In this blog, I will explore two of the nine planetary boundaries (PB) - land-system change and biosphere integrity and discuss their connection with agriculture. I will also provide a thorough assessment of the chosen control variables for these boundaries.
The invention of the Haber-Bosch process, which enabled synthetic fertiliser to be produced, combined with rapid population growth and consumption changes has led to vast agricultural expansion over the last century. This has resulted in agriculture becoming a major driver of both land-system change and biodiversity loss.
Land-System Change
The control variable for land-system change is based on percentage forest cover of the remaining tropical, taiga and temperate forests. This control was chosen as forests are important terrestrial biomes, with strong global teleconnections and links to the climate system. For tropical forests, this involves changing evapotranspiration and for boreal forests, changing albedo. Temperate forests have less important global teleconnections and only makeup 14% of forest carbon sinks. Figure 1 shows the area of forest cover remaining compared to the potential cover, colour-coded to show the position of the control variable with respect to the PB. The red areas show places of high risk, where forest destruction has gone beyond the zone of uncertainty and brown areas represent the areas of potential forest biomes estimated by Ramankutty and Foley, 1999.
More studies have been published illustrating forest cover change. For example, using Landsat satellite data, Hansen et al. 2013, estimated that between 2000 and 2012, 2.3 million km2 and 0.8 million km2 of forest was lost and gained respectively (figure 2). However, this study has been contested as tree cover was defined as vegetation over 5m in height. Therefore, this study does not distinguish between biodiverse rainforests and artificially placed trees, like oil palm trees. The Food and Agriculture Organisation (FAO) figures for forest gain during this period do not match Hansen et al. 2013 as FAO tree cover classification distinguishes between forest types.
Another remote sensing study by Song et al. 2018 illustrates global forest change between 1982 and 2016. Figure 3 illustrates a decline in tree cover and an increase in short vegetation in South America, which has been linked to an increase in cropland and pasture for food production. Figure 3 also shows an increase in tree cover in higher latitudes, which is linked to global warming allowing trees to migrate northwards and the regrowth of forests after agricultural land abandonment.
Figure 3: Long-term land-cover change estimates, expressed as per cent of pixel area at 0.05° × 0.05° spatial resolution. 1 = Tree Cover (TC) gain with Short Vegetation (SV) loss; 2 = Bare Ground (BG) gain with SV loss; 3 = TC gain with BG loss; 4 = BG gain with TC loss; 5 = SV gain with BG loss and 6 = SV gain with TC loss
As the expansion of agricultural land continues to destroy natural biomes, scientists have proposed a new framework for viewing global ecology called anthropogenic biomes (anthromes). Anthromes are based on natural ecosystems but also acknowledge human land use. In 1700, nearly half the terrestrial biosphere was wild. However, crop areas increased from 2% in 1700 to 12% of global land area by 2000. Pastures also shifted from being a minor land use embedded in the seminatural anthrome in 1700 to making up three-quarters of the rangeland anthrome by 2000 (figure 4).
Biodiversity loss
Land-system transformation is not only a consequence of environmental change (such as deforestation due to agricultural expansion) but it is also a cause of environmental change (such as biodiversity loss). As a result of this, the biosphere integrity and land-system change PBs are intrinsically interlinked. There are two control variables for the biosphere integrity PB – genetic diversity, measured in extinctions per million-species years (E/MSY) and functional diversity measured by the Biodiversity Intactness Index (BII).
According to a study by Maxwell et al. 2016, over-exploitation and agriculture activity are the biggest threats facing the 8,688 threatened and near-threatened species on the IUCN Red List. Of all the species that have gone extinct since 1500 AD, 75% were caused by overexploitation or agricultural activity. Figure 5 illustrates the cumulative human impacts to threatened and near-threatened vertebrates. These hotspots vary between taxa and are largely influenced by patterns of species richness.
Despite being a control variable, species extinction is not a good metric for looking at biodiversity loss. This metric is biased towards vertebrates, it doesn’t measure changes to community composition and it is unclear how global extinctions influence ecosystem functioning at a scale relevant to safe operating spaces. Mace et al. 2014, suggested a measure of phylogenetic diversity, functional-diversity and biome condition would be a better control variable for highlighting biodiversity's key role in ensuring a safe operating space.
Unlike species extinction, the BII control variable helps measure the functional diversity of an ecosystem. Figure 6 highlights areas in red where the BII is beyond the proposed safe operating limit. Agriculture can affect the BII through the release of pollutants including greenhouse gases, fertiliser and pesticides; the intensification of farming procedures; value chain impacts such as transport use and food waste and the conversion of natural ecosystems to cropland and pasture.
Solutions
Not all land-system change is negative, and some land used for agricultural production can sustain high levels of biodiversity. A paper by Hobbs et al. 2006 suggests we move away from the one-dimensional dichotomy between nature and humans and instead think about how humans can interact with nature sustainably. This could include the development of sustainable harvest regimes; the maintenance of international policy, such as the Convention on International Trade in Endangered Species; the regulation of pesticide and fertiliser use; the reduction of food waste and public education to promote consumption changes. The 2020 Living Planet Report recommends using the Bending the Curve Initiative to reverse biodiversity loss from land-use change. This initiative has a focus on conservation and transformation of the modern food system.
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