The Role of Old Trees in Ecosystems: Archives of Life and Time

Old trees are among the most majestic and yet undervalued beings in terrestrial ecosystems. For centuries, they have been regarded as symbols of endurance, wisdom and continuity in nature — from the oaks revered by Celtic cultures to the Californian sequoias that began growing before the fall of the Roman Empire.
Today we know that their significance goes far beyond symbolism: old trees fulfil vital ecological functions that neither young trees nor artificial structures can replicate.

In recent years, a growing body of research has shown that it is precisely the oldest trees in the forest that:

store the greatest quantities of carbon,
provide critical habitats for hundreds of species,
regulate nutrient cycles,
stabilise the local climate and microenvironment.

Their complex architecture, slow metabolism and immense biomass make them “ecosystems within ecosystems” — often more important than the rest of the surrounding forest stand. And yet, they are regularly cut down, overlooked and insufficiently protected — both in managed forests and in urban settings.

In this article, we explore what old trees are in ecological terms, what roles they play in the environment, why they are irreplaceable — and what we risk losing if they disappear.
Because by protecting old trees, we protect the entire hidden world beneath them.

What Are “Old Trees”? Definition and Significance

There is no single, universal definition of an “old tree”, as the age considered “old” varies significantly depending on the species, environment and ecological context.
For a European beech (Fagus sylvatica) growing in Central Europe, old age may begin after 150 years. For a bristlecone pine (Pinus longaeva) in the Sierra Nevada, not until after a thousand.
Yet regardless of the exact number of years, old trees share one thing in common: at some point, they stop being merely part of the forest stand and become central structures of the ecosystem.

Old ≠ Large

In popular understanding, an “old tree” is usually associated with size — a thick trunk and a broad canopy.
However, many old trees may be relatively small: growing in harsh conditions (e.g., in mountains or on poor soils), some specimens may be stunted yet centuries old.
Biological age does not always correlate with size — which is why researchers studying old trees use, among others, increment cores (dendrochronology) or non-invasive techniques like trunk tomography.

Old Trees as Keystone Species

Ecology uses the term keystone species to describe organisms whose presence has a disproportionately large impact on the structure of the entire ecosystem.
In this sense, old trees fulfil exactly that role:

Their architecture, metabolic rate and interactions with their surroundings make them central nodes of life.
Their presence influences the local microclimate, water cycling, species diversity and habitat stability.

Example:
In Australia’s eucalypt forests, only trees older than 150 years produce natural hollows large enough to house glossy black cockatoos (Calyptorhynchus lathami) — a species at risk of extinction (Gibbons & Lindenmayer, Forest Ecology and Management, 2002).

The Role of Old Trees in Long-Term Cycles

Old trees serve as unique “time banks” — organisms that not only live for centuries, but also integrate and stabilise ecological processes over long timescales:

Their crowns record climate change (through growth ring width),
Their root systems stabilise the soil for decades,
Their presence supports local mycorrhizal networks, which can only persist in the vicinity of mature trees.

Interesting fact:
Research in the Białowieża Forest has shown that old oaks and lindens act as “hydrological pumps”, maintaining local microclimates with stable moisture levels even during drought (Latałowa et al., Quaternary International, 2015).

Why Does Their Presence Matter?

Old trees:

Cannot be replaced quickly — you cannot “plant” a mature tree. Their functions develop over decades, sometimes centuries.
Are bioindicators of ecosystem health — their presence indicates habitat continuity, lack of disturbance and high ecological stability.
Connect the past with the future — their genotypes, interactions with mycorrhizal fungi and microhabitats form an ecological legacy that cannot be recreated once lost.

Old Trees and Carbon Sequestration and Nutrient Cycling

In discussions about absorbing atmospheric carbon dioxide, there is frequent emphasis on the need to plant new trees.
However, a growing body of research shows that it is old trees that are the most powerful “carbon vaults” in terrestrial ecosystems — and their role in the global carbon balance cannot be replaced by young tree plantations.

Old Trees = the Largest CO₂ Reservoirs

Old trees store vast amounts of carbon in their biomass — both above ground (trunk, branches, canopy) and below ground (roots).
Thanks to their long-term growth and large photosynthetic surface (leaves, needles), they are able to absorb CO₂ efficiently for decades or even centuries.

Research conducted in the rainforests of the Amazon and Pacific regions has shown that:
1% of the largest trees in a forest can store up to 50% of the total carbon contained in the forest biomass (Lutz et al., Nature, 2018).
Old trees often continue to grow actively and absorb more carbon than young, fast-growing individuals (Stephenson et al., Nature, 2014).

Myth: “Old Trees Are Less Productive”

For years, forestry has promoted the idea that once trees reach “maturity”, their growth slows and they become less useful.
However, the latest data challenge this oversimplification:

In many cases, the rate of biomass accumulation (i.e. carbon sequestration) increases with age, especially in trees with thick trunks and strong root systems.
Older trees can process and store more CO₂ than younger ones, as their photosynthetic capacity increases proportionally to their green biomass surface.

