Agroforestry systems: sources of sinks of greenhouse gases?

Abstract

The prominent role of forestry and agroforestry systems in the flux and long-term storage of carbon (C) in the terrestrial biosphere has increased global interest in these land-use options to stabilize greenhouse gas (GHG) emissions. Preliminary assessments suggest that some agroforestry systems (e.g., agrosilvicultural) can be C0 2 sinks and temporarily store C, while other systems (e.g., ruminant-based silvopastoral systems) are probably sources of GHG (e.g., CH 4 ). Agroforestry systems can be significant sources of GHG emissions, especially at low latitudes. Practices such as tillage, burning, manuring, chemical fertilization, and frequent disturbance can lead to emission of CO 2 , CH 4 , and N 2 O from soils and vegetation to the atmosphere. Establishment and management of agroforestry systems incompatible with prevailing edaphic and climatic conditions can accelerate soil GHG emissions. Non-sustainable agroforestry systems are quickly degraded, and woody and herbaceous crops can become significant GHG sources. Silvopastoral systems can result in soil compaction and erosion with significant loss of labile C and N compounds to the atmosphere. Ruminant-based silvopastoral systems and rice paddy agrisilvicultural systems are well documented sources of CH 4 which significantly contribute to the global CH 4 budget. Early assessments of national and global terrestrial CO 2 sinks reveal two primary beneficial attributes of agroforestry systems: 1) direct near-term C storage (decades to centuries) in trees and soils, and, 2) potential 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 goods and services which potentially offset 5-20 ha of deforestation. At a global scale, agroforestry systems could potentially be established on 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 edaphic conditions.