FO6 Dead wood

>> Background information

Development

The volume of dead wood was not measured until the 9th National Forest Inventory (NFI9) of 1996–2003. It is not possible to say much about the volumes before this. Over large areas in northern and eastern Finland the lack of an extensive forest road network prevented the intensive use of forests until the latter half of the 20th century. In these areas there must have been quite large amounts of dead wood. On the other hand, selection cuttings, firewood collection and slash and burn cultivation had lowered the dead wood volumes of southern and western Finland already early on.

The aim of modern forest management practices has been to reduce tree mortality in commercial forests. The amount of dead wood decreases especially when regular thinnings are conducted, but also as a result of soil preparation and artificial regeneration.

The latest National Forest Inventory (NFI11) was carried out during 2009–2013. The total volume of dead wood has increased in southern Finland when compared to the two previous inventories. The volume doubled in protected forest and increased by one quarter in commercial forests between NFI9 and NFI 11. The amount of dead standing trees has increased relatively more than that of dead ground wood.

Dead wood is more abundant in northern than in southern Finland. Contrary to southern Finland, its volume has decreased in commercial forests between NFI9 and NFI11. Over the past decade logging volumes have been record high in the northern half of the country. In northern protected forests dead wood volumes are quite high and have increased slightly since NFI9.

Importance of dead wood

Nearly one quarter of all forest dwelling species, 4 000–5 000 species, depend on dead wood. Some of the species live on small diameter dead wood such as braches and small trunks. However, the total number of species and specially that of rare species is highest on coarse and thoroughly decayed wood. The species that have become rare often utilise only one tree species (commonly deciduous trees), certain decay stages or a particular type of decaying wood (e.g. coarse ground wood).  

Dead standing trees are an important habitat for many invertebrates, lichens and fungi. They also act as nesting sites of several birds such as woodpeckers and tits. The species assemblage on ground wood depends on the stage of decay. The number of species living on very far decayed lichen covered ground wood is not high but all the more specialised.

One third of all threatened forest species live on dead wood. The decrease of dead wood was specified as the primary cause of threat of altogether 159 threatened species.

In a natural forest the volume of dead wood varies according to the forest type and the geographical location of the forest. The highest dead wood volumes have been found in the lush forests of southern Finland. In natural old growth pine and spruce dominated forest the volumes vary typically between 50 and 120 m3/ha. The highest volumes of dead wood occur, under natural circumstances, right after random disturbances such as forest fires or wind damages. In such cases there may be even hundreds of square meters of dead wood per hectare.

According to the current view forest fires were reasonably rare before the escalation of human influence. The natural forest landscape consisted primarily of old forests. In southern Finland threatened polypores have been found to be missing from forest with less than 20 m3 of dead wood per hectare. From the point of view of specialised species there should be nearly ten times as much dead wood than at present.