The conversion of forest stands is a shift in the composition of tree species aiming to adjust it to the composition characteristic of a natural habitat by means of pruning, regenerative cutting or forest thinning (turning a forest into a multi-layered formation). In the Katowice Forest District, the conversion of forest stands comprises mainly pine and birch stands, damaged by industrial activity. In the 20th century, Upper Silesia suffered from severe air pollution, which caused considerable damage to and degeneration of the forests growing in the region. The scale of pollution is well illustrated by the comparison of average particulate matter fallout, which, in the years 1963-1965, reached 484 g/m2/yr in Katowice, while in recent years it has stabilised at values ranging from 20 g/m2/yr in some districts (Muchowiec, Podlesie and Kostuchna) to 100 g/m2/yr in others (Śródmieście, Brynów, Janów and Giszowiec). At the time when the effect of pollution on the forests was particularly strong, the stands were converted with non-native species, considered less susceptible to air contamination (e.g. the black pine, the northern red oak and the Japanese larch). At present, since air pollution has decreased significantly, the conversion of forest stands takes advantage of all native forest-forming tree species, even those intolerant of air pollution, such as the European silver fir and the Norway spruce. Nowadays, a high proportion of broadleaved trees in the composition of Katowice forests is the result of the long-term intensive conversion of forest stands, spanning over the last 50 years.

1. The new forest generation comprised of shade-loving species growing under the canopy of the old stand.

2. The reproduction of shade-tolerant species requires the removal of bird nests in the converted stand in order to provide suitable sun exposure.

3. The restoration of the species composition close to natural is sometimes impossible without human intervention.

4. The larch, which manifests strong resistance to environmental pollution and grows quickly, is used to protect broadleaved species planted in open areas