Trees on farms: an update and reanalysis of agroforestry's global extent and socio-ecological characteristics

Abstract

Agroforestry, the inclusion of woody perennials within farming systems, has been widespread throughout the tropics as a traditional land use developed by subsistence farmers and, more recently, as an important livelihoods’ option promo ted by land - use managers and international development agencies. Agroforestry systems range from subsistence livestock and pastoral systems to home gardens, alley intercropping, and biomass plantations with a wide diversity of biophysical conditions and so cio - ecological characteristics. A quantification of the extent of agroforestry globally was first attempted by the World Agroforestry Center in 2009 in order to address the widely varying estimates about its importance. Since then, the global remote sensin g dataset upon which that estimate was based has been updated, both with improved quality and now including annual datasets available for 11 years (2000 – 2010). The geospatial analysis of remote sensing - derived global datasets conducted in 2009 investigated the correspondence and relationship of tree cover, population density and climatic conditions within agricultural land at 1 km resolution. This has now been reanalyzed based on the improved data, along with an investigation of change trends from the years 2000 (averaged 2000 – 2002) to 2010 (averaged 2008 – 2010). Am ong the key results are that 1) agroforestry appears to increase globally both in extent and in number of people associated with it; 2) remains a significant feature of agriculture in all regions; 3) that its extent varies significantly across different regions (for example, more widespread in Central America and less in East Asia); 4) that tree cover is strongly positively related to humidity; and that 5) there are mixed relationships between tree cover and population density depending on the region. Agroforestry, if defined by tree cover on agricultural land of greater than 10%, is widespread: found on more that 43% of all agricultural land globally, where 30% of rural populations live . Based on ou r current analysis, this land - use type represents over 1 billion hectares of land and more than 900 million people. Agroforestry is particularly prevalent in Southeast Asia, Central America, and South America with over 50% of area under agroforestry. Globa lly, the amount of tree cover on agricultural land increased substantially in the decade under investigation, with the area of >10% tree cover increasing 3%, or more than 828 000 km 2 . South America showed the largest increase in area with >10% tree cover: more than 489 000 km 2 : an increase of 12.6%. South Asia also showed a large increase (6.7%), along with East Asia (5%), Oceania (3.2%) and Southeast Asia (2.7%). In Central America, the area with >10% tree cover increased by 1.6% to become 96% of all agric ultural land. For Sub - Saharan Africa, we found an increase of 2%. Only Northern and Central Asia showed a decrease: - 2.9%. Tree cover apparently is still on the increase as a common feature on agricultural land throughout the world. It is essential that t his is recognized by all involved in agricultural production, planning and policy development