Division of pastures with agrosilvopastoral strips. Photo: Neil Palmer. The main objective of the Sustainable Amazonian Landscapes project SAL is to provide national environmental authorities and local farmers in Colombia and Peru science-based evidence that improves their capacity to mitigate and adapt to climate change, while improving the environmental services and socioeconomic benefits for the farmers. With this panorama, the vulnerability of the livestock production system is heightened by the presence of extreme climate events expressed as increased temperatures on the plains and precipitations in the piedmont, which results in low availability of food in critical seasons. Recognizing this reality, from the Sustainable Amazonian Landscapes project, there has been a move toward the establishment of alternatives of sustainable intensification, among them the silvopastoral systems, which make it possible to improve economic-productive, environmental, and social indicators both at the farm level and at the landscape level.
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By definition, ASPS is a collective name for land-use systems, implying the combination or deliberate association of a woody com- ponent trees or shrubs with cattle in the same site.
Essentially, these systems are a model of production and conservation based on silvi- cultural practices complementary to pre-existing agricultural activi- ties. From this point of view, these practices may be applied in a wide range of ecological and productive conditions. Based on this frame- work, several activities to achieve ASPS are proposed. E-mail address: getinfo haworth. University, P. Box Miami, FL Journal of Sustainable Agriculture, Vol. All rights reserved. Thcir roots are in Mayan civilization, where farmers practiced "roza-tumba-quema" or cutting the forest to cultivate corn from one to three years, after which the abandoned cropped area was allowed to regenerate naturally Kellogg, ; Parsons, ; Reyes-Rodriguez, Mayan farmers also cultivated multispecific gardens with more than 20 multipurpose species in their "milpas" Gomez-Pompa ct al.
Agroforestry practices continued into the Spanish colonial times. In Mexico, they were practiced in the state of Tabasco Arias, Lau, and Sepulveda, , where cocoa was cultivated under shade in natural forest. Today in the Mexican humid tropics, more than five millon hect- ares are under the "roza-tumba-quema" system, where the cultivated areas are used to produce food, while the fallow areas are utilized for forest, wildlife, and animal production purposes Hernandez X. These combinations may be simultaneous or alternate in time and space, and aim to achieve sustain- able production.
If only tree and animal components are prescnt, they are referred as to silvopastoral systems SPS. ASPS also may be considcred as a set of silvicultural practices complementary to other activities agri- cultural or cattle alrcady established in a farm or in a region.
From a sustainable agriculture viewpoint, ASPS should be considered as a biolog- ical strategy in search of sustainability. Research, Reviews, Pructices. The flow diagram Figure I , redrawn from Bronstein , allows a quick and clear view of inputs, outputs, and relationships among components. Some of these interactions, as summarized by scveral authors Borel, ; Bronstein, , Montagnini, ; Torres, , are as follows: 1.
Trees supply organic matter to the soil through the periodic decay of leaves, flowers, fruits, branches, and dead roots. In addition, roots absorb elements from deeper soil laycrs and bring them to the sur- face, making them more available to the pasture.
In the case of nitro- gen fixing trees NFT , soil nitrogen levels are increased. Trees create a microclimate favorable for animals shade and lower temperature. Shade intensity depends on tree density, crown diarne- ter, and crown structure.
Shade protects animals from excessive heating from direct radiation and reduces internal temperature stress. Changes in animal thermal balance, that is, lower air temper- ature than body temperature, leads to lower food consumption De Alba, Whether or not this contributes to higher animal pro- ductivity is a point of controversy. Trees may compete with pasture for water, nutrients, light, and space. Competition effects will be stronger if the requirements of both are similar. Natural leaf fall and pruning help to increase the availability of water, light, and nutrients to system components.
Ap- propriate selection of species and the selective prunings in season and intervals help to ameliorate competition. High numbers of animals or trees arranged in groups can lead to ani- mals crowding together looking for shade. Trampling may result and can affect plant cover and cause soil erosion and soil compac- tion. These conditions can deter tree growth.
Feed preferences of animals can affect forest composition. Over time, those species rejected by cattle can dominate. Animal component changes can accelerate some aspects of nutri- ment cycling by returning manures and urine to the soil. Animals can spread seeds, or scarify them, which favors germination. Generally, grass species growing beneath the tree canopy yield more, have a lower root:shoot ratio, and are of a different composi- tion than those outside the canopy Pinney, Simplified Flow Diagram of an Agrosilvopastoral System.
Redrawn from Bronstein 1 According to Ruiz , some of the factors that favor cattle components in ASPS are: Diversification of production activities within the farm reduces risk of economic disasters.
Small farmers, with land limitations, may use the forest to produce food from animal origin milk, meat without sacrificing areas dedi- cated to crops. In addition to direct advantages, farmers may also obtain economic benefits from fuelwood, timber, posts, and forage, which are used eventually on the farm for cattle management.
Cattle keep pastures and weeds from competing with young trees. In the case of fruit trees or palms, grazing also facilitates the harvest of fruits. Grazing of cover vegetation reduces fire risks. In the particular case of cattle associated with nitrogen-fixing trees, it is logical to assume that these species will contribute to soil fertil- ity, in addition to being a protein supplement when their edible parts are utilized as forage.
