Course 3: Protect and Restore Natural Ecosystems and Limit Agricultural Land-Shifting (Synthesis)
This course focuses on the land-management efforts that must complement food demand-reduction efforts and productivity gains to avoid the harms of agricultural land expansion. One guiding principle is the need to make land-use decisions that enhance efficiency for all purposes—not just agriculture but also carbon storage and other ecosystem services. Another principle is the need to explicitly link efforts to boost agricultural yield gains with protection of natural lands.
The Causes and Consequences of Shifting Agricultural Land
Merely eliminating the need for a net expansion of agricultural land will not avoid all carbon and ecosystem losses because agricultural land is not merely expanding, it is also shifting. At a regional level, agricultural land is shifting from developed to developing countries.53 One reason is that growth in population and food demand is mostly occurring in developing countries. Rising food demand in sub-Saharan Africa, for example, is likely to drive cropland expansion of 100 Mha between 2010 and 2050, even allowing for high estimated yield gains in the region and continued importation of roughly one-fifth of staple foods. Another reason is growing global demand for some highly traded crops that developing countries have learned to grow well, such as soybeans and palm oil.
Agricultural land is also shifting within regions and countries, particularly from less productive and more sloped lands to flatter, more productive, more densely vegetated lands. These shifts result in gross forest losses that are much larger than net losses (Figure 12). Many abandoned agricultural lands do reforest but, unfortunately, the trade-off when native forests are replaced with planting or regrowing forests elsewhere is not environmentally neutral. Conversion of natural ecosystems, which is occurring mostly in the tropics and neotropics, tends to release more carbon per unit of food54 and harm more biodiversity than reforestation of abandoned land offsets elsewhere. The losses of carbon during land conversion also occur quickly, whereas rebuilding carbon in vegetation and soils occurs gradually over longer time periods, exacerbating climate change in the interim.55 The common tendency of countries to replant abandoned land as forest plantations also reduces carbon and biodiversity benefits.
A sustainable food future therefore requires efforts to reduce agricultural land-shifting, minimize the environmental consequences of inevitable expansion in some countries, and more actively reforest abandoned agricultural land. Under the Bonn Challenge—a global effort to bring 350 Mha into restoration by 2030—47 national and subnational actors have now committed to restore over 160 Mha.56
Figure 12 |
Gross forest losses are far greater than net forest losses because agricultural lands are shifting
- 53FAO (2017a).
- 54West et al. (2010).
- 55Hirsch et al. (2004).
- 56See http://www.bonnchallenge.org/commitments. A variety of scenarios exist to achieve global warming of 1.5°C only but all are uncertain and almost all require substantial “negative emissions,” i.e., withdrawals of carbon from the air. We estimate that 585 Mha of reforestation on liberated agricultural land would be needed to fully offset 4 Gt of agricultural emissions. These offsets would persist for 40 years after which other reductions or offsets would be required. This could only be achieved through actions across many menu items in Course 1 (reduce demand), Course 2 (increase productivity), and Course 3 (protect and restore natural ecosystems and limit agricultural land-shifting). The 350 Mha restoration target in the Bonn Challenge includes reforestation, agroforestry, soil enhancement, and other productive forms of restoration. Thus the Bonn Challenge could contribute to the needed 585 Mha.
- 57Laurance et al. (2014).
- 58Wormington (2016).
- 59Jackson (2015); Nepstad et al. (2014); Assunção et al. (2012); Gibbs et al. (2016).
- 60Boyd et al. (2018).
- 61Estes et al. (2016).
- 62In this report, we use the term “restoration” in a relatively narrow sense, meaning to return land to a natural or semi-natural state of vegetation. Other than in the case of peatlands, we usually mean forest restoration. We recognize that the term can be used more broadly, for example, to include agroforestry as a means to restore land to productive use, or more broadly still, to include any measures that restore ecological health to a tract of land, whether or not trees are involved. See, for example, Bessau et al. (eds) (2018); Hanson et al. (2015).
- 63See, for example, Stern (2006); Nabuurs et al. (2007); Sathaye et al. (2011); and Sathaye et al. (2005).
- 64Siddique et al. (2008).
- 65Kolka et al. (2016).
- 66Dargie et al. (2017).
- 67Wetlands International (2017).
- 68Gewin (2018).