Climate change, biodiversity: the essential role of mountain forests


Thanks to its unique atmosphere, the forests They occupy a special place in many human cultures. Like the one in Brocéliande, they participate in the construction of tales and legends: witches, goblins, goblins and goblins would be found there. korigan

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

Its contribution in terms of biodiversity and its capacity to absorb COtwo of our atmosphere are considerable.

There is a debate about the importance of the contribution of trees and forests to the sequestration of COtwo. A first estimate places the absorption of CO at 205 gigatons of carbon (GtC).two trees in worldwide every year. This estimate was considered too optimistic and was revised downwards, at 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 is four times annual fossil fuel emissions (10 GtC/year), but only a small fraction of the 660 GtC of total historical anthropogenic emissions.

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

7,500 bird species

But what is a forest? You will no doubt agree that it is an ecosystem dominated by trees. We can distinguish three main types of forests : boreal, temperate and tropical.

The most notable feature of a forest is the density of trees and the variability in their height. This is what allows these ecosystems to host about 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 species of mammals).

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

The so-called ancient ones are the most valuable, as they are particularly rich in species.

Primary forests are structurally more intact and complex than secondary forests and therefore provide superior ecosystem services.

In general, old-growth forests support 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 primary forests are home to rarer species especially adapted to these ecosystems.

a very old pine tree in the RBI of the Cirque de Campus.

Abundant life

While forests may seem immutable, they are dynamic. There nests a swarming life but invisible to the inexperienced eye. Billions of microbes break down dead plants and animals, making nutrients available to other organisms.

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

Organisms absorb, transform and transport nutrients. The wind disperses the pollen, fertilizing planes and trees miles away. In mature 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 out there. During photosynthesis they absorb COtwo to feed and grow, thus releasing oxygen (and a small fraction of COtwo).

Much of the carbon stored in terrestrial ecosystems is therefore found in forests. As forests age, plants grow, die and decompose, so primary forests are fuller of plant matter that stores carbon in their soil than secondary forests.

Old-growth forests can contain 30-70% more carbon than old-growth forests. degraded forests of similar size, making them essential in the fight against the climate crisis.

mountainous forest.

The forests suffer

Like all ecosystems and species, forests suffer. They suffer from water stress, they suffer from degradation, they suffer from exploitation, pollution and changing conditions that take too long to adapt to. Not to mention the damage caused by harmful species.

Nitrogen pollution is a formidable threat. Emitted by intensive farming and ranching, power plants, road traffic and other sources, it has continued has increased since it was first measured in 1950.

Nitrogen deposition makes soils more fertile and this excessive fertilization disrupts the fungal symbiosis with tree roots, as increased atmospheric nitrogen concentrations lead to decrease mushrooms ectomycorrhizal.

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

Globally, there is an estimated 1,110 million hectares (11 million kmtwo) of mature forests (36% of all forests), roughly the size of Europe. Around 70% of these old-growth forests stretch between Brazil, Canada and Russia, where humans continually decimate unprotected parts of these wonderful ecosystems.

Giant trees of the Marcadau valley

In Europe, only a few hectares of old-growth forests remain, most of which are in hard-to-reach mountainous areas. These access difficulties have saved these areas from logging in the past.

Therefore, montane forests are 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 see giant trees that can be up to 500 years old (Photos).

Marcadau valley. DS, provided by the author

In an area of ​​the Ariège Pyrenees, which now has the status of an Integral Biological Reserve (RBI), there are trees between 150 and 200 years old. A forest that is ultimately quite 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, something rare in Europe, as can be seen in this video, shot in an RBI located in the circus of Campuls. This RBI protects old growth forest on a very steep and almost inaccessible part of the mountain.

mountainous forest.

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 or pathogen species, others may not be affected and thus may maintain much of the forest processes, increasing the recovery potential of the entire forest.

Forest loss due to the increasing impacts of climate change will become more frequent. In temperate regions, we have perhaps the best opportunity to further expand our forest areas, to combat the two global catastrophes we are experiencing: climate change and biodiversity loss. To do this, we must find a common strategy and understand that by protecting our mountain forests, we are protecting ourselves.


Created in 2007 to accelerate and share scientific knowledge on major social problems, the Axa Research Fund has supported almost 650 projects around the world, led by researchers from 55 countries. For more information, visit the website of Axa Research Fund or follow us on Twitter @AxaResearchFund.

Translated from English by FastForWordThe conversation

dirk s. schmellerProfessor of Conservation Biology, Axa Chair of Functional Ecology of Mountains at the École Nationale Supérieure Agronomique de Toulouse, University of Toulouse III – Paul Sabatier

This article is republished from The conversation under Creative Commons license. Read theOriginal article.





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