Mountain forests are essential for biodiversity

• Forests play an extremely important role in mitigating climate change and witnessing biodiversity loss, according to our partner The Conversation.

• The uptake of CO₂ by trees globally would amount to 42 gigatonnes of carbon (GtC) each year.

• This analysis was conducted by Dirk S. Schmeller, Professor of Conservation Biology.

Thanks to their unparalleled atmosphere, forests hold a special place in many human cultures.

Like that of Brocéliande, they participate in the construction of tales and legends: one would find there witches, elves, goblins and korrigans...

But beyond the myths they convey, they play an extremely important role in mitigating climate change and witnessing the loss of biodiversity, two major challenges we are currently facing.

The Brocéliande forest © mll / Flickr CC BY-NC 2.0

Their contribution in terms of biodiversity and their ability to absorb CO₂ from our atmosphere are considerable.

There is a debate about the importance of the contribution of trees and forests to CO₂ sequestration.

A first estimate puts the CO₂ absorption of trees globally at 205 gigatonnes of carbon (GtC) each year.

This estimate was considered too optimistic and revised downwards to 42 GtC.

Since these are model estimates and the models come with assumptions, these corrections are not unusual.

The actual value could be between the declared values.

This 42 GtC represents four times annual fossil fuel emissions (10 GtC/yr), but only a small fraction of the 660 GtC of total historical anthropogenic emissions.

Nevertheless, the world's forests have an important role to play in mitigating climate change.

​7500 species of birds

But what is a forest?

You will no doubt agree that it is a tree-dominated ecosystem.

We can distinguish three main types of forests: boreal, temperate and tropical.

Boreal forest in Quebec © Kerbla Edzerdla / Wikimedia CC BY-SA 3.0

The most remarkable feature of a forest is the density of trees and the variability in their height.

This is what allows these ecosystems to house nearly 7,500 species of birds (75% of all birds), 5,000 species of amphibians (80% of all known species), and more than 3,700 mammals (68% of all mammalian species).

It is here that we understand why forests play such an important role in halting the loss of biodiversity.

The so-called old ones are of the greatest value, as they are particularly rich in species.

Old-growth forests are structurally more intact and complex than secondary forests and therefore provide superior ecosystem services.

In general, old-growth forests are home to more species than their younger counterparts, which are more disturbed by human activities and climate change.

In other cases, primary and secondary forests may support a similar number of species, but old-growth forests support rarer species specially adapted to these ecosystems.

A very old pine tree in the RBI at Cirque de Campuls © Dirk S. Schmeller (via The Conversation)

teeming life

While forests may seem immutable, they are dynamic.

A swarming life but invisible to the untrained eye is nestled there.

Billions of microbes break down dead plants and animals, making the nutrients available to other organisms.

Pollinators and seed dispersers (insects, mammals, birds) help trees reproduce by moving pollen between stationary trees and seeds into gaps where they are more likely to survive.

Organisms absorb, transform and transport nutrients.

The wind disperses the pollen, fertilizing planes and trees miles away.

In old-growth forests, these myriad ecological processes are intact and provide essential services to humans.

When it comes to climate change, trees are one of the best carbon storage units there is.

During photosynthesis, they take in CO₂ to feed and grow, releasing oxygen (and a small fraction of CO₂).

Much of the carbon stored in terrestrial ecosystems is thus found in forests.

As forests age, plants grow, die and decay, so old-growth forests are fuller of carbon-storing plant matter in their soil than secondary forests.

Ancient forests can hold 30-70% more carbon than degraded forests of a similar size, making them essential in the fight against the climate crisis.

VIDEO:

​Forests are suffering

Like all ecosystems and species, forests suffer.

They suffer from water stress, they suffer from degradation, they suffer from exploitation, pollution and changing conditions to which they are too slow to adapt.

Not to mention the damage caused by harmful species.

Nitrogen pollution is a formidable threat.

Derived from intensive agriculture and animal husbandry, power plants, road traffic and other sources, it has been steadily increasing since it was first measured in 1950.

Nitrogen deposition makes soils more fertile and this over-fertilization disrupts fungal symbioses with tree roots, as increased atmospheric nitrogen concentrations cause ectomycorrhizal fungi to decline.

This disturbance, coupled with higher temperatures, allows trees to grow faster, but due to the lack of a functional symbiosis with root fungi, their wood is of lower quality.

Globally, an estimated 1.11 billion hectares (11 million km2) of old-growth forests remain (36% of all forests), roughly the size of Europe.

About 70% of these ancient forests are spread between Brazil, Canada and Russia, where humans are continually decimating the unprotected parts of these wonderful ecosystems.

​Giant trees of the Marcadau Valley

In Europe, there are only a few hectares of old-growth forests left, most of which are in hard-to-reach mountain areas.

These access difficulties have saved these areas from logging in the past.

Mountain forests are therefore of particular importance for the conservation of intact and species-rich areas.

For example, in the French Pyrenees, in the Marcadau Valley (Pyrenees National Park), you can observe giant trees that can be up to 500 years old (Photos).

The Marcadau Valley © Dirk S. Schmeller (via The Conversation)

In an area of ​​the Ariège Pyrenees, which now has the status of Integral Biological Reserve (RBI), there are trees between 150 and 200 years old.

A forest ultimately rather young and yet one of the oldest forests that we still have in France.

In an RBI, there is no human activity, so it is a strictly protected site, which is something rare in Europe, as we can see in this video, filmed in an RBI located in the circus of Camp.

This RBI protects old growth forest on a very steep and almost inaccessible part of the mountain.

VIDEO:

Mountain Forests – Forest Management Issues

Find a common strategy

A greater diversity of trees also means a greater diversity of animal and microbial species.

In general, greater diversity is considered to protect the entire forest from pest species and pathogens, making it more resilient to external pressures, such as the effects of climate change.

Even if some tree species are affected by a pest species or pathogen, others may not be affected and can therefore maintain much of the forest processes, increasing the recovery potential of the entire forest .

Our “BIODIVERSITY” file

Forest loss due to the increasing impacts of climate change will become more frequent.

In temperate regions, we have perhaps the best chance of further expanding our forest areas, in order to combat the two global catastrophes we are experiencing: climate change and biodiversity loss.

For this, we must find a common strategy and understand that by protecting our mountain forests, we are protecting ourselves.

Planet

Pyrenees: Why global warming is accelerating in the mountains

Planet

Global warming: Why the French forest needs a "basic treatment"

This analysis was written by Dirk S. Schmeller, Professor of Conservation Biology, Axa Chair in Functional Mountain Ecology at the École Nationale Supérieure Agronomique de Toulouse, University of Toulouse III – Paul Sabatier.

The original article was translated from English and published on The Conversation website.

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Declaration of interests

●

• CO2

• Biodiversity

• Tree

• Forest

• Global warming

• Video

• The Conversation

• Planet

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