- Rubber plantations have been a main historical cause of tropical deforestation, and are generally responsible for a range of environmental and social ills.
- But rubber grown in agroforestry systems–in combination with fruit and timber trees, useful shrubs, medicines, and herbs–is shown by a new report to increase ecosystem services and biodiversity, while sequestering carbon and diversifying farmers’ incomes.
- Additional to providing shelter and forage for a range of species, rubber trees are not shown to suffer yield declines due to implementation of the more sustainable method.
- Mongabay interviewed the three authors of the new report, “Rubber agroforestry–feasibility at scale,” to learn more.
Agroforestry is the most beneficial agricultural technique from a climate and biodiversity perspective: growing food, fuel, fiber, medicines and more under the cover of, or adjacent to, woody perennials like trees and shrubs makes intuitive sense for sustainability. And science agrees: these systems currently sequester 45 gigatons of carbon globally across a global area the size of Canada, according to one estimate published in the journal Nature, and ‘shade grown’ is an increasingly common label on consumer products.
Yet one of the main drivers of deforestation – the conversion of tropical forests to monocultures of commodity crops like oil palm, coffee, and cocoa – is not often mentioned in this context, despite agroforestry’s ability to improve such crops’ sustainability and in some cases, yields, too. For its ongoing agroforestry series, for instance, Mongabay recently interviewed a researcher in Brazil who has documented greater yields from oil palms grown in agroforestry systems (which also did not rely on chemical fertilizers or pesticides, a practice for which oil palm monocultures are infamous).
Now rubber can be added to the list of commodity crops which can get a sustainable makeover via agroforestry without suffering a loss in yields. In the new report “Rubber agroforestry–feasibility at scale,” authors Maria Wang, Eleanor Warren-Thomas, and Thomas Cherico Wanger synthesize current knowledge of the environmental and social benefits of rubber agroforestry and provide detailed recommendations for large-scale implementation across Asia, Africa, and Latin America.
“Our report provides evidence that agroforestry yields are similar to those in rubber monocultures – especially if the same planting density is maintained, and high-yielding planting material is used. Rubber yields in Brazil even increased compared to monocultures when rubber was intercropped with beans,” says co-author Wanger in this exclusive interview.
Not only does this system benefit carbon sequestration and crop diversification (which increases farmers’ food security), it also boosts biodiversity: “Rubber plantations containing additional trees (e.g. cocoa, banana, jackfruit and guava) …were also used by endangered golden-headed lion tamarins and Wied’s marmosets, as part of their home range,” in one example their report notes from Brazil.
The trio of researchers discussed these findings with Mongabay via email, and their responses have been lightly edited for clarity and brevity.
Mongabay: Rubber is mostly grown by smallholder farmers in monocultures across Southeast Asia: what social and environmental costs come with this?
Thomas Cherico Wanger: Indeed, monocultures are the dominant farming method for rubber production in some of the most biodiverse areas of the world. A major environmental cost is the reduction of natural forest cover to establish new rubber plantations. The consequences are carbon emissions, reduced carbon sequestration capacity, plant and animal biodiversity loss, and a decline in downstream ecosystem services such as clean drinking water, biocontrol or pollination. Moreover, monocultures increase the risk of soil erosion, climate impacts and pest outbreaks relative to diversified or mixed systems.
These environmental impacts affect the entire rubber supply chain and the livelihoods of smallholder farmers, despite the benefits that rubber cultivation can bring as a very valuable cash crop. Smallholders are also suffering from higher vulnerability to rubber price volatility: without additional crops or products from their land, they lose out when rubber prices fall.
What are the benefits for people, environment, and wildlife from rubber grown in agroforestry systems?
Eleanor Warren-Thomas: What’s really exciting about our report is that we provide very strong evidence that rubber agroforestry systems can provide multiple benefits on all these fronts. For people to benefit from agroforestry, these systems must work for them – this may require technical information and support, access to traditional knowledge or farmer networks, but also policy environments that support farmers to diversify, such as facilitating markets or modifying conditions for farmers subsidies. On the environmental side, evidence from China shows that simply intercropping secondary plants between rows of rubber trees, whether tea, cinnamon, ginger or nitrogen-fixing shrubs, increases the amount of water getting into the soil, and reduces soil erosion. On the livelihoods side, there are examples from Laos, Liberia, Thailand, Sri Lanka, Cote D’Ivoire and Nigeria where intercropping with extra food crops, or agroforestry with other cash crops, improves food security and income. In some cases, agroforestry meant an additional meal available to households each day, whereas in others it provided a social function that was highly valued.
