Rola martwego drewna w regeneracji drzewostanu łęgu jesionowo-olszowego (Fraxino-Alnetum) zasiedlonego przez bobry

The paper concerns the structure of natural regeneration in ash−alder riparian forests (Fraxino−Alnetum) colonized by beavers (Castor fiber) taking into account the substrate, on which it appears (soil and deadwood). Study was conducted in 2016 on twelve sampling plots located in the Orłówka valley in the Białowieża National Park (eastern Poland), where beavers settled around 2005. We counted natural regeneration occurring on the ground and on deadwood on each plot. Also we identified volume of deadwood, decay status and water cover. A decade after the occurrence of beaver ponds, the density of natural regeneration is 5575 saplings per hectare and the regeneration on deadwood is 28% of the total. Black alder is the dominant species. The regeneration occurring on the soil is richer in species and has a larger share of shrub species. In the case of regeneration on the deadwood, seedlings appear first on trees fallen before the flood. Over the time, the role of deadwood as a substrate for the development of regeneration increases and the role of fallen trees is the greater, the greater is the fraction (coverage) of the flooded areas. Studies show that the continuous occurrence of the deadwood accelerates habitat regeneration after a disturbance such as the occurrence of a beaver pond.