Root biomass of Fagus sylvatica L. stands depending on the climatic conditions

Fine root biomass of forest trees is a recognised indicator of environmental changes in the conditions of global climate change. The present study was carried out in six old-growth beech forests (112-140 years) located in different climatic conditions on the range border of Fagus sylvatica L. in Poland. The root biomass was investigated by soil coring method in the upper soil layers (0-5 cm, 5-15 cm and total layer 0-15 cm). The significantly greater total root biomass was found in the beech stands, which characterised by higher average precipitation and lower average annual temperatures in the period 2000-2005. The share of roots of diameter > 5 mm increased with increasing depth of top soils. Biomass of fine roots (diameter ≤ 2 mm) decreased with increasing depth of upper soil layers. The average biomass of fine roots ranged from 175.36 to 418.16 g m^-2 in the soil layer 0-15 cm. The significant differences of fine root biomass were found between studied stands in the soil layers 0-5 cm and 0-15 cm. Also, it was found significant positive correlation between fine root biomass in the soil layer 0-15 cm and precipitation during the growing season in 2006. Precipitation in the study period was connected with very high rainfall in August 2006, repeatedly exceeding the long-term monthly levels. Regional climatic conditions, in that extreme weather events in growing seasons can significantly to affect changes of fine root biomass of forest trees, consequently, changes of relationships between the growth of above- and below-ground of the old-growth forest stands.