In terms of biodiversity, there is a spectrum of complexity in agroforestry systems, from jungle-like systems that yield very little rubber, to very simple and ‘clean’ intercropping systems. Systems with more complexity tend to support more biodiversity – ‘jungle rubber’ in Indonesia has been shown to support forest-dependent bird and plant species, while even relatively simple intercropping systems in Thailand contained more butterfly species than monocultures. There are also benefits for understudied aspects of biodiversity, such as soil macrofauna and microbes. Agroforests could also play a really important role as stepping stones in the landscape between remaining areas of natural forest, as they are likely to be more wildlife-friendly thanks to the additional vegetation cover. It’s also possible to improve bird diversity in rubber farms just by allowing more understory plants to grow. But it’s important to emphasize that none of the studied agroforestry systems can support as much biodiversity as natural undisturbed forest.
Can you describe what a typical rubber agroforest looks like?
Maria Wang: In the literature, the term ‘rubber agroforest’ has been used to describe widely different systems, from jungle rubber with little management to production-driven, simple inter-plantings of timber species (like teak [Tectona grandis] and mahogany [Swietenia mahagoni]) with clonal rubber trees, to a more complex mix of clonal rubber with two or more annuals, perennial shrubs and trees. Short-term intercropping of light-demanding crops with young rubber trees is a common practice, e.g. maize, pineapple, and banana.
A typical rubber agroforest in southern Thailand could have rubber trees alongside fruit trees (e.g. mangosteen [Garcinia mangostana], snake fruit or salacca [Salacca edulis]), vegetables (e.g. gnetum [Gnetum gnemon], stink bean [Parkia speciosa]), and sometimes timber trees (e.g. ironwood [Hopea odorata] or neem [Azadirachta excelsa]).
There is also a variety of livestock that can be part of the mix (i.e. ‘silvopasture’) – we found reports of farmers keeping bees, cows, chickens, pigs, goats, sheep, fish ponds, rabbits and snails in rubber plantations – although larger livestock may damage trees.
What kinds of chemicals are normally applied to rubber crops?
Maria Wang: The recommendations may differ by country, but the chemicals normally applied include inorganic fertilizers (e.g. nitrogen, phosphate, potassium, and magnesium), herbicides for weed control like glyphosate (Roundup) and paraquat, fungicides for disease control, and stimulants (e.g. Ethephon). In addition, formic acid or sulfuric acid is often used as a coagulant for the latex.
Agroforestry reduces the need for weeding because of increased plant cover, and leguminous cover crops and manure reduce the need for fertilization. However, rubber disease is still an issue, and some intercrops like cassava may be a carrier of white root rot (Rigidoporus lignosus). Current knowledge gaps include whether smallholders grow natural insecticides and if they typically apply green manure or livestock manure as fertilizer in their rubber agroforests or monoculture plantations. Both aspects should be considered when developing good agricultural practices for smallholders.
Researchers in Brazil have demonstrated higher yields for oil palms grown in agroforestry systems: do we know what the yield is for agroforestry grown rubber?
Thomas Cherico Wanger: On average, latex yields are the lowest in Indonesia at around 1 ton/ha and the highest in Thailand at 1.8 tons/ha. However, these yields differ between agroforestry practices. For instance, in Indonesia, jungle rubber produces only 0.5 tons/ha, but monocultures with clonal varieties can produce 1.8 tons/ha. Much of this variation depends on the planting density of rubber trees (which is low in jungle systems) and the planting material.
So, keeping these differences of agroforestry systems in mind, our report provides evidence that agroforestry yields are similar to those in rubber monocultures – especially if the same planting density is maintained, and high-yielding planting material is used. Rubber yields in Brazil even increased compared to monocultures when rubber was intercropped with beans, and studies from several countries have found intercropping has a positive effect on rubber tree growth, and can lead to earlier commencement of tapping time.
