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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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.