Rooted solutions: How trees sustain human and planetary health

He who plants a tree, plants a hope.

–Lucy Larcom

Felix Mittermeier / Pexels

Trees are among the most dynamic systems on Earth, quietly orchestrating ecosystems while profoundly influencing human and planetary health. Beyond their well-documented roles in carbon storage and oxygen production, trees are vital change agents in the fight against climate change, biodiversity loss, and food insecurity. Their ability to transform landscapes, enhance ecological resilience, and support the transition toward more sustainable food systems positions them as a cornerstone of the 21st century grand challenges.

Trees as climate champions

Trees sustain life on Earth in countless ways.

Beneath the surface, their roots stabilize soil, absorb rainwater, and prevent erosion, while above ground, their canopies regulate temperature and humidity. During storms, tree canopies intercept 25.6% of rainfall, significantly reducing the risk of flooding. Trees also create small, localized climates that provide shade and mitigate heat stress for crops and livestock. Equally vital is their role in carbon sequestration, positioning them as indispensable allies in the fight against climate change. 

A single mature tree produces approximately 22 kg of oxygen annually while absorbing 9 kg of CO2–an amount comparable to the foodprint of just one day on a high-meat diet!

As natural air purifiers, trees are vital to improving environmental quality and supporting urban health. They help mitigate heat in cities by providing shade and lowering ambient temperatures while filtering pollutants like particulate matter and carbon dioxide, and releasing life-sustaining oxygen. Mature trees (>76.2 cm in diameter), with their larger canopies and extensive root systems, are especially effective in removing 60-70% more air pollution annually than younger trees (<25.4 cm in diameter). This increased efficiency yields significant public health benefits and economic savings, including the costs avoided through reduced air pollution and its associated impacts.

Trees for human health

Trees significantly impact human health through improved air quality while simultaneously fostering physical and mental well-being. As integral components of green infrastructure, tree-enriched green spaces have been consistently associated with reduced stress levels and improved mental health, as demonstrated in various cross-sectional studies.

A comprehensive narrative review of experimental and observational studies highlights that regular exposure to nature, including green spaces, is linked to lower chronic diseases, such as cardiovascular conditions and obesity. This is largely attributed to the promotion of physical activity, as these spaces encourage walking, running, cycling, and other forms of outdoor exercise.

In cities, trees act as natural filters, removing airborne pollutants that contribute to respiratory diseases and potentially preventing thousands of premature deaths each year. By mitigating environmental stressors and fostering healthier lifestyles, trees offer profound public health benefits, highlighting their importance in urban planning and policy.

Trees and the resilience of our food systems

Regarding food, trees are sources of fruits, vegetables, spices, medicines, and timber. Their existence supports above- and below-ground biodiversity, stabilizes agricultural landscapes, and builds ecosystem resilience to climate shocks and economic disruptions. 

For example, in Kutai National Park in East Kalimantan, tree species such as Borassodendron borneense (Bendang) and Eusideroxylon zwageri (Ulin) have been identified as resilient to climate change and fire events. These species were recommended for reforestation efforts due to their ability to recover quickly after disturbances (eg, droughts and fires) while supporting endemic wildlife species, including orangutans. 

Trees also play a role in the resilience of household diets.

With the global population projected to reach 9 billion by 2050, increasing pressure on food systems demands innovative solutions. Forests and tree-based landscapes offer nutrient-rich foods, contributing to dietary diversity and food security. 

Traditional agroforestry systems in Indonesia, such as Parak in Sumatra, Dusung in Maluku, and Kaliwu in Sumba, exemplify the potential of integrating trees with agricultural crops. These systems enhance biodiversity, sustain local economies, and improve dietary diversity, serving as models for sustainable food production.

Scaling up tree-based food production thus presents a transformative opportunity for reshaping food systems to meet both nutritional and environmental goals. 

For instance, a study in Burkina Faso mapped edible products from 56 food tree species and highlighted how seasonal food nutrient gaps were mitigated through tree fruits like mangoes and papayas, which provide diverse vitamins.

Integrating nutrition objectives into forest conservation and restoration initiatives can amplify the role of trees in promoting sustainable diets.

This means that tree crops not only meet daily nutritional requirements but also serve as critical resources during crises, such as droughts and famines, by providing seeds, tubers, leaves, and stems when crops fail. 

Integrating agriculture, forestry, and nutrition-focused efforts unlocks innovative pathways to build more resilient and equitable food systems, leveraging the multifunctional benefits of trees to address pressing nutritional and environmental challenges.

Trees for our tomorrow

Trees are much more than sources of shade and resources–they are the backbone of sustainable food systems, climate resilience, and human well-being. Reimagining our relationship with trees and embracing their transformative potential empowers us to create a future where both people and the planet can flourish. The urgency to act is clear–because trees truly matter.

As individuals, we can make a meaningful difference by advocating for more green spaces and participating in impactful tree-planting initiatives, such as Trees4Trees and LindungiHutan. Supporting local reforestation efforts or community-led tree-planting projects enables us to directly combat climate change. By planting just nine trees, each of us can offset approximately 4,500 kg of carbon over the 35-year lifespan, contributing to a healthier, more sustainable planet.

