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When in the seventeenth and eighteenth centuries European settlers arrived in New England, the northeastern part of the United States, forest was the dominant form of vegetative cover, making agriculture difficult. Initially, the Europeans went in search of areas already cleared by Native Americans (the original inhabitants of the continent) that would be suitable for planting crops, to thereby save themselves from the backbreaking labor involved in clearing forestland. Eventually, however, population growth outstripped the supply of cleared land, forcing the European settlers to cut down more forest themselves. For most of the settlers, cleared, arable land was the landscape most familiar to them from life back across the ocean. It took time to become accustomed to the hard labor involved in cutting down the woods. In the northern colonies, trees were usually chopped down, although occasionally a technique known as girdling was used. Girdling, a practice far more common in the South, involved cutting a horizontal channel all the way around the tree, which stopped the flow of sap, the liquid that carries food to all parts of a plant. Deprived of sap, the leaves would die and the branches eventually fell off, leaving the surrounding land dry and suitable for planting. New Englanders, however, generally clear-cut the forest, in part because the demand for fuel wood and lumber encouraged it. The market for potash, an alkaline substance that came from burning hardwood trees, also strongly motivated farmers to cut and burn the woods. Used to manufacture soap, glass, and gunpowder and to bleach linens and print calicoes, potash served a range of industrial uses but at the expense of farms, which lost the nutrients that the wood ashes would otherwise have released back into the soil had they not been exported to market. With their very existence dependent on the successful production of food, farmers had little, if any, time for removing stumps and stones. Instead, they adapted to the half-cleared fields by planting corn (maize) and grass, both grew well in such an environment. A pattern of "extensive" farming began to emerge. Rather than carefully tending arable land, engaging in crop rotation, manuring, and removing all stumps and stones – all recognized as part of proper agricultural practice in Europe – New England farmers simply exploited the soil and then forged ahead with the cleaning of new land. Cutting down trees remained hard work, but it was easier to partially clear the land, plant it, and then move on to another small plot than to constantly improve the soil on one field to the high Old World (European) standards. The settlers were too busy figuring out how to produce food rapidly to worry about efficient agricultural practices. Early on, the settlers adopted the Native American practice of planting corn along with beans and pumpkins or squash. These plants reinforced one another, resulting in high agricultural yields. The stalks of corn facilitated the growth of beans by giving them a structure to climb. The beans replenished the nitrogen that the corn drained out of the soil, bolstering fertility. And the pumpkins were a valuable source of food in the pioneer environment. After a few seasons, however, the settlers slowly began the process of transforming New England into an image of the Old World, planting European grains such as wheat and rye alongside the maize, a crop they never abandoned, in part because it proved a more reliable source of food. New England, unlike the South, did not center its economy on an export crop like tobacco. Nor were its soils as fertile as those in the mid-Atlantic area (south of New England), which by the eighteenth century was the great grain-producing region of the colonies instead. New England's soil had a moisture content that made it especially suited for growing grass. Grass played the pivotal role in the region's farm ecology: the grass fed cattle that, in turn, produced manure that was spread over the fields as fertilizer for growing corn and other crops. Grass and cattle thus helped to maintain soil fertility – the key to reproducing a sustainable form of farm life – by recycling nutrients back into the fields.