Forest host Science


Gray-surfaced, dead pines stand like guards around a pond called Huhmari. They are the only visible evidence of repeated floods caused by Finland’s largest rodents in the Häme forest.

University lecturer Petri Nummi leaps ahead of me and points out woodcarvers of all ages. The tallest hongs suffocated more than 30 years ago when the Evo beavers first dammed a stream flowing from a pond.

A couple of beavers chewed wood on their teeth, again. They assessed the angles of inclination and occupational safety, gnawed the trunk one-sidedly and only so far that the wind eventually felled the tree in the desired direction. They swam the logs and pulled them to the bottom, dragged the rubble, patted the mud on the bottom with their feet like masons.

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They labored to keep the mouth of the colony covered with water, even in dry times. There were other benefits to the dam basin. Beavers that grow to 30 pounds move awkwardly on land. As the water level rose and the shoreline shifted, safe waterways opened up for them.

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Like humans, beavers know how to use water for support mowing. The wider pond also meant wider transport options for building materials.

The beavers repaired the researcher’s dam

As the beavers did, the size of the pond doubled, perhaps even tripled. All the conifers within a radius of twenty meters from the current shoreline suffocated under the flood. Deciduous trees were dumped by the inhabitants as building materials for the dam and nest.

Nummi remembers the steps of the pond, as he has been studying beavers in the Evo area for 40 years. The initial impetus came during a course of study at a course at the Lammi Biological Station, twenty kilometers away.

One evening, biology students were tasked with reflecting in groups on the impact of various disturbance factors on the forest ecosystem. The disturbance addressed to Nummi’s pop pool was a beaver.

Later, a bachelor’s thesis and master’s thesis were refined on the topic. In his dissertation, Nummi observes the effect of beavers on birds. In order to calculate the numbers of birds from the same place both before and after the arrival of the beavers, Nummi decided to build an artificial beaver dam for his experiment.

Compressing trees and rocks into the running water was surprisingly heavy, even with the help of an excavator and the trees being felled with a chainsaw. Nummi recalls collecting rocks from the forest on a snowmobile sled in the twenty-degree frost of sweat and wondering how beavers would survive the job with their paws and teeth alone.

The end result was successful. The artificial dam has been standing for 38 years.

“The best reward for the work was when a couple of years later a couple of beavers arrived at the dam pond and built a nest on its shore. They seemed to approve of my construction, even though they repaired it a bit, ”Nummi smiles.

Dozens of beetle beetles in every butt

The flood caused by the beaver is devastating to the nearby trees, but overall the dam pond creates more life than it destroys. It will already be seen the following spring after the construction of the dam.

“Whenever a beaver dams a pond, it gets a colt,” Nummi says.

Mortar also became a summer paradise for small tents and mallards. Evo ponds are usually 60 to 70 centimeters deep from their shores, but when flood water rises, lower water is also created. It multiplies the area in which the pups of half-diver ducks reach out to eat from the bottom. Sky goats and forest wolves also enjoyed the wading pool.

There was enough to eat. Plants trapped under the flood released new nutrients into the water, and the pond began to pile up invertebrates. Nummi has investigated the matter by dipping mini-sized cans of glass jars and plastic hoppers in Evo’s ponds, which he calls bullshit.

“In Majavalampi, a couple of hundred beetles were found in every pond, in other ponds the amount of prey could be counted with your fingers,” Nummi describes the difference.

A lot of flying insects also hatch in the stagnant water, which is to the liking of bats in addition to birds. Nummi and his partners have calculated that at least bats and reindeer from bats are more likely to eat from beaver ponds than from other lakes of similar size.

Apparently, in addition to the catch, they are attracted by the sparse woods that provide airspace for pilots.

The domicile changes every three years

Nummi shows a tent box hanging near the flood line, which is still waiting for the residents in March. Once upon a time, a female tent equipped with a radio monitoring device was nesting in it, which soon after the chicks hatched led them into the Huhmar water to feed.

The following year the tent returned to the same bowl, but the beavers had abandoned their ponds. The dam no longer retained water, and as the snow closed, a shrunken pond was revealed next to the bowl.

“When the chicks hatched, the transmitter was able to detect that the mother was leading them to another pond to grow,” Nummi says.

All that was left of the ducklings’ paradise was wet land. Between the decaying trees, new trees began to push their roots into the soil fertilized by the bottom mud. Field moles cleared their own labyrinths into the rising grass, from which Flies and snowmen ran over them.

Beacons change their domicile on average every three years. At that time, they usually had time to eat the deciduous trees on the shores. In more lush areas, for example, in North America, animals can inhabit the same pond for generations.

Repeated migrations lead to a wide variety of habitats in the forest: floodplains, meadows drying up floods and decaying wood that is rare in commercial forests.

“Majava is renewing the forest at a smoother pace and more predictably than, for example, forest fires or storms,” says Nummi.

As new beaver ponds emerge, it is easy for species that prefer certain habitats to migrate with the beavers as the dam pool slowly turns back into the forest.

There are also quality differences in deforestation. The decaying trees standing in the pond are wetter than their fate-overturned or flame-compensated counterparts, so they also offer their decayers their own conditions.

This benefits, for example, from lichens that resemble the tip of a pin. Evo has noticed that their species and individuals are at their highest in lighthouse wetlands. The evenly moist rotting wood is to their liking.

There is a dart knocking on the opposite shore. Various beetles and their larvae also thrive in aching and decaying trees.

I don’t get a knocker in my eyes, but Nummi says that these main ones are comfortable with demanding bottoms. Another species found here only in lighthouse ponds is the endangered cape frog.

Johanna Junttila
is the editor of Tiede Luonto magazine.

You can read the full article in Science Nature issue 3/2022 or digilehdet.fi:stäif you are a subscriber to a Sanoma magazine.


Source: Tiede by www.tiede.fi.

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