The effect of gaps size on colonization process in Molinietum caeruleae meadows with different habitat conditions
The disturbances defined as an external factor causing biomass removal are a key component of all ecosystems. In phytocenoses with a continuous vegetation cover and a large proportion of perennial plants the fine-scale disturbances create gaps, which are the temporary competitor-free microsites suitable for plant recruitment. The investigations of natural colonization of different size gaps in Molinietum caeruleae meadows were carried out in patches dominated by small species creating delicate, erect or procumbent stems (MC), prevailed by large-tussock grasses (GR), and overgrown by willows (SA). Each patch was represented by ten plots, divided into four square subplots of 0.16 m2, 0.09 m2, 0.04 m2 and 0.01 m2. In each of them the aboveground parts of plants were clipped and removed with the litter. The seedlings recruitment was observed in 2007–2009. The highest species richness in gaps was observed in the MC patch and might be caused by week competition for light from neighbouring plants with delicate, procumbent stems and narrow leaves. The smaller rate of recruitment in SA and GR patches could be caused by overshading willows as well as by the competition from large and dense tussocks of Deschampsia caespitosa and Molinia caerulea. At all patches species richness declined with the decreasing gap size. The developed seedling pool represented both species occurring in the surrounding canopy and such which were not found there. However, their contribution varied between particular patches. Regardless gap size, the MC seedling pool was dominated by species which did not occur in the established vegetation, whereas in GR gaps both groups were represented by similar numbers of taxa and the SA gaps become dominated by species present in the surrounding canopy. Irrespective of patch character, in each subplot the medium-seeded species were represented most abundantly. The recruitment of genets of large-seeded species decreased, while the abundance of individuals of small-seeded taxa increased with the increasing gap size. In the light of the performed study, one might suggest that extent-controlled disturbances can be used as an effective way of the conservation of Molinietum caeruleae patches dominated by small meadow species being outcompeted by large-tussock grasses and over-shaded by willows.
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