Höckerschwäne (Cygnus olor) am Mauserplatz Alfsee (Niedersachsen) : Herkunft, Zusammensetzung und Bruten

Im Rahmen eines Beringungsprojektes an Höckerschwänen im Weser-Ems-Gebiet wurden am Alfsee als einzigem größeren Mauserplatz im südwestlichen Niedersachsen 1998, 2000 und 2003 insgesamt 34 Höckerschwäne mit Halsringen markiert und weitere sechs andernorts beringte Vögel wiedergefangen oder abgelesen. Der Anteil der immutablis-Mutante war mit 36 % auffallend hoch. Die beringten Vögel erbrachten insgesamt 4296 Ablesungen, davon 1107 in über 20 km Entfernung zum Alfsee. Für acht Vögel wurden spätere Ansiedlungen an Brutplätzen belegt, davon insgesamt vier am Alfsee oder im näheren Umfeld (Hasetal, Dümmer), in den übrigen Fällen 35-100 km entfernt in alle Himmelsrichtungen. Trotz rückläufiger Mauserbestände mauserte die Mehrheit der beringten Vögel in den Folgejahren erneut am Alfsee oder im angrenzenden Hasetal, andere wählten bis zu 135 km entfernte Gewässer. Winterbeobachtungen konzentrierten sich auf das Hasetal und die Mittelweser, ansonsten streuten die Funde im Jahreslauf in alle Himmelsrichtungen. Mehrere Vögel wurden in Ostdeutschland beobachtet. Die teils vergleichsweise großen Funddistanzen erklären sich auch durch die Verwendung von Halsringen. Auffallend gering war der Austausch mit den küstennahen Populationen, gerade angesichts der dort intensiven Beringungstätigkeit. Dies deutet an, dass diese Vögel tendenziell zu einem anderen Subareal zählen könnten.34 Mute Swans were neck-collared and 6 further birds ringed elsewhere were recorded at Lake Alfsee, Western Lower Saxony in 1998, 2000 and 2003. The proportion of the polish morphe is high (36 %). We got 4296 resightings of the ringed birds; 1107 resightings were recorded in more than 20 kilometers distance from Lake Alfsee. Eight birds were recorded at later breeding places, including four birds at Lake Alfsee or in the surroundings and the other birds in distances from 35 to 100 kilometers in all directions. Although the moulting population at Lake Alfsee declined since the end of the 1990-ties, the majority of the birds returned to this place for moulting in following years. Other birds choosed new moulting places in distances up to 135 km. Resightings in winter concentrated in the surrounding meadows of Hase River and in the meadows of Weser River, but resightings throughout the year cover all directions. A few birds were recorded from eastern Germany. The comparetively high distances of the resightings are influenced by the use of neck collars. The interactions with the populations close to the coast of the Northern Sea are remarkably low, although there has been a high activity of ringing in those areas. This may point out that the birds moulting at Lake Alfsee belong to a different subpopulation this is more or less spatial separated

Dispersal and choice of wintering- and moulting grounds of Mute Swans Cygnus olor ringed as juveniles in Western Lower Saxony

