AGROFORESTRY SYSTEMS - SOURCES OR SINKS OF GREENHOUSE GASES

The prominent role of forestry and agroforestry systems in the flux an d long-term storage of carbon (C) in the terrestrial biosphere has inc reased global interest in these land-use options to stabilize greenhou se gas (GHG) emissions. Preliminary assessments suggest that some agro forestry systems (e.g., agrosilvicultural) can be CO2 sinks and tempor arily store C, while other systems (e.g., ruminant-based silvopastoral systems) are probably sources of GHG (e.g., CH4). Agroforestry;system s can be significant sources of GHG emissions, especially at low latit udes. Practices such as tillage, burning, manuring, chemical fertiliza tion, and frequent disturbance can lead to emission of CO2, CH4, and N 2O from soils and vegetation to the atmosphere. Establishment and mana gement of agroforestry systems incompatible with prevailing edaphic an d climatic conditions can accelerate soil GHG emissions. Non-sustainab le agroforestry systems are quickly degraded, and woody and herbaceous crops can become significant GHG sources. Silvopastoral systems can r esult in soil compaction and erosion with significant loss of labile C and N compounds to the atmosphere. Ruminant-based silvopastoral syste ms and rice paddy agrisilvicultural systems are well documented source s of CH4 which significantly contribute to the global CH4 budget. Earl y assessments of national and global terrestrial CO2 sinks reveal two primary beneficial attributes of agroforestry systems: 1) direct near- term C storage (decades to centuries) in trees and soils, and, 2) pote ntial to offset immediate GHG emissions associated with deforestation and subsequent shifting agriculture. Within the tropical latitudes, it is estimated that one ha of sustainable agroforestry can provide good s and services which potentially offset 5-20 ha of deforestation. At a global scale, agroforestry systems could potentially be established o n 585-1275 x 10(6) ha of technically suitable land, and these systems could store 12-228 (median 95) Mg C ha(-1) under current climate and e daphic conditions.