Soil sickness in forestry trees.

The auto toxicity of tree species secretions, regulates the stand structure. The negative effects of one plant species on soil, cultivated in one place for long time and the associated problems have been summarized (12). The soil fatigue is a cyclic phenomena, caused by the unilateral development of soil microflora, allelopathy, accumulation of toxins in the soil, development of pathogenic microorganisms, other pests and weeds changes in soil pH and disturbed soil structure etc.

In agriculture, soil fatigue is connected to allelopathy, however, in forestry little data are available. The monoculture of tree stand for long periods slowly intoxicates the soil, leading to the gradual changes in tree species composition. These accumulated toxic substances may be absorbed by other plants and microorganisms, bound to these plants and after some time the former composition of stand could be restored. Based on of current typology, the changes in tree species structure are not considered, as it may be due to site conditions. Therefore, autointoxication (besides other anthropogenic effects) contributes to the weakening of individual tree species, which gradually causes dieback in fir or attack of pests and diseases on elm, spruce and oak.