Das Wanderverhalten von Höckerschwänen aus dem nordwestdeutschen Raum war bislang im Gegensatz zu vielen Nachbarländern nur wenig untersucht. Wir stellen daher hier Wanderungsbewegungen juveniler Höckerschwäne im ersten Herbst ihres Lebens sowie zur Überwinterung und Mauser vor der ersten Brutansiedlung dar, wobei überwiegend ein Zeitraum von fünf Jahren betrachtet wird. Im westniedersächsischen Weser-Ems-Raum mit Schwerpunkt an der Unterems wurden zwischen 1998 und 2006 316 nicht flügge Höckerschwäne nahe ihrer Geburtsorte zusätzlich zu den Vogelwartenringen mit farbigen Halsbändern beringt. Daten von 217 dieser Vögel konnten mindestens für den ersten Winter ausgewertet werden. Im ersten Herbst verblieben über 92 % der juvenilen Vögel nahe ihrer Geburtsorte, im ersten Winter noch 62,6 %. Die übrigen wanderten größtenteils küstenparallel nach Südwesten oder Nordosten. Im zweiten Winter zogen die Vögel im Mittel signifikant weiter vom Geburtsort weg, bis zum fünften Winter verringerten sich die Entfernungen wieder signifikant. Für 22 Individuen konnte eine wiederholte Nutzung entfernt gelegener Überwinterungsplätze nachgewiesen werden. Geschlechtsspezifische Unterschiede sind bei der Wahl der Überwinterungsplätze nicht erkennbar. Vorjährige Höckerschwäne mauserten im Mittel in 125 km und maximal in 311 km Entfernung zum Geburtsort, aber selten nahe dem Geburtsort. Die mittlere Entfernung blieb in den Folgejahren weitgehend konstant. Die Mauserplätze lagen wie die Überwinterungsgebiete überwiegend südwestlich oder nordöstlich der Geburtsorte. Eine Mauserplatztreue über bis zu sechs Jahre wurde ebenso festgestellt wie großräumige Mauserplatzwechsel. Geschlechtsspezifische Unterschiede sind auch bei der Mauser nicht nachzuweisen. Insgesamt zeigen die tiefer im Binnenland beringten Vögel nach Südosten parallelverschobene Wanderungsbewegungen und geringen Kontakt zu ihren Artgenossen aus den küstennahen Brutpopulationen. Auch eine Mauser im Ostseeraum führt kaum zu einem Individuenaustausch mit dort ebenfalls mausernden Vögeln der Brutpopulationen aus dem niedersächsischen Binnenland und Ostdeutschland.The migration of Mute Swans has not been studied extensively in Northwestern Germany before, in contrast to neighbouring countries. We describe movements of Mute Swans in the first autumn of their lifes as well as their distribution while wingmoulting and wintering before their first settlement as breeders. We mostly consider the first five years in the lifes of the birds. From 1998 to 2006, we marked altogether 316 juvenile Mute Swans with neck collars at their places of birth in Western Lower Saxony. Most markings were carried out in the marshes of the River Ems close to the North Sea Coast. For a total of 217 birds, we are able to describe at least movements in their first winter. In the first autumn, 92% of the juveniles stayed close to their places of birth. In the first winter, still 62.6% stayed there, the other birds moving on parallel to the North Sea Coast, either in southwestern or in northeastern direction. Movements in the second winter were on average significantly farther than in the first winter, whereas from the second to the fifth winter, the mean distances decreased significantly. We did not find any sex-specific differences in choosing wintering places. Second-year birds moulted on average 125 km and in maximum 311 km away form their places of birth; a moult close to the place of birth only occured in few cases. Similar to the wintering grounds, moulting grounds were situated mostly either southwest or northeast of the places of birth, some of them even at the Baltic Sea. Differences between sexes were not found. Single birds used the same moulting ground for up to six successive years, whereas other individuals changed the moulting grounds over large distances. Birds marked farther away from the coast in southern parts of the study area followed migration routes almost parallel to those of the birds born closer to the coast. Birds originating from inland populations did not have many spatial contacts with those from the populations breeding closer to the coast. Although birds born close to the North Sea Coast regularly moult at the Baltic Sea, an exchange with birds from breeding populations of Eastern Germany could not be found

Verbreitung gefährdeter Gefäßpflanzen im Bereich der Artlandbäche (Landkreis Osnabrück)