It is indeed important to look beyond these yield benefits. Rubber agroforestry provides insurance against price volatility risk, can reduce climate and pest impacts, increase soil water content and thereby improve microclimatic conditions when compared to monocultures.
‘Jungle rubber’ has been in production a very long time, where is it most commonly grown in agroforestry systems today?
Eleanor Warren-Thomas: The term ‘jungle rubber’ is often used to define systems in Indonesia where Hevea rubber trees are planted under the natural forest canopies, but these systems have only existed since the introduction of rubber to Asia in the 19th/20th century. But of course Hevea brasiliensis is native to and widespread across the Amazon. Tapping of latex from wild trees has the millennial history you are referring to – we call this ‘wild rubber’ in our report, and mostly refers to Brazil (Acre), Bolivia and Peru. This was hugely exploited by colonists during the 20th century rubber boom, to the detriment of peoples living in the region, and led to the rubber tappers’ social movement in Acre in the late 20th century. Wild rubber tapping has now become almost unprofitable due to the low density of wild rubber trees and the distances needed to travel between them. Some communities still practice wild rubber tapping, but it is rarely a main economic activity.
Measuring the area of jungle rubber in Indonesia is a really tricky thing to do! As the canopy is often of natural forest trees, it is not readily detectable from space using remote sensing. In addition, jungle rubber is often practiced in places that are hard to access and data on land management may be scarce. So, the best estimates of area come from government reports, but the accuracy of these estimates is a bit unclear. The area of jungle rubber systems elsewhere in Asia is not really known – there are a handful of known examples from Thailand, although these are monocultures ‘gone wild’ rather than planting within natural forest, and as it is prevalent in Kalimantan, there could also be areas of jungle rubber in Malaysian Borneo.
Though it has a long history, what is the future for agroforestry-grown rubber? Who can help smallholder farmers transition to this sustainable method?
Maria Wang: We found that national policies were an important factor determining the uptake of rubber agroforestry, so national extension centers should ideally be involved for long term success, and it wouldn’t hurt to have well thought out policies to support smallholders – financially and materially – to try out agroforestry.
Grassroots networks and farmer co-ops are important to accelerate the transmission and adoption of agroforestry practices, especially those that local farmers have found to work well for them. ICRAF, CIRAD and other research institutes and universities are well placed to provide evidence-based recommendations for agroforestry practices, as well as to conduct ongoing research. Global Platform for Sustainable Natural Rubber (GPSNR) has shown interest in agroforestry as one of the tools for transitioning to a sustainable rubber industry, but more work needs to be done to move the focus from maximizing yields via conventional best practices to a more holistic approach involving the whole rubber agro-ecosystem.
Corporations can definitely play an important role in financing and increasing demand for agroforestry-grown rubber! In our report, we highlight Einhorn’s partnership with agroforestry farmers in southern Thailand, which has helped the farmers secure a price premium and direct access to a dedicated processor, thus contributing to the financial sustainability of agroforestry rubber. However, Einhorn is a small company and can only purchase 30-35% of the agroforestry latex produced, so there is definitely lots of room for other companies to step up and grow this industry.
What is the potential climate benefit of rubber agroforestry?
Eleanor Warren-Thomas: Clearance of natural forest to make way for rubber cultivation systems of any kind, whether monoculture or agroforestry, will result in carbon emissions from the vegetation and soil, and huge biodiversity loss. From the perspective of climate change and biodiversity conservation, keeping natural forests in place and avoiding any deforestation is absolutely paramount. But, where land has already been cleared for cultivation, rubber can offer greater carbon drawdown and storage than, say, annual crops, and with agroforestry there are additional carbon benefits relative to monocultures.
After the initial carbon emissions from natural forest clearance to make way for rubber, there are two key things to think about when it comes to carbon in rubber systems. First, the amount of carbon stored in the system by the plants growing on it and the soils. In general, adding more plant biomass to an agroforestry system will increase the amount of carbon sequestered and stored in that system, so any system with more plants, especially woody species, will draw down and store more carbon.
Second, the cyclical process of plantation systems, versus maintaining constant cover. When rubber trees are felled at the end of a plantation cycle (e.g. after 20 years) some carbon is stored long-term as timber, but much is re-emitted through burning or decomposition. So, it’s not just the stock that matters, but the so-called ‘time-averaged’ carbon stock that tries to take this into account. Some agroforestry systems aren’t cyclical – some permanent jungle rubber agroforests exist, which is best for carbon storage – or are replanted on a 40-year cycle rather than a 20-year cycle, which will have carbon benefits.
