Nature reserve on Adelsö
The nature reserve Adelsö-Sättra Naturreservat represents a large piece of primeval coniferous forest in the northwest of the island Adelsö, about 30 kilometres northwest of Ekerö.
Spared from human intervention for a long time, the Adelsö-Sättra Naturreservat, consisting of a dense natural forest and extends over a flat hill with a slightly sandy yet nutritious subsoil. About two thirds of the tree population consists of coniferous mixed forest with very old spruces and pines and the remaining third consists of pure pine forest.
The amount of deadwood caused by fallen trees is significantly higher than in a cultivated forest. When trees collapse due to age or storms, they remain as they fell and at various stages of decay form important habitats for a host of insects, including many beetle species.
Some mosses and lichens also need dead wood as well as the insects in order to exist. According to Swedish standards, the nature reserve is regarded as a key biotope that makes an important contribution to the conservation of endangered species, which have often become rare because they do not have viable grounds in the cleared commercial forests.
A special indicator that the Adelsö-Sättra Naturreservat is an intact biotope is the presence of the witches cauldron (Sarcosoma globosum). The spherical fungus, which pushes its fruiting body out of the soil in early spring, grows only in intact spruce and pine forests and is protected throughout Sweden.