2.1 Location and characteristics
The study area – the Lower Oder Valley National Park – is situated about 100 km north-east of Berlin at the border to Poland (Fig. 1).
Fig. 1: Location of the Lower Oder Valley National Park (Map design T. Rothenbücher).
The national park is part of a German-Polish network of protected areas. In 1992 it was decided to build an “Inter-National Park” in the Lower Oder Valley that combines German and Polish protected areas located on both sides adjacent to the river Oder (Vössing 1998). In Poland it consists of the two landscape protection areas “Cedynia”
and “Dolina Dolneyj Odry”. In Germany the “Lower Oder Valley National Park” and the adjacent landscape protection area “Nationalparkregion Unteres Odertal” are part of the “Inter-National Park” (Fig. 2).
Fig. 2: Map of the Lower Oder Valley National Park and adjacent landscape protection areas in Poland and Germany.
(ProLine Concept Berlin, 2003)
The region’s characteristic is a 3 to 4 km wide floodplain next to the river Oder that is dominated by grassland habitats. This floodplain is the dominant feature of the German national park which comprises an area of 10,500 ha. Its characteristic habitats are wet meadows (“Feuchtgrünland”), sedges (“Seggenriede”), cane brake (“Röhrichte”), oxbow lakes and small patches of alluvial forests. Each year about 4,700 ha of the floodplain are inundated during the typical winter floods (Mönninghof 1997). Despite dyke building and management of the flooding regime since the beginning of the 20th century (see section 2.2), one can still find semi-natural conditions in the floodplain which are unique in Central Europe (Dohle 1999, Mönninghof 1997).
2.2 History
Until the middle of the 19th century the present national park area was more or less untouched by man. Afterwards the river Oder became canalised and an artificial waterway was build running parallel to the river Oder. Dykes were built around the area between the two waterways and the former floodplain was drained with the aim to construct a protection against floods, to facilitate navigation on the river Oder and to make effective and profitable land use possible in the floodplain (Vössing 1998). Since 1931 flooding has been regulated in the newly formed polder area. In the so called “dry polder” the dykes prevent inundation throughout the whole year. In contrast, in the “wet polders” flood gates that are integrated into the dykes are opened between 15th November and 1st April each year so the typical winter flood can inundate the polder area. After closing the flood gates to prevent inundation during spring and summer the water is pumped out of the polder area and the level of the groundwater is artificially lowered to make land use possible (Fig. 3) (Dohle et al. 1999).
Within 80 years the natural floodplain had been transformed into pasture land. During the time of the GDR, starting in the 1960s, land use was intensified which included using fertiliser and sowing productive grass species (Gille 1999, Schalitz & Petrich 1999). During the same time nature conservationists became aware of the importance of the current national park area as resting, breeding and foraging grounds for many birds.
The commitment of the local ornithologists for conservation issues finally led to the designation of an area of 5,400 ha as “wetland of international importance” once the GDR acceded to the “Ramsar Convention on Wetlands”2 in 1978. After the political change in 1989 many areas valuable for nature conservation in the GDR were designated as protected areas – among these the Lower Oder Valley (Garrelts et al.
2005). In 1995 the area was designated as national park by the parliament of Brandenburg3.
Fig. 3: Management of the flooding regime. “Wet polder” (left) and “dry polder” (right) separated by a dyke. The picture at the top was taken in March, the one at the bottom in July. (Photos:
H. Lüssow, J. Rothenbücher)
2.3 Plans for future development
At present, the national park is still in the developmental stage as the flooding regime is regulated and a large proportion of the grassland is used for fodder production and grazing. Fodder production by mowing is presently the major land use in the national park. Most meadows are cut twice a year i.e. at the beginning of June and September.
Only about 10% of the national park area are currently declared as core zone. Here the flooding regime is still regulated, but the sites have been abandoned and left for succession since 1995 (Jehle & Pankoke 1999).
The aims and the purpose of the Lower Oder Valley National Park are outlined in the
“National Park Law” that was passed on 22nd June 1995.
The purpose of the national park is
• to protect, to manage, to preserve and to develop the natural functions of the Lower Oder Valley which includes the floodplain, flora and fauna, wetlands, meadows, alluvial forest and dry grassland,
• to protect and to develop natural processes on a large area undisturbed by anthropogenic impacts,
• to preserve and regenerate the natural flooding regime,
• to allow environmental friendly recreation,
• to develop tourism and
• to conduct environmental education4.
