“Feedback mechanism”: specialist - about the climatic role of forests and the rules of reforestation

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Scientists from the University of Sheffield have come to the conclusion that planting forests alone without involving a whole range of measures cannot solve the problem of global warming.

According to scientists, planting reduces the ability of the Earth's surface to reflect the sun's rays, since forests are darker than steppes and meadows, and also affects the concentration of methane and ozone in the atmosphere.

In total, all these indirect effects neutralize the beneficial effect of forest planting by about a third.

Do you agree with these assessments?

- No, not quite.

The fact is that in their normal state, forests are pure absorbers and accumulators of carbon dioxide.

The normal state of a forest is when it is not cut down by clear felling, does not burn as a result of fires, is not damaged by pests and diseases and other anthropogenic and natural factors.

For healthy forests, we even use a special term - a carbon pump, which pumps CO2 out of the atmosphere and deposits it in biomass for long periods - tens or hundreds of years.

As for the argument that forests reflect the sun's rays less than other ecosystems, that is, have a lower albedo, this is partly true.

Albedo is a really important indicator when we talk about climate, since the atmosphere is heated by the Earth's surface.

However, forests directly absorb part of the solar energy spectrum during the process of photosynthesis, shade the area, and as a result, solar radiation does not reach the surface of the earth.

Therefore, under the cover of a forest it is always cooler than in open areas.

In addition, forests actively evaporate moisture, which also helps cool the air.

Forests have a complex mitigating effect on climate.

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— Previously, other scientists found that anthropogenic impact has changed the forests in the Amazon Basin so much that they begin to emit more carbon dioxide than they can absorb, and also emit significant amounts of methane.

A similar situation is observed in Indonesia, Malaysia, Cambodia and Laos.

Why have the tropics become carbon producers in recent decades?

“Indeed, if forests are subject to the strong anthropogenic impacts that I mentioned earlier, this could disrupt the carbon cycle.

Tropical forests, including those in the Amazon, are suffering from clear-cutting and fires.

Thus, forests in this region are being actively cut down to free up land for agricultural needs.

True, it cannot be said that tropical forests as a whole have stopped absorbing carbon dioxide; this is rather true for individual areas.

But in any case, it is important to limit anthropogenic impact on forests; this is provided for by the UN Framework Convention on Climate Change.

A set of such measures is called sustainable forest management.

— You mentioned clear cuttings.

How do they differ from normal fellings?

— This does not mean clear cuttings so much as cuttings after which the forest is not restored.

Forest cutting itself, if it is done according to the rules, is not a problem.

It is important that after felling, natural, artificial or combined reforestation measures are carried out in its place.

Such measures are provided for by Russian legislation in the field of forestry, as well as in the legislation of other countries.

Unfortunately, in practice these measures are not always applied, and then logging harms the forest ecosystem.

— We touched on the state of forests in the tropics.

What is it like in more northern latitudes?

— In general, the situation with the state of forests is more favorable, although there are also clear-cuts and forest fires.

The latter are being actively combated in Russia by the Federal Forestry Agency and its subordinate organization FBU Avialesookhrana.

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— On the shores of the Arctic Ocean, bare tundra disappears, bushes sprout, and willows grow 3 m in height.

At the same time, in the tropics, hundreds of thousands of hectares of forest are destroyed every year, and climate change negatively affects the remaining trees.

Can these new forests at least partially compensate for the negative processes that are taking place in other areas of the planet?

- Yes of course.

This is how the feedback mechanism manifests itself, scientifically speaking.

In general, climate warming is a positive phenomenon for plants, including trees.

As well as the saturation of the atmosphere with carbon dioxide, which plants eat during photosynthesis.

For example, in greenhouses, plants are specially fed with carbon dioxide to increase productivity.

So, as carbon dioxide accumulates in the atmosphere and average temperatures and humidity rise, forest areas will expand.

And then the reverse process will begin - plants will help remove excess CO2 from the atmosphere.

During the process of photosynthesis, carbon changes from a gaseous state to a solid state and can be stored in this form for a very long time.

“It was recently discovered that changes in temperature and humidity caused by global warming have reduced the ability of plants to photosynthesize and absorb carbon dioxide.

So far, mainly agricultural producers are paying attention to this problem, since their yields are falling, special drugs are being developed to relieve abiotic stress.

What is the situation with forests?

How much is their ability to absorb oxygen affected by climate change?

“Plants can indeed experience climate stress, which reduces the level of photosynthesis.

Typically, the most severe stress in plants is caused by droughts and hot winds.

Although overall atmospheric humidity is increasing due to global warming, droughts may occur locally.

