Carbon sequestration in pastures, silvo-pastoral systems and forests in four regions of the latin American Tropics

Tropical America (TA) holds 8% of the world's population, 11% of the world's continental area, 23% and 22%, respectively, of the world's forest and water resources, and 13% of the world's pasture and agro-pastoral land, this representing 77% of TA's agricultural land. Recent interest in carbon sequestration and preliminary research suggest that well-managed pasture systems in TA could provide a good combination of economic production, poverty reduction, recovery of degraded areas and delivery of environmental services, particularly, carbon sequestration. This paper presents 3-year research results generated by the "Carbon Sequestration Project, The Netherlands Cooperation CO-01002" on soil carbon stocks (SCS) for a range of pasture and silvo-pastoral systems prevalent in agro-ecosystems of TA compared to native forest and degraded land. In the tropical Andean hillsides, Colombia (1350-1900 m.a.s.l., 1800 mm rainfall/yr, 14-18°C mean annual temperature, medium to high slopes, medium fertility soils), SCS from Brachiaria decumbens pastures were statistically lower than those from native forest, but higher than those from natural regeneration of a degraded pasture (fallow land), degraded pasture and mixed-forage bank. In contrast, in the humid tropical forest of the Atlantic Coast, Costa Rica (200 m.a.s.l., 28-35°C, 3500 mm/year, poor acid soils), pasture or silvo-pastoral systems with native or planted pasture species such as Ischaemum ciliare, Brachiaria brizantha + Arachis pintoi and Acacia mangium + Arachis pintoi showed statistically higher SCS than native forest. Similar rankings were found in the humid tropical forest of Amazonia, Colombia (800 m.a.s.l., 30-42°C, 4200 mm/yr, flat, very poor acid soils) where improved Brachiaria pastures (monoculture and legume-associated) showed statistically higher SCS than native forest. In the sub-humid tropical forest of the Pacific Coast, Costa Rica (200 m.a.s.l., 6-month dry season, 2200 mm/year, poor acid soils) no statistical differences in SCS were found between land-use systems. In tropical ecosystems, improved pasture and silvo-pastoral systems show comparable or even higher SCS than those from native forests, depending on climatic and environmental conditions (altitude, temperature, precipitation, topography and soil), and represent attractive alternatives as C-improved systems