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).

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The new challenges of historical game species: niche of Finnish forest reindeer is shrinking

Historically Finnish forest reindeers (Rangifer tarandus fennicus) have been important game animals in Finland and north-western Russia. Now their numbers are low. Because Finland is the only EU member that has forest reindeers, it has a great responsibility in managing the species. Maintaining hunting possibilities is also seen as important.

Forest reindeer is historically important game species © Veli-Matti Väänänen

Forest reindeers prefer lichen forests © Veli-Matti Väänänen

Forest reindeers were hunted to extinction from Finland at the end of the 1800s. During the last 60 years forest reindeers have made a comeback. Forest reindeers survived in Russian Karelia, from where they migrated naturally to eastern Finland (Kainuu) and were further one introduced in western Finland. Even now forest reindeers live in only these two areas in Finland. The two existing Finnish forest reindeer populations are not in contact to each other. The eastern Finnish population is still in contact to the Russian population, but the subpopulations of the western population might suffer from inbreeding.

Twisted forest ecosystem

The forest reindeer has caused a problem between the current forest management, hunting and nature conservation. Finnish forest industry has efficiently taken forests into commercial use and changed the forest structure. Forest reindeers need old lichen forests, but these have become rare due to commercial forestry. This development has been beneficial for the moose (Alces alces), which has increased their density. This maintains high wolf (Canis lupus) densities, which in turn increases the predation pressure of forest reindeers. The forest reindeer population in eastern Finland has therefore declined alarmingly. A further problem is that the wolf is also endangered and their hunting is strictly regulated. The conservation acts for these two species are thus conflicting, creating an EU-level conservation problem. The western Finland’s forest reindeer population has probably suffered from too high hunting pressure combined with predation pressure. The increase of the western population has therefore stopped. The Russian Karelian forest reindeer population is also declining due to overhunting.

Calf mortality is observed to be worryingly high in Kainuu forest reindeer population. Calf  in Korkeasaari Zoo in Helsinki © Sari Holopainen

Calf mortality is observed to be worryingly high in Kainuu forest reindeer population. Calf in Helsinki Zoo © Sari Holopainen

The historical distribution of forest reindeers in Finland covered more northern parts than nowadays, but now they are forced to stay in the southern parts. Northern Finland (Lapland and parts of Kainuu) is reserved for domestic reindeer herding, and the southern border of the area is covered by reindeer fences. The good thing about this fence is that it prevents the hybridisation of the forest and domestic reindeers, thus guaranteeing the pure gene pool of the forest reindeer.

Are there any solutions?

The question now is how to increase the distribution and population size of forest reindeers and maintain this species as a game animal in Finland. Reintroducing forest reindeers to new areas is already planned by the official wildlife and forest institutes. The reintroductions must be well prepared, because forest reindeers might cause damage to farmers, forest owners, commercial lichen collectors and domestic reindeer herders. Traffic accidents have also appeared.

In addition, The Finnish Association for Nature Conservation has suggested that the reindeer fence could be moved northwards to offer the forest reindeers access to their historical areas. The forest reindeer management plan (2007) suggests that the question with forest reindeers and wolves should be combined, and their management should be assessed together. Wolves are natural predators of forest reindeers, but currently species ratio is skewed, and the limiting of wolves seems to be needed in Kainuu. Russian Karelian forest reindeers are now also under research. Cooperation of Finnish and Russian researchers is awaited to produce new information about the Karelian population and its threats. Results should help build a shared management plan of forest reindeers between Finland and Russia.

Stumps as refuges for bryophytes

Bryophytes are plants that don´t have true vascular tissue, although some can have special tissue for water transportation. Bryophytes are a scientific division that contains the mosses, liverworts and hornworts. They are known to be epixylic, which means that they grow on the surface of wood, usually on dead wood, but don’t receive any nutrition from it. This is because bryophytes don’t have roots. They have three alternative reproduction methods, as they can reproduce by propagules, spores or both. Dispersion occurs via reproduction units. The dispersion distance can be up to ten meters, but usually the distance is only 40 centimeters.

Pohlia moss (Pohlia nutans) is one of the most universal mosses. © Mia Vehkaoja

Pohlia moss (Pohlia nutans) is one of the most universal mosses. © Mia Vehkaoja

Bryophytes form an important part of forest biodiversity. For example, Finland has approximately 100 bryophyte species that live on dead wood (49 hepatics and 51 mosses). There are three main environmental conditions favored by bryophytes. They prefer environments that are moist and shady, with wood in middle to late decay stages, and that have relatively large logs (at least 30 centimeters in diameter). These kinds of environments are mostly found in old-growth forests in their natural state.

The situation is totally different in managed forests, where usually almost all of the dead wood is removed. So there are just a few substrates left for bryophytes to grow on. A new trend is to use intensified residue harvesting to maximize profits. Intensified residue harvesting also collects the branches, tops and stumps from logging areas. These are used as bio-fuel from forestry. Especially stumps were previously left at logging areas, where they created important refuges for bryophytes, as well as composed a large portion of the sites’ coarse woody debris.

Thinning is proven to be better for bryophytes than clear-cutting. The main reason behind this superiority is the canopy cover. Canopy cover increases the moisture content of the stumps and ground, creating a moist and shady habitat for bryophytes.

Dead wood left in forests is crucial for bryophyte species. Forestry management methods have decreased the amount of dead wood in forests for decades; minimizing the amount of refuges for bryophytes. Furthermore, intensified residue harvesting removes even the few habitats formerly left in the forest for bryophytes and other dead wood-dependent organisms. Forestry also creates another challenging problem for bryophytes: fragmentation. The dispersion distance of bryophytes is up to ten meters. After forest management practices the distance to the nearest dead wood or stump can be several hundred meters, so it will impossible for bryophytes to find a substrate to disperse to.

Mosses growing on bark. © Sari Holopainen

Mosses growing on bark. © Sari Holopainen

The Nordic countries, which have a strong interest in utilizing bio-fuel from forestry, should wake up to the problem of declining dead wood amounts in forests. A threshold should be set for this practice to aid in preserving sustainable amounts of dead wood and upholding biodiversity. Bryophytes are big creators of diverse ecosystems. They therefore need to have a stronger conservation status than currently. The fundamental way of restoring the biodiversity of boreal forests is leaving enough dead wood in the forests. Dead wood conserves a huge number of other species in addition to bryophytes, such as beetles and fungi.

To find out more, read the article behind the story.