Early thinnings in the State Forests in Poland – development or regress?

Early thinning operations performed in relatively young stands, the most important element of the forest ecosystem, have a much greater impact on their stability than late thinning performed in the stands of older age classes. As regards early thinning, the method of tending cuts based on positive selection (selection and promotion of superior trees) developed by Ilmurzynski has formally been operating in the Polish ‘Principles of silviculture’ and forest practice in the State Forests since 1961. The paper analyses changes in the provisions of subsequent editions of the ‘Principles of silviculture’ (from 1953 to 2012) concerning early thinning operations and their implementation into forest practice in the stands managed by the State Forests. A gradual departure from the superior tree selection method as well as properly performed positive selection is observed. These changes could already be found in 1979. The lack of consistency in determining the aim of thinning treatments makes each of them a separate part of the operation. Because of the lack of consistent selection and promotion of specific trees, the conditions for positive selection are not met. The current ‘Principles of silviculture’ [2012] operating in the State Forests do not recommend the consistent selection of superior trees, but advise early thinning treatments based on the principle of negative selection corresponding to weak upper thinning (grade D according to method of the Association of German Forest Experimental Station from 1902). However in the practice, early thinning treatments similar to moderate lower thinning are often carried out instead (grade B according to method of the Association of German Forest Experimental Station from 1902). Such recommendations and operations regarding early thinning are the main cause of the lack of stability and resistance of stands to the impact of abiotic and biotic factors contributing to reducing the productivity of the forest. We consider it necessary to introduce modifications depending on the use of elements of the future tree method (reduction of the number of superior trees per ha) and group thinning (selection and permanent identification of the groups of superior trees). We propose the following number of superior trees per ha selected during the first early thinning operation: 200−300 for pine, 250−400 for spruce, 100−200 for oak, and 150−200 for beech. The current dissonance between the operating provisions and their arbitrary implementation into forest practice does not increase the silvicultural quality resulting from thinning treatments, which translates into the stability and productivity of stands. To prevent such a situation, we recommend conducting a series of regular training courses for forest staff on permanent thinning sample plots in all forest districts