Global Tree Cover and Biomass Carbon on Agricultural Land: The contribution of agroforestry to global and national carbon budgets.

Robert J Zomer,Meine Van Noordwijk,Jianchu Xu,Antonio Trabucco,Mingcheng Wang,Antje Ahrends,Deborah Bossio,Henry Neufeldt

doi:10.1038/srep29987

Abstract

Agroforestry systems and tree cover on agricultural land make an important contribution to climate change mitigation, but are not systematically accounted for in either global carbon budgets or national carbon accounting. This paper assesses the role of trees on agricultural land and their significance for carbon sequestration at a global level, along with recent change trends. Remote sensing data show that in 2010, 43% of all agricultural land globally had at least 10% tree cover and that this has increased by 2% over the previous ten years. Combining geographically and bioclimatically stratified Intergovernmental Panel on Climate Change (IPCC) Tier 1 default estimates of carbon storage with this tree cover analysis, we estimated 45.3 PgC on agricultural land globally, with trees contributing >75%. Between 2000 and 2010 tree cover increased by 3.7%, resulting in an increase of >2 PgC (or 4.6%) of biomass carbon. On average, globally, biomass carbon increased from 20.4 to 21.4 tC ha−1. Regional and country-level variation in stocks and trends were mapped and tabulated globally, and for all countries. Brazil, Indonesia, China and India had the largest increases in biomass carbon stored on agricultural land, while Argentina, Myanmar, and Sierra Leone had the largest decreases.

Highlights

Global carbon, water and nutrient cycles have all been profoundly impacted by the historical and ongoing increase of agricultural production worldwide[1,2,3,4]
Agroforestry - a diversified set of agricultural production systems that integrate trees in the agricultural landscape - is often discussed in this regard as a strategy that can be used both for adaptation and mitigation
Between 2000 and 2010 there was an additional increase of 2% tree cover, resulting in an increase of >2 PgC biomass carbon. (Our delineation of agricultural land in 2000 and 2010 remained constant (GLC 2000) to exclude any confounding trends such as agricultural expansion, abandonment, and/or forest clearing.) This gives a mean value of 20.4 tC ha−1 in 2000, and 21.4 tC ha−1 in 2010, which is more than four times larger than the Intergovernmental Panel on Climate Change (IPCC) Tier 1 global estimate of 5 tC ha−1

Summary

Introduction

Water and nutrient cycles have all been profoundly impacted by the historical and ongoing increase of agricultural production worldwide[1,2,3,4] Both land use change to agriculture and agricultural production have contributed, and continue to contribute, significantly to the projected impacts of global climatic warming[5], with notable implications for food security[6,7,8]. Almost 50% of all potentially vegetated land surface globally has been converted to croplands, pastures and rangelands[1,3,4], and these continue to expand to feed the planet’s growing population[8] Today most of this expansion is taking place in the tropics where an estimated 80% of this expansion is replacing forests[14]. We test this by combining IPCC Tier 1 default estimates for carbon stored in a variety of land cover types across different bioclimatic and ecofloristic zones[28] with previously published tree cover data based on 250 m resolution MODIS satellite remote sensing imagery[31]

Methods

Results

Conclusion