By Malini Williams
Modern commercial agriculture remains one of the world’s largest contributors to greenhouse gas emissions and is incredibly destructive to the ecosystems surrounding farmlands and pastures. It is estimated that livestock produce around 20% of anthropogenic greenhouse gas (GHG) emissions, through digestive processes, grazing, and food production (Hawken, 2017). These GHGs include carbon dioxide, methane, and nitrous oxide. Methane and nitrous oxide are particularly dangerous, owing to their warming potentials being over 30 and over 250 times that of carbon dioxide, respectively (Environmental Protection Agency). Agricultural lands cover around 38% of land globally, and this number will continue to grow as forests and natural habitats are cleared to make way for more cropland and grazing lands (Rojas-Downing et al, 2017). New lands are being cleared at an alarming rate, as soil nutrients and water availability are being depleted in existing agriculture lands, leaving it arid and unproductive. Livestock grazing contributes to further desertification of grasslands, and it is estimated that this produces 100 million tons of carbon dioxide annually (Rojas-Downing et al, 2017).
Thus, there is a growing call for research and investment into sustainable farming practices that can offset or reduce the negative impacts of commercial agriculture. With a growing population, projected to reach near 9 billion, and world food demand expected to increase between 59% and 98% by 2050 (Valin et al, 2013), existing cropland will need to increase in productivity whilst minimizing its impact on the environment.
Enter silvopasture, an ancient farming practice that combines trees and grazing pasture into a single symbiotic system for raising livestock such as cattle and sheep (Hawken, 2017). It has been used for millennia in Mediterranean countries such as Spain and Portugal and has spread in recent decades to parts of South America and the United States (Hawken, 2017). Silvopasture has gained attention in recent years as an alternative farming method, as it not only uses land in a sustainable manner by allowing it to be multi-use, but is also economically viable.
When properly managed, silvopasture can improve water quality, soil nutrients, and profitability for small farms (Jose, Walter, & Kumar, 2019). It has been found that silvopasture has higher soil organic carbon than open pasture systems, and that silvopastoral systems sequester 5 to 10 times as much carbon as treeless pastures of the same size (Jose & Dollinger, 2019; Hawken, 2017). Trees also moderate water availability by providing cooler microclimates and protective environments, which can help farmers and livestock adapt to drought and severe weather, the incidences of which will continue to rise with progressive climate change (Hawken, 2017). Silvopastoral systems can, in addition, provide a diverse source of income for farmers, as alongside livestock, tree products such as nuts, fruit, mushrooms, and wood can be sold (Hawken, 2017). Not only is silvopasture less damaging to the environment, but it also has a positive impact on livestock grown in these systems. Trees provide shade required by animals to avoid expenditure of extra energy on thermoregulation, which in turn leads to higher weight gain and, in the case of cattle, higher milk yield (Jose, Walter, & Kumar, 2019). These silvopastoral systems also provide rich food for livestock, increasing livestock health, and farm productivity. Most grass and legume forages have enhanced quality when grown in silvopasture, compared to open pasture (Jose & Dollinger, 2019). Studies have also shown that livestock living in silvopasture can better digest the forage, emitting lower amounts of methane during the digestive process (Hawken, 2017).
A classic example of silvopasture is the dehesa system of southern Spain, where the famous jamón ibérico originates. The dehesas use grasslands with trees, typically Mediterranean oaks, interspersed throughout the landscape (Joffre, Rambal, & Ratte, 1999). The pigs used for jamón ibérico graze on the grasses and acorns from the oak trees, which are a high-quality stock feed (Joffre, Rambal, & Ratte, 1999). The oak trees can also be sold for cork and firewood, further adding to the economic value of the dehesa system (Joffre, Rambal, & Ratte, 1999).
However, the growth of silvopasture has been limited by its associated costs and the need for technical expertise to implement these systems. Experts estimate that the net first cost to implement this agricultural solution would be between $206 billion and $273 billion globally; Farmers could face individual costs of $400 to $800 per acre (Hawken, 2017). Additionally, farmers would have to grow and protect trees from drought and pests, as well as care for them with pruning and fertilizers. They must also be cautious in choosing the right tree species and herbaceous understory species, so that competition for soil nutrients, water, and light is not too intense (Jose, Walter, & Kumal, 2019). These considerations illustrate why Silvopasture is complicated and requires intense management for all its potential benefits to be fulfilled.
Although difficult to implement, the multitude of benefits of silvopasture cannot be ignored. There will be steep costs to implement, but it has been estimated that the lifetime global profit of implementing silvopastoral systems could be between $1.75 trillion to $2.4 trillion (Hawken, 2017). Around 351 million acres of global farmland already use silvopasture, and implementing the system on a further 200 million acres by 2050 could reduce carbon dioxide emissions by 31.2 gigatons (Hawken, 2017). Silvopasture will continue to increase in popularity, as the protective qualities of the system will help insulate farmers from the drought and extreme weather brought on by climate change. Increasing silvopastoral systems around the world may help curb greenhouse gas emissions from one of the biggest polluting sectors, and facilitate the necessary large-scale changes required to halt climate change.
References:
Environmental Protection Agency (n.d.) Understanding Global Warming Potentials. Available from: https://www.epa.gov/ghgemissions/understanding-global-warming-potentials [Accessed 8 November 2020]
Hawken, Paul (ed.) (2017) Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming. New York City, Penguin Random House.
Joffre, R., Rambal, S., & Ratte, J.P. (1999) The Dehesa System of Southern Spain and Portugal as a Natural Ecosystem Mimic. Agroforestry Systems. 45, 57-79. Available from: doi: 10.1023/A:1006259402496
Jose, Shibu & Dollinger, Jean (2019) Silvopasture: A Sustainable Livestock Production System. Agroforestry Systems. 93, 1-9. Available from: doi: 10.1007/s10457-019-00366-8
Jose, Shibu, Walter, Dusty, & Kumar, B. Mohan. (2017) Ecological Considerations in Sustainable Silvopasture Design and Management. Agroforestry Systems. 93, 317-331. Available from: doi: 10.1007/s10457-016-0065-2
Valin, Hugo, Sands, Ronald D., van der Mensbrugghe, Dominique, Nelson, Gerald C., Ahammad, Helal, Blanc, Elodie, Bodirsky, Benjamin, Fujimori, Shinichiro, Hasegawa, Tomoko, Havlik, Petr, Heyhoe, Edwina, Kyle, Page, Mason-D’Croz, Daniel, Paltsev, Sergey, Rolinski, Suzanne, Tabeau, Andrzej, van Meijl, Hans, von Lampe, Martin, & Willenbockel, Dirk. (2013) The Future of Food Demand: Understanding Differences in Global Economic Models. Agricultural Economics. 45, 51-67. Available from: doi: 10.1111/agec.12089
Rojas-Downing, M. Melissa, Nejadhashemi, A. Rouyan, Harrigan, Timothy, & Woznicki, Sean A. (2017) Climate Change and Livestock: Impacts, Adaption, and Mitigation. 16, 145-163. Available from: doi: 10.1016/j.crm.2017.02.001
Imperial Bioscience Review 