Anthropogenic influence on the distribution patterns of plant species and habitat diversity along German Federal Waterways

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2015

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DOI:
http://dx.doi.org/10.22029/jlupub-16655

Abstract

Rivers and their floodplains are hotspots of biodiversity. In their natural state, they are shaped by dynamic conditions in space and time that are mainly driven by flooding and sediment transportation. Humans have always used riparian systems for their needs. Measures such as river straightening or the construction of barrages and levees have altered the hydraulic conditions and the floodplain landscapes. This results in a significant loss of ecosystem functions, floodplain area, habitat space and thus biodiversity. Nowadays, two thirds of the floodplain area in the Northern part of the world are lost, and only 10 % of the remaining floodplains are in an ecologically functional state. Therefore, the protection of floodplain biodiversity is one of the major concerns of the Convention on Biodiversity.Especially the German Federal Waterways, i.e. rivers, streams and canals used for shipping traffic, are strongly regulated. To improve the ecological status of these waterways, the management needs to incorporate measures for the protection of floristic diversity. However, it is not known how multiple anthropogenic alterations affect the plant species diversity of floodplains in concert, which are the most important factors, and whether these effects are comparable across regions. Thus, an inventory of plant species composition, diversity, and the most important factors influencing both is needed to develop recommendations for an ecological waterway management.The main objectives of this work were (1) to inventory the plant species diversity in the floodplains and adjacent areas of the German Federal Waterways and to determine the most important relations between regional differences, anthropogenic influence and phytodiversity; and (2) to draw conclusions for the incorporation of biodiversity demands in waterway management regimes.In a comparative study (chapter 2), we inventoried plant species composition and diversity in 20 study sites representative for the German Federal Waterways. The study sites comprised upland and lowland river stretches covering a range of anthropogenic alterations.The aim was to determine which species form the floodplain vegetation of Federal Waterways, how composition and diversity is affected by multiple human influences (e.g. regulation by barrages, bank protection, and shipping traffic) and whether the detected patterns are visible across regions and thus universally valid. While biodiversity patterns strongly differed between upland and lowland rivers, the anthropogenic influence was visible across all study sites. With increasing human influence, floodplain species were replaced by generalist species adapted to terrestrial conditions, since human alterations often lead to a disconnection of the river and the floodplain and inhibit the natural flooding regime. As a consequence, species richness partly increased within the studied habitats.Since knowledge on the bank vegetation of canals was scarce, canals were excluded from the comparative study and considered separately in a case study (chapter 3). The aim of this study was to gain knowledge about similarities and differences between natural and artificial waterways (canals), their bank vegetation and biodiversity. Similar to the comparative study, species richness was higher along the canal. The bank vegetation was composed of more terrestrial species while the vegetation along the river contained a higher amount of floodplain species. Accordingly, functional divergence, which is related to a higher ecological niche differentiation, was higher along the river.The findings of both studies suggest that management should aim to reinstall more natural hydraulic conditions and to reconnect rivers and floodplains to improve the ecological status of the floodplains of German Federal Waterways. On the short term, this might lead to a decrease in species numbers, since the invaded terrestrial species will be affected. However, on the long term, more dynamic conditions will lead to the small-scale pattern of habitats that are the main cause for floodplain biodiversity and that will sustain specialized and often endangered species. Even along artificial or strongly inhibited waterways, a management of benign neglect will allow for succession and thus higher habitat diversity.

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