Trees are infrastructure made of living tissue
A mature tree can look passive.
It stands in one place for decades, perhaps centuries. Yet during that time it is continuously exchanging water, carbon and energy with its surroundings. Its roots alter soil. Its leaves intercept rain and sunlight. Its canopy changes temperature and humidity. Its flowers and fruit feed other organisms. Its trunk stores carbon. Its cavities become shelter. When it dies, its wood continues to support fungi, insects and nutrient cycling.
At the scale of a forest, watershed, farm or city, these processes become infrastructure.
That is why the importance of trees is much broader than the familiar list of “oxygen, shade and wood”. Trees help regulate climate and water, protect soils, support biodiversity, contribute to food systems and provide livelihoods and cultural value. Their effects differ by species and location, but their influence is woven into many systems people depend on.
Trees and carbon: a major climate role
Trees absorb carbon dioxide during photosynthesis and incorporate carbon into wood, roots, leaves and other tissues. Forest soils and dead organic matter store additional carbon.
FAO estimates that forests cover roughly 31 percent of the world’s land surface and store hundreds of gigatonnes of carbon. That makes forest conservation, restoration and sustainable management central to climate policy.
The process is not limitless. A tree does not absorb carbon at the same rate forever, and forests can lose stored carbon through fire, drought, decomposition, harvesting or clearing. Different forest types store very different amounts above and below ground.
The climate significance of trees therefore comes from the whole carbon cycle: keeping large existing stocks out of the atmosphere, increasing stocks where forests recover and using forest products sustainably where appropriate.
Protecting mature forests and adding well-chosen trees are complementary actions, not substitutes for reducing fossil-fuel emissions.
Trees shape water in complicated ways
Trees are deeply connected to the water cycle.
Rain strikes leaves and branches before reaching the ground. Roots create channels in soil and can improve infiltration. Forest litter protects the surface from raindrop impact. Vegetation slows erosion and reduces the amount of sediment entering streams.
Forests also use water and return large quantities to the atmosphere through evapotranspiration. This moisture can influence humidity, clouds and rainfall locally and far downwind.
FAO’s Forest and Water Programme describes forests as important to streamflow regulation, groundwater recharge, erosion control, sediment reduction and atmospheric water recycling. Forested watersheds are also major sources of freshwater for cities and agriculture.
These benefits should not be simplified into “trees create water”. In some dry catchments, additional tree cover can reduce the amount of water flowing in rivers because trees transpire more water than the vegetation they replace. Forest-water relationships are therefore among the clearest examples of why ecological benefits depend on context.
Soil protection begins above and below ground
Bare soil is vulnerable to wind and water erosion.
Tree canopies intercept rainfall, while roots bind soil and stabilise slopes and riverbanks. Leaf litter cushions the soil surface, adds organic matter and supports organisms that build soil structure.
In agricultural landscapes, tree belts can reduce wind speed and help protect crops and topsoil. On steep terrain, forest cover can reduce erosion and sediment movement when compared with poorly managed bare land.
FAO notes that forests and trees can maintain soil fertility, reduce erosion and support water quality. Around the world, hundreds of millions of hectares of forest are designated primarily for soil and water protection.
Trees are not a guarantee against landslides or floods, but healthy vegetation can be an important part of risk reduction and watershed management.
A tree is habitat from roots to canopy
To many organisms, a tree is not scenery. It is home.
Bark supports lichens and insects. Leaves feed caterpillars and browsing animals. Flowers provide nectar and pollen. Fruits and seeds feed birds and mammals. Cavities shelter bats and nesting birds. Roots interact with fungi and soil organisms. Fallen branches and dead trunks support decomposers.
Forests contain the majority of the planet’s terrestrial biodiversity, according to FAO. Tropical rainforests are especially species-rich, but trees also support life in temperate forests, drylands, savannas, agricultural landscapes and cities.
The ecological value of a tree depends partly on its relationships. A locally native species may support insects and birds with which it has co-evolved. An exotic ornamental tree may still provide shade or carbon storage but offer different habitat value.
This is one reason biodiversity-oriented planting looks beyond the number of trees and considers species identity, age, structure and connectivity.
Trees support agriculture
Forests and farms are sometimes presented as competitors for land, and at the frontier of deforestation they often are.
But trees also support agriculture.
They provide habitat for wild pollinators and predators of agricultural pests. Windbreaks protect crops. Shade can reduce heat stress for livestock and some crops. Tree roots can stabilise soil and cycle nutrients. Forested catchments can support water quality.
FAO’s 2025 work on forest-agriculture links emphasises the influence of forests and trees on temperature, rainfall patterns, water availability, soil fertility, pollination and pest management.
Agroforestry deliberately brings some of these relationships onto farms by combining trees with crops or livestock. It is not suitable everywhere, but it demonstrates that productive landscapes do not have to be divided into “forest” and “agriculture” as completely separate systems.
