By Lucy Dablin
A solution exists that can change the fate of the Amazon Rainforest. A solution that would alleviate poverty, increase food security, restore biodiversity and reduce demand for deforestation. It seems counterintuitive, but these benefits can all be achieved by establishing agricultural systems that combine forestry with cattle1, known as silvopasture.
Inga edulis growing in one of the experimental agroforestry plots in a cattle pasture in Pando, Bolivia, established by Herencia in association with the Royal Botanic Gardens, Kew.
Photo copyright Lucy Dablin
Cattle have traditionally been viewed as the antithesis to forest conservation in the Amazon, analogous with the widespread establishment of pastures of African grasses and pasture degradation in just 7-10 years. It is estimated that over half of all the pastures in the Amazon are degraded, an area amounting to over 30 million hectares in Brazil alone2.
Brahman cattle, a breed of the Indian Zebu cattle Bos taurus indicus are widely used in the Amazon. They have thick skin, which helps protect them against insects, and are tolerant to the hot climate of the Amazonian pastures.
Photo copyright Lucy Dablin
The current model of livestock production in the Amazon is not sustainable, but this paradigm is being challenged by new research that integrates trees into cattle pastures. These silvopastoral systems can prevent further degradation of productive land, and can actually rehabilitate degraded lands back to a productive state.
The presence of trees in pastures helps to maintain and improve soil fertility. Trees can act as ‘nutrient pumps’, as they can access nutrients from deep in the soil. These nutrients are recycled back into the system as leaf or root litter, making nutrients available to pasture grasses.
Some trees also have an advantageous relationship with rhizobia – bacteria that infect a tree’s roots and form nodules that capture or ‘fix’ nitrogen from the atmosphere. Nitrogen is a major limiting factor for plant growth and one of the key ingredients in most fertilisers, so rhizobia can provide a major boost to productivity. Trees also promote complex soil food webs, and make new habitat available to ecosystem engineers such as decomposers, predators, and parasitoids that control harmful insects.
Silvopastoral systems have been found to offer improved production and sustainability over traditional pasture systems. In temperate climates, some silvopastoral systems, such as the Mediterranean dehesa ecosystem, have been productive for over 4,500 years. In Colombia and Mexico, the introduction of silvopastoral systems increased the number of animals that could be grazed per hectare by 200-500%3.
The presence of shade trees can reduce heat stress in cattle, and may increase their weight, milk production or reproductive success. Trees also protect pastures from drying out and provide extra fodder for cattle in times of drought, which suggests trees are a smart safeguard against climate change for smallholder livestock farmers. Silvopastoral systems also generate additional products that can increase a farmer’s income, such as timber, fuelwood and fruits.
Considering the plethora of benefits associated with silvopastoral systems, it is surprising silvopasture has not become more popular among cattle farmers in the Amazon. The most common problems faced by smallholder farmers include lack of technological knowledge and access to start-up funds necessary to overcome the initial investment in a system that becomes more productive in the medium- to long-term.
Tropical Rainforests are the most productive ecosystems on the planet, yet all the nutrients are held vertically in trees. Once the trees are removed, the horizontal pasture is washed away by heavy rains. Erosion leads to pastures becoming unproductive in 7-10 years.
Photo copyright Lucy Dablin
While a number of studies have focused on silvopastoral systems around the globe, there are still few studies reporting on this system in the neotropics, and even fewer exploring the potential for silvopasture on degraded lands in the Amazon. Attempts to incorporate exotic but widely used forage shrubs have failed. For example, Leucaena lucocephala is poorly adapted to the acidic, nutrient poor soils that dominate the majority of the Amazon. The Amazon has the highest plant diversity on the planet, yet this wealth of natural capital has been underutilised in the context of livestock production.
This will be the focus of my PhD research. I plan to develop a framework for evaluating the silvopastoral potential of native tree species in the Amazon, working in collaboration with the Royal Botanical Gardens, Kew and University College London. My inspiration for this avenue of research came from Kew’s work in Bolivia. Kew was trialling agroforestry systems in communities in rural Pando, to increase agricultural production and reduce the incentive for slash-and-burn agriculture. The community’s enthusiastic uptake of these systems showed that they were clearly working.
The system they used employed the native rainforest tree, Inga edulis (or the ‘ice cream’ bean), a nitrogen-fixing rainforest tree that appears to thrive in degraded and compacted soils, to increase the fertility of the surrounding soil and boost the productivity of adjacent crops. Two experiments were also established in degraded cattle pastures, and while growth was noticeably slower in these heavily degraded soils, the Inga edulis still had good survival and growth rates.
Then without warning, one of the farmers in the trial took down the fence protecting the Inga edulis plants from cattle, and they ate all of the trees. A disaster for the experiment, but it led the scientists at Kew to realise that if cattle can eat Inga edulis, then the Inga family of plants could be excellent candidates for silvopastoral systems. I plan to experimentally manage Inga edulis and other native tree species to evaluate their silvopastoral potential on a three-hectare experimental farm in the Amazon.
It is likely that, in the forest with the highest biodiversity on the planet, there are many species that could be candidates for inclusion in silvopastoral systems. Developing a framework to identify and characterise these species is a complex task. But, it’s exactly this kind of niche avenue of research that is intrinsically appealing to the casual rehabilitation agri-conservationist. And it is an avenue that may yield some interesting results over the coming weeks, months or years, as scientists explore the idea further.
Whether or not silvopasture will yield a panacea for degraded Amazonian soils still remains to be seen. I know it’s early, and it’s unlikely, but I’m either curious or crazy enough to want to find out.
References
1. D. M. Broom, F. A. Galindo, E. Murgueitio (2013) Sustainable, efficient livestock production with high biodiversity and good welfare for animals. Proceedings of the Royal Society B DOI: 10.1098/rspb.2013.2025
2. Serrao, E.D., Uhl, C., Nepstad, D., 1993. Deforestation for pasture in the humid tropics: Is it economically and environmentally sound in the longterm?, in: Proceedings of the XVII International Grassland Congress, Rockhampton, Australia and Palmerston North, New Zealand. p. 2215−2221.
3. Murgueitio, E, Calle, Z., Uribe, F., Calle, A., Solorio, B. (2011) Native trees and shrubs for the productive rehabilitation of tropical cattle ranching lands. Forest Ecology and Management, Volume 261, Issue 10, 15 May 2011, Pages 1654-1663, ISSN 0378-1127, DOI: 10.1016/j.foreco.2010.09.027.
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