While farming methods vary, traditional manipulated "agroecosystems" generally differ from natural ecosystems in several ways. Whereas conventional farming generally involves maintenance at an early successional state, monoculture, crops generally planted in rows, simplification of biodiversity, intensive tillage, which exposes soil to erosion, use of genetically modified organisms and artificially selected crops. agroecology minimizes these practices if possible.
An agroecosystem is a key idea in agroecology - they are defined as "semi-domesticated ecosystems that fall on a gradient between ecosystems that have experienced minimal human impact, and those under maximum human control, like cities.". Thus agroecosystems are generally defined as novel ecosystems that produce food via farming under human guidance. At its most narrow, "agroecology refers to the study of purely ecological phenomena within the crop field, such as predator/prey relations, or crop/weed competition."
The agroecologist views any farming system primarily with an ecologist's eye; that is, it is not firstly economic (created for a commodity and profit), nor industrial (modeled after a factory). In fact, agroecosystems are both understood and designed following ecological principles. An example is the control of problematic pests through introduction of other species, not application of pesticides to kill that pest. A common example of this would be intercropping to attract beneficial insects within rows of a given plagued crop. The insects would balance the disturbed ecology represented by the pest, thus eliminating unsustainable practices such as increasingly intensified pesticide use.
The term itself appeared in the late 1970s. It arose from the recognition that Green Revolution-era agroecosystems were highly dependent upon inputs such as pesticides, capital-intensive machinery, and specific seed varieties engineered or bred in the global North. The impacts of such agricultural systems have tended to exacerbate the intertwined social, political, and economic problems of the developing countries, or the global South.
K.H.W. Klages is credited as one of the first to discuss ecology and agriculture.
Practitioners take a critical view of modern industrial agricultural techniques, and see the industrial model as fundamentally or radically (at its roots) unsustainable.
Some current world issues that tie into agroecology - and its coupling of agronomy with the social sciences - include food sovereignty and rural development.
An important movement which can be related to agroecology is agrarianism. Another current trend that has informed much work in agroecology is traditional agriculture or indigenous agriculture.
Because of the ideological differences between industrial or mechanized agriculture and agroecology, its application has thus far been relatively limited in the U.S. (the country where industrial agriculture has been advanced the furthest). Latin America's experiences with North American Green Revolution agricultural techniques have opened space for agroecologists. Some countries where agroecological research and practice have flourished include Costa Rica, Cuba and Brazil.
Traditional or indigenous knowledge represents a wealth of possibility for agroecologists. The relationship between agronomists and traditional (often subsistence farmers) practitioners has been termed an "exchange of wisdoms." This recognizes that Western science has some solutions and innovations to offer, while local knowledge systems developed over thousands of years have just as much, if not more, to offer. This becomes more evident still when the importance and uniqueness of local ecologies are understood as underpinning agricultural systems.
Most of the historical farming in Madagascar has been conducted by indigenous peoples. The French colonial period disturbed a very small percentage of land area, and even included some useful experiments in sustainable forestry. Slash-and-burn techniques, a component of some shifting cultivation systems have been practised by natives in Madagascar for centuries. As of 2006 some of the major agricultural products from slash-and-burn methods are wood, charcoal and grass for Zebu grazing. These practises have taken perhaps the greatest toll on land fertility since the end of French rule, mainly due to overpopulation pressures.
The Madagascar dry deciduous forests have been preserved generally better than the eastern rainforests or the high central plateau, presumably due to historically less population density and scarcity of water; moreover, the present day lack of road access further limits human access. There has been some slash-and-burn activity in the western dry forests, reducing forest cover and the soil nutrient content. Slash-and-burn is a method sometimes used by shifting cultivators to create short term yields from marginal soils. When practiced repeatedly, or without intervening fallow periods, the nutrient poor soils may be exhausted or eroded to an unproductive state. Further protection of Madagascar's forests would assist in preservation of these diverse ecosystems, which have a very high ratio of endemic organisms to total species.
A switch to slash-and-char would considerably advance preservation, while the ensuing biochar would also greatly benefit the soil if returned to it while mixed with compostable biomass such as crop residues. This would lead to the creation of terra preta, a soil among the richest on the planet and the only one known to regenerate itself (although how this happens exactly is still a mystery). The nascent carbon trading market may further bring direct economical benefits for the operators, since charcoal is a prime sequester of carbon and burying it spread in small pieces, as Terra preta requires, is a most efficient guarantee that it will remain harmless for many thousands of years.
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