Abstract
Sandtjern nature reserve, located on the Gardermoen Delta, SE Norway, consists of a series of kettle holes that are subjected to severe annual wet-dry cycles due to flooding. In the rainy season in late autumn, the kettle holes fill up with water since drainage is prohibited due to frozen ground and no outflow passages is present. The flooding water is present throughout the winter, before the area starts to dry up in spring, through its sandy soil, resulting in dry conditions for the rest of summer. The vegetation is clearly divided into different belts, or zones, in the areas subjected to flooding. As of today, Sandtjern nature reserve is the only known location where such a floodplain system is present. The aims of this study were to investigate which environmental factors that structured the species composition, as well as to evaluate the uniqueness of this floodplain system. The floristic composition was recorded for a total of 151 1×1 m plots, placed in the kettle holes as well as their surrounding areas. Factors such as flooding period, shading, slope, aspect and micro topography as well as several soil edaphic factors, that could possibly explain the zonation of the vegetation, were also recorded for each plot. By the use of multivariate analysis (ordination), a gradient in species composition was found, capturing the main floristic differences between vegetation belts. A complex gradient of environmental variation, based on the recorded environmental variables, was also discovered. Flooding period seemed to be the main factor of this complex gradient structuring the main gradient in species composition. In addition, one of the vegetation belts seemed to be clearly influenced by grazing and former human interference. Although many similarities were found with studies of vegetation on floodplains, riverbanks and lakesides, this system seemed to be unique. The main difference between this and other flood affected nature types was found to be the nearly complete stagnation of the flood water throughout the flooding period. The Nature in Norway (NiN) system, which aims to summarize all nature-type variation in Norway, defines this area as an open alluvial system on sand with prolonged flooding. It is suggested that a future definition should also address the stagnation of the flood water.
Sandtjern nature reserve, located on the Gardermoen Delta, SE Norway, consists of a series of kettle holes that are subjected to severe annual wet-dry cycles due to flooding. In the rainy season in late autumn, the kettle holes fill up with water since drainage is prohibited due to frozen ground and no outflow passages is present. The flooding water is present throughout the winter, before the area starts to dry up in spring, through its sandy soil, resulting in dry conditions for the rest of summer. The vegetation is clearly divided into different belts, or zones, in the areas subjected to flooding. As of today, Sandtjern nature reserve is the only known location where such a floodplain system is present. The aims of this study were to investigate which environmental factors that structured the species composition, as well as to evaluate the uniqueness of this floodplain system. The floristic composition was recorded for a total of 151 1×1 m plots, placed in the kettle holes as well as their surrounding areas. Factors such as flooding period, shading, slope, aspect and micro topography as well as several soil edaphic factors, that could possibly explain the zonation of the vegetation, were also recorded for each plot. By the use of multivariate analysis (ordination), a gradient in species composition was found, capturing the main floristic differences between vegetation belts. A complex gradient of environmental variation, based on the recorded environmental variables, was also discovered. Flooding period seemed to be the main factor of this complex gradient structuring the main gradient in species composition. In addition, one of the vegetation belts seemed to be clearly influenced by grazing and former human interference. Although many similarities were found with studies of vegetation on floodplains, riverbanks and lakesides, this system seemed to be unique. The main difference between this and other flood affected nature types was found to be the nearly complete stagnation of the flood water throughout the flooding period. The Nature in Norway (NiN) system, which aims to summarize all nature-type variation in Norway, defines this area as an open alluvial system on sand with prolonged flooding. It is suggested that a future definition should also address the stagnation of the flood water.