The distribution of the vascular plants on the North Frisian Island, Amrum

Abstract Amrum is a small barrier island on the north-west coast of Germany. The distribution of vascular plants was examined by surveying their 1km2 grid square occupancy across the whole island. These data were used in a study on the recent vegetation change in the island. These data include 3786 observations of 450 taxa collected in two surveys in 2007 and 2008.


Introduction
Amrum is a small barrier island off the coast of Schleswig-Holstein, Germany. It covers an area of about 20 km , though considerable areas of saltmarsh vegetation are exposed at low tide. Amrum has been the subject of many botanical surveys and this survey continues that tradition (Christiansen 1961, Türk 1994, Petersen 2000, von Seemen 1899, Schiøtz 1860. Amrum is approximately 10 km long and 3 km wide at its widest point (Fig. 1). Its main habitats run in north-south bands along the island. In the west are open sand flats with a sparse fore-dune vegetation, moving eastward there is a complete dune succession ending in conifer plantations. Beyond the plantations is arable farmland and grazing. Along the eastern shore are mainly saltmarshes and mudflats. Other important habitats include freshwater ponds, marshes and ditches, heathland, urban areas and the seawall.
These data were used in a study of change in the islands flora (Groom 2010). They are published in the hope that they will help future studies.

Sampling methods
Study extent: The survey covered all vegetated areas of the island were access was permitted. In fact, this covers most of the island, however, some nesting bird colonies and private gardens are completely inaccessible. A map of Amrum showing the main landscape features and the 1km grid used for the survey. The grid is based upon the spatial reference system EPSG:31467 -DHDN / Gauss-Kruger zone 3.

Coordinates:
Sampling description: The biodiversity of each 1 km varies considerable so there was no set time limit for surveying a particular square. Grid squares were surveyed as intensively as considered necessary to find all but the rarest species. Aerial photographs, maps, previous surveys and local experts were all used to direct surveying to all potentially important habitats. The grid is based upon the spatial reference system EPSG:31467 -DHDN / Gauss-Kruger zone 3 (Fig. 1).
Quality control: Some Salix specimens where identified by R.D. Meikle.

Geographic coverage
Description: Amrum is one of the North Frisian Islands, Schleswig-Holstein, Germany. Its western coast faces the North Sea and the eastern coast faces the Wadden Sea ( Fig. 1  Examples of some of the habitats and plants found on Amrum. islandGroup The name of the island group in which the observation occurred. island The name of the island in which the observation occurred. country The name of the country in which the observation occurred. countryCode The ISO 3166-1-alpha-2 country code. stateProvince The first-level administrative subdivision of the country in which the observation occurred.

continent
The continent in which the observation occurred. verbatimCoordinates The geographic coordinates of the observation written out.
verbatimSRS The spatial reference system of the verbatim coordinates.
footprintWKT A Well-Known Text (WKT) representation of the shape that defines the location.
footprintSRS The spatial reference system of the footprint WKT coordinates.
habitat A textual description of the habitat in which the taxon was observed. coordinateUncertaintyInMeters The limit of the distance (in meters) from the given coordinates describing a circle within which the locality must lie. decimalLongitude The longitude of the location the observation was made, in decimal degrees. decimalLatitude The latitude of the location the observation was made, in decimal degrees. geodeticDatum The geodetic datum to which the latitude and longitude refer. pointRadiusSpatialFit The ratio of the area of the point-radius to the actual area of the spatial representation of the location