Agriculture in England is today intensive, highly mechanised, and efficient by European standards, producing about 60% of food needs with only 2% of the labour force.Biofuels present new opportunities for farmers against a background of rising fears about fossil fuel prices, energy security, and climate change.Sheep, goats and cattle came in from mainland Europe, and pigs were domesticated from wild boar already living in forests.There remained a very wide variety in English agriculture, influenced by local geography; in areas where grain could not be grown, other resources were exploited instead.In the Weald, for example, agriculture centred on grazing animals on the woodland pastures, whilst in the Fens fishing and bird-hunting was supplemented by basket-making and peat-cutting.The medievalist John Munro notes that "[n]o form of manufacturing had a greater impact upon the economy and society of medieval Britain than did those industries producing cloths from various kinds of wool.The planting of legumes, commonly used as a fodder crop, protected soil fertility due to their nitrogen fixing capabilities.This created a four-crop rotation (wheat, turnips, barley and clover) which allowed fertility to be maintained with much less fallow land.[22] New agricultural practices like enclosure, mechanisation, four-field crop rotation and selective breeding enabled an unprecedented population growth, freeing up a significant percentage of the workforce, and thereby helped drive the Industrial Revolution.[23] The 18th and 19th centuries also saw the development of glasshouses, or greenhouses, initially for the protection and cultivation of exotic plants imported to Europe and North America from the tropics.