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During the reign of Maria Theresa, the first law on the protection of forests was created in the territory of Austria-Hungary. The queen also strongly supported the planting of avenues in the country, precisely because of the positive impact of trees on the landscape and the environment. They provided shade for marching soldiers, reinforced road bodies and provided fruit for the population or pollen for bee colonies. We should not forget the effects of trees even in the context of improving air quality.

How trees improve air quality

We could summarize their benefits in three points:

1. They improve air quality thanks to the leaves and needles, into which dust particles (PM1 particles and smaller) are infiltrated directly through the vents and thus the amount of impurities in the air is reduced.

2. They reduce the speed of air flow, thanks to which the dust is more likely to settle on various surfaces and not be in the air we breathe.

3. They mechanically capture polluting substances on leaves and needles, which subsequently prevents them from swirling again.

Trees with sticky and hairy leaves or a structured surface are more effective, on the contrary, the lowest ability to capture dust particles can be attributed to trees with smooth and leathery leaves (pines, mountain ash, or evergreen - eucalyptus). Various studies report an average decrease in PM10 concentration in different types of greenery ranging from 32% for conifers, 28% for suitable broad-leaved trees, 16% for shrubs and 9% for lawns.

Trees act as natural atmospheric filters that capture microscopic dust particles and a whole range of different pollutants such as ozone, nitrogen oxides, sulfur and ammonia. The ability of trees to capture pollutants from the air, absorb CO2 and produce oxygen can, together with the natural cooling effect, significantly contribute to reducing overall air pollution and smog levels, especially in large cities and residential agglomerations. Some trees produce phytoncides - substances with proven antibacterial effects on the human body (similar to, for example, garlic). They enter the human body during breathing, where they help in the fight against toxic microorganisms as natural antibiotics. These functions are especially important in the fight against air pollution not only from traffic and can be applied in the planning of public spaces.

What should be considered if we plant trees near sources of air pollution

The shape and size of the crown of adult trees should correspond to the specific location and the effect we need to achieve. In deep street canyons, between tall buildings, large trees with a compact crown should not be planted. Shrubs or vegetated walls should have priority, otherwise pollutants can accumulate in the space under the crowns, where it is not desirable because pedestrians move there.

If the source of pollutants is located in shallow street canyons, and at the same time there is space for pedestrians or cyclists, medium-sized trees should be planted with sufficient spacing to avoid creating a tunnel effect. Tree plantings with compactly connected crowns are recommended especially in pedestrian zones or inner blocks, where tree crowns can create a barrier against the spread of pollutants from the surroundings. When planting hedges, which are supposed to be a barrier against pollutants from the air, their height should be at least 2 m and width at least 1.5 m, in order to achieve the desired insulating effect.

In open space, these principles are different. If air flow is not affected by the proximity of buildings, then tree canopies have a positive effect in preventing the deposition of pollutants in the immediate vicinity of roads. Therefore, they can form a barrier between the road and sidewalks for pedestrians and cyclists. However, one should not forget the tolerance of selected trees to pollution and stress factors in the urban environment, such as salinization and soil compaction or shading. These are important properties so that trees are healthy and can fulfill their ecological and environmental functions.

We also plan to plant trees for better air in the Populair project

Several partners of the project from among the self-governing regions are aware that the planting of trees is beneficial not only for the air, but will positively affect the landscape, contribute to increasing ecological stability and, last but not least, the awareness of citizens about our project. As part of their activities, they are currently preparing tree plantings - as a measure to improve local air quality. First, it is necessary to select suitable locations. Subsequently, the processing of the survey, whether the location of the trees would not interfere with the protective zones of utility networks. After consultations with the traffic inspectorate and the owners of neighboring plots, they will proceed to the development of project documentation.

The first plantings have already taken place in the Banskobystrica region, where the air quality manager, Ladislav Bíro, cooperates with several cities and jointly involves pupils and local communities in the plantings. The trees planted from this initiative are already growing in Zvolen and Jelšava. Planting trees together is also a tool for establishing cooperation and building mutual trust.

If you are currently solving the dilemma of Christmas trees, live or artificial, try this: instead of a Christmas tree in the living room, plant a tree instead. It's not too late! As long as the soil is not frozen, you can plant. The Christmas warming, which is a typical phenomenon in our territory, is a good opportunity for this. It is important not to forget to cover the roots well with a thick layer of mulch, and if it is dry, not to forget to water it - even in winter. However, we remind you that to plant a tree, you should have the consent of the owner of the land, or the statement of the manager of public greenery, who will also advise you on choosing a suitable type of wood.

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