References:

1. Stancil, P. by J.M. (2015) The power of one tree - the very air we breathe, USDA. Available at: https://www.usda.gov/media/blog/2015/03/17/power-one-tree-very-air-we-breathe (Accessed: 26 November 2024). 

2. Agriculture (1992) FORESTS, TREES AND FOOD. Available at: https://www.fao.org/4/u5620e/u5620e05.htm (Accessed: 26 November 2024). 

3. Alivio, M.B., Šraj, M. and Bezak, N. (2023) ‘Investigating the reduction of rainfall intensity beneath an urban deciduous tree canopy’, Agricultural and Forest Meteorology, 342, p. 109727. doi:10.1016/j.agrformet.2023.109727. 

4. Shaamala, A. et al. (2024) ‘Strategic tree placement for Urban Cooling: A novel optimisation approach for desired microclimate outcomes’, Urban Climate, 56, p. 102084. doi:10.1016/j.uclim.2024.102084. 

5. Franklin, S.L. and Pindyck, R.S. (2024) A supply curve for Forest-based CO2 Removal, MIT Center for Energy and Environmental Policy Research. Available at: https://ceepr.mit.edu/wp-content/uploads/2024/03/MIT-CEEPR-WP-2024-04.pdf (Accessed: 26 November 2024). 

6. Isaifan, R.J. and Baldauf, R.W. (2020) ‘Estimating economic and environmental benefits of urban trees in desert regions’, Frontiers in Ecology and Evolution, 8. doi:10.3389/fevo.2020.00016. 

7. Arifwidodo, S.D. and Chandrasiri, O. (2024) ‘Urban Green Space Visitation and mental health wellbeing during COVID-19 in Bangkok, Thailand’, Frontiers in Public Health, 11. doi:10.3389/fpubh.2023.1292154. 

8. Barquilla, C.A., Lee, J. and He, S.Y. (2023) ‘The impact of greenspace proximity on stress levels and travel behavior among residents in Pasig City, Philippines during the COVID-19 pandemic’, Sustainable Cities and Society, 97, p. 104782. doi:10.1016/j.scs.2023.104782. 

9. Shanahan, D.F. et al. (2016) ‘Health benefits from nature experiences depend on dose’, Scientific Reports, 6(1). doi:10.1038/srep28551. 

10. Jimenez, M.P. et al. (2021) ‘Associations between Nature Exposure and Health: A review of the evidence’, International Journal of Environmental Research and Public Health, 18(9), p. 4790. doi:10.3390/ijerph18094790. 

11. Astell-Burt, T., Feng, X. and Kolt, G.S. (2013) ‘Greener neighborhoods, slimmer people? evidence from 246920 Australians’, International Journal of Obesity, 38(1), pp. 156–159. doi:10.1038/ijo.2013.64. 

12. Nowak, D.J. et al. (2014) ‘Tree and forest effects on air quality and human health in the United States’, Environmental Pollution, 193, pp. 119–129. doi:10.1016/j.envpol.2014.05.028. 

13. IUCN study identifies tree species for climate-resilient reforestation (2022) IUCN. Available at: https://iucn.org/news/species/201902/iucn-study-identifies-tree-species-climate-resilient-reforestation (Accessed: 26 November 2024). 

14. Dzakiyah, I.F. and Prasati, I. (2019) ‘ANALISIS PERUBAHAN TUTUPAN LAHAN AKIBAT BENCANA ALAM MENGGUNAKAN CITRA LANDSAT 8 Studi Kasus di Kota Palu dan Kabupaten Donggala’, Seminar Nasional Infrastruktur Berkelanjutan [Preprint]. 

15. Huss, C.P., Holmes, K.D. and Blubaugh, C.K. (2022) ‘Benefits and risks of intercropping for crop resilience and Pest Management’, Journal of Economic Entomology, 115(5), pp. 1350–1362. doi:10.1093/jee/toac045. 

16. Luedeling, E. et al. (2016) ‘Field-scale modeling of tree–crop interactions: Challenges and development needs’, Agricultural Systems, 142, pp. 51–69. doi:10.1016/j.agsy.2015.11.005. 

17. Tengnäs, B. (1994) Agroforestry Extension Manual for Kenya. Nairobi: International Centre for Research in Agroforestry. 

18. Jamnadass, R.H. et al. (2013) ‘Agroforestry, food and nutritional security’, World Agroforestry Centre [Preprint]. doi:10.5716/wp13054.pdf. 

19. Rosenstock, T.S. et al. (2019) ‘A planetary health perspective on agroforestry in Sub-Saharan africa’, One Earth, 1(3), pp. 330–344. doi:10.1016/j.oneear.2019.10.017. 

20. Cannarella, C. and Piccioni, V. (2011) ‘Traditiovations: Creating innovation from the past and antique techniques for rural areas’, Technovation, 31(12), pp. 689–699. doi:10.1016/j.technovation.2011.07.005. 

21. Zada, M. et al. (2022) ‘Contribution of small-scale agroforestry to local economic development and livelihood resilience: Evidence from Khyber pakhtunkhwa province (KPK), Pakistan’, Land, 11(1), p. 71. doi:10.3390/land11010071.