John Simaika warns that soil erosion is likely to be a big source of food insecurity.
As seen from space, we live on a blue planet – a planet full of water – with a little green and brown here and there. A closer look, however, reveals that especially around coasts, there is often a brown soup coming from streams entering the ocean, for example off the east coast of Madagascar (Green & Sussman 1990). The majority of times, this is associated with land use, starting far upstream of the wide rivers that then carry once fertile soils, accumulated over hundreds of kilometers, into the oceans. A lot of this soil will have been washed into streams by a process known as erosion, the natural enemy of soil formation. Erosion can be water-based or wind-based. In most cases, water erosion is of concern. In a world where the weather is predicted to become more extreme, soil erosion by water will, for many reasons increase significantly.
But why should we care about ‘dirt’? Well, because dirt is alive, an ecosystem of its own, that is so diverse, that it carries a plethora of organisms in just a teaspoon. In that teaspoon will be bacteria and fungi, part of the so-called microfauna, and nematode worms, mites and springtails, to name a few of the larger mesofauna. This might not seem all that significant, but soil ecosystems are responsible for the global storage and release of CO2 (Guo & Gifford 2002), a greenhouse gas known to cause global climate change (IPCC 2014). It is the capacity of soils overall to store carbon that aids in mitigating climate change (Lal 2004), but this capacity, and its response to a changing climate is not yet well understood (Frey et al. 2013). With limits on time for action, soil conservation and the creation of carbon sinks or pools is high on policy agendas.
Apart from their role in climate change mitigation, soils are responsible for good plant growth and thus maintain animal life, including human life. Soil quality, topography and microclimate are essential ingredients to plant crop health and thus good quality food. The effects of climatic change on soil per se are complex, as they depend on soil type (the physical composition), topography, biological soil composition (those little microbes and invertebrates mentioned earlier), ecosystem type (for example grassland or forest), local climate, the direction of rainfall change, land use and land management (Blankinship et al. 2011; Panagos et al. 2015).
Rainfall patterns and intensity in particular, are a direct concern: While areas that are already dry are predicted to become drier, those that are wet are becoming wetter still (Burt et al. 2016). The real concern is with the intensity of rainfall events. Fewer rainfall days are predicted, with more rainfall overall, in those days. It is the intensity of the rainfall that causes more soil to erode quicker. In a warmer, wetter world, rates of soil erosion will therefore increase (Burt et al. 2016). Already, in Europe, the mean soil loss rate (2.2 t ha-1 yr-1 for non-erosion-prone areas) exceeds the average soil formation rate (1.4 t ha-1 yr-1) by a factor of 1.6. About 12.7% of arable land in the European Union experiences unsustainable rates of soil loss (>5 t ha-1 yr-1), a pattern which is considered a major threat to food security for the European Union (Panagos et al. 2015). Factoring in more intense rainfall events in the future, would translate to higher incidences of crop damage (IPCC 2012) and to even greater losses of soils and carbon stocks across greater agricultural landscapes (Reichstein et al. 2013).
With about 11 billion people to feed, agriculture will have to intensify, presumably on smaller pockets of land, as increasingly erosion and salinization take their toll on the landscape. Anti-erosion measures will have to be implemented such as reduced or no tillage, the planting of cover crops, keeping plant residues at the soil surface, the maintenance of stone walls, and the increased use of grass margins and contour farming (Panagos et al. 2015). Urban populations will have to adapt, and new innovative ways of making food in cities will have to take precedence. Urban agriculture might take the shape of roof-top and balcony gardens, and hydroponic installations. Urban gardens and public parks could also increasingly play a role in food security, as they will be increasingly used to grow food. It could also mean that our reliance on high impact foods such as red meat will have to take a backseat to eating insects (van Huis 2013). Food production in the city would not only add utilitarian value, but potentially decrease greenhouse gas emissions and improve air quality (Lee et al. 2015), while increasing the aesthetic appeal of city life, where at least some people would experience a sense of place and being.
John P. Simaika is a Conservation Ecologist at the Department of Soil Science, Stellenbosch University. His research is applied, focusing predominantly on the conservation of insects in land- and water-scapes. He is an active member of the IUCN Freshwater Conservation Sub-Committee, and is Conservation Chair of the South African Chapter of the Society for Conservation Biology. To find out more, visit https://johnsimaika.wordpress.com/.