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

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.

Tropical forest-transition landscapes: a portfolio for studying people, tree crops and agro-ecological change in context

“…Before the data collected in any of the sampling frames can be used for valid conclusions about hypotheses -such as those framed in Table 1 -the sampling processes (steps 2 and 3 in Figure 3) need to be assessed for additional biases. The noticeable continental-scale differences in relations between tree cover, climate and human population densities noted by Zomer et al (2016) suggest major variations at that scale. At the next scale, the diversity of actors and their interactions is the key to understanding the socialecological systems involved (Galudra et al 2014;Minang et al 2015).…”

“…This level of tree cover is still possible in (peri-) urban areas while primarily agricultural areas can have around 10% tree cover (Zomer et al 2016). Agro-ecological zones clearly influenced the interactions between human population densities and tree cover (Figure 6 (c,d)).…”

“…Common institutional concepts of forests are a complement of and incompatible with agriculture (Van Noordwijk et al 2008). Meanwhile, tree-based concepts recognize the dichotomy as a continuum (Zomer et al 2016). 'Agroforestry' and 'Community-Managed Forests' emerged institutionally as 'boundary object' (Van Noordwijk 2014).…”

“…The first main factor we adopted in characterizing the agro-ecological zones was the aridity-humidity index, that is the ratio of precipitation and potential evapotranspiration at an annual time scale. The higher the index, the more humid the area [Zomer et al (2016) renamed the index from 'aridity' to 'aridity-humidity']. We modified the CGIAR-CSI (2012) classification by adding a water-tower category (Table 3).…”

Where are the trees outside forest in Brazil?

“…A recent global study demonstrated the importance of trees on agricultural land and their significance for carbon sequestration at a global level (Zomer et al, 2016). Using remote sensing data, the authors showed that 43% of the 22.2 million km 2 of agricultural land globally had a tree cover of at least 10% in 2010, an increase of 2% since 2000.…”