Forests are often called the lungs of our planet. They absorb carbon, support untold webs of life, conserve soil, filter water, and regulate climate. When it comes to addressing climate change, biodiversity loss, and ecological collapse, many people understandably zero in on tree planting. Trees feel hopeful. They are visible, tangible. Governments launch planting pledges, corporations make afforestation commitments, and communities hold tree-planting events. But there is a critical piece of the story that is too often glossed over: protecting the forests that already exist—especially old-growth, primary and intact forests—is at least as important, often more so, than planting new trees. Without strong forest conservation, tree planting in many forms may be insufficient—or even counterproductive.
In what follows I explore why preserving what we already have is urgent and powerful: the unique carbon storage, biodiversity, ecosystem complexity, cost and time advantages, and the dangers of relying solely on reforestation or plantations. I also offer ways forward: how we can protect existing forests, support the people who steward them, and integrate mindful restoration where it makes sense.
The Power of Old and Intact Forests for Carbon Storage
Old-growth and primary forests are far more than just a collection of trees. They are carbon vaults. A mature forest doesn’t merely sequester carbon in its living tree biomass; it accumulates carbon in deep soils, in dead wood, in organic leaf litter, in root systems, and even in standing dead trees (snags).
Research shows that old-growth forests continue to act as carbon sinks over hundreds of years—not just when they are young and growing fast, but long afterward. A study of forests up to 800 years old found that many such forests have positive net ecosystem productivity—meaning they absorb more CO₂ (including soil and litter components) than they release. This counters the old assumption that aging forests always become carbon neutral.
Old growth forests store substantially more carbon per hectare than younger forests or managed forests. For example, a global assessment showed that forest stands older than 200 years hold about 98 megagrams of carbon per hectare, while stands under 20 years hold about 43.5.
Another study in temperate forests compared old‐growth stands in the eastern United States with surrounding younger forests, and found the old stands stored at least 30 percent more carbon overall. A striking portion of that extra was in dead wood—in downed logs and standing dead trees. In those old stands, dead wood accounted for nearly 20 percent of the total carbon stored—far more than in younger forests.
When old-growth forests are converted to younger forests or plantations (through harvesting or clearcutting), we don’t only lose living biomass; carbon that was stored in soils and dead wood often gets released. Even if reforestation or planting occurs afterward, it can take centuries for that forest to re-accumulate the same amount of carbon. In some modeled cases, converting old-growth forests in western Oregon and Washington to younger fast-growing forests increased atmospheric CO₂ for at least 200 years, compared with keeping the old growth intact.
So in terms of greenhouse gas emissions and the climate crisis, protecting old forests is one of the fastest, highest-leverage approaches we have.
Why Biodiversity Depends on Old Forests, Not Just Plants
A forest is so much more than trees. It is habitat. It is soil microbial communities, fungi, insects, birds, mammals, amphibians, reptiles. Many species are specialized for niches found only in mature, undisturbed forest. Restoration or plantations may attempt to mimic forest structure, but recreating the complexity of a mature forest takes centuries, when it’s even possible.
The evidence is strong that primary (undisturbed) forests harbor more species, more rare species, and species that cannot survive in secondary or planted forests. In one large-scale tropical study, comparing primary, secondary, and plantation forests across many taxa (plants, birds, insects, etc.), researchers found that almost 60 percent of tree and liana genera were only ever recorded in primary forest. The share of species unique to primary forest averaged about 25 percent across all taxa (versus 8-11 percent in plantations and secondary forests).
Beyond species richness, it's also about community composition. Secondary forests and plantations often lack the full complement of species that primary forests have, especially those sensitive species, those with specialized niches, or those that require old trees, dead wood, complex microhabitats. Many amphibians, certain insects, and understory plants fall into this category.
Biodiversity value isn’t simply aesthetic. Healthy, intact ecosystems provide services: pest control, pollination, seed dispersal, maintaining soil fertility, water purification, and resilience to disturbance and climate extremes. Destroying intact forest not only eliminates species, but undermines ecosystem functions that are vital for human well-being.
Forest Conservation Is More Immediate and Often More Cost-Effective
Restoring or planting trees is important. But in many cases it is slower, less certain, and more expensive when compared to preserving what remains. When we protect a standing forest from logging, fire risk, fragmentation, or other threats, many benefits follow immediately:
The carbon stored stays stored. There is no need to wait decades or centuries for new growth to replace older trees, soil carbon, dead wood, etc.
Habitat is preserved. Species that depend on complex forest structures, canopy layers, fallen logs, stable microclimate, mature trees, continue to survive.
Ecosystem services such as water filtration, soil stabilization, flood control, and local climate regulation continue uninterrupted.
