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Federal Research Center 
"Krasnoyarsk Science Center of the Siberian
Branch of the Russian Academy of Sciences"

 Федеральный исследовательский центр «Красноярский научный центр Сибирского отделения Российской академии наук»

Federal Research Center 
"Krasnoyarsk Science Center of the Siberian
Branch of the Russian Academy of Sciences"

What is forest thinning? Scientists of the Institute of Forest SB RAS explain why it is necessary to cut trees in the forest

15 February 2021 г.

Что такое рубки ухода? Зачем рубить деревья в лесу: рассказывают ученые Института леса им. В.Н. Сукачева СО РАН
Residents of Akademgorodok in Krasnoyarsk and the media drew attention to the trees being cut in the forest. Scientists of the V.N. Sukachev Institute of Forest FRC KSC SB RAS, namely,  researcher of the Laboratory of Phytocenology and Forest Resource Management, Candidate of Biological Sciences Maria Kiriyenko and senior researcher of the Laboratory of Ecological Urban Planning, Candidate of Agricultural Sciences Ivan Kosov, explain why it is necessary to do so in order not to lose the entire forest.

- Why is it necessary to cut down trees in the forest?

Maria Kiriyenko: This is not simple cutting. This is selective sanitary thinning of forest, when diseased trees are removed from the main canopy, those affected by fungal diseases or by insect pests. We remove trees lagging in growth due to a lack of light, nutrients or those which have already begun to dry out, as well as windfall and windbreak trees are removed. These trees are dangerous because they are primarily infested by insects and can pose a threat to healthy trees. Such thinning is carried out to improve forest plantations. Pine forest in Akademgorodok is overburdened. For these plantations to function well and fulfill their ecological functions, it is necessary to make the density optimum for trees of this age.

- Why else are the trees to be removed dangerous?

Ivan Kosov: The most dangerous are withered trees, because when they fall they can kill someone, damage wires, or fall on a car. No one can predict when it will happen. This is not a simple cutting, but a forest maintenance activity. That is why we remove stunted, dying, drying and emergency trees. They are infected with various diseases: phytopathogens, cancer, and viruses. They are damaged by various insects: barbel, bark beetle, horntail and others, which literally destroy them. The main problem with overgrown stands is that they are weakened because they lack nutrients due to their density. Added to this is a high anthropogenic load. Moreover, pine is not resistant to gas and dust pollution. The traffic on the roads has become much more intensive in recent years, and the amount of exhaust gases has increased. All this is stressful for trees. Since they do not have enough nutrition, they often get sick and, mostly, they pass into the category of weakened trees and dry out.

- How do "wild" forests cope with this situation?

Maria: We are very often asked why we are interfering with nature? There are wild forests where everything is fine. But in the so-called "wild" forests, there are natural mechanisms of self-regulation and self-maintenance. The natural change of generations in trees takes decades, but here we are dealing with artificial recreational forests with an increased anthropogenic load. And since man has already intervened here and violated the natural mechanisms of self-maintenance of the ecosystem, our forest cannot cope without our help. In addition, we are dealing with a forest stand consisting of a single tree species of the same age, which tends to be less stable than mixed stands of different age.

Ivan: Of course, the forest can regulate the density on its own, but it will take decades, while people need results right now, and thus, this process should be regulated. This is what we are doing.

- How is this issue solved in other countries?

Maria: I studied the European practice in this area. There are very few natural forests there. Europeans are very careful about green spaces. They have a widespread practice: forests with a high recreational load are simply fenced off, a sign with the inscription “the forest is on vacation” is hung up and people are not allowed there for some time. During this time, which is about three to five years, the forest ecosystem has time to recover. Living ground cover and soil microorganisms are restored, new species of insects appear, and thus, there occurs natural renewal. I like this practice a lot.

It would be interesting to try this in Krasnoyarsk as well. But are the residents of Krasnoyarsk and Akademgorodok ready to do this? Here, we have to choose: either we want to preserve the forest, being ready to sacrifice our interests, or we will have to help the forest, taking care of it, because the forest cannot do it on its own. If we look at the forest in the upper Akademgorodok, in many places, especially on the paths, there is no living ground cover because of people. With a high anthropogenic load, not only trees are affected. Even soil microorganisms are affected. When the soil is highly compacted, oxygen hardly enters the soil, soil microorganisms poorly multiply, and consequently, the soil-forming processes slow down or do not proceed.

We conducted research in the forest plantations of Akademgorodok. In the areas with the low anthropogenic load, there are plants even from the Red Book, for example, the lady's slipper orchid. If we do not exploit the forest so intensively, these rare plant species will recover.

- Do people harm the forest only by trampling it?

Ivan: The main problem in the city is gas pollution. There are trees which are quite resistant to toxic gases, but pine is not. It is very sensitive to air pollution. Therefore, for example, it should not be planted in the city center along the main roads. Spruce is a more gas-resistant species, but there’s another problem with it. It is very demanding on moisture. Under natural conditions, it grows near streams, in lowlands, where there is increased soil moisture. But within the city, spruce plantations must be constantly watered. The main task in working with urban forests is to care for old plantations and to plant new ones which are resistant to new environmental conditions.

- Trampling the soil, pollution, is there any other harmful human impact?

Maria: Bonfires not extinguished, glass bottles resulting in fires due to the lens effect and other things. All this, including the previously listed factors, leads to the fact that the area of forests in our country is rapidly decreasing. Therefore, forests within the city, experiencing a high anthropogenic load, must be under special control.

Ivan: Mechanical damage exposing the wood is also still common and has a bad effect on the life of trees. The tree has a natural defense reaction - to tar the open part. If the tree could not cover this part, viruses, fungal spores, or pests penetrate there. The death of a tree becomes just a matter of time. If the tree is also weakened, then the process can significantly be accelerated. Mechanical damage is very typical for plantations in Akademgorodok. People often walk here, gather together for some meetings, conduct trainings and even use trees in their sport activities. Sometimes trees are damaged by ignorance. Like humans, the tree has "immunity". The stronger it is, the longer it will be able to withstand various impacts. It is important for all of us to take care of trees, namely, not to damage the bark, roots and to remember that the city environment is already hard for trees.