Crops

Among plant crops that humans continue to obtain from natural ecosystems, trees are among the most no-table. In the parlance of forestry, the terms "virgin" and "primary" are used to refer to older, natural forests from which wild, unmanaged trees have not yet been harvested by humans. "Secondary" forests have sustained at least one intensive harvest of their resource of trees in the past, and have since grown back. In general, the ecological characteristics of secondary forests are quite different from those of the more natural, primary forests that may have once occurred on the same site.

Trees have always been an important crop for humans, being useful as sources of fuel, food (edible fruits and nuts), and wood for tools, structures, furniture, paper, and vehicles (boats, wagons, etc.). Even today, trees harvested from natural forests are important crops in most countries. Tree biomass is an essential source of energy for cooking and space heating for more than one-half of the world's people, almost all of whom live in relatively poor, tropical countries. Trees are also an important crop for people living in richer countries, mostly as a source of lumber for the construction of buildings and furniture and as a source of pulpwood for paper manufacture.

In many places, the primary natural forest has been depleted by the cutting of trees, which has often been followed by conversion of the land to agriculture and urban land-uses. This pattern of forest loss has been common in North America, Europe, and elsewhere. To compensate to some degree for the loss of natural forests in those regions, efforts have been made to establish managed forests, so that tree crops will continue to be available.

Trees are not the only plant crops gathered from wild, unmanaged ecosystems. In particular, people who live a subsistence lifestyle in tropical forests continue to obtain much of their food, medicine, and materials from wild plants, usually in combination with hunting and subsistence agriculture. Even in North America, small crops of a few wild food plants continue to be gathered. Some examples include harvests of wild rice (Zizania aquatica), strawberry (Fragaria virginiana), low-bush blueberry (Vaccinium angustifolium), and fiddleheads (from the ostrich fern, Matteucia struthiopteris). Other minor wild crops include various species of edible mushrooms and marine algae.