What is an Old-Growth Forest and Why are They Important?

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Written By Kira Nash

Eco-Conscious Nature Enthusiast

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Home » Tree Conservation » What is an Old-Growth Forest and Why are They Important?

Before I say anything else, I will emphasize that old-growth forests really are vital. When you consider that the planet has lost 52% of its biodiversity in the past four decades, the value of the ecosystems that old-growth forests provide cannot be overstated.

But you might wonder what is an old-growth forest, and why are they important?

The second part of that is easy; the first, not so much.

Old-growth forests may also be referred to as ancient woodland, virgin forests, primeval, intact, undisturbed, or primary forests. This last term is as opposed to secondary forests, also called second-growth forests, where the woodland has regrown after a timber harvest or other clearing.

There are also young-growth forests, but these can be either secondary forests or quite literally just young, i.e., new, forests.

From the Amazonian rainforest to Bryan Wood in Wales and the forests of Central Siberia, old-growth forests can be found all over the world. And they’re under threat everywhere, from climate change, pollution, and human interference like logging and agriculture.

Old-Growth Forest Definitions

There are definitions for old-growth forests, but there are more than a few of them. What’s worse, none of them is especially specific. This allows for different organizations with different objectives to mould the definitions to their benefit.

As Bard Kahn from the Forest Stewardship Council said, standards are “a judgment call; if you ask Greenpeace, it’s going to be a different answer than a timber company.”


For example, the United Nation’s Food and Agriculture Organization describes an old-growth forest anywhere in the world as “a naturally regenerated forest of native species, where there are no clearly visible indications of human activities and the ecological processes are not significantly disturbed.”

They also give an updated definition which includes the traditional practices of indigenous and local communities.

The problem with the FAO’s definition in both its parts is that it’s vague and subjective. “Clearly visible”, “significantly disturbed”: those are both subject to interpretation. They’re also not the only definitions.

Mushroom Colony growing on a fallen log
Photo by adege at Pixabay

British Columbia

The government of British Columbia in Canada, where there are many old-growth forests, base their definition on the ages of the trees in any given patch of woodland, the wood’s biogeoclimatic zones, and how often the area is subject to natural disturbances like wind, fire, or landslides.

In British Columbia, the majority of coastal forests are labelled old-growth if their trees are more than 250 years old, and sometimes interior forests are defined as old-growth if their trees are at least 140 years old.

Minnesota (an American example)

In the state of Minnesota, an old-growth forest has “developed over a long period of time, essentially free from catastrophic disturbances”. Their definition goes on to include things like rare and native plant species, and large, old trees of long-lived species, etc., but again, it’s not overly specific.

The EU

In an attempt to clarify the situation and avoid misinterpretation of the term, deliberately or otherwise, the European Union is currently attempting to devise a definition structure rather than a single definition. The hope is that, by using a set of identifiable criteria, they can create a framework that’s both clear and adaptable.

The UK

In the UK, old-growth forest is called ancient woodland. There, the definition is a little more concrete: woods that have existed since 1600 in England, Wales, and Northern Ireland, and 1750 in Scotland.

However, even that can prove difficult, because although there are often excellent old land records to show the appearance (or disappearance) of forests and wooded areas, those records — 17th century maps or even estate inventories — may be difficult to obtain and decipher.

Oxford England Medieval Landscape
Photo by Gordon Johnson at Pixabay

They also don’t account for minor incidents of clearing which may still change the character of the woodland, nor do they take into consideration tiny patches of woodland which have remained even when the land around them has changed.

While overall, giving a date to help define ancient woodland or an old-growth forest is very useful, it only works where the landscape, local history, and record keeping allow it. It wouldn’t work in the Amazonian rainforest, for example.


It’s clear from the multiple definitions given above that some standard is needed. Although what defines “old” or “ancient” in terms of chronology will vary from country to country, the attributes that make an established forest ecosystem so important remain relatively constant. To save these precious environments from exploitation’s, we must know what we’re protecting.

Characteristics of Old-Growth Forests

Using a combination of the EU’s proposed framework structural definition and resources from other organizations, I’m going to try to give you some specifics as to what you might find in an old-growth forest or ancient woodland.

Plant Species

The plants growing in a forest can often be one indication of the age of the forest overall. Called “ancient woodland indicator plants” in the UK, these plants will be different depending on the location of the forest.

Bluebell flowers growing on forest floor
Photo by Les Whalley at Pixabay

Every area will have a collection of plants that, if found growing (and especially if found growing in significant quantities) in a forest, will give a clue as to its status as an old-growth forest. Particular species of lichens, insects, and molluscs may also reveal ancient woodland.