Die Niederungen der Artlandbäche (Landkreis Osnabrück, Niedersachsen) wurden 2001 auf die Vorkommen von Gefäßpflanzen der „Roten Liste“ untersucht. Alle Vorkommen wurden parzellenscharf erfaßt, einem Biotoptyp zugeordnet und die Artmächtigkeit halbquantitativ geschätzt. Insgesamt gelangen 575 Funde von 52 Sippen der Roten Liste einschließlich Anhang. Hiervon gelten lediglich 5 als stark gefährdet, die übrigen als gefährdet oder möglicherweise gefährdet. Sieben weitere Sippen sind im Untersuchungsgebiet seit 1982 verschollen. Die aktuellen Vorkommen konzentrieren sich auf die Oberläufe der Artlandbächemit ihren Auen und Bruchwäldern sowie Quellsümpfen. Hier wachsen zahlreiche Sippen in großen Populationen (zum Beispiel Caltha palustris, Carex echinata, Valeriana dioica, Viola palustris). Nassgrünländer sind dagegen stark zurückgegangen und überwiegend nur noch fragmentarisch ausgebildet, das Floreninventar ist hier stark verarmt. Weite Bereiche an den Unterläufen der Artlandbäche weisen aufgrund intensiver landwirtschaftlicher Nutzung nur noch wenige Vorkommen gefährdeter Gefäßpflanzen auf.Siphonograms listed in the the Red Data Book of Lower Saxony were mapped in the meadows of the streams inArtland area (western Lower Saxony) in 2001. All finds were registered in each plot, assigne to a biotope type and counted semiquantitatively. 578 finds of 52 species were made in all. According to the Red Data Book 5 species are „seriously endangered“, the others are „endangered“ or „possibly endangered“. Five more species have been extinct in the area studied since 1982. The actual finds are concentrated in the region of upper courses with their wet forests and spring swamps. These biotopes contain a large number of endagered species in mostly great populations, e. g. Caltha palustris, Carex echinata, Valeriana dioica and Viola palustris. A serious loss is however to be seen in plant communities of wet grassland. Large areas in the lower courses are intensively used for agriculture and have only a small number of endangered plants

Entwicklung und aktuelle Situation der Verlandungsvegetation des Dümmers (Niedersachsen)

Die Verlandungsvegetation des Dümmers wurde seit Beginn des 20. Jahrhunderts mehrfach untersucht. 2006 erfolgte erstmals eine flächendeckende Kartierung der gesamten Verlandungszone. Seit der 1953 abgeschlossenen Eindeichung war diese massiven Veränderungen unterworfen. Bereits kurz nach Deichschluss kam es zu einer massiven Reduktion der seeseitigen, durchfluteten Schilfbestände (Phragmites australis). Weite Röhrichtpartien entwickelten sich zunächst zu Wasserschwaden-Beständen (Glyceria maxima), dann wieder zu Schilfröhrichten. Nach einer zwischenzeitlichen Stagnation der Röhrichtabbrüche in den 1980er Jahren kam es in den letzten 15-20 Jahren zu erneuten erheblichen Flächenverlusten. Die ehemals typischen Teichbinseninseln (Schoenoplectus spp.) sind inzwischen weitestgehend verschwunden. Die Wasserrosenfelder (Nuphar lutea, Nymphaea alba) verloren seit den 1990er Jahren erheblich an Fläche. Alle Verluste an der Verlandungsvegetation dürften zunächst durch die Gewässerbelastung, in neuerer Zeit vor allem durch zu hoch gehaltene Sommerwasserstände verursacht sein. Die ehemals üppige und artenreiche submerse Vegetation starb nach der Eindeichung vollständig ab. Nach einer unerwartet eingetretenen Klarwasserphase wurde 2001 erstmals wieder Potamogeton pectinatus nachgewiesen, seitdem wurden weitere Laichkraut-Arten, zwei Arten der Armleuchteralgen (Chara fragilis, Nitella mucronata) und weitere Tauch- und Schwimmblattpflanzen nachgewiesen. Die voraussichtlich 2009 erfolgende Umleitung des Bornbaches, über den ein Großteil der heutigen Nährstofffracht in den Dümmer gelangt, dürfte die Bedingungen für die submerse Vegetation entscheidend verbessern.The silting vegetation of Lake Dümmer has been investigated at different times throughout the 20th century. In 2006 we made the first complete mapping of all vegetation types. Since embanking had been finished in 1953, the vegetation changed dramatically. Reedbanks reduced much and the vegetation changed from dominance of Phragmites australis to Glyceria maxima, later Phragmites took back large parts. After a stagnation of devastion of reedbanks, after the 1980ties again large areas of reedbanks disappeared. Small islands of Schoenoplectus spp., which were very typical for the lake, nearly disappeared. The vegetation of the emergent plants Nuphar lutea and Nymphaea alba has started to disappear in the 1990ties. All devastation of silting vegetation seem to correlate with water pollution in the first decades, in recent years the water levels in summer are too high for reproduction of plants. The submerse vegetation was quite rich in species and biomass before embanking, then it completely disappeared. Since 2001, there is a slight recovery of such vegetation, including some species of Potamogeton spp. and Characeae. After the diversion of the Bornbach, a highly polluted stream in 2009, nitrification will be reduced giving good perspectives for a further recovery of submerse vegetation