Example:
A 100-year-old Douglas fir (Pseudotsuga menziesii) can absorb over 50 kg of CO₂ per year, significantly more than a 20-year-old specimen of the same species.

Nutrient Cycling: Trees as “Life Donors”

Old trees not only store carbon — they also play a central role in the recycling of nutrients within ecosystems:

Fallen leaves, bark and dead branches form litter that nourishes the soil microbiome.
The roots of old trees engage in complex relationships with mycorrhizal fungi and bacteria, supporting the circulation of nitrogen, phosphorus and other micronutrients.
Even in the process of dying, an old tree continues to “feed” the ecosystem — its decaying biomass becomes a source of life for thousands of organisms.

Carbon Stability Over Time

One unique advantage of carbon sequestration by old trees is that it is long-term.
While the biomass of grasses, herbaceous plants or young trees may burn or decompose quickly, carbon stored in the trunks of old trees remains stable for hundreds of years, unless the tree is felled or destroyed.

Why This Matters for the Climate

In the context of climate change:

The loss of old trees results in the immediate release of dozens of tonnes of CO₂ into the atmosphere.
Planting young trees to replace felled old ones will not compensate for this loss for decades — if ever.

Interesting fact:
In just one old-growth forest reserve in British Columbia (Canada), the removal of one hectare of ancient forest can result in the loss of up to 500 tonnes of stored carbon — the equivalent of the annual emissions of an average car over more than 100 years (Sillett & Van Pelt, Forest Ecology and Management, 2020).

The Importance of Old Trees for Biodiversity and Ecosystem Stability

Biodiversity and ecological stability are the two pillars of a healthy ecosystem. Old trees function as regulators, stabilisers and organisers of biological life within this system.
Their presence alters not only local flora and fauna — it also influences long-term ecological processes such as succession, resilience to disturbances, and post-disaster regeneration.

“Umbrella Effect” – Old Trees as Guardians of Young Generations

Large, expansive canopies of old trees:

reduce evaporation of water from the soil,
stabilise the forest floor microclimate (reducing temperature and humidity fluctuations),
shield young seedlings from excessive sunlight and frost.

As a result, young plants growing in the vicinity of old-growth trees have a higher chance of survival, especially in challenging environmental conditions.

Example:
In temperate zones, seedlings of common hornbeam (Carpinus betulus) show up to twice the survival rate when growing in the shade of mature oaks, compared to open ground (Zajaczkowski et al., Annals of Forest Science, 2017).

The Tree as an Ecosystem Anchor

Old trees:

maintain soil structure thanks to their extensive root systems,
stabilise local hydrology,
act as “centres” of the mycorrhizal network — the fungal systems of old trees link numerous younger plants in a web of resource and signal exchange.

In this sense, old trees act as biological anchors — holding the forest in place, both physically and functionally.

Resistance to Disturbances

Ecosystems containing old-growth trees demonstrate greater resistance to:

strong winds (thanks to flexible, extensive crowns and deep roots),
drought (due to wider root spread and better water management),
invasive species (greater biodiversity = stronger competition).

Research from boreal forests in Canada has shown that the presence of old trees significantly reduces the spread of invasive species following wildfires (Johnstone et al., Ecology Letters, 2016).

Positive Feedback: More Old Trees = More Life

The presence of old-growth trees promotes the preservation of many other life forms:

More hollows → more birds → better insect population control.
More deadwood → more fungi → faster decomposition → improved soil quality.
More developed mycorrhizal networks → more effective plant regeneration.

It is precisely through these interconnected systems that old trees increase the ecosystem’s functional diversity — that is, the number of ecological services it can perform.

A Forest of All Ages = A Stable Forest

Age diversity within the forest stand (young, middle-aged and old trees) increases a forest’s ability to withstand sudden changes — if one generation is destroyed (e.g. by a storm), another can take over its functions.
Old trees form a key element of this structure — without them, the system loses its most vital services: retention, cooling, habitat provision and hydrological balance.

Threats to Old Trees and Their Protection

Although the role of old trees in ecosystems is invaluable, it is they who most often fall victim to short-sighted economic, urban planning and technocratic decisions.
They are too often seen as obstacles — to development, infrastructure, or “rational forest management”. The result? Systematic loss of old-growth trees worldwide.

1. Forestry Practices: Old = Inefficient?

In many countries (including Poland), forest management still relies on clear-cutting once trees reach a specified “harvest age”.
For many species, this age is 80–120 years — precisely the point at which trees begin to perform their most valuable ecological functions.

Consequently:

old trees are rare in managed forests,
many species dependent on hollows, deadwood or stable microclimates disappear,
forests are young, even-aged, and highly vulnerable to disturbances.

Example:
In Germany, only 6% of forests retain semi-natural character (Bundesamt für Naturschutz, 2021). In Poland, the situation is similar — forests containing old-growth trees constitute only a small fraction of state-managed land.

2. Urbanisation and Infrastructure

In cities, old trees are often lost due to:

road and construction development,
lack of proper protective procedures,
poor documentation or administrative error.

