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

Advertisements

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

Frogs love beaver-created wetlands

Amphibian and wetland loss is occurring globally at an increasing rate. Since the 1900s, approximately half of the world’s wetlands have been destroyed. During this time up to two-thirds of European wetlands were lost at a regional scale. This trend is reflected by the fact that 23% of Europe’s amphibians are threatened.

Wetlands in the boreal region are frequently constructed through the damming activities of an ecosystem engineer, the beaver (Castor sp.). They create and maintain special habitats by constructing dams. Beaver-created wetlands are open and sunny due to tree felling and flooding-induced tree mortality. They produce large quantities of woody debris and detritivorous invertebrates, e.g. chironomids and Asellus. Beaver ponds contain structurally heterogeneous vegetation.

Beaver-created wetlands contain structurally heterogeneous vegetation, as well as open water areas. © Mia Vehkaoja

Beaver-created wetlands contain structurally heterogeneous vegetation, as well as open water areas. © Mia Vehkaoja

According to our new study beaver-created wetlands increase frog species heterogeneity and abundance. There are only three native anuran species in Finland (the common frog, the moor frog and the common toad), and all of them were found in beaver ponds. The moor frog (Rana arvalis) was only found in beaver ponds, where the common frog (Rana temporaria) was also most abundant. The common toad (Bufo bufo) prefers deeper wetlands than the other two species, but because beaver ponds contain both shallower and deeper parts, it was also found from the beaver ponds.

Beaver wetlands offer high quality habitats for anurans and facilitate the occurrence of moor frogs. The shallow and warm water areas accelerate the hatching and metamorphosis of tadpoles. The rich aquatic vegetation provides attaching places for spawn and protection against predators. The abundant vegetal detritus, zooplankton and aquatic invertebrates offer nutrition for both larvae and adults. In addition, beaver-created wetlands create overwintering habitats that are less likely to freeze down to the bottom.

Both the moor frog (Rana arvalis) and the common frog (Rana temporaria) are the most abundant in beaver ponds. © Mia Vehkaoja

Both the moor frog (Rana arvalis) and the common frog (Rana temporaria) are the most abundant in beaver ponds. © Mia Vehkaoja

Beaver facilitation includes both habitat amelioration and resource enhancement. Frogs are not the only group that is benefitted by beaver activity. Other such groups are ducks, bats, woodpeckers and many invertebrates. These ecosystem engineers could be used in wetland restoration, and furthermore the beaver clearly promotes amphibian conservation.

Where do the ducks come from? (The European view)

Ducks and geese can be seen in huge flocks and high densities in the temperate zone during the winter. Both are also heavily hunted in their wintering areas. But during the summer, many of the ducks and geese head far north, to the taiga and tundra, to breed in very low densities. They spread out into the millions of wetlands located at high latitudes. Ducklings are reared in barren wetlands, where food limits their survival.

Ducks that breed far, far away in north

Boreal wetlands are the main breeding areas for several European duck species. Without Russian breeders, over 90% of the common teals and common goldeneyes breed in boreal area covering Finland, Norway and Sweden. In addition, more than half of the European goosanders, red-breasted mergansers, pintails, wigeons and tufted ducks breed in these three countries.

Picture Seppo Leinonen www.seppo.net

Picture Seppo Leinonen www.seppo.net

Large share of the ducks hunted in western and southern Europe is thus originated from the boreal wetlands. Guillemain et al. (2014) conducted an isotope research of the teals hunted in France during the winter. These small ducks turned out to spend their summers mainly in the area reaching from Finland to Siberia. Teals are thus mainly produced in the boreal biome, but most of them are hunted in the temperate zone. Such source – harvest area – knowledge is not concerned in the European duck management, but in North America the process is better known, and work as a tool of the adaptive harvest management.

Changing boreal wetlands

It is expected that climate change will affect the wetlands, especially in the boreal biome, where the warming is rapid (IPCC). Alaskan wetlands are currently becoming smaller and their quality from the biodiversity and productivity perspective is declining. Some areas in Russia are expected to suffer drought while some should get more precipitation. How these changes affect the biota of the wetlands, especially concerning seasonal wetlands, is poorly known. In addition to the direct changes in the wetland habitats, the changing phenology of the spring due to climate warming might cause a miss-match phenomenon with ducks and their invertebrate food. Invertebrate availability is especially important for the females before egg-laying and for the young ducklings. If the phenology of ducks and invertebrates differs, it might have a negative effect to the ducks breeding success. However, an increasing temperatures might compensate the lack of food to some extent.

