Development of young substitute larch (Larix decidua Mill.) stands after first thinning

European larch (Larix decidua Mill.) is one of the most important tree species in substitute stands of the Krušné hory Mts. (northern part of the Czech Republic). At present, young larch stands have dynamic height growth and their canopy is closing. Therefore, the proper forest treatment with respect to all functions of these stands is an urgent issue. The aim of the study is to recognise when it is possible to start with thinning and what types of thinning regimes are more suitable in larch stands with respect to their functions as substitute tree species stands. Research was conducted on experimental series Kalek established in a larch monoculture in 1999 (stand age of 12 years) at an elevation of 780 m above sea level in the category Piceeto-Fagetum oligo-mesotrophicum - Calamagrostis villosa. The presented analysis has two main parts: (a) effect of closing canopy on growth of larch - comparison of the groups of trees from border and inside rows and (b) effect of opening canopy on growth and development of young larch stands - comparison of two partial plots (500 m2 each): the one without thinning and the other with thinning (negative selection mainly from above at the age of 13 years). Comparative analyses of trees from border and inside rows showed high growth dynamics of these young larch stands, and therefore the first thinning is necessary in this stage (by 15 years of age). In spite of air pollution, the growth of experimental stands is supernormal and exceeds the data from growth tables, but 60% of individuals showed some malformations, mostly one-sided or two-sided stem curvature. Five years after the first thinning we found a significantly lower h/d ratio of mean stem on the thinned plot in comparison with the plot without thinning. On the other hand, the applied thinning had no effect (five years after realisation) on the h/d ratio of dominant trees (200 thickest trees per hectare).