Four reasons why beaver wetlands are paradise for pin lichens

Beaver activity enhances the occurrence and diversity of pin lichens (Caliciales). Both the number of species and individuals is much higher in beaver-created wetlands than in other types of boreal forest landscapes. There are four reasons behind this:

1. High amounts of deadwood. Pin lichens grow on both living trees and deadwood. Decorticated deadwood in particular is preferred by pin lichens. Beaver-induced flooding kills trees in the riparian zone and produces high amounts of decorticated snags.

Pin lichen on decorticated stump. © Mia Vehkaoja

2. Diversity of deadwood types. Beaver activity produces snags, logs and stumps. Snags are created by the flood, whereas logs and stumps are also produced by beaver gnawing. The diversity of deadwood tree species is also wide, containing both deciduous and coniferous tree species. The diversity of deadwood types maintains a high diversity of pin lichen species.

3. High humidity conditions. High humidity conditions are favorable for many pin lichen species. Old-growth forests are usually the only places in the boreal forest belt that contain high humidity conditions. There the shading of trees creates a beneficial microclimate for pin lichens. Lighting, on the other hand, becomes a limiting factor for pin lichens in old-growth forests. Most snags in beaver wetlands stand in water, where steady and continuously humid conditions are maintained on the deadwood surface.

Snags produced by a beaver flood in Evo (southern Finland). © Mia Vehkaoja

4. Sufficient lighting conditions. Because most of the deadwood in beaver wetlands stands in water, it is concurrently in a very open and sunny environment. Many boreal pin lichens are believed to be cheimophotophytic (cheimoon=winter), meaning that they are able to maintain photosynthesis also during winter at very low temperatures. The algae member of pin lichens requires enough light for photosynthesis. Open beaver wetlands make photosynthesis possible for pin lichens during both summer and winter. Snow also enhances light availability during winter.

More information: Vehkaoja, M., Nummi, P., Rikkinen, J. 2016: Beavers promote calicioid diversity in boreal forest landscapes. Biodiversity and Conservation. 26 (3): 579-591.

The beaver – our wetland rescuer

The beavers (Castor canadensis and Castor fiber) have recovered from near extinction, and come to the rescue of wetland biodiversity. Two major processes drive boreal wetland loss: the near extinction of beavers, and extensive draining (if we exclude the effects of the ever-expanding human population). Beaver dams have produced over 500 square kilometers of wetlands in Europe during the past 70 years.

 

The wetland creation of beavers begins with the flood. As floodwaters rise into the surrounding forest, soil and vegetation are washed into the water system. The amount of organic carbon increases in the wetland during the first three impoundment years, after which they gradually begin reverting back to initial levels. The increase in organic carbon facilitates the entire wetland food web in stages, beginning with plankton and invertebrates, and ending in frogs, birds and mammals.

The previous shoreline is very evident from an aerial photograph. Also the beaver flooded area shows clearly. © Antti Nykänen

Beaver-created wetlands truly become frog paradises. The wide shallow water area creates suitable spawning and rearing places. The shallow water warms up rapidly, and accelerates hatching and tadpole development. Beaver-created wetlands also ensure ample nutrition. The organic carbon increase raises the amounts of tadpole nutrition (plankton and protozoans) in the wetland, along with the nutriment of adult frogs (invertebrates). Furthermore, the abundant vegetation creates hiding places against predators for both tadpoles and adult frogs.

Beaver-created wetlands are perfect rearing places for frogs. The warm water accelerates hatching and the abundant aquatic vegetation gives cover against predators. © Mia Vehkaoja

The flood and beaver foraging kill trees in the riparian zone. Deadwood is currently considered a vanishing resource. Finnish forests have an average 10 cubic meters of deadwood per hectare, whereas beavers produce over seven times more of the substrate into a landscape. Beaver-produced deadwood is additionally very versatile. Wind, fire and other natural disturbances mainly create two types of deadwood: coarse snags and downed logs. Beavers, on the other hand, produce both snags and downed logs of varying width, along with moderately rare deciduous deadwood. The more diverse the deadwood assortment is, the richer the deadwood-dependent species composition that develops in the landscape.

Beaver-created wetlands produce especially standing deadwood. © Mia Vehkaoja

Deadwood-dependent species are one of the most endangered species groups in the world. The group includes e.g. lichens, beetles and fungi. Currently there are 400 000 to a million deadwood-dependent species in the world. Over 7000 of these inhabit Finland. Pin lichens are lichens that often prefer snags as their living environment. Beaver actions produce large amounts of snags, which lead to diverse pin lichen communities. Snags standing in water provide suitable living conditions for pin lichens; a constant supply of water is available from the moist wood, and the supply of light is additionally limitless in the open and sunny beaver wetlands.

 

The return of beavers has helped the survival of many wetland and deadwood-associated species in Finland, Europe and North America. Only 1000 beavers inhabited Europe at the beginning of the 20^th century. Now over a million beavers live in Europe. I argue that this increase has been a crucial factor benefitting the survival and recovery of wetland biodiversity. Finland and the other EU member states still have plenty of work to do to achieve the goals of the EU Water Framework Directive. Both the chemical conditions and the biodiversity of wetlands / inland waters affect the biological condition and quality of wetlands.

 

The whole research published here

Pin lichens — the tiny color blots on deadwood

Have you ever entered a forest and seen a person hugging a tree, peering up along the trunk? From this day onwards you can breathe freely again, because you have just encountered a pin lichen biologist at work, and not some bizarre tree-hugging ritual.

Pin lichen biologist peering up along the trunk. © Stella Thompson

Pin lichens, or more formally known as Calicioids, are a diverse and monophyletic lichen group, which usually inhabits deadwood. As their name suggests, they resemble pins. They are tiny, approximately between one millimeter and five centimeters in size. The best way to observe them is to peer up along the trunk of a tree. The spores accumulate into a mazaedium (a cup-shaped part of the fungi), from which they can cling onto the hairs and feathers of animals, or passively disperse otherwise. The spores can be recognized as soot-like dust on your fingers.

Pin lichens growing on deadwood. This species Mycocalicium subtile can be identified with often paler infested area than the surrounding wood. © Mia Vehkaoja

Although it is relative easy to observe pin lichens with the bare eye, species identification is usually conducted using a loupe or microscope. Further observation opens an entire new world of colors. The algae parts of many pin lichen species are brightly colored in yellow, green, or red. On other species, the stalk of the fungal part forming the actual pin structure can also be quite colorful: white, green, yellow, or brown.

Rust-stained pin lichen (Chaenotheca ferruginea) thrives on conifers, and it is quite widely distributed in temperate to cool temperate areas of the Northern Hemisphere. © Mia Vehkaoja

There are approximately 70 different pin lichen species in Finland, but unfortunately they are a very deficiently studied group. Some species are parasites. They sponge on e.g other pin lichen species or mosses. Even pin lichen fossils have been found within amber. Using these fossils we are able to model the tree structures of forests that grew over a million years ago. This tiny, yet fascinating, species group deserves to receive more attention. Furthermore, observing them is relatively easy, because they don’t move and make a run for it. All you need is a pair of sharp eyes.

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

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

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).