Invasive Species Compendium

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Abstract

Floristic and phytocenotic indicators of the conditions of riparian forests in the urban river valley.

Abstract

Urban river valleys are exposed to strong anthropogenic pressure, but despite these distortions they provide important habitats in urban areas. Not embanked forests are particularly valuable in urban river valleys as they represent fragments of natural vegetation in a highly changed environment. The study assesses the flora and structure of forest communities in a riparian urban forest complex that is under the direct influence of river water. Las Pilczycki Forest in Wrocław (SW Poland) is such a riparian forest island. We analysed the species richness and composition in terms of the phytocoenoses variability and their syntaxonomic classification. We also investigated if the vegetation can indicate a spatial differentiation in habitat conditions. Floristic and phytosociological data were collected from 70 circular plots (100 m2 each) located in a grid. A total of 81 species were recorded, with a mean of 21 species per plot. Most frequent were: Acer campestre, Acer platanoides, Anemone nemorosa, Ficaria verna, Fraxinus excelsior, Galium aparine, Geum urbanum, Impatiens parviflora and Sambucus nigra. In biological spectrum the most numerous were hemicryptophytes, megaphanerophytes and geophytes. The number of alien species was minor (9% of the flora). The most frequent anthropophyte was Impatiens parviflora. Soil moisture, acidity and fertility indices exhibited spatial correlations and they were higher in the western part of the forest. The moisture index was also higher in the northern part. Species richness ranged from 13 to 32 (with a mean of 21 species). Two forms of Ficario-Ulmetum minoris were identified: with Galanthus nivalis and with Tilia cordata. The first was a well-structured riparian community, while the latter one represented the drained floodplain forest. Vegetation units are spatially separated, in the western part of the forest prevails form with Galanthus nivalis, while in the east - with Tilia cordata. In isolated alluvial forests of urban area local site conditions are crucial for the vegetation patches, because of the distortion of river valleys. The absence of flood embankments is not a sufficient condition for maintaining proper structure of riparian forests.