Wintering population of tufted duck has increased 24 797% in Finland. At the same time the populations in Western European countries have declined ~40% (Lehikoinen et al. 2013). © Sari Holopainen

Wintering population of tufted duck has increased 24 797% in Finland. At the same time the populations in Western European countries have declined ~40% (Lehikoinen et al. 2013). © Sari Holopainen

The numbers of wintering ducks in the boreal are increasing due to a milder winter climate. Several species that were scarcely wintering in Finland some decades ago are now common and numerous. Correspondingly their numbers in their old wintering sites have decreased. Some migratory species might not reach their old wintering areas anymore; a phenomenon that has been observed for instance in the UK. This shift in wintering areas will affect the quarries of the species in question.

 

Read more

Guillemain et al. 2013: Effects of climate change on European ducks: what do we know and what do we need to know? Wildlife Biology

 

Hot spots of boreal landscape

The beaver (Castor spp.) is a known ecosystem engineer that modifies its environment quite drastically. It builds a dam and raises floodwaters into surrounding forests, killing trees, and releasing organic material into riverine systems and lakes. The rising water level changes both the abiotic and biotic conditions of a wetland. Many organisms, from water lice to water birds, benefit from these changes. Beavers facilitate these species by offering both nesting and sheltering areas in the form of low bushes and trees by the water’s edge, increased aquatic plant communities for nutrition, and ice-free water areas for extended periods.

Beaver-created wetlands are cyclic ecosystems. Beavers usually inhabit a site for one to three years and then move to the nearby site, where the whole process starts again. After the beaver has left the site, the abandoned site reverts quite slowly back to the original. So the beaver’s actions endure much longer than they occupy the site, and commonly they return to former sites within 10 years.

 

Beaver-created wetlands can be seen as a biodiversity hot spots. This pic is from eastern Finland. © Mia Vehkaoja

Beaver-created wetlands can be seen as a biodiversity hot spots. This pic is from eastern Finland. © Mia Vehkaoja

The beavers’ actions can be seen as quite sharp shifts in an ecosystem, but the very nature of the changes that the beavers create tends to be rather stable. As the beavers transform the ecosystem they also enable resilience in landscapes. Beaver-created wetlands increase the heterogeneity of the landscape, and can be seen as biochemical and biodiversity hot spots. They maintain several declining species, especially in the northern Boreal Hemisphere, where eutrophic wetlands are relatively rare.
The EU has an ongoing project called the Return of Rural Wetlands. The size of the EU funding in this project in Finland is a little over a million Euros. The other million Euros come from the Finnish Government and the rest from the Finnish Wildlife Agency. The aim of the project is to create a new frame and a good start for the future nationwide program for wildlife habitat conservation, restoration and re-creation. So people are creating new wetlands using tractors and diggers, and by bringing soil and water from elsewhere.

Beavers would do the same work for free. Instead of misspending lots of money on labor, expensive machines and moving earth, we could use some part of the funding to re-introduce the European beaver (Castor fiber) to a wider area. In this way we would save money, get the same results, if not even better ones, and help our original, once extinct species to recover. In addition, Finland would achieve the obligations of EU Inland Water Directive.

The new re-introduction of the European beaver project would involve the same interest groups as the Return of Rural Wetlands project. Some of the re-introductions could be conducted on state-owned lands and some on privately owned land. There are several local landowners involved in the Return of Rural Wetlands project, so there is a good possibility that they would be interested in the same kind of project as well. Regional hunting clubs would want to be involved, as beaver-created wetlands offer improved hunting and fishing opportunities, because their habitat engineering increases the number of game and fish species. It might be easy to get regional authorities and policymakers to engage in the project, because of the EU obligations that abide them. Furthermore, the policymakers would conserve the biodiversity of Finland, and gain the respect of The Finnish Association for Nature Conservation and the public. When all these interest groups are involved in and the role of power is divided to various levels, a revolution in wetland creation is possible. When such a project succeeds in Finland, it should be possible to implement it also in other EU countries.

 

The Mallard (Anas platyrhynchos) favors beaver-created wetlands, especially during breeding season. © Mia Vehkaoja

The Mallard (Anas platyrhynchos) favors beaver-created wetlands, especially during breeding season. © Mia Vehkaoja

The beaver’s actions extend wider than just creating suitable wetlands for several species. Beaver-created wetlands produce high amounts of dead wood. Dead wood is a decreasing natural source and the species dependent on dead wood are under threat. There are numerous bryophyte, lichen and beetle species that rely on moist dead wood. The resilience of beaver-created wetlands is more general than specified, as its transformability reaches from wetlands into the forest.

Beavers provide also other ecosystem services to humans. They mitigate flood peaks by retaining rainwater and drought conditions by slowly releasing water. Beaver-created wetlands act as buffer zones by filtering impurities, e.g. heavy metals, thus increasing water quality. They facilitate and conserve endangered and declined species, and create interesting hiking and relaxation possibilities for humans. All in all, beaver-created wetlands are one of the key ecosystems in boreal areas to be conserved.

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