[Silvicultural treatments and their selection effects]

Selection can be defined in terms of its observable consequences as the non random differential reproduction of genotypes (Lerner 1958). In the forest stands we are selecting during the improvements-fellings and reproduction treatments the individuals surpassing in growth or in production of first-class timber. However the silvicultural treatments taken in forest stands guarantee a permanent increase of forest production only in such cases, if they have been taken with respect to the principles of directional (dynamic) selection. These principles require that the trees determined for further growing and for forest regeneration are selected by their hereditary properties, i.e. by their genotypes.For making this selection feasible, our study deals with the genetic parameters and gives some examples of the application of the response, the selection differential, the heritability in the narrow and in the broad sense, as well as of the genetic and genotypic gain. On the strength of this parameter we have the possibility to estimate the economic success of several silvicultural treatments in forest stands.The mentioned examples demonstrate that the selection measures of a higher intensity will be manifested in a higher selection differential, in a higher genetic and genotypic gain and that the mentioned measures show more distinct effects in the variable populations - in natural forest - than in the population characteristic by a smaller variability, e.g. in many uniform artificially established stands.The examples of influences of different selection on the genotypes composition of population prove that genetics instructs us to differentiate the different genotypes of the same species and gives us at the same time a new criterions for evaluating selectional treatments. These criterions from economic point of view is necessary to consider in silviculture as advantageous even for the reason that we can judge from these criterions the genetical composition of forest stands in the following generation, it means, within the scope of time for more than a human age.