Which agroforestry system stores the most carbon?

By reviewing 86 published studies on carbon sequestration, scientists have assessed which agroforestry systems that are the most efficient regarding carbon sequestration and where these are located. Read the full article in Agriculture, Ecosystems and Environment or the summary below.
 
The rural land use sector, e.g. agriculture and forestry, has a unique opportunity to become net sink of greenhouse gases. To seize this opportunity it is important to understand how different systems contribute with carbon sequestration. Agroforestry, when trees and crops are grown together, has been identified as a promising land management system to increase the storage of carbon in above ground biomass and in the soil. However, the carbon sequestration potential varies significantly between different agroforestry systems and climates.
 
This meta-study concluded that the net accumulation of carbon is greatest when grassland is converted to silvopastures (forest combined with livestock), underutilised land is transformed to homegardens, or cropland is modified to improved fallows. When croplands are transformed to woodlots the soil releases carbon and thus becomes a source of greenhouse gases. This also occurs when grasslands are transformed to agroforestry fields, likely because of the initial soil disturbance when trees and crops are planted. The study also showed that the carbon sequestration rate in general is higher in tropical systems compared to other climate zones. This applies to both above and below ground carbon storage.
 
Furthermore, the study found that above ground sequestration rates are greatest shortly after establishment of an agroforestry system and then decrease with time. The decline ceases after ten years and after that the above ground sequestration rates are quite small. When it comes to soil carbon, there is a release of green house gases directly after planting followed by an increase of the rates for around 5-10 years. After this period the accumulation of carbon approaches zero as organisms in the soil become more efficient when degrading added organic matter.
 
Agroforestry has a great potential to become one of the most important mitigation strategies to climate change, especially as agroforestry in general is a resilient land management system. By identifying the most efficient practises for climate mitigation in each climate zone and on each continent, decision makers and project planners can make informed decisions about which agroforestry practises to promote. However, more research on this topic is needed as the current methodologies to study sequestration rates are inconsistent and rarely include methane and other greenhouse gases.
 
Feliciano, D., Ledo, A., Hillier, J. & Nayak, D.R. Which agroforestry options give the greatest soil and above ground carbon benefits in different world regions? Agriculture, Ecosystems and Environment. 254:117-129.