Elevated concentrations of atmospheric greenhouse gases (GHGs), particularly carbon dioxide (CO 2 ), have affected the global climate. Land-based biological carbon mitigation strategies are considered an important and viable pathway towards climate stabilization. However, to satisfy the growing demands for food, wood products, energy, climate mitigation and biodiversity conservation-all of which compete for increasingly limited quantities of biomass and land-the deployment of mitigation strategies must be driven by sustainable and integrated land management. If executed accordingly, through avoided emissions and carbon sequestration, biological carbon and bioenergy mitigation could save up to 38 billion tonnes of carbon and 3-8% of estimated energy consumption, respectively, by 2050.P otential pathways to climate stabilization require the deployment of a broad portfolio of solutions to increase energy efficiency, replace fossil fuel use and remove GHGs. The technological solutions available to address these challenges can be broadly divided into two camps: (1) non-biological solutions that do not involve the biosphere, such as wind and solar farms for the generation of electricity and (2) biological solutions that do involve biospheric components of the natural and managed carbon cycle, such as bioenergy or reforestation. Biological solutions are distinctive in at least two ways. First, large terrestrial and ocean carbon sinks (reservoirs that accumulate and store carbon) already exist and remove more than half of the annual anthropogenic CO 2 emissions from the atmosphere 1,2 . Thus, understanding and management of the dynamics of these sinks is of paramount importance. Second, most biological mitigation activities require additional harvesting of the Earth's plant production (that is, net primary production) beyond its current 38% use 3 . However, these requirements face the limitation that a third of the terrestrial plant production is belowground, which is not economically harvestable, and another third takes place on difficult or remote terrain. Thus, there is a clear natural limit to the global fraction further available for human exploitation. Only 10% of the land surface, equivalent to 5 PgC per year (petagrams of carbon per year ¼ 10 15 g ¼ a billion metric tonne) 3 , remains. There is a need to exploit a larger fraction of biomass production for the purpose of climate change mitigation that would place this goal in direct competition with the agendas of food security, energy security and often biodiversity conservation 4 , all of which also require increasing quantities of biomass and land to meet their goals (Fig. 1). In addition, an emerging bio-economy intending to replace many of the petroleum-based products by plant-based products 5,6 will put further demands on biomass production.New technologies will contribute to improving the sustainable production and conversion of biomass for a range of food, fibre, energy, health and industrial products. However, with new demands, there will also be unprece...