It is important to realize also that disadvantages exist Ruiz, Most important are: Compaction effects on the soil are harmful but could be compen- sated for by the effect tree roots have on soil porosity, infiltration ca- pacity, and soil aeration. However, this topic requires more research. Velocity and size of water drops from tree crowns to plants or crops under them can cause damage to flowers and fruits.
Cultural practices, such as mechanized harvest of crops, "henifica- cion," or "ensilado," are interfered with by the trees. Planning with sufficient space is necessary. Sometimes ASPS has been considered a subsistence practice.
This negative connotation may prevent wider acceptance. Furthermore, effects to improve these systems can be interpreted as a means to maintain the poverty status of the subsistence small farmer. Also, formal experimentation with these combinations is complex, not only from a practical point of view, but biometrically.
They also require a long term commitment which not too many institutions are willing to assume. Where young timber trees are planted in pasture lands, problems oc- cur due to trampling and browsing by grazing animals Heuveldop, An obvious bottleneck for small farmers in rural areas is the lack of availability of suitable plant material Heuveldop, The cattle census of accounted for 2. These activities occupied an area of 2. However, in many farms the presence of forest fallows is common, especially when cattle activities are discontinued because of low market prices for meat.
It is estimated that around , hectares of abandoned pasture lands are under fallows of different ages Miiller et al. Although these statistics exist, it is unknown at the farm level what area percentage is managed under ASPS or has a forest component. A research component on natural resources with emphasis in forests, soil, and water was added. An example of the first c a s d e e s in pastures-has been evaluated in the grasslands of the College of Agriculture of the Humid Tropical Region known as EARTH in Spanish , Las Mercedes de Guacimo, Costa Rica, where 29 different tree species have been identified within an area of approximately hectares Table 1.
Other examples of successful ASPS that have remained throughout time are: a One developed in the highland areas of Costa Rica, on volcanic soils, where alder Ainus acuminata is planted with pastures of kikuyo grass Pennisetum clandestinunz and green forage such as elephant grass fi purpureum.
The alder trees, selected for their fast growth in year rotations trees reach cm diameter , provide timber, fuelwood, and also have the added advantage of being an actinorhizal tree it is host to the nitrogen-feg actinomycete Frankia in nodules of their root tissue ; and b Another one developed in the Atlantic lowlands, where laurel Cor- dia alliodora is frequently found in pastures.
During pasture maintenance, farmers favor its natural regeneration, leaving it to grow. The tree is currently a valuable timber cash crop and it is said that it contributes to the maintenance of soil structure and pasture productivity. Trees in Pasture Lands at E. Colleae in the Atlantic Lowlands of Costa Rica. Tree species identified i n pasture lands at E. College, in the Atlantic lowlands of Costa Rica.
Latin name Local name Family Bursera simaruba indio desnudo Burseraceae Castilla elastica hule Moraceae Cecmpia spp. These integrated economic-ecological models, although constrained by their positivist approach Harvey, , in which physical models are used to simulate economic behavior Loner- gan, , have been useful. They improve the understanding of natural resources problems, the environment, and the production process.
On other hand, the worldwide drastic reduction of forest areas, concur- rent, with the increased demand for forest products, leads to a paradigm: production and supply of forest products. Because most of the farmers in the humid tropics live on and farm small parcels, it is financially too risky for them to experiment with small plantations of trees.
Even a plantation of 2 or 3 hectares would replace other uses. This represents a large financial decision. Farmers have to see that the planting of trees is both technically and economically feasible.
Within this framework, AFS should be considered as a palliate for the domestic and community supply of woody resources in an ecological, economical, and social framework: Ecological, because of its multispecific and sometimes multistrati- fied structure. AFS increases the efficiency of radiation capture and utilization of horizontal and vertical space of the agroecosystem.
Economic, because of its production, not only of food, protein, and fiber of the agricultural component, but also the production of the woody component such as fuelwood, timber, forage, poles, shade, and the contribution of organic matter to the soil, which saves fertilizer. Social, because the trees in particular timber trees represent a re- serve of standing capital which is a stability factor contributing to in- ternal security for the socio-economic component of the system-the rural family.
Also, because of its external projection, AFS could ameliorate the needs of timber supply at the community level.
Agro-silvopastoral systems is a collective term for land-use systems, which combine a woody component trees or shrubs with cattle on the same site. These systems represent a model of production and conservation based on silvi-culture, the practice of growing trees, complementary to pre-existing agricultural activities. It is foremost in drylands that forests and agrosilvopastoral systems play crucial economic, social and environmental roles. These include improved environmental sustainability and resilience of wider landscapes.
Agroforestry practices in conjunction with pastoral activity have profoundly shaped the present-day landscape of Serra da estrela. Although reduced in size, these activities still form a main productive component of the economy in this region. Essentially, these systems are a model of production and conservation based on silvi-cultural practices complementary to pre-existing agricultural activities. The Mediterranean region is characterized by a high variability in bioclimates with variable, often difficult to predict rainfall patterns, demanding the diversification of agricultural as a strategy to increase resilience M.