We have a very handy table in our report outlining carbon stock measurements from a range of systems if anyone is looking for numbers and more detail. But generally, yes, agroforestry will offer greater carbon drawdown and storage than monocultures, although the magnitude of the benefit will depend on the system.
Gains in latex yields from rubber plantations have been driven lately by development of high-yielding clones and improved tapping strategies: are these applicable to agroforestry systems, too?
Thomas Cherico Wanger: Technically there are no limitations…compared to monocultures, agroforestry systems provide additional opportunities to reduce pest pressures and avoid climate impacts. For instance, if cover crops are planted, soil erosion and nutrient runoff are reduced, and secondary crops can increase humidity in rubber systems. These mechanisms may help explain why rubber tree growth is reported to be greater in some agroforestry systems than in monocultures, and why evidence so far shows yields are unaffected. As for other agroforestry systems such as cocoa and coffee, reducing climate impacts will avoid yield declines in the mid- to long-run, so they provide additional benefits to these immediate yield boosters through clones and enhanced tapping strategies.
How long does a rubber agroforest remain productive, are they typically cut and replaced at the rate of monocultures?
Maria Wang: We have not come across any studies comparing the long-term productivity of rubber agroforests versus monocultures, but in both cases improved tapping methods can prolong the productive life of rubber trees, and this is an area that needs more work in terms of farmer training and knowledge sharing. In terms of cutting and replanting practices, it really depends on the type of agroforest, the farmers’ decisions, and in some cases rules around subsidies. In the case of traditional jungle rubber, rubber trees are typically only replaced when they are well past their prime, on an individual basis. In timber-rubber intercropping systems, the cutting might be timed according to the lifecycle of the timber trees. But in most cases where rubber trees are the primary source of income for the agroforest, rubber is felled using a similar lifecycle to rubber monocultures, which are typically cut and replaced after 20-30 years when latex production slows.
What are the main barriers to wider implementation of rubber agroforestry?
Thomas Cherico Wanger: Although rubber agroforestry strategies have many benefits, the uptake of agroforestry practices has been slow. A main barrier for instance in Thailand is policies in favor of monocultures that are only slowly transitioning towards promoting agroforestry systems. From a smallholder perspective, it is critical to ascertain land tenure rights to make long term investments worthwhile. In addition, high rubber prices make agroforestry practices less attractive, because these systems generally require more labor to harvest intercrops. In general, labor shortages due to economic development and urban immigration are a key barrier for agroforestry implementation. For producers, there is also a lack of knowledge about agroforestry and a concern about rubber yield reductions. In the context of tightly-managed larger plantations, the adoption of agroforestry or diversified planting would be a new and untested model, but one which could provide long-term benefits via improved soil quality and water use. As such, starting small, testing how different intercrops are performing, and then scaling up the successful cases is critical.
See related: To save chocolate’s future, ‘start now and go big’ on agroforestry
What else do you want to share about your findings?
Eleanor Warren-Thomas: A take-home from all of this research is that we have found little evidence for negative impacts of adopting agroforestry practices in rubber systems so far. We have found cases where agroforestry doesn’t work well due to a lack of markets for secondary products, or a shortage of labor – but where farmers have choices to design systems that work for them, the benefits are clear.
Alongside many others, we suggest that agroforestry may actually be a more precautionary and less risky approach for people’s livelihoods, their environments and the wider ecosystems we live in than monocultural practices, and should be treated as such.
To quote from report: “Overall, creating an environment where farmers have access to knowledge, information, capital, markets and importantly, the autonomy to choose which components of agroforestry best suit their needs and constraints would allow them to exercise creativity and sovereignty in their farms and livelihoods.”
Access the full 125-page report about rubber agroforestry here.
This interview is part of Mongabay’s ongoing series about agroforestry.
Erik Hoffner is an editor for Mongabay, find him on Twitter via @erikhoffner.
Related audio from Mongabay’s podcast: Agroforestry is an ancient climate change solution that boosts food production and biodiversity, listen here:
