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European beech is a superior competitor among the trees of Central Europe, often growing in pure stands. We proposed a hypothesis, that once beech has reached dominance in forest community, it's recruitment could become limited due to the gradual accumulation of pathogens attacking seeds and seedlings. We employed data on seed production and germination along with a field experiment to estimate the germination success of beech in two old-growth forests. Beech produced more seeds than the co-occurring coniferous trees, but less than 1% of beechnuts germinated in the next season. In the field experiment, the percentage of decayed beechnuts was 57% in the Carpathians and 61% in the Alps. Most of the dead germinants and decayed beechnuts were infested by fungi. The average number of fungal colonies per one sample in the Carpathians was significantly higher after mast year than one year before, while the differences between the Alps and Carpathians after mast years were statistically not significant. Fungi have been isolated from practically all dead beechnuts and dead germinants. The number of beechnuts per seed trap, the number of germinants around it and the relative number of fungal colonies obtained from plastic boxes placed in the same sample plot were not significantly correlated. The mortality of germinants continued throughout the spring; the number of life germinants in the middle of May amounted to 0.87% of the initial number of beechnuts in the Carpathians and only 0.28% in the Alps. High rates of beechnut and germinant mortality could probably offset the huge reproductive effort of European beech in old-growth stands and limit the possibility to attain absolute dominance by that species. However, our hypothesis that the build-up of fungal pathogens on the forest floor old-growth stands is able to stop the regeneration of beech still needs to be tested using larger data sets.
Studies of the sex structure and recruitment rates of silver eels from a population occurring in natural conditions in a large lake complex were conducted in the 1985-1990 period based on a sample of 6998 specimens. The fish were caught in 60 connected lakes with a combined surface area of 300 km2 using box traps, cross traps, stownets on stakes and electric fishing. It was determined that the share of males in the eel population occurring in the lakes was barely 1.03%, and in the group of fish with body lengths (Lt) of up to 46.0 cm it was 3.17%. Silver and yellow eels were noted among both males and females. The share of silver eels increased from 0 to 100% in the body length categories from 39.0 to 46.0 cm among males and from 47.5 to 95.0 cm among females. In both instances, the dependence of the share of silver eels on the total length of the body was described with linear regression with a high correlation coefficient and high regression significance (P < 0.05). The studies indicated that in the lakes of northeastern Poland, which are located within a large complex that is permanently connected, the share of males is small and the recruitment of silver eels from this group occurs within a narrower and lower size range than it does in females.
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