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.

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Vanishing wigeons and fading horsetails

Over 20 years ago Finnish and Swedish duck researchers began the “Northern Project” and conducted vegetation measurements on 60 Finnish and Swedish lakes while also counting their duck populations. The study lakes were located from southern Sweden and Finland to Lapland in both countries. Researchers found that the water horsetail (Equisetum fluviatile) grew abundantly on many of the study lakes. Breeding Eurasian wigeons (Anas penelope) were also abundant according to the study.

The water horsetail prefers eutrophic lakes and wetlands. Horsetails are an ancient plant group that has existed for over 100 million years. They are thus living fossils.

Wigeons also utilize eutrophic lakes during the breeding season. Adults are vegetarians, but wigeon ducklings also consume invertebrates, a common trait in young birds.

Wigeon brood foraging within water horsetails at Lofoten. © Sari Holopainen

Wigeon brood foraging within water horsetails at Lofoten. © Sari Holopainen

The vegetation mappings and duck surveys connected to the Northern Project were repeated in 2013–2014. The researchers wished to find reasons for the deep decline in breeding wigeon numbers. They observed that wigeons had disappeared from several lakes where they were found on 20 years ago. When the habitat use of wigeon pairs was studied, the pairs were observed to particularly prefer lakes with water horsetails. In Evo, southern Finland, the feeding habitats of wigeon broods were followed over a period of 20 years. Broods were found to forage significantly more often within water horsetails than in other vegetation.

Wigeons therefore prefer lakes with water horsetail present throughout their breeding season. However, the long-term research by the Northern Project has shown that water horsetail has declined and even disappeared from many lakes in Sweden and Finland: this is a large-scale phenomenon. The wigeon is suspected to suffer due to vanishing water horsetail populations. Also, Finnish pair surveys in addition to reproduction monitoring show negative trends for the wigeon.

Health water horsetail at Lofoten © Sari Holopainen

Health water horsetail at Lofoten © Sari Holopainen

The reasons behind diminishing water horsetail numbers are not known. Impact from alien species can be suspected locally. Glyceria maxima, an alien species in Finland, appears to be growing in areas were water horsetail has traditionally grown. Grazing by the muskrat (Ondatra zibethicus) could also be a reason, but the species does not occur in southern Sweden. The whooper swan (Cygnus cygnus) could be another potential grazer, and the species’ populations have rapidly increased during the last decades. But these species can only have local effects, which do no not apply to the whole study area. Researchers cannot exclude other possible explanations, for example diseases or changes in water ecosystems. Despite water horsetail having commonly existed in boreal lakes, their influence in the water ecosystem is poorly understood. This study suggests that the water horsetail has an important role, and its disappearance will be reflected in the food web.

 

Read more: Pöysä, H., Elmberg, J., Gunnarsson, G., Holopainen, S., Nummi, P. & Sjöberg, K. Habitat associations and habitat change: seeking explanation for population decline in breeding wigeon Anas penelope. Hydrobiologia.  

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

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

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

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 20th 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 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

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

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

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).

Battle of the foxes

Guest author: Samuli Karppinen

“It was the fifth red fox for the same day”. “Foxes are everywhere”, I thought numerous times during my summer job time in the region of Inari. I was amazed at the number of red foxes (Vulpes vulpes) present in the very northern part of Finland. Nearly every day and no matter where I went, I discovered foxes. I observed foxes close to settlements, and at the end of forest gravel roads. They were mainly lonely adults, but litters of the same year were common too. In addition, the number of red fox dens supported the idea that they succeed well in the northern part of Finland. The arctic fox (Vulpes lagopus) is adapted to life in arctic areas. In Finland, arctic foxes have bred in the regions of Inari and Utsjoki. Arctic fox populations are similar in size to those in Sweden and Norway. Population size at the end of the 1800s was estimated to be 15 000 individuals. At present, the size of the population is estimated to be only 120 individuals. Despite yearly sightings of arctic foxes in Finland, it is nearly 20 years since the last confirmed arctic fox litter. During the summer I began wondering how red foxes influence the declining arctic fox population?

The Arctic fox in Polar Park Norway. © Sari Holopainen

The Arctic fox in Polar Park Norway. © Sari Holopainen

Intensive hunting in the early 1900s was the ultimate reason for the collapse of the Fennoscandian arctic fox population. Even though arctic foxes were protected in 1940, the population did not return to its earlier size. There are several probable causes. Due to changes in reindeer husbandry, arctic foxes cannot exploit the same number of carrions. Global warming causes problems to arctic species and the arctic fox does not stretch the point. Climate change affects snow cover, which reflects on the amount of lemmings. Lemmings are a vital food source for arctic foxes. Arctic fox brood and litter sizes are bigger when the amount of voles and lemming are at their highest point. In addition, global warming is raising the tree line to higher altitudes on the fells. This improves the survival of red foxes in the areas inhabited by the arctic fox.

The red and arctic foxes cannot inhabit the same territory. Research has uncovered that red foxes colonize and annihilate arctic fox dens. The red fox is very adaptable to different habitats and competes for food with the arctic fox. The striking winning picture of the Wildlife Photographer of the Year 2015 –competition underlines the interactions between the two species. The arctic fox is smaller than the red fox and loses the competition for food and habitats. Exploring the number of litters in the last 20 years, it can be seen that while red fox litters have grown, arctic fox litters have declined. The first idea to prevent the spreading of red fox populations is extensive hunting. At the beginning of the millennium, red foxes were intensively hunted in the fell areas of Enontekiö and Utsjoki under the Naali Life – project. The catch quotas appointed by the Ministry of Agriculture and Forestrywere fulfilledvery well by hunters each year. Unfortunately, the hunting alone and the short hunting period in particular had hardly any significance for the arctic foxes.The hunting probably only improved the living conditions of the remaining red foxes and the population might even have strengthened.

