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Abstract
Geografisk Tidsskrift—Danish Journal of Geography 110(1):25–35, 2010
During the last decades, the number of perennial colonies of piscivorous birds especially cormorant colonies in North-western Europe has grown rapidly due to protection. Their impact on vegetation has been recognized, as many trees containing perennial colonies of piscivorous birds have collapsed, but the bird's influence on the soil conditions has only in few cases been studied in detail. In this study the influence of perennial colonies of piscivorous birds on soil nutrient contents and accumulation of carbon, nitrogen and phosphorus in a humid climate has been determined by measuring pH, electric conductivity and content of carbon, nitrogen, phosphorus, calcium and potassium in a reference area and in two cormorant sub-colonies. In general, the soils exposed to cormorant guano had lower pH and higher contents of plant available phosphorus, calcium and potassium compared to the control reference soil, especially in the top horizons, and the magnitude of increase in nutrient content varied with the bird-dropping density and the age of the colony. In addition, soil influenced by cormorants had a higher electric conductivity compared to the control reference and can be classified as saline soils. Under influence of the cormorants the herb vegetation below the nesting areas has been changed.