Additionally, the national park’s area has been federally funded as project area in the context of a program for riparian nature conservation (“Gewässerrandstreifenprojekt”) since 1992. In the long run it is planned to restore the floodplain to semi-natural conditions. To accomplish this aim the flooding regime will be altered on a preferably large area as close to a natural flooding dynamic as possible, i.e. longer and more frequent flooding events. Many ideas have been developed to achieve this goal. A very pragmatic approach is to leave the flood gates open during the whole year. More sophisticated ideas include trenching the dykes along the river Oder or connecting oxbow lakes to create an artificial river within the polder area (IUS 1998). Furthermore, it is planned to stop the artificial lowering of the groundwater level in those areas that are no longer used for fodder production. It is planned that by 2010 50% of the national park area will be declared as core zone and left for succession whereas in the remaining 50% resting, breeding and foraging habitats for endangered species (e.g. corncrake) will be optimised by conservation management. Thus current plans for national park development try to realise two conservation strategies side by side, i.e. conservation management for the target species corncrake (Crex crex) and conservation of processes.
2.4 Climate
The Lower Oder Valley is situated in the transition zone between temperate and continental climate. It is characterised by its cold winters and hot summers. On an average, about 530 mm precipitation and 120 days of frost per year are recorded for the region. These climate data resemble those gathered in continental regions like the Ukraine and differ notably from those observed in the nearer Atlantic region (Vössing 1998).
In figure 4 the mean temperature values for each month of the years 2001 and 2002 in comparison to the monthly average values of the years 1961-1990 are plotted.
Fig. 4: Mean air temperature values (°C) for each month of the years 2001 and 2002 in comparison to the monthly average value of the years 1961-1990, meteorological station Angermünde (DWD 2002).
In 2001 the mean monthly temperature was below the average value in June and December while in all other months the mean temperature reached at least the average value. From January to September 2002 the mean monthly temperatures were higher than the average values and were lower in October and December. The mean annual temperatures of both years were higher than the average annual temperature of the years 1961-1990 (8.3°C), i.e. 8.8°C in 2001 and 9.4°C in 2002 respectively.
The amounts of precipitation for each month of the years 2001 and 2002 are summed up and compared to the monthly average values (sums) of the years 1961-1990 (Fig. 5).
Fig. 5: Precipitation values (mm) are summed up for each month of the years 2001 and 2002 and are compared to the monthly average value of the years 1961-1990, meteorological station Angermünde (DWD 2002).
In August and September 2001 precipitation largely exceeded the average values while in July and October rainfall was comparably low. In 2002 unusually high amounts of precipitation were recorded in February, August and October whereas in December hardly any rainfall was documented. In both years precipitation exceeded the average annual values of the years 1961-1990 (531.9 mm). In 2001 552.0 mm in 2002 675.7 mm rainfall were recorded.
Thus, both years of the study were warmer and wetter than an average year with 2002 exceeding both temperature and precipitation values of 2001.
2.5 River Oder
The headwaters of the river Oder are situated in the Odergebirge in the north-east of the Czech Republic. The river is 854 km long and flows into the Baltic Sea near Stettin (Poland). The catchment area comprises about 118,861 km², of these only 5% are located in Germany. The area between Hohensaaten (Germany) and Stettin (Poland) is called the Lower Oder Valley. Here the river Oder is a typical Central European lowland river where regular floods occur during winter and spring, and high water levels in summer are more rare events (Fig. 6). Floods during winter are mostly due to ice blockage on the river Oder whereas inundation during spring is the result of the snowmelt in the low mountain ranges of the catchment area. However, heavy rainfall in the region of the headwaters can lead to high water levels during summer, but these occur on an average only once in ten years (Vössing 1998). The last severe summer flood leading to a flooding of the “wet polders” occurred in 1997 (Fig. 6).
Fig. 6: Mean monthly water level from November to October of the years 1996/97, 2000/01 and 2001/02 compared to the monthly average value of the years 1992-2002, gauging station Stützkow (WSA 2002).
During the winter preceding the growing season 2001 water levels were generally lower than the average value of the last ten years. From the middle of July until the end of October 2001 water levels were unusually high. However, there was no need to open the flood gates but large parts of the river bank were inundated between seven and 80 days during summer. In winter 2001/02 water levels were much higher than the average value, but during summer they stayed mostly below the average levels.