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

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.