4 reasons why vanishing deadwood is a great catastrophe

Deadwood amounts have dramatically declined all over the world. Here I present four reasons why deadwood is so important:

1. Deadwood remains in the forest for a long time
When wood decays, it transforms into carbon dioxide, water and minerals. These are exactly the materials that a living tree binds during photosynthesis. The complete degradation of a tree takes 50 to 100 years in northern regions. Deadwood therefore remains a part of the forest ecosystem for a long time, thus enabling the survival of species depending on deadwood as a substrate.

2. Deadwood is nutrition for fungi and invertebrates

Fungi are the main decomposers of deadwood, but bacteria and invertebrates also take part in the decaying processes. These organisms have special digestive compounds, enzymes, to cut the wooden structure into more easily digestible forms. This works in the same way as the enzymes in our own stomachs that cut the food we eat into more usable shape. Fungi can be divided into three main decomposer groups: white, brown and soft rot. White-rot fungi, e.g. Phellinus nigrolimitatus, lives mainly on deciduous wood, whereas brown-rot fungi, such as Coniophora olivacea, are mostly in charge of decomposing conifers. Beetles (Coleoptera), ants (Formicidae) and termites (Isoptera) are examples of invertebrates that use deadwood as a form of nutrition, but e.g. pin lichens (Calicioid) can also more or less decompose wood.

Pin lichens (Calicioids) grow on deadwood surface. © Mia Vehkaoja

Pin lichens (Calicioids) grow on deadwood surface. © Mia Vehkaoja

3. Deadwood is home for animal offspring
Deadwood is home for thousands of species. For some species deadwood can be an incubation place and a safe nest for newborn offspring. Several beetles and termites lay their eggs inside deadwood, where the hatching larvae are safe in their own chambers. As for Nematocera, Brachycera and Aculeata, the deadwood-decomposing fungi functions as a rearing place for larvae. In addition to invertebrates, birds, bats and flying squirrels (Pteromys volans) also use the holes in deadwood as nesting places. Furthermore woodpeckers (Picidae) as cavity nesters are a good indicator for deadwood abundance.

Several beetle species lay their eggs inside deadwood. © Mia Vehkaoja

Several beetle species lay their eggs inside deadwood. © Mia Vehkaoja

4. The disappearance of deadwood creates local extinctions at the very least
Nowadays deadwood is a dying natural resource. Forestry has decreased the amount of deadwood in Finnish forests by over 90%, concurrently causing the local extinctions of several species. Species that depend on deadwood throughout their entire lives are at greatest risk. Such species include the fungi Phellinus igniarius and the three-toed woodpecker (Picoides tridactylus).

Advertisements

A whole new universe in dead wood

Before I took part in the course Biodiversity in dead wood (organized by the University of Helsinki), I thought that there is dead wood only aboveground. So it was an elevating experience to realize that most of the dead wood is underground. Boreal forests have more underground dead wood than for example broadleaved forests. Underground dead wood is very common in Finland as there are lots of pine-dominant bogs. There pines sink underground before they are decayed, and lots of underground dead wood is produced.

Standing dead pine, possible becoming a kelo. © Stella Thompson

Standing dead pine, possible becoming a kelo. © Stella Thompson

One other special characteristic for Finland forests is kelo, which is a dead standing pine. Usually the kelo has lost its pine bark. Kelo trees have unique biodiversity, which is completely different than for example in dead birch. It is quite typical that the saproxylic species are specific to certain tree species. This feature enhances the saproxylic diversity in forests. Saproxylic species are defined as any species that depends upon decaying woody material.

The carboniferous was a starting point for saproxylic evolution. Almost immediately when the first trees arrived on land, the first decomposing fungi evolved. After fungi the first decomposing invertebrates developed. The rapid specification of the saproxylic species occurred in the Triassic and Jurassic ages. The first termites existed about 100 million years ago. The evolution of saproxylic beetles is better known than the evolution of basidiomycetes. This is due to better preserved fossils.

There are approximately 400 000–1 000 000 saproxylic species in the world, and in the Nordic countries the same number is 7589 known species. Finland alone has 4 000–5 000 dead wood species. This is about 20–25 % of all forest species. It could be argued that there are several unknown saproxylic species in the Nordic countries. Solely in Finland, almost every year new saproxylic species are found. Boreal forests have almost as much dead wood as tropical forests. This correspondence between the two forest types results from the different decaying rates.  The decaying rate of tropical forests is much faster.

Basidiomycetes decaying goat willow (Saprix caprea). © Stella Thompson

Basidiomycetes decaying goat willow (Saprix caprea). © Stella Thompson

The decaying rates also differ in different parts of boreal forests. In the fast-decaying parts 90% of organic matter can be decomposed in 50 years, whereas the same process will take 100 to 200 years in the slow-decaying parts. At an early successional stage the decaying process is usually slow and accelerates towards the pristine forest stage. The main hazard to saproxylic species is forestry. For instance in Finland forestry has reduced the amount of dead wood from 60–120 m3 per hectare to 2–10 m3 per hectare. This reduction is severe. The new trend in forestry, at least in the Nordic countries, is bio-fuel in the form of intensive residue harvesting. This means that even the branches, crowns, and stumps are collected from the logging area. This leads to an even more decreased amount of dead wood in forests. It can be quite easily calculated that without dead wood about 25% of Finland’s forest species are lost. Why is nobodytaking strong action to prevent this from happening? Researchers and conservationists should come together, and force decision-makers to see the dramatic downside of residue harvesting.

Dead wood on top of lingon- and blueberries in boreal forest. © Mia Vehkaoja

Dead wood on top of lingon- and blueberries in boreal forest. © Mia Vehkaoja

 

Check out also this amazing article about Ancient Forest Found Thawing Beneath Melting Glacier in Alaska