and/or feed proliferate in the ponds and wet meadows that beaver engineer.22 As a consequence, the pre-seventeenth-century Connecticut Valley, with its thriving beaver population, supported far more species and a greater overall biomass than did the eighteenth-century watershed.
Figure 2. This vignette from a 1715 British map of North America greatly exaggerates the size of beaver colonies (which usually contained no more than six individuals), but does show that turn-of-the-eighteenth-century Europeans possessed some awareness of the beaver’s impact within a landscape. Hermann Moll, “A View of ye Industry of ye Beavers” (1715). A New and Exact Map of the Dominions of the King of Great Britain on ye Continent of North America, London: 1715. Courtesy of the John Carter Brown Library at Brown University.
Despite the hostility ascribed to the legendary Ktsi Amiskw, the Pocumtucks and other Native Americans living in New England prior to the seventeenth century enjoyed a largely symbiotic relationship with the region’s beaver. Although beaver was considered a delicacy among many of the nations of the northeast, their meat never formed a staple of Native American diets. Instead, beaver contributed to Native American food supplies by creating novel habitats in which numerous other species could flourish. Multiple species of fish, frogs and toads, tortoises, and freshwater mussels made their homes in beaver ponds and contributed to the dietary diversity and seasonal food security of Native communities.23
Beaver also transformed streamside woodlands in ways that supported Native American hunting and foraging. As they cut timber, beaver ranged up to one hundred yards beyond their dams. Selectively cutting down trees, beaver created gaps in the canopies of woodlands bordering their ponds. These new parklike stretches of woodland promoted the growth of myriad plant species whose growth was otherwise held in check by a lack of sunlight.24 The growth of new succulents, in turn, attracted game animals like deer and moose, which also browsed the aquatic plants of the beaver pond. Native American communities made use of these new parklands both by harvesting edible plants, like blueberries, and by hunting the game they attracted.
Finally, the beaver meadows that emerged at the end of a pond’s life cycle provided perhaps the most important benefit to local Indian communities. Just as beaver ponds trapped sediment, they also became a holding site for organic material. Streams and rivers swept along leaves, branches, grasses, animal carcasses, and other decaying matter and deposited them as they entered the slack waters of the beaver pond. Algae and bacteria decomposed this natural compost, returning nutrients to the soil at the pond’s bottom. As sediment and organic detritus accumulated, the pond floor slowly rose and eventually gave way to a lush meadow. Wild food plants and other succulents flourished in the rich soils of these newly emerged meadows. This flora, in turn, continued to provide excellent browsing for the deer and moose that had formerly fed upon the pond’s aquatic vegetation. The fertile soils of former beaver ponds also made excellent planting grounds for the horticultural nations living in southern New England. Because beaver ponds acted as natural nutrient traps, soils in beaver meadows would have contained over four times the nitrogen of soils in surrounding areas.25 And since maize draws heavily on nitrogen in soils during its growth cycle, beaver meadows could offer Indian agriculturalists far better yields than surrounding planting sites.
For their part, Native Americans set seasonal fires to preserve meadows against the encroachment of forests and to maintain parklike woodlands for hunting. As a side effect, Native American landscape management promoted the growth of certain tree species at the expense of others. Many of the fast-growing tree species best able to take advantage of the seasonal recycling of nutrients through burning—like aspen and birch—happened to be those most favored by beaver as food and construction material.26 In the long term, Indian burning practices created habitat more favorable to beaver colonization at the same time that beaver engineered a landscape that favored human hunting, foraging, and farming.
As they worked to engineer their environment, beaver also served as an important buttress against ecological disturbance. Ponds and wetlands acted as reservoirs during periods of drought. They СКАЧАТЬ