Although many of these trees are classified as natural monuments, their protection is often illusory, especially when in conflict with “development needs”.

Interesting fact:
In Poland, a natural monument can be declassified by municipal council decision if deemed necessary for investment — a serious legal loophole.

3. Climate Change

Old trees — though resilient — are increasingly vulnerable to:

prolonged droughts (especially with falling groundwater levels),
violent storms and winds (linked to climate change),
new pathogens and pests spreading due to warming temperatures.

At the same time, the loss of these trees diminishes the ecosystem’s ability to adapt to those very same changes, creating a dangerous feedback loop.

4. Mismanagement in Conservation

Even in protected areas, old trees are sometimes removed:

“for safety” (e.g. along tourist trails),
due to “fire hazard”,
in the name of “landscape maintenance”.

Often lacking:

proper assessment procedures of the ecological value of individual trees,
qualified dendrologists in decision-making processes,
awareness that old does not mean sick or dangerous.

What Can (and Should) Be Done?

1. Legal and Policy Measures:

Introduce systemic protection of old-growth trees outside national parks (e.g. in managed or municipal forests),
Make declassification of natural monument status more difficult,
Create “maps of ecologically valuable trees” in cities and rural areas.

2. Education and Civic Monitoring:

Educate foresters, planners and decision-makers about the role of old trees,
Support grassroots initiatives and local campaigns (e.g. “Save the Lime Avenue”).

3. Reserves and Buffer Zones:

Designate untouchable zones around old trees, including in commercial forests,
Launch “Old Growth Forest Network” style programmes, modelled after US initiatives.

Case Studies: Protecting Old Trees Around the World

Although old trees are under threat globally, a growing number of initiatives are successfully working to protect them.
Below are some inspiring examples from various countries — showing that conservation policies can be modern, science-based and publicly supported.

1. Australia – Eucalypt Old-Growth and Hollow-Dwelling Species

In south-eastern Australia, ancient eucalypts are the only habitat for many hollow-nesting birds, including the glossy black cockatoo and the superb parrot.
In response to dramatic declines in such species, the state of Victoria introduced:

Logging moratoria on trees over 150 years old,
Hollow-tree mapping and targeted habitat protection,
Programmes to conserve “paddock trees” — lone old trees in agricultural landscapes.

Outcome:
Populations of some bird species have begun to stabilise, and the number of recorded hollow-bearing trees increased by over 40%, thanks to improved monitoring systems (Gibbons et al., Conservation Biology, 2021).

2. Poland – Natural Monuments and the Białowieża Forest Legacy

Poland has a long-standing tradition of protecting individual trees as natural monuments — over 35,000 trees currently hold this status.
In addition:

The Białowieża Forest conserves thousands of old oaks, lindens, ashes and spruces over 200 years old,
It remains one of Europe’s best-preserved examples of primeval forest, where the natural life cycle of trees is observed without human interference.

Fun fact:
In Białowieża, over 1,700 species of saproxylic fungi (those that decompose wood) have been recorded — many of which depend on old, dead trees at various stages of decay.

3. United States – Old Growth Forest Network

In the USA, the nationwide Old Growth Forest Network aims to:

Identify and protect ancient trees in every state,
Incorporate these areas into a permanent network free from logging,
Raise public awareness of the value of old trees.

The initiative combines local government, science and community activism. As of 2024, the network includes over 190 sites, including groves of sequoias, oaks, maples and mixed forests.

4. United Kingdom – Ancient Tree Inventory

The Woodland Trust in the UK maintains a public database of the country’s oldest trees — the Ancient Tree Inventory.
Anyone can submit a tree by providing:

GPS location,
Estimated age and species,
A photo and description.

Thanks to this initiative, over 180,000 ancient trees have been identified, many of which have since received additional legal protection at the local level.

Outcome:
Growing public awareness has sparked dozens of local campaigns to protect and maintain heritage trees.

5. India – Sacred Trees and Cultural Protection

In many parts of India, ancient trees — especially banyans, neem and sacred fig — are protected by deep-rooted cultural traditions.
In rural communities, taboos prohibit cutting certain trees, regardless of economic value.

Although this form of protection is informal, it has proven remarkably effective:
Many of these trees are over 500 years old and still provide essential ecological services in agricultural landscapes.

Old trees are far more than just “big trees”. They are living archives of time, guardians of biodiversity and essential pillars of ecosystem stability. Their presence influences climate, carbon cycling, habitats for hundreds of species and soil health.
Their complex structure, deep ecological ties and sheer longevity make them irreplaceable ecological infrastructure — far beyond what new plantings or green technologies can offer.

In an era increasingly dominated by short-term thinking, old trees remind us of nature’s patience, complexity and interdependence.
Their value lies not just in tonnes of carbon or species counts, but in the living memory of the land — and the continuity they represent.

More than ever before, we must ask ourselves:
Can we allow nature to endure — not for our use, but for life itself?

Because when an old tree is lost, a whole world disappears — and rebuilding it takes more time than we have.