Often, protecting land is cheaper per unit of carbon or biodiversity preserved than restoring or replanting forests, especially in remote or degraded areas with soil compaction, invasive species, erosion, or altered hydrology.
For instance, primary forests store between 30 and 70 percent more carbon than other (secondary or managed) forests. To lose that is to lose a built-up carbon bank that would require many decades to rebuild.
Also, preservation avoids many hidden costs: protecting forests means enforcing against illegal logging, fighting fire, controlling land conversion, and often working with local communities to maintain forest health. While these have costs, they are often less than those associated with planting, protecting saplings, dealing with mortality of planted trees, correcting for failure to regenerate, and managing plantations.
The Risks and Trade-Offs of Relying Too Heavily on Tree Planting
Tree planting sounds like a win, and in many contexts it is, but not all tree planting is created equal. Sometimes “planting” is used as a greenwashing tool, or as a substitute for conserving what remains. Some risks:
Monocultures vs diversity
When large tree planting programs favor fast-growing species, or monocultures, the biodiversity value is low. These plantations seldom mimic the layered structure, species mix, or the soil and microbial complexity of primary forest. Studies show that plantations have significantly lower richness and abundance across trophic levels compared to primary forests. In some meta-analyses the species richness in plantations is 30-40 percent lower.
High mortality, maintenance demands
Young trees in planted landscapes often die due to drought, pests, improper species selection, competition with weeds, or soil degradation. Without ongoing care, many planted trees fail. They may survive as saplings but never reach maturity. Planting projects often underestimate long-term costs: watering, protection, ensuring that understory regenerates, controlling invasives, ensuring connectivity to existing forest patches.
Carbon payback time
Even when planting succeeds, there is a “payback” period. It can take decades for planted trees to grow biomass sufficient to match what was lost when mature or old forest was cleared. During that period, carbon emissions from soil disturbance, decay of dead wood, or from clearing land might outweigh uptake. Unless the planted area is strictly protected and matured, it might never “repay” the carbon debt.
Land trade-offs
If plantations replace natural grasslands, wetlands, or savannas, the net ecological gain might be negative, even with more trees. If planting initiatives displace indigenous or local land use without involvement, they can cause social harm or lead to conflict.
Greenwashing & policy misuse
Corporations or governments may claim planting millions of trees while continuing policies that allow deforestation, forest degradation, or destruction of old growth. Planting often becomes a badge rather than a real fix. Some policies may permit cutting primary forests and then promise to plant new ones elsewhere, which does not preserve the qualities of the original forest.
Putting It in Perspective: What We Already Have, What We’ve Lost, and What’s at Risk
It helps to understand how much forest remains and what condition it’s in. While the numbers differ depending on definitions and data sources, some broad patterns are consistent:
Primary and intact forests have been shrinking, especially in tropical regions (Amazon, Congo Basin, Indonesia), boreal forests in certain parts of the world, and in temperate zones where old forest patches have been logged or fragmented. According to the International Union for Conservation of Nature (IUCN), primary forests (including intact forest landscapes) represent a crucial portion of global forest cover, forest types that remain mostly undisturbed by large-scale industrial land use. These forests are often located in remote areas, managed or inhabited by Indigenous communities, or under protection.
Yet only a fraction of those primary forests are formally protected. Roughly 20 percent of the world’s primary forest is in protected areas; much of the rest faces threats from logging, agricultural expansion, mining, infrastructure, and climate impacts.
Conversions of old or primary forest to plantations, agriculture, or disturbed forests continue to contribute massively to greenhouse gas emissions. One study in the Brazilian Amazon illustrated that secondary forests—those regrowing after clearing—have offset less than 10 percent of carbon emissions caused by old-growth deforestation, at least in certain analyses.
Conservation, Restoration and the Role of Indigenous Peoples & Local Communities
Protecting existing forests isn’t just an environmental or biological issue, it’s often a human rights, cultural heritage, and social justice issue. Many of the world’s primary forests are on lands stewarded by Indigenous peoples and local communities. These communities have knowledge, traditions, and cultural systems deeply intertwined with their forests.
A growing body of evidence shows that Indigenous land stewardship often results in better conservation outcomes. Where Indigenous communities have secure land rights, traditional governance, and are empowered in decision-making, rates of deforestation, forest degradation, and biodiversity loss are significantly lower. Protecting these lands is both morally imperative and practical.
In policy and climate discussions, supporting Indigenous stewardship is increasingly recognized as a key lever for conservation. For example, in global agreements, Indigenous peoples are often included as co-stewards of protected lands, or partners in conservation-finance mechanisms. Maintaining traditional knowledge, safeguarding land tenure, and helping communities resist exploitation or illegal land conversion are essential.