ReSurveyGermany: Vegetation-plot time-series over the past hundred years in Germany

Vegetation-plot resurvey data are a main source of information on terrestrial biodiversity change, with records reaching back more than one century. Although more and more data from re-sampled plots have been published, there is not yet a comprehensive open-access dataset available for analysis. Here, we compiled and harmonised vegetation-plot resurvey data from Germany covering almost 100 years. We show the distribution of the plot data in space, time and across habitat types of the European Nature Information System (EUNIS). In addition, we include metadata on geographic location, plot size and vegetation structure. The data allow temporal biodiversity change to be assessed at the community scale, reaching back further into the past than most comparable data yet available. They also enable tracking changes in the incidence and distribution of individual species across Germany. In summary, the data come at a level of detail that holds promise for broadening our understanding of the mechanisms and drivers behind plant diversity change over the last century

Langfristige Veränderungen von Flora und Vegetation des Grünlandes in der Dümmerniederung (Niedersachsen) unter dem Einfluss von Naturschutzmaßnahmen

Wet grasslands represent endangered ecosystems which since the 1950ies have severely decreased in area and habitat quality, especially in the fen areas of northern Germany. Since the 1980ies, large efforts have been undertaken to restore these grasslands. These measures are considered as very difficult because of the irreversible degradation of the peaty soils by melioration and intensive agricultural usage. The effects of re-wetting including temporal inundation and of the impoverishment in nutrients on wet grasslands have been extensively studied. There is also vast experience about the effects of experimental management techniques. However, there is a lack of long-term studies spanning 15 years or more. The surroundings of lake Dümmer (western Lower Saxony) have been rich in wet grasslands. Here, large vegetation surveys were made around 1950 just before the start of melioration, as well as during the period of intensive agricultural use and during the still ongoing process of restoration since the early 1990ies. These vegetation data are accompanied by land use data, mappings of target species and permanent plot surveys conducted since the mid 1990ies. On the whole, these data are unique for Germany and allow an examination of the restoration-driven successional dynamics under changing environmental conditions as well as of the development of species richness. These results also allow us to evaluate the possibilities and limits of large-scale restoration of species-rich wet grasslands. The data analysis included spatial analysis with a Geographic Information System, phytosociologial table work, ordination of vegetation plots with Detrended Correspondence Analysis and an ecological interpretation with the help of Ellenbergs indicator values. Calthion meadows and Agrostis canina grasslands were the most common vegetation types around 1950, but severely decreased after melioration. Molinion meadows and Nardetalia communities completely disappeared. Restoration management caused a pronounced change in vegetation: arable land, new-sawn grasslands and Elymus repens grasslands disappeared, while flood grasslands and Carex acuta sedge fens increased in abundance. Reeds with Phalaris arundinacea and Glyceria maxima almost developed periodically. The ongoing nutrient impoverishment allowed Agrostis canina grasslands to re-settle, resulting in an increase of species typical for small-sedge fens. Differences in site factors, especially in nutrient contents, between the present and historical conditions appear to have considerable effects on the distribution of many species, but are less obvious in the actual distribution of certain vegetation types. Nearly all plant species that are listed in the Red data book of Lower Saxony and that were noticed in the study area in recent times as well as the target species of conservation increased in abundance and spread out over large parts of the study area following restoration. Some highly rare species which were extinct in the study area and its surroundings for many years re-established most likely via long-distance dispersal, namely Bromus racemosus, Dactylorhiza incarnata and D. majalis. The occurrence of target species was positively influenced by a high level of re-wetting and nutrient impoverishment, whereas land use proved to be less important. Most species appear to be able to deal with either mowing or grazing, or a combination of both. Only few target species like Oenanthe fistulosa and Senecio aquaticus that need a comparatively high level of nutrients showed a slight decrease in abundance during recent years. The populations of Caltha palustris stabilized in size and were not affected negatively by long-time inundation. Finally, some species which are problematic for land use increased in abundance in response to restoration, especially Deschampsia cespitosa and the toxic plant Equisetum palustre. The species richness of the wet grasslands has shown a steady linear increase, and there are no indications for a weakening of this trend. Heavily degraded peaty soils showed significantly lower species numbers than less degraded peat. In conclusion, extensive restoration efforts cannot guarantee success in re-establishing species-rich wet grasslands with endangered target species, but in this study they had strongly positive effects on total species richness and on the abundances of most target species. Main factors of success are large-scale, consequent impoverishment, ongoing usage of the grasslands and an adjustable rewetting. The level of peat degradation was determined as a major limit of restoration success. A low level can enable the restoration of more or less species-rich grassland and a recolonisation of a couple of target species, a lot of them endagered

