The Royal National City Park contains one of Svealand’s largest concentrations of ancient oaks. From the point of view of nature conservation the park oaks are of national importance.
The surviving oaks in the Royal National City Park form extremely species-rich habitats. Over 1000 species of insects thrive in one solitary giant oak on Djurgården! One of the park’s most significant species which is dependent on the oak is the highly threatened broad-banded oak-bark longhorn beetle, Plagionotus detritus.
The oaks suffer from regular attacks of the oak-leafroller. These moths can eat the crown of an oak almost bare in one season, but do not cause any real threat since new leaves grow back.
Oak timber has always been much sought after for its strength and hardness. Previously all oaks belonged to the crown and the punishment for felling an oak was very high. Djurgården had an oak plantation whose acorns were used to start the oak plantation on the island of Visingsö in the 1830s, to assure ample supplies of oak timbers for the royal Swedish navy.