Old-growth forests in general tend to be home to more species of trees, plants, animals, and insects than secondary forests. In fact, the Amazonian rainforest hosts at least 10% of the planet’s known biodiversity.

The Trees

Of course, what’s a forest without trees? However, while you might think that an old-growth forest would have exclusively enormous trees, that’s not the case.

While old trees can grow extremely large, issues of the forest’s location may affect the size even of very old trees. Forests growing at altitude, on poor soil, or in inhospitable climates may not be populated with large trees.

It may also arise that significant winds, fire events, or an invasion of pests would create the opportunity for new growth. It is quite possible to have sizeable areas of young trees in an old-growth forest.

In addition to a wide variety of living trees, old-growth forests also often have a number of standing dead trees, or snags. Although they’re no longer alive, these trees still provide a vital habitat for other forest dwellers.

Ancient Trees

While young trees are not unusual in old-growth forests, old trees are a great indicator of old growth. There are a few specific characteristics that may help you to identify a very old tree.

Ancient trees generally have fairly open, flattened crowns and branches with a large diameter. They may also, instead of having flattened crowns, have raised crowns with few branches.

They may show signs of decay and have scars, hollow trunks, burrs, broken treetops, or cracks. Often ancient trees are very wide or (depending on the species) very tall, but as mentioned above, the age of a forest’s trees is not a foolproof guide to the age of the forest.

The Forest Floor

An old-growth forest or ancient woodland will have a great diversity of life on the ground. Fallen branches and dead, rotting tree trunks provide homes for a myriad of animal, plant, and fungal life.

The plant life growing around the bases of the trees will be incredibly varied, with a wide range of native species. There may also be a preponderance of shade-tolerant understory plants: those that can live happily under the canopies of larger trees.

The ground surface in old-growth forests can be very uneven. This is the result of disturbance by animals and also due to the mounds left by fallen trees as they rot and become part of the forest floor.

Wild garlic growing on forest floor
Photo by Mabel Amber at Pixabay

The Canopy

Old-growth forests tends to have multilayered canopies from the diversity of tree species and ages present. They may also have gaps in their canopies from where large trees have died or fallen and not yet been replaced by growing saplings.


Many in-depth definitions of old-growth forests, and the EU’s proposed definition structure, emphasize the degree of naturalness required for a forest to be considered old-growth. This naturalness is used as an indicator of the forest’s freedom from human intervention and interference.

Even where the effects of human involvement can still be observed, if they are “strongly blurred” due to the effects of time, the forest may still qualify as old-growth. And of course, where indigenous practices still occur with regularity, a forest may be old-growth and show recent signs of human impact. The distinction may seem subtle, but it is critically important.

Why are Old-Growth Forests So Important?

I’ve already touched upon some of the ways in which old-growth forests and ancient woodland are so desperately important to the environment.


Old-growth forests are incredibly biodiverse regions. Home to vast numbers of plants, animals, insects, lichens, and fungi, these ecosystems are oases of life in an increasingly depleted world.

In the UK, ancient woodland hosts more threatened species than any other habitat. This is a pattern repeated in old-growth forests throughout the world; in Canada, endangered grizzly bears, caribou, and lichens live in the old-growth temperate rainforests.

Rainforest dwelling Dormouse
Photo by saguari at Pixabay

While it may not seem immediately apparent how the potential loss of a rare lichen matters, it’s always critical to remember that our entire planet is an interdependent ecosystem.

The loss of one species can induce the disappearance of another, and so on. It’s like a domino effect, apart from that, as the chain goes on, each domino knocks down not another one, but another many.

More than 50% of the species in tropical forests depend on old-growth areas; were those forests to be destroyed, those species could not recover.

The Fight Against Climate Change

All trees sequester carbon dioxide, but old-growth forests are able to store between 30% and 70% more CO2 than equivalent disturbed woodlands. Mature forest soils may also sequester carbon; research into this is ongoing.

Many old-growth forests also protect layers of permafrost, which itself stores a considerable amount of carbon dioxide, much more than the trees hold themselves. Removing the forests would mean a rapid melting of the permafrost and a rapid release of all its stored CO2.

Possible Fire Protection

New research in Oregon in the United States has suggested that old-growth forests may experience less severe wildfires than young-growth forests. This is undeniably important for the endangered species who call local forests home and who are threatened by fire activity.

Undiscovered Remedies, Medicines, and Cures

50% of currently used medications have been developed using plant-based substances. The treatment for malaria, along with some cancer drugs, diabetes medications, and treatments for rheumatic disease, etc., have all come from plants or trees.

