The dead wood – snags (standing dead trees) and coarse woody debris (fallen dead trees), is one of the most important ecosystems in forests. Fungi and bacteria in decaying dead wood change it into nutrients for other plants, trees and invertebrates. Insects, snails, lizards and small mammals in big coarse woody debris make their habitats, feed and hide from predators or bad weather conditions. Snags and coarse woody debris with a big diameter (at least 25 cm) are more valuable as the decaying process in them is slower and, inside their trunks, the microhabitat is more unchangeable. A dead tree is more inhabited than a verdant new tree. For example, decaying wood can be inhabited by approximately 800 species of beetle. Some animals and wood fungi settle in newly dead tree, but others – in decaying wood. Different population of species adapt themselves for each stage of decaying. Dying or recently dead trees are attacked by bark beetles, wood-borers and jewel beetles which eat mainly cambium (delicate meristematic tissues between the bark and the wood). In the autumn of the same year, a lot of the species have left the tree. In the following year, wood-borers spread, and they eat mainly wood. In the third year, wood fungi spread in the tree, and from that time, it is inhabited by the species of insects which depend on the fungi tissues there. Most species, which appear at the later decaying stages, spend more time in the trunk. Most insects feed only at larva stage. For several species the larva stage in the wood lasts for some years, but the adult stage (outside the wood) – just for one or two weeks. A dead tree left in the forest does not make any harm, on the contrary – it serves as a habitat for the natural enemies of pests. Decaying trunks get covered with moss and club-moss till they decay completely and turn into soil for other trees. The dead wood is an important indicator of a healthy forest ecosystem.
