Northern red oak (Quercus rubraL.) is one of the most important introduced tree species in the Czech Republic, occupying about 6,000 ha with ca. 900,000 m3of the standing volume. The presented study aims to evaluate its soil forming effects on natural oak sites. Soil chemistry of the upper soil layers (F+H, Ah, B horizons) was studied in three pairs of stands of both species. In each stand, four bulk samples were taken separately for particular horizons, each consisting of 5 soil-borer cores. The soil characteristics analysed were: pH (active and potential), soil adsorption complex characteristics (content of bases, exchangeable cation capacity, base saturation), exchangeable acidity (exchangeable Al and H), total carbon and nitrogen content, and plant available nutrients content (P, K, Ca, Mg). Total macronutrient content (P, K, Ca, Mg) was analysed only in holorganic horizons. Results confirmed acidification effects of red oak on the upper forest soil layers such as decreased pH, base content, base saturation, all nutrient contents in total as well as plant-available form and increased soil exchangeable acidity (exchangeable Al) in comparison to the sessile oak stands, especially in holorganic horizons and in the uppermost mineral layer (Ahhorizon). Northern red oak can be considered as a slightly site-soil degrading species in the studied sites and environmental conditions in comparison to native oak species.

Podrázský V., Vacek Z., Kupka I., Vacek S., Třeštík M., Cukor J. (2018): Effects of silver fir (Abies alba Mill.) on the humus forms in Norway spruce (Picea abies (L.) H. Karst.) stands. J. For. Sci., 64: 245-250.The effects of silver fir (Abies alba Miller) on the soil compared to Norway spruce (Picea abies (Linnaeus) H. Karsten) were evaluated. Altitude of the study site is 790 m a.s.l., mild slope of 10° facing SW, forest site is spruce-beech on acid soil. The forest floor and top soil horizons (L + F1, F2 + H, Ah) were sampled in 4 replications beneath unmixed Norway spruce and silver fir groups. Comparing the soil-forming effects of both species, few significant differences were found in the Ah horizon -contents of total C, N, exchangeable Al and plant available Ca were higher beneath spruce. The soil improving role of silver fir compared to spruce was confirmed at the studied locality.

ABSTRACT:The paper documents the mid-term changes of the soil characteristics and upper soil dynamics in the stands of introduced tree species, grand fir and Douglas-fir, on the former agricultural lands. These species were compared with Norway spruce stand and original grassland in the same site conditions at the Hrubá Skála locality (Eastern Bohemia). The plot was established in 1980 on Luvisol type of soil, sandy clay. Altitude ranges between 350 and 360 m a.s.l., mean annual temperature was 7.8°C, mean annual precipitation 703 mm. Results confirmed the starting process of the development of humus forms typical for forest ecosystems, despite the initial stage was dominant. The amount of surface humus (holorganic horizons) did not differ between the tree species stands and the agricultural land, but the grassland humus layer contained much more mineral particles. The grand fir was confirmed as a species favourably affecting the site, Douglas-fir affecting it less favourably in the given conditions compared with Norway spruce. Different dynamics was documented for soil reaction, characteristics of soil adsorption complex, soil acidity and nutrient dynamics.