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Better health – for people and the planet – grows on trees

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Market in the village of Minwoho, Lekié, Center Region, Cameroon. Photo by Ollivier Girard/CIFOR
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Originally posted on EurekAlert! website.

Tropical fruit trees can improve health, reduce hunger, boost incomes and fight climate change. So why don’t we grow and eat more?

Two of humanity’s biggest problems – the climate crisis and abysmal eating habits – can partly be solved by one healthy solution: eating more food from trees, specifically tropical ones. While global trends in agriculture and diets are not easily reversed, scientists say that creating incentives to grow and eat more mangos, avocados and Brazil nuts – and dozens of tree-sourced foods most people have never heard of – can be both attainable and sustainable.

Writing in People and Nature, researchers outline the myriad nutritional, economic and environmental-health potential of increasing the production and consumption of tropical fruits. They present an overview of benefits from tree-sourced foods in terms of nutrition and discuss the barriers and risks of scaling up supply to a global level.

“Planting the right type of trees in the right place can provide nutritious foods to improve diets sustainably while providing other valuable ecosystem services such as carbon sequestration,” said Merel Jansen, the lead author from ETH Zurich and the Center of International Forestry Research. “It also can contribute to development issues related to poverty reduction, biodiversity conservation, and food security.”

In spite of the diversity of edible plants – there are more than 7,000 – the global food system is founded on extraordinarily low diversity. Almost half the calories consumed by humans come from only four crops: wheat, rice, sugarcane and maize. The overconsumption of these energy-rich but nutrient-poor foods – in combination with underconsumption of more nutritious foods – has contributed significantly to malnutrition, which afflicts some two billion people. Moreover, their cultivation has caused widespread losses of biodiversity and contributed to climate change.

Brazil nuts are just one recognizable example of a highly-nutritious tree-sourced food.

For these reasons, experts are calling for a transformation of global food systems characterized by the cultivation and consumption of foods that simultaneously deliver nutritional, environmental and health benefits. Because tropical tree species, which may exceed 50,000, have this potential they can be a critical part of the solution, say the authors.

“Leveraging the diversity and local knowledge of tree species in tropical landscapes offers an excellent nature-based solution to match the rising global demand for diversified, healthy and sustainable diets, and to re-valuate native tree species and local farming practices,” said Chris Kettle, the principal investigator of this work, from the ETH Zurich and Alliance of Bioversity International and CIAT.

The world’s hundreds of millions of smallholder farmers, who have been often pushed aside by the industrialization of food systems, have the potential to be key players in food system transformation. With the right incentives, investments and involvement, smallholder farms could scale up agroforestry systems to produce more, healthy food, while simultaneously diversifying their income sources.

Marginalized groups and women also stand to gain from tree-sourced food sources, especially when the foods are harvested from trees that are not planted but grow spontaneously or and have the potential for natural regeneration that can be managed. This is because, in part, women farmers tend to have limited access to land, credit and other assets.

There are many clear opportunities to incorporate food-producing trees into landscapes. The majority of global cropland does not incorporate trees but has a high potential for doing so. Further, vast tracts of land in the tropics have been cleared for agriculture and then abandoned, and coordinated restoration efforts could include the establishment of sustainably managed agroforestry systems.

Brazil nut trees exemplify the concept of conservation through sustainable use. Credit: E.Thomas

Avoiding pitfalls

Increased demand for tree-sourced products has potential downsides. The establishment of industrial cacao plantations in West Africa and oil palm plantations in south-east Asia have deforested landscapes, degraded soils, harmed biodiversity and increased carbon emissions. Avocado farms in Mexico, made profitable by increased demand north of the border, have been recently targeted by organized crime. Dependency on single products can lead to widespread shocks when prices crashed, as has happened to cacao farmers in Côte d’Ivoire.

“A combination of interventions by states, markets and civil society across the supply chain – from producers to consumers – is necessary to guarantee that increases in demand are supplied from sustainable production systems that are diverse, and that will not lead to large-scale deforestation or other unwanted side effects,” said Jansen.

To make increased tree-sourced food production an integral part of the global food system transformation, the authors propose the following:

  • Consumer demand: More information needs to reach consumers about tree-source food. “To radically change diets, extensive behavioral change campaigns will likely be necessary, especially to increase the consumption of underutilized nutritious and healthy foods,” the authors say.
  • Land tenure: One barrier to the implementation of tree-based food production systems is insecure land tenure rights. These are particularly important since tree-crops can require substantial up-front expenses and return on investment can take years. Secure land rights are considered key to overcoming these barriers.
  • Investment costs and pay-back time: Intercropping with annual crops, payment for ecosystem services, redirecting annual crop subsidies, and provision of micro-credits to establish agroforestry systems can create funding opportunities. These can help alleviate high investment costs and long pay-back times.
  • Supply chain development: Developing supply chains for potentially popular products is essential for rural communities to access markets. NGOs, private investors and the public sector can all contribute.
  • Genetic resource conservation: Investment in the conservation of genetic resources that underpin diversity is necessary for crop tree systems to flourish. Additionally, reliable seed sources and seedlings need to be available for the establishment of tree crop farms.
  • Technological development: Development of propagation methods, planting techniques and post-harvest technologies for currently undomesticated trees can help to better use the enormous diversity of trees in our food systems.
  • Diversification: To avoid the pitfalls of monoculture systems including price shocks and environmental degradation, sustainable crop tree systems must include a variety of plants and crops.
Smallholder farmers such as this Brazil nut harvester stand to benefit. Credit: R.Brouwer.

