IDENTIFICATION AND INVENTORY OF AQUATIC PLANT-COMMUNITIES USING REMOTE-SENSING

The littoral vegetation, mainly reeds and floating leaved vegetation, of the large Swedish lakes Mälaren, Hjälmaren, Vänern, and Vättern has been mapped during the period 1969-1975. The plant communities covered wide areas along the lake shores and no method other than aerial photography could be used for mapping the distribution of plant communities. Infrared colour film was used from a height of 1 500 m. Field observations were conducted to facilitate interpretation of pictures. Stratified sampling and counting of vegetation along random transects was used for calculating the biomass of the lakes and observing future changes. The aquatic vegetation in the area consists largely of stands dominated by a single species of Phragmites australis, Schoenoplectus lacustris, Typha angustifolia or Nuphar lutea. They could therefore be identified without great difficulty on the photographs. Interpretation was performed with great success and distribution maps of emergent and floating-leaved vegetation have been drawn of the entire lakes Mälaren and Hjälmaren and parts of the two largest lakes of Sweden, Vänern and Vättern (Fig. 1). Totally 2 400 photographs have been interpreted and the entire shore length of 4 500 km thoroughly mapped. The results have previously been reported in Swedish with English summaries (Andersson, 1972; 1973; 1975; 1978a, b;Andersson and Eriksson, 1974). A rapid development of remote sensing techniques made it interesting to test whether data from an airborne multispectral scanner could be used for mapping aquatic macrophytes. Results of that computer classification are discussed and compared with maps made by interpretation of IR-colour photographs. © 1990 Institute of Botany, Academy of Sciences of the Czech Republic.