Food, fuel and income
The importance of trees is also immediate and material.
Forest and tree products include fruits, nuts, seeds, mushrooms, honey, fodder, medicines, resins, fibres and wood. FAO reports that billions of people use forest and non-timber forest products for food, medicine or livelihoods, while more than two billion people continue to rely on wood or other traditional fuels for cooking.
For many rural households, trees act as economic buffers. Forest foods and products can supplement income when crops fail or employment disappears. In drylands, trees may provide fodder during periods when grasses are scarce.
These benefits are often undervalued because they are consumed directly by households rather than sold through formal markets.
Trees in cities
Urban trees perform a different but increasingly important set of functions.
Shade reduces the amount of solar radiation reaching streets, pavements and buildings. Evapotranspiration can cool the surrounding air. Tree cover can therefore help moderate the urban heat island effect, especially when distributed where people actually walk and live.
Trees can intercept some stormwater, reduce noise and provide habitat in highly modified landscapes. Green spaces are also associated with opportunities for recreation and contact with nature, although the health benefits depend on access, safety and design.
Urban forestry comes with management challenges. Roots can conflict with infrastructure. Pollen can worsen allergies. Trees require water, pruning and protection from heat and construction damage. Poor species selection can increase storm failure or invasive-species risks.
The lesson is not that every street needs the same tree. It is that cities should treat tree canopy as long-term infrastructure requiring planning and maintenance.
Trees do not “make” all the oxygen we need
The popular statement that forests are the “lungs of the Earth” gives trees credit for something real—photosynthesis releases oxygen—but often explains it poorly.
Terrestrial plants and ocean organisms both contribute to global oxygen production. At the same time, plants, animals and microbes consume oxygen through respiration, and decomposition consumes oxygen as organic matter breaks down. Mature ecosystems recycle much of the oxygen they produce.
The atmosphere already contains an enormous reservoir of oxygen. The urgent reasons to protect forests are therefore not that humans will suddenly run out of breathable oxygen if trees are lost.
They are carbon storage, biodiversity, water regulation, soil protection, climate moderation, livelihoods and many other ecosystem services.
Trees are important enough without a misleading metaphor.
A single tree and a forest are not equivalent
Tree planting is often discussed as if all tree cover were interchangeable.
It is not.
A roadside tree may provide valuable shade but little habitat connectivity. An orchard produces food but differs from a natural woodland. A timber plantation may supply renewable materials while supporting less biodiversity than an old forest. A mangrove tree performs coastal functions that a similar-sized inland tree cannot.
The value of trees therefore comes from both the organism and the system around it.
Species, age, density, soil, climate, management and landscape position determine what benefits emerge.
Why old trees deserve special attention
Large old trees can hold disproportionately high ecological value.
They contain substantial stored carbon, complex branch structures, hollows and deadwood features that younger trees may take decades to develop. Their root systems and canopies influence local conditions at a scale seedlings cannot immediately reproduce.
Replacing a mature tree with several saplings may eventually recover some functions, but not instantly.
This is a general principle of restoration: planting is important, but conservation prevents the loss of ecological capital that takes a long time to rebuild.
Trees matter because systems depend on them
It is tempting to search for one sentence explaining why trees matter.
There is no single answer because trees perform different roles in different places.
They can be carbon stores, habitat, food sources, windbreaks, soil stabilisers, cultural landmarks, sources of medicine and timber, shade structures, components of watersheds and parts of complex atmospheric water cycles.
Their importance emerges from accumulation: billions of individual organisms collectively shaping landscapes and human economies.
That makes the most useful question more specific than “Are trees good?”
It is: Which trees, in which place, managed for which purpose, as part of which ecosystem?
Answering that well is what turns tree planting and forest management from symbolism into environmental policy.
Sources / Further Reading
FAO — Forests — https://www.fao.org/forests/en
FAO — International Day of Forests 2025 key messages — https://www.fao.org/international-day-of-forests/past-years/2025/key-messages-2025/en
FAO — Forest and Water Programme: The Forest-Water Nexus — https://www.fao.org/in-action/forest-and-water-programme/overview/en/
FAO — Sustainable forest management for soil and water conservation — https://www.fao.org/forestry/sfm/sfm-for-soil-and-water-conservation/en
FAO — Sustainable forest management for biodiversity conservation — https://www.fao.org/forestry/sfm/sfm-for-biodiversity-conservation/en
FAO — Climate and ecosystem service benefits of forests and trees for agriculture (2025) — https://www.fao.org/family-farming/detail/en/c/1754952/
Suggested Internal Links
Understanding the Importance of Rainforests — Planned internal link
Understanding the Role of Forests in Climate — Planned internal link
Understanding Reforestation — Planned internal link
Understanding Biodiversity Loss — Planned internal link
What Is the Urban Heat Island Effect — Planned internal link
Understanding the Importance of Pollinators — Planned internal link
