In both high- and low-income countries, there are significant areas of cultivated land and pasture that are not best suited to those uses, such as marginal lands. These marginal lands, which are relatively unproductive, are used for agricultural purposes for the first time, or too intensively at an unsustainable level because of agricultural production needs to feed increasing numbers of people. Excessive agricultural impact from grazing or cultivation can lead to rapid loss of land productivity. In order to ensure long-term use of such marginal lands it is widely agreed that agricultural impact on marginal lands should be reduced to or below the land's carrying capacity.
This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends employing appropriate, environmentally sound and economically feasible agricultural and pastoral technologies.
Low-impact production systems such as agroforestry can be adopted, and should be considered in former forested marginal land that is now used for agricultural production. Agroforestry includes trees as a main component in a multi-crop production process. The interaction of the trees with the crops leads to soil protection and the conservation of water and nutrients since trees bind soils and protect soils from wind and water erosion, and their roots hold nutrients in the soil and draw nutrients to the surface.
The Guesselbodi forest management plan in Niger has been designed to produce long-term sustainability of the Sahelian land resource and with popular participation. The parcelled national forest is being managed with many goals, both of the researchers and local villagers, to maximize the restoration of degraded land and species and to be viable in the long and short-term to the region are the main priorities. It is a rare example of a complementary interaction of outside scientists and local knowledge and concern. The project deals with soil erosion, restoration, fuelwood tree species, carrying capacity for rangeland and farmland, windbreaks, water harvesting, agroforestry, among other development topics. It has also had to deal with issues of indigenous management, ineffectiveness and destruction of production-oriented development, and popular participation with external researchers.
Prickly-pear cacti are widely cultivated in Sicily; the most widespread and economically important is Opuntia ficus-indica. In Sicily it has, since its introduction, played an important role in the exploitation of marginal areas and has an extensive history of traditional cultivation practices, leading to the present intensive production of late fruit. The flowers and cladodes of the plant are also used.