A long-term deviation from the natural species composition of our forests resulted in marked changes in the relative tree species composition where coniferous species began to predominate in the species composition at the expense of broadleaved species. The changes mostly affected the natural distribution of beech, the proportion of which decreased from the original 40.2% to the present 6.9%. On the other hand, the proportion of spruce increased from the original 11.2% to the present 52.8% (MZE 2008).Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) is evidently rightly considered to be the most important and perspective introduced species in the Czech Republic. It is given by more than 150-year tradition of its growing in this country and its potential to grow up very well at acid, mesotrophic and gleyed sites of the 2 nd to the 5 th forest vegetation zone. As a rule, Douglas fir also naturally regenerates there creating mixtures with a number of autochthonous species. For its dynamic intensive growth (Bušina 2007) it is an optimum species for repair or enrichment planting already at an early age. Above all, it is necessary to stress its quite exceptional production potential markedly exceeding all domestic conifers AbsTRAcT: The paper presented evaluates reserves and chemical composition of forest floor of three stands of Douglas fir, spruce and spruce with beech at acid sites (3K) in the Hůrky Training Forest District (TFD) and at a mesotrophic site (4H) in the Křtiny Training Forest Enterprise (TFE). The aim of the study was to evaluate: (i) reserves of forest floor, (ii) soil reaction, (iii) total content of carbon and nitrogen for the forest floor layers, (iv) C/N ratio, and (v) the content of dissolved organic carbon (DOC). The lowest reserve occurs in the Douglas fir stand at a mesotrophic site (25.0 t/ha), the highest accumulation occurs in the spruce stand and in the spruce/beech stand at an acid site (79.4-79.6 t/ha). The soil reaction is strongly acid to acid. The most favourable values of pH for forest floor and soil at acid (4.6 ± 0.4) and mesotrophic sites (5.2 ± 0.4) occur in the Douglas fir stand. It also corresponds to C/N ratio (23-26). The highest reserve of carbon in forest floor occurs at the acid site 34.7 t/ha (1.3 t/ha nitrogen). The lowest reserve of carbon in forest floor at the mesotrophic site amounts to 8.5 t/ha (0.4 t/ha nitrogen). The higher content of DOC in stands at acid sites can result in a higher risk of soil acidification.

ABSTRACT:The study deals with the monitoring of dissolved organic carbon (DOC) concentrations in seepage water sampled from differently managed forest plots in the Drahanská vrchovina Upland. Simultaneously, the input of DOC in precipitation and throughfall is evaluated. Preliminary results show higher mobility level of carbon substances in forest soil in a pure spruce stand compared to mixed stand or a pure beech stand. DOC can be one of suitable characteristics to evaluate the conversion effectiveness of spruce monocultures.