Crops

Agroforestry is a forest-related analogue of agriculture. In agroforestry, trees are usually cultivated under intensively managed conditions, to eventually be harvested as a source of lumber, pulpwood, or fuelwood. In many regions, this sort of intensive forestry is being developed as a high-yield alternative to the harvesting of natural forests.

The most important trees grown in plantations in the temperate zones as agroforestry crops are species of pines (Pinus spp.), spruces (Picea spp.), larch (Larix spp.), and poplar (Populus spp.). Depending on the species, site conditions, and economic product that is desired, intensively managed plantations of these trees can be harvested after a growth period of only 10 to 40–60 years, compared with 60 to more than 100 years for natural, unmanaged forest in the same regions. Increasingly, these temperate species of trees are being selectively bred and hybridized to develop high-yield varieties, in parallel with the ways in which food crops have been culturally selected from their wild progenitors during the process of domestication.

Unfortunately, there is a downside to such practices. Large monocultures of genetically uniform crops, whether of trees, corn, or any other plant, are by their very nature more vulnerable to climate variation, pests, and disease than are more diverse plant communities. The large-scale replacement of managed natural forests with uniform high-yield varieties has led to the appearance of pseudoforests in places such as Sweden and parts of the United States: large tracts of land covered by uniform specimens of one species of tree, supporting little wildlife. Habitat loss from monocultural tree cropping has placed over a thousand forest-dwelling species on the endangered list in Sweden alone.

Fast-growing, high-yield species of trees are also being grown under agroforestry systems in the tropics, for use locally as a source of fuelwood, and also for animal fodder, lumber, and pulpwood. Various tree species are being grown in this way, including species of pine, eucalyptus (Eucalyptus spp.), she-oak (Casuarina spp.), and tree-legumes (such as Albizia procera and Leucaena leucocephala). Plantations of slower-growing tropical hardwoods are also being established for the production of high-value lumber, for example, of mahogany (Swietenia mahogani) and teak (Tectona grandis).