Since the dawn of time, the tree has been a companion, and in a way, a friend of a man in his estates. The meaning of trees has been differently understood in the past, however, it is now generally known, that trees and stands in cities, next to the decorative meaning, play an important role in maintaining the best possible climatic and sanitary conditions.

The influence of the city's vegetation on the psyche of its inhabitants is also noteworthy. You should be aware, that in the city center it is impossible to restore or create "natural" conditions with the help of vegetation, that is, free from the unfavorable influences of city life. The improvement of living conditions in highly urbanized districts is possible only through comprehensive solutions, mainly in terms of rational reconstruction of these districts and the proper location of burdensome industrial plants and other parts of the city. Appropriate living conditions are a relative concept that depends on the place and time. The rules for their determination should be based primarily on the assessment of human health conditions.

People's high adaptability should be emphasized. This is best evidenced by the dynamically developing societies of large cities in terms of culture and economy. Urban greenery can significantly facilitate the adaptation of people to onerous urban conditions. Comprehensive effect of trees with color, shape, the smell, a game of light and shadow, movements under the influence of wind and noise, changes in appearance at different times as opposed to the permanent appearance of street surfaces and building walls, it causes psychological problems in every human being, and even psychosomatic reactions. For example, light green birches, young beeches, cherry blossoms' give wings to thoughts . However, alders, fir trees, cyprysy, willows and junipers tend to go deeper, melancholic reflection. The calming effect of the scent of blooming linden on the human psyche is known - that is why the trials of the Slavic and Germanic tribes were held under the linden trees. On the other hand, the chiefs eagerly held war councils under a mighty oak, which gave them energy.

As our research capacity expands, many of the tree functions become measurable, and thus the understanding of the great importance of trees to the human environment increases.

Retaining solid air pollutants.

This is a proven function of quite important importance. It results from the following processes:

– "Combing" dust from the masses of dusty air flowing through the greenery,

– acceleration of deposition (sedimentation) dust as a result of a significant reduction in the speed of movement of air masses,

zmniejszanie ponownego wzbijania się pyłów osadzonych na ziemi, the so-called. secondary pollination.

Absorption of gaseous pollutants in the atmospheric air.

This process, in the literal sense, is possible, Although, only then, when the concentrations of gaseous pollutants are relatively low, such, which plants can withstand throughout the growing season, e.g.. to approx 0,1 ppm SO2 (sulfur dioxide), however, the indirect role of vegetation in this regard may be important. As a result of the overall impact on the microclimate, vegetation intensifies the processes of air self-cleaning. Hydrocarbons are an important and necessary component of the group of pollutants in the atmosphere in the city. Turned out, that the waxes found on the leaves (needles) can absorb hydrocarbons, which are then discharged into the soil and mineralized there within a few days by microorganisms (with the exception of certain persistent polycyclic aromatic hydrocarbons, like for example. carcinogenic 3,4-benzopyrene).

Purification of the atmosphere from radioactive admixtures.

The relatively high activity of trees as a filter of solids was found, as well as gaseous radioactive pollutants. Leaves from the so-called. the windward side of the tree, i.e.. facing the wind, show 4 times higher radioactivity than from the leeward side. Only sparsely wooded districts were found in the air 60 – 75 % radioactive pollution in relation to the part of the city completely devoid of plants. 1 kg of leaves can retain a value of radioactive mass within a few days 1 Curie.