Long-term changes in flora and vegetation of the grasslands in the surroundigs of Lake Dümmer (Lower Saxony) influenced by conservation management

Wet grasslands represent endangered ecosystems which since the 1950ies have severely decreased in area and habitat quality, especially in the fen areas of northern Germany. Since the 1980ies, large efforts have been undertaken to restore these grasslands. These measures are considered as very difficult because of the irreversible degradation of the peaty soils by melioration and intensive agricultural usage. The effects of re-wetting including temporal inundation and of the impoverishment in nutrients on wet grasslands have been extensively studied. There is also vast experience about the effects of experimental management techniques. However, there is a lack of long-term studies spanning 15 years or more. The surroundings of lake Dümmer (western Lower Saxony) have been rich in wet grasslands. Here, large vegetation surveys were made around 1950 just before the start of melioration, as well as during the period of intensive agricultural use and during the still ongoing process of restoration since the early 1990ies. These vegetation data are accompanied by land use data, mappings of target species and permanent plot surveys conducted since the mid 1990ies. On the whole, these data are unique for Germany and allow an examination of the restoration-driven successional dynamics under changing environmental conditions as well as of the development of species richness. These results also allow us to evaluate the possibilities and limits of large-scale restoration of species-rich wet grasslands. The data analysis included spatial analysis with a Geographic Information System, phytosociologial table work, ordination of vegetation plots with Detrended Correspondence Analysis and an ecological interpretation with the help of Ellenbergs indicator values. Calthion meadows and Agrostis canina grasslands were the most common vegetation types around 1950, but severely decreased after melioration. Molinion meadows and Nardetalia communities completely disappeared. Restoration management caused a pronounced change in vegetation: arable land, new-sawn grasslands and Elymus repens grasslands disappeared, while flood grasslands and Carex acuta sedge fens increased in abundance. Reeds with Phalaris arundinacea and Glyceria maxima almost developed periodically. The ongoing nutrient impoverishment allowed Agrostis canina grasslands to re-settle, resulting in an increase of species typical for small-sedge fens. Differences in site factors, especially in nutrient contents, between the present and historical conditions appear to have considerable effects on the distribution of many species, but are less obvious in the actual distribution of certain vegetation types. Nearly all plant species that are listed in the Red data book of Lower Saxony and that were noticed in the study area in recent times as well as the target species of conservation increased in abundance and spread out over large parts of the study area following restoration. Some highly rare species which were extinct in the study area and its surroundings for many years re-established most likely via long-distance dispersal, namely Bromus racemosus, Dactylorhiza incarnata and D. majalis. The occurrence of target species was positively influenced by a high level of re-wetting and nutrient impoverishment, whereas land use proved to be less important. Most species appear to be able to deal with either mowing or grazing, or a combination of both. Only few target species like Oenanthe fistulosa and Senecio aquaticus that need a comparatively high level of nutrients showed a slight decrease in abundance during recent years. The populations of Caltha palustris stabilized in size and were not affected negatively by long-time inundation. Finally, some species which are problematic for land use increased in abundance in response to restoration, especially Deschampsia cespitosa and the toxic plant Equisetum palustre. The species richness of the wet grasslands has shown a steady linear increase, and there are no indications for a weakening of this trend. Heavily degraded peaty soils showed significantly lower species numbers than less degraded peat. In conclusion, extensive restoration efforts cannot guarantee success in re-establishing species-rich wet grasslands with endangered target species, but in this study they had strongly positive effects on total species richness and on the abundances of most target species. Main factors of success are large-scale, consequent impoverishment, ongoing usage of the grasslands and an adjustable rewetting. The level of peat degradation was determined as a major limit of restoration success. A low level can enable the restoration of more or less species-rich grassland and a recolonisation of a couple of target species, a lot of them endagered

