The natural boreal coniferous forest has many decaying trees, up to 140-180 m3/ha, or about 20-30 % of the number of living trees. The competition for space results in the deaths of less favoured trees. The complete decay of a conifer tree requires up to 200 years but a deciduous tree will decay more rapidly.
Many organisms, such as large mushrooms, ticks, beetles, diptera and hymenoptera live in rotting wood. Up to a quarter of the total amount of organisms in the forest live in the deadwood. Many birds, including the great spotted woodpecker and black woodpecker, the lesser spotted woodpecker, three-toed woodpecker and the white-backed woodpecker also need deadwood cavities to nest in and also eat the other organisms that live in the deadwood.
The decaying trunk of a fallen tree affects the humidity and temperature of its environment. Beetles and fungi often specialise in living on specific tree species at different stages of decay. Also, certain species depend on another species already being present in a decaying tree. Where the bark has fallen away from a gradually decaying tree, the rarest and most endangered species are to be found but as a trunk decomposes, the number of wood-eating organisms decreases and they are replaced by those who use it only for shelter.
Old-growth forests are forests untouched by forestry. In such forests, there is abundant standing and fallen deadwood. Such forests are very valuable natural sites and without conservation measures they are at risk of being lost entirely.
Photo: Jyrki Oja