Riparian hardwood forests of Quercus robur, Ulmus spp and Fraxinus spp that are present along major rivers are valuable communities protected by the EU Habitat Directive and recommended for monitoring. Part of the reason for that is relative rarity on the scale of Europe as a whole, and also in Poland. This in turn reflects the way in which fertile habitats were, in their majority, deforested long ago, drained and changed into grasslands or arable land. Additionally, the greater part of these habitats have lost their specific features, as a result of river engineering and – primarily – the construction of the river embankments that have acted to limit flooding and alluvial processes, in that way also initiating change in the composition of both soils and plant communities. Specifically, this article presents selected results of the research project: Riparian hardwood forest services in the middle Vistula river valley. One of the main objectives thereof was to assess the condition of forest ecosystems from which flooding has now been absent for at least 50 years, as well as to prepare guidelines for actions necessary to maintain or restore their diversity, and proper ecological and biological functions. Our research questions therefore revolved around components of riparian hardwood forest ecosystems have been most changed … and why? The research was conducted in six riparian hardwood forests (to date unmonitored) located in the valley of the middle Vistula (in Mazowieckie voivodship). Relevant work was carried out using the standard monitoring guidelines – as primarily based on an assessment of vegetation composition and structure together with water conditions. However, in the work in question, these were augmented by additional analyses allowing for detailed characterisations of soil, the topoclimate, and the species diversity achieved by selected groups of invertebrate (Hymenoptera: Apidae: Bombus and Haplotaxida: Lumbricidae). The communities selected represent multi-functional, species-rich forests. Extensive use of the studied riparian mixed forests ensures that deadwood resources are quite considerable. Moreover, the studied forests exert a strong impact when it comes to mitigation of climate locally. The observed soil types indicate fertile and biologically-active habitats, as well as to soil development largely determined by the height of the groundwater table causing the gleyic process in the lower parts of profiles. However, in some forest patches it is possible to note transformations related to habitat drying, with significant canopy gaps and disturbances of topsoil and the undergrowth. There was a great abundance of invasive alien plant species (mainly Impatiens parviflora) in the undergrowth. Moisture conditions have an impact on the occasional occurrence of Lumbricidae associated with wet and flooded areas. In turn, the domination by Bombus of open-habitat species indicates a transformation of forest structure, and the patchy nature of riparian forests located in a rural landscape. The obtained results demonstrate that protective actions should focus on ensuring adequate soil-moisture conditions, and on restoring the natural structure of vegetation with a view to invasions of alien species being hampered. Another important issue is the proper use of land adjacent to forest patches, as fallows prove to be invaded quickly by the kenophytes preferring abandoned and disturbed places.
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