Some beetles have outer shells with specialized indentations specifically matched to the shape and size of the spores of wood decomposing fungi. Fungal spores become securely lodged in these cup-like structures. As the beetles burrow into wood they inoculate it with fungi. The boreal forest is well-adapted to development following natural disturbances. In fact one characteristic feature of the boreal forest is that it generally lacks late successional species that develop under an intact forest canopy.
Fire is the major natural disturbance agent in the boreal forest.
Large scale insect outbreaks can weaken or kill trees over vast areas, often leading to forest fires. For the period 1981-1989 an estimated 3.0 million ha burned annually in the former Soviet Union, nearly all in the taiga region of Russia. During the 20th century Canada has experienced about 1 million hectares burned annually in forest regions, the great majority in the less accessible boreal forest in the north and west of the country. In years with prolonged hot and dry periods of summer weather, Alaska experiences millions of hectares burned, mostly in a few very large fires. In both North America and Eurasia where human settlements and transportation routes are present in the boreal forest the great majority of the number of individual fires are human caused.