The effects of Carpinus betulus expansion on soil properties under changing climatic conditions

Carpinus betulus (CB) is becoming increasingly important in the forests of Central Europe and is significantly increasing its proportion in various habitat types. We have analysed how the increase in CB affects soil properties. The study was conducted in the Białowieża Forest (BF). We monitored the changes in CB cover between 1962 and 2013 on 56 permanent plots and collected samples of the litter sub-horizons and the content of the underlying A horizons for laboratory analyses in 2014. During the study period, there was a significant increase in CB cover in the second tree layer by an average of 17.4 % (±1.8) and in the shrub layer by 3.8 % (±1.0), as well as an increase in species diversity from 41 % in the past to 59 % currently. The C/N ratio of the Oi sub-horizon was 32.0 (±0.9), and NH₄+ compounds predominated over NO₃-, with all nitrogen forms most closely associated with the C/N ratio. In the Oea sub-horizon, the C/N ratio was 23.4 (±0.4), and the sum of mineralised nitrogen reached 8%, with a clear predominance of NO₃-. The characteristic most strongly associated with the increase in CB coverage was the NO₃- content in the Oea sub-horizon. The MID analysis confirmed that the change in CB cover was not only significant, but also ecologically important. We suggest that there is a feedback loop in which the generally observed climate changes lead to trees occupying new habitats that supply the forest floor with high quality litter, which in turn affects the soil and promotes the persistence of changes in the species composition of the forest.