More losses than gains during one century of plant biodiversity change in Germany

Long-term analyses of biodiversity data highlight a 'biodiversity conservation paradox': biological communities show substantial species turnover over the past century, but changes in species richness are marginal. Most studies, however, have focused only on the incidence of species, and have not considered changes in local abundance. Here we asked whether analysing changes in the cover of plant species could reveal previously unrecognized patterns of biodiversity change and provide insights into the underlying mechanisms. We compiled and analysed a dataset of 7,738 permanent and semi-permanent vegetation plots from Germany that were surveyed between 2 and 54 times from 1927 to 2020, in total comprising 1,794 species of vascular plants. We found that decrements in cover, averaged across all species and plots, occurred more often than increments; that the number of species that decreased in cover was higher than the number of species that increased; and that decrements were more equally distributed among losers than were gains among winners. Null model simulations confirmed that these trends do not emerge by chance, but are the consequence of species-specific negative effects of environmental changes. In the long run, these trends might result in substantial losses of species at both local and regional scales. Summarizing the changes by decade shows that the inequality in the mean change in species cover of losers and winners diverged as early as the 1960s. We conclude that changes in species cover in communities represent an important but understudied dimension of biodiversity change that should more routinely be considered in time-series analyses

Are we restoring functional fens? : The outcomes of restoration projects in fens re-analysed with plant functional traits

In peatland restoration we often lack an information whether re-established ecosystems are functionally similar to non-degraded ones. We re-analysed the long-term outcomes of restoration on vegetation and plant functional traits in 38 European fens restored by rewetting (18 sites) and topsoil removal (20 sites). We used traits related to nutrient acquisition strategies, competitiveness, seed traits, and used single- and multi-trait metrics. A separate set of vegetation records from near-natural fens with diverse plant communities was used to generate reference values to aid the comparisons. We found that both restoration methods enhanced the similarity of species composition to non-degraded systems but trait analysis revealed differences between the two approaches. Traits linked to nutrient acquisition strategies indicated that topsoil removal was more effective than rewetting. After topsoil removal competitive species in plant communities had decreased, while stress-tolerant species had increased. A substantial reduction in nutrient availability ruled out the effect of initial disturbance. An ability to survive and grow in anoxic conditions was enhanced after restoration, but the reference values were not achieved. Rewetting was more effective than topsoil removal in restricting variation in traits values permitted in re-developing vegetation. We found no indication of a shift towards reference in seed traits, which suggested that dispersal constraint and colonization deficit can be a widespread phenomena. Two functional diversity indices: functional richness and functional dispersion showed response to restoration and shifted values towards reference mires and away from the degraded systems. We concluded that targeting only one type of environmental stressor does not lead to a recovery of fens, as it provides insufficient level of stress to restore a functional ecosystem. In general, restoration efforts do not ensure the re-establishment and long-term persistence of fens. Restoration efforts result in recovery of fen ecosystems, confirmed with our functional trait analysis, although more rigid actions are needed for restoring fully functional mires, by achieving high and constant levels of anoxia and nutrient stresses

ReSurveyGermany: Vegetation-plot time-series over the past hundred years in Germany

Vegetation-plot resurvey data are a main source of information on terrestrial biodiversity change, with records reaching back more than one century. Although more and more data from re-sampled plots have been published, there is not yet a comprehensive open-access dataset available for analysis. Here, we compiled and harmonised vegetation-plot resurvey data from Germany covering almost 100 years. We show the distribution of the plot data in space, time and across habitat types of the European Nature Information System (EUNIS). In addition, we include metadata on geographic location, plot size and vegetation structure. The data allow temporal biodiversity change to be assessed at the community scale, reaching back further into the past than most comparable data yet available. They also enable tracking changes in the incidence and distribution of individual species across Germany. In summary, the data come at a level of detail that holds promise for broadening our understanding of the mechanisms and drivers behind plant diversity change over the last century