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Decomposition is an important carbon flux that must be accounted for in estimates of forest ecosystem carbon balance. Aim of this research is to provide estimate of fine woody debris decomposition rates for different tree species and sample sizes also taking into account the influence of specific microsite meteorological conditions on decomposition rates. In this paper we present results of the first two years of the experiment designed to last six years. Study was conducted in managed lowland oak forest in central Croatia. Decomposition rates (k) of fine woody debris (diameter 0.5–7 cm) for four species (Querus robur L., Carpinut betulus L., Alnus glutinosa Gaernt., Fraxinus angustifolia L.) in four size classes were estimated using litter bag method and mass loss equation of Olson (1963). Overall average k in our study was 0.182 ± 0.011 year-1. Results indicate that decomposition rate is affected by the size of the debris, with the smallest diameter branches (<1 cm) decomposing is significantly faster (k = 0.260 ± 0.018, P <0.05) than the larger one. Tree species from which debris had originated also affected decomposition, although to a lesser extent, with hornbeam samples having significantly (P <0.05) higher average decomposition rate (0.229 ± 0.028), compared to that of ash samples (0.141 ± 0.022). Proportion of variability in k explained by variables ‘species’ and ‘size class’ was assessed with general linear model (R² = 0.644) also taking into account variables like soil temperature and soil water content. Sample size class explained 22.2%; species explained only 9.4%, while soil water content and temperature combined explained 32.8% of the variance of k. Rate constants obtained within this study might be useful in modelling ecosystem carbon balance for similar lowland forest ecosystems in Europe.
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.
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