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.