When and Where Tree Planting Makes Sense, But Only as Part of a Broader Strategy
This isn’t an “either-or” situation: new tree planting has an important place. But its success and value depend heavily on how, where, and why it’s done.
Restoration is powerful in severely degraded landscapes, in areas where natural regeneration is feasible, in regions where degraded lands are no longer under threat of immediate conversion, or where planting helps reconnect forest patches. Planting native species, using diverse species mixes, ensuring genetic diversity, careful site preparation, invasive species control, and long-term maintenance are all essential practices.
Mixed species plantings, for example, often outperform monocultures in long-term carbon retention and resilience. They also better support biodiversity and are more resilient to pests, disease, climate extremes. Some modeling (in boreal lands, including Canada) shows that medium density mixed stands of deciduous and coniferous trees can sequester significantly more carbon than pure conifer plantations, and maintain greater resilience.
Allowing for natural regeneration (secondary forests) can sometimes be even more cost-effective than planting. But secondary forests face challenges: they might be frequently disturbed before mature; they may lack seed banks or diversity; they may be invaded by non-native species; or fragmentation may reduce their resilience.
Why Preservation Must Be Priority One
Putting together all the pieces, the case is clear: forest conservation must be prioritized in climate, biodiversity, and land use policy.
First, because the carbon stored in mature and primary forests is vast, and losing it implies immediate emissions, reducing that carbon sink, and making climate goals harder or impossible to meet.
Second, because biodiversity is under threat, especially of species that rely on old forest structure. The loss of primary forests irreversibly impacts species extinctions and ecosystem function.
Third, protecting existing forests is often more cost effective, more reliable, and yields returns immediately, whereas planting has delays, mortality, and many potential pitfalls.
Fourth, policy frameworks and funding often emphasize tree planting (perhaps because it is more politically appealing or easier to quantify) but sometimes do so in ways that ignore or even undermine forest protection (for example, allowing clearing primary forest and replacing it with new tree plantations elsewhere). Without policies that preserve what exists, many planting efforts may just shift harm rather than reduce it.
Pathways Forward: How to Protect Forests & Leverage Restoration Responsibly
To effect change in meaningful ways, here are strategies that individuals, communities, governments, and organizations can pursue:
Legal protection of old, primary, and intact forest landscapes: Strengthen laws, land-use planning, enforce protections. Expand the area under protection in a way that is ecologically meaningful (not just pieces, but connected landscapes).
Secure land rights for Indigenous and local communities: Recognition and enforcement of land tenure tends to correlate with lower deforestation. Support Indigenous knowledge systems, stewardship, and co-management.
Integrate forest conservation in climate policy: Carbon accounting, emissions trading, offsets, sustainable finance should give real credit for preserving existing forests, not just for planting new ones. Policies should avoid perverse incentives that encourage logging now in order to “offset” with future planting elsewhere.
Prioritize restoration where it is needed and viable: Restoration should be in areas beyond the point of immediate threat, where natural regeneration is possible or where planting can help reconnect habitat corridors or degraded landscapes. Use native species, diverse mixes, ensure safeguarding from fire, pests, invasives, drought.
Reduce the pressures that drive deforestation: Demand for agricultural land (especially for commodities such as palm oil, soy, beef), logging, mining, infrastructure expansion threaten forests. Consumers, companies, governments can shift supply chains, support sustainable agriculture, enforce zero-deforestation commitments, reduce consumption of high-impact products, and promote alternative livelihoods.
Improve monitoring, transparency, funding, and enforcement: Use remote sensing, citizen science, and on-the-ground monitoring to detect illegal clearances, degradation, fires. Increase funding for conservation programs. Ensure enforcement of laws and policies; without enforcement legal protection is only paper.
Raise public awareness and build political will: People often see tree planting as the “easy, positive” story. But awareness of what’s at stake with forest preservation helps shift priorities, supports more nuanced policy, and encourages support for protecting what we already have—not just growing new forests.
Conclusion: The Lungs We Already Have Need Care
Tree planting is inspirational. It offers hope, a visible way for people to engage. And when done well, restoration is a vital part of the solution. But hope is not enough. Unless our efforts and policies are anchored in preserving and protecting the remaining old, intact, primary forests, we risk losing irreplaceable carbon stores, biodiversity, ecosystem services, and the resilience that mature ecosystems provide.
Protecting the “lungs of the Earth” must come first. Let us nurture what is still alive, what has already stood for centuries, for its own sake and for ours. Then restore where restoration makes sense, always with diversity, long-term care, and respect for the land and people who steward it.