We haven’t been seeing the farm for the trees

Every day, carbon-storing forests are cleared to make way for farms to produce the food our growing planet needs. But finally there is some good news when it comes to the relationship between farming, forests, and carbon. As it turns out, farms have significant amounts of tree cover that have never been included in global carbon accounting. What’s more, tree cover on farms is on the rise.

A study published recently in the journal Scientific Reports set out to correct the carbon ledgers by calculating and adding this hidden cache of carbon storage. What they found was that farms sequester four times as much carbon as current estimates indicate.

Researchers used remote sensing and a land cover database to map and tabulate tree cover by country and region, as well as globally. They used Intergovernmental Panel on Climate Change carbon biomass maps for agricultural land as a baseline and added to it the carbon biomass for mixed forest, according to the amount of tree cover found on the farms.

Researchers found that 43 percent of farmland across the globe had at least ten percent tree cover in 2010. Including the carbon sequestering capacity of this tree cover increased storage capacity estimates for farmland from 11.1 gigatonnes of carbon to 45.3 GtC. At least 34 GtCs of this storage capacity is from trees. They also found that between 2000 and 2010, tree cover on farms increased by two percent. This resulted in a 2GtC, or 4.6 percent, increase in biomass carbon.

Of course, when it comes to trees, farms, and carbon, we are still in the red. The annual increase between 2000 and 2010 of tree cover on farms contributed 0.2 GtC per year to global carbon pools. Meanwhile, land use conversion in the tropics causes annual losses of 0.6 to 1.2 GtC.

Including trees on farmland—known as agroforestry—has positive effects beyond carbon sequestration. It improves soil fertility, increases biodiversity and watershed conservation, and can have positive effects on hydrological cycles. So it is not only time to correct the carbon ledgers, the authors say, but to take a more systematic approach to this mitigation opportunity on the many farms where they found tree cover was below its potential. —Catherine Elton | 12 August 2016

Source: Zomer, RJ et al (2016). Global Tree Cover and Biomass Carbon on Agricultural Land: The contribution of agroforestry to global and national carbon budgets. Scientific Reports. DOI: 10.1038/srep29987

Header image: ©Jonathan Thacker