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Outcome Evaluation Approach – 5 Case Studies from FTA

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Yordana Yawate, carries a sack of sago pith to be filtered on the banks of the Tuba river in Honitetu village, Maluku province, Indonesia. Photo by Ulet Ifansasti/CIFOR
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Two recent publications discuss how to effectively assess the impact of transdisciplinary (TDR) research and apply these methods to 5 case studies.

The creation of the CGIAR Research Programs (CRP) was aimed to increase the social, economic, and environmental impacts of research. These programs have intentionally developed broader and deeper partnerships with a wide range of policy and development actors (i.e., international conservation and development organizations, NGOs, policy actors, other stakeholders), as well as with other researchers and research organizations. These efforts mirrored a shift in the broader research environment toward more engaged, problem-centred research. Such research, known variously as Transdisciplinary Research (TDR), Mode 2 Research, and Sustainability Science, among other terms, actively involves stakeholders to help ensure the relevance of the research, incorporate a broader range of expertise in the research process, and promote the co-generation of knowledge with research users.

In theory, engaged TDR approaches should help address complex sustainability problems and contribute to more and better outcomes. However, the increased complexity of these approaches makes impact assessment even more challenging than for traditional research approaches. Research impact assessment is chronically challenged by the fact that the uptake and use of research-based knowledge is incremental, with multiple steps and other intervening factors, often with long time-lags. Measuring and attributing impact are difficult. CGIAR research impact assessment has typically attempted to measure the benefits of improved technologies generated by CGIAR research; this assumes that the main contributions of the research are bundled within an improved plant variety or other technology package. TDR deliberately aims to contribute to several impact pathways simultaneously, by supporting capacity-building and empowerment among partners, facilitating dialogue and political processes, co-generating knowledge that will be implemented directly by partners, as well as through more conventional research products. However, empirical evidence of whether and how transdisciplinary approaches contribute to (more) effective scientific and social outcomes remains limited.

CIFOR Senior Associate Scientist Brian Belcher and his team in the Sustainability Research Effectiveness Program (SRE) at Royal Roads University have developed methods to assess TDR. The SRE Program has also conducted a series of case studies of completed FTA research projects to investigate the link between transdisciplinary research and societal effects. They recently published two papers to share lessons from their work.

A refined method for theory-based evaluation of the societal impacts of research [pdf]
A refined method for theory-based evaluation of the societal impacts of research” (Belcher et al., 2020) provides a detailed description of concepts and a method for assessing the relationship between research processes, outputs, and outcomes. The Outcome Evaluation Approach uses an actor-centred Theory of Change as the analytical framework, and accounts for complexity by recognizing the role of other actors, context, and external processes in change. The article provides stepwise guidance on how to:

  • document a theory of change;
  • determine data needs and sources;
  • collect data;
  • manage and analyze data; and
  • present findings.


The paper responds to the need for appropriate methods to demonstrate (for accountability) and analyze (for learning) whether and how research projects contribute to change processes, in an effort to make research more effective in addressing complex sustainability challenges.

Linking transdisciplinary research characteristics and quality to effectiveness [pdf]
Linking Transdisciplinary Research Characteristics and Quality to Effectiveness: A Comparative Analysis of Five Research-for-Development Projects” (Belcher et al., 2019) reports lessons from outcome evaluations [1] of five FTA projects. The five projects:

  1. Brazil Nut Project (BNP)
  2. Sustainable Wetlands Adaptation and Mitigation Program (SWAMP)
  3. Fire and Haze Indonesia (F&H)
  4. Global Comparative Study on Forest Tenure Reform-Peru (GCS-FTR), and
  5. Support to the Development of Agroforestry Concessions in Peru (SUCCESS)



represent a wide range of research approaches, social and policy contexts, and outcomes. Each case study used the Outcome Evaluation Approach described in Belcher et al. (2020) to document the project’s Theory of Change and assess whether and how outcomes were realized. The analysis also used Belcher et al.’s (2016) Transdisciplinary Research Quality Assessment Framework (QAF) to characterize each project by the degree to which its design and implementation conformed with transdisciplinary criteria.

Each project had a deliberate focus on moving beyond knowledge production to influence policy and practice. To do that, the projects employed a variety of strategies that crossed disciplinary bounds and engaged a range of partners and stakeholders at different levels. The results demonstrate that projects employing more transdisciplinary characteristics make more diverse contributions as they tend to leverage more diverse mechanisms of change. The participation of various system actors contributed to projects’ relevance and strongly contributed to the uptake and use of the research. Projects that invested most in developing and facilitating participation (e.g., the Global Comparative Study on Forest Tenure Reform-Peru and the Support to the Development of Agroforestry Concessions in Peru projects) were the most successful in generating social learning and building coalitions. Projects that employed the most traditional scientific models (e.g., the Brazil Nut Project and the Sustainable Wetlands Adaptation and Mitigation Program) but still invested in outreach and engagement, were able to realize significant outcomes. Research project efforts to support social processes helped translate and broker knowledge outputs and made substantial additional contributions through capacity-building, initiating and supporting discourse, and relationship-building.

Given the results, it is clear that research aiming to influence policy and practice change should consider integrating and reflecting on TDR characteristics more intentionally from the early planning stages and throughout the whole research process. This new Outcome Evaluation Approach will help linking outcomes, outputs and TDR more effectively, justifying the need for more transdisciplinary science, with an increase in overall results and global benefits.

[1] Two individual  project outcome evaluation reports have been published (Brazilian Nut, SWAMP), while the others are forthcoming (F&H, GCS-FTR, SUCCESS).

FTA is the world’s largest research for development program to enhance the role of forests, trees and agroforestry in sustainable development and food security and to address climate change. CIFOR leads FTA in partnership with Bioversity International, CATIE, CIRAD, INBAR, ICRAF and TBI. FTA’s work is supported by the CGIAR Trust Fund.

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