Trees outside forests: agro-, community, and urban forestry

Planted forests are often considered to consist of tree plantings at a scal e large enough to satisfy such objectives as commercial production of timbe r and fiber, protection of watersheds, and preservation of natural habitats . However, trees are planted also at greatly reduced scales in agroforestry systems or as community woodlots to provide a mixture of products and serv ices to resident households, local communities, and regional cultures. Agroforestry systems represent a major form of small-scale tree planting, w here trees are grown in purposeful combinations with agricultural crops and /or livestock in order to take advantage of tree-crop interactions, and the reby enhance crop production, diversify farm output, stabilize or improve s oils, or ameliorate harsh environmental conditions. Some important examples of these systems in tropical countries include homegardens, alley cropping , improved fallows, intercropped trees for shade and fodder production, and trees planted in hedgerows and along fence lines. Throughout the tropics, there is a large variety of indigenous practices and species mixtures that represent adaptations of these systems to meet localized needs and opportun ities. Research and development programs have supported the expansion and r efinement of many of these systems during the last 20 years, but substantia l constraints on tree planting still exist in the form of land-tenure pract ices, population pressures that relegate agroforestry practices to degraded lands, subsistence needs that prevent extended periods of tree growth, and insufficient technical information or technology dissemination. Agroforestry systems in temperate, industrialized countries include combina tions of trees, pasture, and livestock; fruit or nut trees interplanted wit h vegetable or grain crops; windbreaks and shelterbelts; multispecies ripar ian buffer strips; and forest farming systems for specialty crops. Compared to the tropics, however, temperate-zone systems tend to focus on one or tw o high-value crops, often involve some level of mechanization, and frequent ly represent an opportunistic approach to improving the economic profitabil ity of farms rather than meeting subsistence needs. In both tropical and te mperate regions, agroforestry systems and community woodlots will be an imp ortant component of new sustainable agriculture and environmental protectio n programs. Although species diversity is an essential feature of all agroforestry syst ems, community forests generally involve planting only a few species in sma ll woodlots near farms, around villages, along roads, and as riparian buffe rs. Provincial or state governments and the local populace are often involv ed in landownership and plantation establishment. Major objectives of these forests are production of fuelwood for local consumption and of other tree products for market; soil stabilization, reclamation, or improvement; and protection of water quality. As with many other planted forests, the number of species widely used in community forests has been relatively small, wit h the genera Eucalyptus, Pinus, and Acacia providing the bulk of the specie s. Major issues with these "planted forests'' focus on rights for use of th e products, tending responsibilities once trees are established, protection until trees are large enough for their designated use, increasing interest in using "native'' species, and greater community involvement in planning and management. Trees planted along streets and waterways, or as woodlots in parks and othe r public places, represent a major group of planted forests in many urban a nd periurban landscapes. In addition to providing many of the same environm ental services that agroforests and community forests do, these urban plant ings have unique aesthetic and recreational value. For much of the world's ever-increasing urban population, these may be the only tangible reference points for understanding planted forests. These relatively little-recognized forms of planted forests - planted trees , to be more appropriate - are now receiving much greater attention. There are, however, some serious technical and sociopolitico-institutional constr aints to their development as more widely adopted systems in both tropical and temperate regions.