Distribution patterns of vascular plant taxa in the federal states of Lower Saxony and Bremen, Germany, with respect to their naturalisation and threat status

Distribution patterns of vascular plant taxa in the federal states of Lower Saxony and Bremen, Germany, with respect to their naturalisation and threat status Detailed knowledge about the spatial distribution of richness centres is a prerequisite for the development of national strategics for the conservation of vascular plant species. However, different groups of plant taxa may have different relevance depending on their naturalisation and threat status. In this study we investigate the spatial distribution of plant species richness centres in the area of the federal states of Lower Saxony and Bremen, based on data from the plant survey of Lower Saxony (Niedersachsisches Pflanzenarten-Erfassungsprogramm). Our analyses include: 1.) The complete floristic list (1819 taxa) 2.) Three groups of taxa defined by their naturalisation status (1509 indigenous taxa, 160 archaeophytes, 145 established neophytes), 3.) Two groups of taxa defined by their threat situation (unthreatened versus threatened taxa, including 643 taxa which have been Red Listed with status I, 2, 3, G or R). Based on the complete floristic list, a clumped distribution pattern was observed. Site conditions in the Quaternary coastal and lowland areas arc relatively homogeneous and, with exception of the major stream valleys of the Weser, Aller, and Elbe, relatively species-poor. The upland area with its heterogeneous site conditions shows the overall highest taxonomic richness. The large group of indigenous taxa shows a distribution very similar to that of the complete floristic list. Archaeophytes are concentrated in the coastal area of Bremen, the Weser and Aller plains, the old moraine loess landscapes, and in smaller cities. High diversity of established neophytes is mainly found in congested urban areas and several other small-scale centres of diversity. Red List species are mainly indigenous (91 %), 8 % are archaeophytes and only 1 % are neophytes. Their diversity centres are spatially highly differentiated: at the coast only the islands in the North Sea are small hotspots, while in the lowlands relatively large hotspots are situated in the Wend land, the Luneburg Heath, and the Elbe-Weser triangle north of Bremen. In the uplands, the area around Gottingen, the uplands of the Weser and Leine valleys, and the Harz mountain margins are well-defined hotspots of Red List taxa. Many of these endangered species are presumably specialists adapted and limited to natural and semi-natural habitats.