Sycamore, Acer pseudoplatanus, is an invasive tree species which is spreading rapidly in Norway. Photo: Sissel Rübberdt
Some non-native species have been deliberately imported into Norway; others have escaped from breeding facilities, or been unintentionally imported by various means of transport, or with merchandise from other parts of the world. Some species have simply accompanied another species that has been imported.
Most organisms arriving in a new environment are unable to adapt, and therefore die. Others survive and breed without doing any harm to their new surroundings. A few do significant harm to the natural environment, property, agriculture or other activities.