I note that trees suffer less from such extreme events than, for example, agricultural plants, since the root system of trees goes very deep, several meters.

Therefore, trees are able to survive even serious droughts and recover faster after them.

So forests are less susceptible to stress than other ecosystems.

• Seedlings in the Zaoksky plant nursery.

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• © Vitaly Belousov

— What tree species accumulate carbon dioxide best?

— It depends on how quickly the tree is able to accumulate phytomass, that is, we are talking about fast-growing trees.

For example, in Latin America, eucalyptus plantations are often planted for the needs of the pulp and paper industry because it grows quickly.

Such plants quickly accumulate carbon in phytomass, but they have a short “farm rotation” (the period between planting and cutting.

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) - as a rule, such trees are grown specifically for the production of cellulose.

It is also very good when wood is used to produce biofuel, which then replaces part of the fuel produced from fossil hydrocarbons, or is used to produce forest products with a long life, such as building materials.

Which tree species are preferable to plant to maintain climate balance, taking into account the national economy’s needs for wood, is determined within the framework of special modeling.

Such research is also being conducted in Russia.

— Is it always necessary to plant cleared areas artificially? Isn’t it easier to wait until the forest recovers naturally?

— There are three types of reforestation:

natural, artificial and combined, which combines natural and artificial.

Sometimes it is enough to simply promote the natural regeneration of the forest, when there is a lot of viable regrowth of the main forest-forming species in the cleared area.

In this case, when cutting down, you need to try to preserve this young growth, and then carefully clear the cutting area to give the young plants the opportunity to develop.

But in cases where there is no such regeneration, it is necessary to resort to artificial reforestation and create forest crops.

The third method, combined, includes both planting trees and supporting natural regrowth.

If this is not done, and no reliable undergrowth of the cut down species has been preserved in the clearing, then first of all, in the natural course of events, fast-growing, pioneer species, mainly birch and aspen, will appear here.

They grow quickly and absorb carbon well.

Then, in the process of natural succession, they are replaced by coniferous species.

They grow slower but are better at sequestering carbon because their wood is more biostable and decomposes slowly.

The problem is that natural reforestation through changing species takes much longer than artificial reforestation.

• Timber rafting along the Angara and Yenisei rivers

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• © Ilya Naimushin

— What is the state of Russian forest lands today?

— Russian forests are pure carbon sinks.

According to rough estimates, they absorb about 600 million tons of carbon dioxide per year.

This is approximately a third of the volume of greenhouse gases emitted in Russia during the same period.

In Russia, forests occupy a very large area, the total forest area is about 1.2 billion hectares.

Moreover, a significant part of these forests does not have transport accessibility and logging and other forestry activities are not carried out there.

Therefore, a very large proportion of forests in Russia are in a natural state and fulfill their climatic functions.

However, they periodically suffer from forest fires.

They are often caused by dry thunderstorms, when there are electrical discharges, but there is no rain to extinguish the resulting fire.

In part, such fires can even be beneficial for forest ecosystems.

In hard-to-reach remote areas, large amounts of dead wood and detritus accumulate, which interfere with natural reforestation.

During forest fires, detritus burns out.

In addition, in some varieties of pine trees, the cones open and the seeds enter the soil only after fires.

If there are no fires at all, then such species will not be able to reproduce.

Therefore, in hard-to-reach areas where there are no populated areas, economic facilities, communications and the like, fires are often not extinguished, but care is taken to ensure that they do not spread towards populated areas.

Such areas are classified as forest fire control zones.

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Do new technical means, such as UAVs, help to conduct such monitoring?

— Yes, unmanned aerial vehicles are part of the four-level system for fighting forest fires today.

The first level of monitoring is satellites, the second is aviation, which is used by Avialesookhrana.

Then come UAVs and ground patrols.

Nowadays, mobile communication towers with all-round cameras are also used to monitor the situation in forests.

In the fight against fires, the most important thing is to detect the source of fire at an early stage, then it can be quickly eliminated.

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— When restoring cleared areas, are the same plants planted as those that grow in the wild, or those that have already been selected?

How difficult is the task of selecting valuable tree species?

— As a rule, these are local breeds, zoned for a given forest area.

Selection is actually carried out; when preparing seeds, the material is taken from the so-called plus trees - those of higher quality in height, trunk shape and, most importantly, growth rate.

Another thing is that the selection of woody plants is a more complex task than that of agricultural plants, since pine and spruce, for example, take 80-100 years to grow.

Therefore, the results of selection become known very slowly.

Methods of genomic selection can help in this case - for example, when the potential of a plant is determined by its genotype rather than phenotype, as well as genetic marking and editing.

This allows you to speed up

getting results.

Such research is also being conducted at our university.