Cattle production has long been associated with deforestation in Latin America (Barbier and others, 1994; Binswanger, 1991; Browder, 1985; Downing and others, 1992; Kaimowitz, 1996; Kaimowitz and others, 2004; Mahar, 1988; Mertens and others, 2002; Myers, 1981; Repetto and Gillis, 1988; Schneider, 1994), and as such has been an important cause of the loss of natural habitat and biodiversity in the region. In most countries, the prevailing policy framework encouraged deforestation for timber extraction and conversion of forest areas to pastures and crops, which were encouraged by subsidized credit, guaranteed prices, and other incentives. The extent of these policy distortions has been substantially reduced in recent years (Faminow, 1998) but pressure from poor landholders and—in some areas—large scale ranches continues to result in large-scale deforestation in many areas. In many countries, the legal framework encourages this process, by granting titles to land that is deemed to be ‘improved’ (that is, cleared and used for agriculture).
Table 1 summarizes changes in pasture and forest area in Colombia, Costa Rica, and Nicaragua. Forest cover has been in retreat throughout the region. The area under annual crops has fallen in many countries (Nicaragua is an exception, as the end of unrest in the early 1990s allowed a considerable expansion of agricultural land into areas that had been unsafe). There has been some expansion of permanent crops, although this trend has reversed in recent years, due to low coffee prices. Permanent pasture, on the other hand, has expanded steadily in all countries for which data are available, although at different rates. Appendix 1 provides more detailed data on land use changes in Central America and Colombia in the last decade. These data show that these patterns were common throughout the region.
Table 1. Changes in pasture land and forest area in Colombia,
Costa Rica, and Nicaragua
Colombia |
Costa Rica |
Nicaragua |
||||
Area, 2000 |
Change 1990-2000 |
Area, 2000 |
Change 1990-2000 |
Area, 1995 |
Change 1990-1995 |
|
Annual crops |
2,818 |
–14.7 |
225 |
–13.5 |
2,457 |
25.2 |
Permanent crops |
1,766 |
6.2 |
281 |
12.2 |
291 |
14.3 |
Permanent pasture |
40,925 |
2.1 |
2,339 |
0.4 |
4,820 a |
.. |
Natural forest area |
49,650 |
–3.6 |
1,966 |
–7.5 |
3,278 b |
–26.4 c |
Notes: |
||||||
In addition to the environmental problems caused by the initial loss of forest, traditional approaches to pasture are often unsustainable. After an initial period of high yields, soil fertility is depleted and grass cover diminishes, resulting in soil erosion, contamination of water supplies, air pollution, further loss of biodiversity, and degradation of landscapes. Lower income for producers results in continuing poverty and in pressure to clear additional areas.
Silvopastoral systems, which combine trees with pasture, offer an alternative to prevalent cattle production systems in Latin America. They provide a deeply rooting, perennial vegetation which is persistently growing and has a dense but uneven canopy. These systems can be grouped in four major categories (Murgueitio, 1999):
Appendix 2 illustrates some of these systems in the RISEMP project sites, as well as the degraded pastures they are meant to replace.
Silvopastoral systems can provide a range of on-site benefits (Dagang and Nair, 2003). The introduction of trees in pasture areas can improve pasture productivity. Silvopastoral systems tend to increase nutrient re-cycling across a deep portion of the soil profile occupied by the root systems of a wide variety of plants associated with silvopastoral systems. Depending on the species of trees being used and on local climate characteristics, trees extract water and nutrients from soil horizons inaccessible to grasses, and deposit the nutrients on the ground with the natural fall of foliage, twigs, and fruits. The biomass and amount of nutrients released by pruning the trees of the agroforestry systems varies depending on the kind of management in use. As much as 18 tons/ha of dry matter can be deposited on the ground annually, and the amount of nitrogen flowing through the system can reach values of up to 380 kg/ha/year (Alpizar and others, 1983). In addition, the trees can provide direct benefits in the form of products such as fruit, fuelwood, fodder, and timber. From the farmers’ perspective, the benefits of silvopastoral systems derive from (a) additional production from the tree component; (b) maintaining and/or improving pasture productivity; (c) diversification of production; and (d) contribution to the overall farming system (for example, by providing fodder or income at a time when other sources do not) (Current and others, 1995). The shade provided by trees may also enhance livestock productivity, especially milk production.
The increased complexity of silvopastoral systems relative to traditional pastures means they often bring important biodiversity benefits (Dagang and Nair, 2003). These take two main forms. First, they tend to support much higher species diversity than traditional pastures. Second, they help connect protected areas.
Silvopastoral systems have been shown to play a major role in the survival of wildlife species by providing scarce resources and refuge; to have a higher propagation rate of native forest plants under these scattered trees; and to provide shade for grazing animals, and shelter for wild birds (Harvey and Haber, 1999). Food availability for wild birds is high in silvopastoral systems, and the complex structure of the vegetation provides a more adequate nesting substrate and better protection against predators than other agroecosystems. Silvopastures and other agroforestry systems also harbor a larger and more complex assemblage of invertebrates than monoculture pastures (Dennis and others, 1996). By providing alternative sources of fuelwood and other wood products, silvopastoral systems can also help reduce pressure on remaining natural habitats.
In agricultural landscapes characterized by the fragmentation of the natural habitats, silvopastoral systems can serve as biological corridors, helping to connect remaining habitats. At the regional level, silvopastoral systems may play an important role in the implementation of the Mesoamerican Biological Corridor, given the vast area of pasturelands in Central America and Colombia. It is expected that these corridors would provide adequate habitat for wildlife while facilitating seed dispersal and the regeneration of the native vegetation (Saunders and Hobbs, 1991).
Silvopastoral systems are capable of fixing significant amounts of carbon in the soil under the improved pastures and in the standing tree biomass (Fisher and others, 1994). Research in Colombia (Ramirez, 1997), Panama, and Costa Rica (CATIE, 1999; Pfaff and others, 20000) has shown that soils under silvopastoral systems have higher carbon content. Additional carbon is sequestered by the trees found in such systems. Moreover, grass-based pastures tend to sequester most of the carbon in the deeper part of the soil profile (between 40 and 100 cm depth), thus making it less prone to oxidation, and hence loss (Fisher and others, 1994; Beinroth and others, 1996).
Silvopastoral systems are also likely to affect water services, though the specific impact is likely to be site specific. Infiltration generally increases with the presence of trees, reducing superficial runoff with its attendant soil erosion. Improved livestock management can help reduce compaction, thus further reducing surface runoff. The presence of trees also leads to increased evapotranspiration, however, thus tending to decrease water yield (Bosch and Hewlett, 1982; Bruijnzeel, 1990).
In hilly areas, trees have an additional protective role in the ecosystem, that of preventing landslides (Bruijnzeel, 1990). Not only is the presence of trees essential for soil protection on slopes, but also the variety of species is important. Trees of different root depths are required for effective soil anchorage, in particular during torrential rain events accompanying tropical storms.
