In addition to the arable crops that commonly entered rotations a further dozen 'permanent crops' and 'garden crops' covered 3,476,200 ha. In part these were produced for sale but they also represented essential elements of semi-subsistent polyculture in less commercial parts of the country. The vine was the most widely cultivated special crop during the July Monarchy and displayed at least six important characteristics. As a permanent crop it did not enter rotations. It flourished on sloping and stony ground that was unsuitable for growing cereals; it provided a marketable commodity; and was highly valued. It required intensive labour inputs and supported higher densities of population than would have been possible from cereal cultivation alone. The other special crops possessed some but not all of these characteristics. For example, olives, mulberries, chestnuts and walnuts were tree crops in the same sense as the vine and were thereby excluded from rotations, but hemp, flax and market-garden crops were also excluded, while colza, hops, madder, tobacco and beets were sometimes included in rotations but sometimes excluded.