Fox cub in Inari. © Samuli Karppinen

Fox cub in Inari. © Samuli Karppinen

Finnish hunters are active in culling semi-predators, like red foxes. It seems that Finnish hunters actively cull semi-predators up to the height of the Arctic Circle. Active culling does not occur in the regions of Inari and Utsjoki, at least in the same scales.Reasons for this are clear: hunters are less enthusiastic, distances are long, the road network is sparse, and snow coveris thick. Maybe hunters of northern Finland don’t feel that culling is as important as hunters in southern Finland do. Red fox culling has to be continuous and intensive year after year for it to have positive effects on the arctic fox population. In 2015, the Finnish wildlife agency, as a part of Management of invasive Raccoon Dogs (Nyctereutes procyonoides) in the north-European countries project, started a project to cull the raccoon dog population in Lapland. A similar project, focused on the red fox, could be a good motivator for local hunters to cull the red foxes.

Research has indicated that lynx (Lynx lynx) regulate red fox populations. Foxes do not succeed in areas where lynx populations are abundant. One of the reasons for red fox success in the fell areas could be a lack of lynx. Unfortunately, it is not realistic to expect that lynx could be the arctic fox’s rescuer. The EU-Life project SEFALO+ (Save the Endangered Fennoscandian Alopex lagopus) has shown that a combination of actions, supplementary feeding, red fox culling, and protection of dens, could cease the decline of the arctic fox population and even enhance it. Nevertheless, I began wondering whether all these actions to save the arctic fox population in the Nordic countries will merely delay their extinction? Their population is small and genetic variation low. Diseases may heavily impact such a small population. Another possible threat to the arctic fox is the occurrence of escaped farm foxes on the mountain tundra. They can breed with wild arctic foxes, but hybrids do not survive in the wild. There are many problems and threats, which Fennoscandian arctic fox population have to face to avoid extinction.

Beavers restore the dead wood of boreal forests

Dead wood is a necessary element for numerous species living in the boreal zone. It functions as a food resource, nesting space or growth substrate for several mammals, fungi, insects, and birds. Dead wood is produced through two main mechanisms: senescence and disturbances e.g. forest fires or wind damage. A controlled forest has less ageing trees and disturbances, and currently up to 90% of Fennoscandian forests have been influenced by forest management. The recent drop in dead wood levels due to intensive forest management across the globe has concurrently led to dead wood-dependent (= saproxylic) species becoming rare as well, which weakens food webs and ecosystem functionality. Managed forests may only contain a few cubic meters of dead wood per hectare, while dead wood levels in old-growth forests and forests influenced by disturbances can rise up to hundreds of cubic meters per hectare.

Beaver, the ecosystem engineer © Sari Holopainen

Beaver, the ecosystem engineer © Sari Holopainen

Strong disturbances are less frequent in moist lowland areas of the boreal zone, where dead wood is mainly created as single trees die due to competition and ageing. However, beavers act as wetland ecosystem engineers, raising floodwaters through the damming of water systems. These floodwaters kill surrounding shore forests due to oxygen deprivation, thus creating significant amounts of dead wood into the habitats. In certain cases the flooding may kill entire forest stands. Beavers can therefore be considered the main natural disturbance factor of lowland forests.

Beavers require wood for food and as a building material for their nests and dams. Foraging for woody materials causes the resource to run out within a few years, forcing the beavers to move location. The process of flooding and dead wood creation begins again in a new area, thus producing a continuation of dead wood hotspots into the landscape. Eventually after several years the beavers can return to a previously inhabited location, which will be then be repeatedly subjected to their engineering. These hotspots may be very important to dead wood -dependent species, especially as they uphold a network and continuous supply of different-aged dead wood.

Calculating dead wood levels at a beaver flood - spot the researchers! ©Mia Vehkaoja

Calculating dead wood levels at a beaver flood – spot the researchers! ©Mia Vehkaoja

Despite an overall decrease in dead wood levels, certain types of dead wood have become rarer in the boreal forest than others. Currently the rarest forms are standing dead trees (snags) and deciduous dead wood. Both have declined more rapidly than other types due to forest management actions and attitudes. Beavers create a broad range of dead wood types (e.g. downed wood, stumps and coniferous dead wood), but they particularly aid in the production of snags and deciduous dead wood. This is good news for many saproxylic species, as these organisms are often strongly specialized, utilizing very specific dead wood types.

The dead wood produced by beaver-induced flooding is also very moist, which may affect the wood-decay fungi species that begin colonizing the dead wood. For example, sac fungi are more tolerant of wet conditions, and may therefore outcompete Basidiomycetes at beaver sites. This in turn will lead to differing invertebrate communities that utilize sac fungi instead of Basidiomycetes. Very different dead wood –dependent species assemblages may therefore be formed at beaver sites compared to fire areas of clear-cuts. The interactions of these species are currently poorly understood.

The beaver offers a possibility for all-inclusive ecosystem conservation compared to the conservation of single species. The species could be used to produce dead wood and restore the shore forests of wetlands.

Our research group has recently published an article concerning the impacts beavers have on boreal dead wood. The article can be accessed from http://www.sciencedirect.com/science/article/pii/S0378112715005757

Calculating dead wood levels at a beaver flood - spot the researchers! ©Mia Vehkaoja

Calculating dead wood levels at a beaver flood – spot the researchers! ©Mia Vehkaoja