Scientists are certain that the natural world is home to even more medicines than we’ve yet discovered: to destroy their habitats would be at our peril.

Preserving Culture and Cultural Heritage

It may not seem important in our fast-paced, internet-driven world, but there are several points to consider here.

The first is that just because you’re reading this article online doesn’t mean that the entire world has gone exclusively digital. Many people still depend on the forests for their survival. You might even be one of them; using the internet doesn’t preclude a regular interaction with natural spaces.

Charcoal Kiln
Photo by Paul Henri Degrande at Pixabay

Old-growth forests support indigenous people and traditional practices, whoever practices them, and cultural practices and traditions that involve forest habitats are essential to the communities they support.

The second important issue with regard to the preservation of culture is that, for all we strive to be modern technophiles, our ultimate needs and ultimate natures as human beings have not changed. We are creatures of nature. We’ve evolved over millennia along with the woodlands.

They’re a part of our history, an anchor to what we are. Destroying the earth’s natural places means destroying a link to our past and to the bridges that have carried us to where we are today. It may sound philosophical, but we are more than we currently acknowledge!

Quite Simply, Trees

Forest Ecosystem
Image by Bureau of Land Management at Flickr

Trees are living beings. Elder and venerable trees, like elder and venerable forest ecosystems, deserve to be allowed to live in peace. Honestly, who are we to decide that a 500-year-old forest should be destroyed to make space for our unsustainable living habits?

At Rainbow Ridge in Humboldlt County, California, four elderly activists were arrested for attempting to stop logging trucks from entering the area.

Rainbow Ridge is home to what may be the last undisturbed area in California of old-growth Douglas fir trees and part of the enormous Cascadia Temperate Rainforest: more than 2500 miles long and one of the largest carbon sinks — or carbon-storing forests — on earth.

The activists are reported to have said “Elders defend elders.”

Threats to Old-Growth Forests

Perhaps unsurprisingly, the threats to old-growth forests are more or less all human-induced.

Logging and clearing for agriculture account for an immense loss of forested land every year. The earth has lost 81 million hectares of forest since 1990, although in one very small positive, the rate of deforestation from 2010-2020 was half of that from 2000-2010. Things may be moving in the right direction, but not fast enough.

Wood processing at a sawmill
Photo by aleksandarlittlewolf at Freepik

Climate change poses an unbelievably large threat to ancient woodland. From droughts to floods, severe and extreme weather events or just a shifting of a region’s climate to something different, forests are very susceptible to the changes wrought by our anthropogenically motivated changing climate.

Old-growth forests may also be under threat from invasions by pests and diseases. While such events are not new, trees often develop defenses against standard, known invaders.

However, with human involvement in forest ecosystems and the consequences of climate change, forests are being confronted with new pathogens against which they have no acquired protection.

These sorts of invasions can results in the deaths of hundreds, even thousands of trees, and destroy entire ecosystems.

What We Can Do to Protect Ancient Forests

Moss covered tree trunk
Photo by topntp26 at Freepik

One of the first steps is to help authorities to identify and protect areas of old-growth forest. If you live somewhere with woodland, do some investigating.

If it’s not already designated as old-growth but you think it might be, check it out. If you’re convinced, contact your local woodland conservation agency, environment authority, or even university.

You can also make sure that your lifestyle choices don’t negatively impact forests (or in fact the environment in general) any more than they absolutely have to. If you need to buy furniture, buy used / second-hand. If you need new wood, make sure it’s certified by the Forest Stewardship Council or another reputable organization.

Use recycled paper and card. Recycle your paper and card. Cut down your CO2 emissions and encourage others to do the same. Do what you can to live more sustainably.

If you live near an ancient woodland or old-growth forest and its under threat, get involved. Work to help protect it, save it, raise awareness. The forests can’t protect themselves from humans, but other humans can do it for them.

At least for the foreseeable future, working to save and preserve old-growth forests is an ongoing fight. But it’s one that we must all take up.

As a young forest activist in California so aptly said to journalist Will McCarthy, “When you’re doing forest defense, all your losses are permanent and all your victories are temporary.”

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Kira Nash

Eco-Conscious Nature Enthusiast

Kira Nash lives with her family in the sunny French countryside amidst bees and swallows. A writer, editor, and artist by trade, she also teaches creative meditation. She's passionate about nature and ecology and tries to live as green a life as possible. In her spare time, she surfs, reads, and plays with her cats, although not usually all at once. She loves tea a little too much.

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