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Friday, September 30, 2016

The Otter river Beavers of England

In a previous blog, I wrote about the Tay-catchment beavers in Scotland.  Now the English have got in on the act.  A couple of beavers 'appeared' in the Otter River, on the South Coast of England in Devon.  This has resulted in three breeding pairs at present (Sept 2016).  In a great move, the Powers-that-be have allowed the introduction of a second pair further up in the catchment so that when the two populations meet, there will be greater genetic diversity in the united populations.  First a little information on where you can see these beavers.

You head for Devon on the South Coast out toward the West and set your navigator to Otterton.  It is a village near the mouth of the Otter River.  There are a number of places you can stay and I can heartily recommend the Kings Arms.  Book ahead because tourism is picking up with people coming to see the beavers.
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Kings Arms in Otterton

To see the beavers, I would highly recommend getting there before first light in the morning.  You will also see beavers in the evening and even occasionally in the middle of the day but morning seems to be the best time.  Starting from the Kings Arms, you walk west along the main road (back the way you entered Otterton) past a working flour mill on the left and across the bridge that crosses the Otter River.  Just past the bridge, you will find a gate on your right and beyond the gate a well trodden path.

Head upstream (downstream is also a nice walk and you can walk along side a wetland and down to the sea).  As you head upstream, you will pass a weir that directs water to the flour mill in Otterton.  It has a fish ladder built into it.
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Otterton flour mill weir with fish ladder

A short way further on you will pass a wooden bridge over the Otter.  It arks up to the East side which is considerably higher than the west side where you are walking.  From here on, keep an eye on the small trees to the left of the path.  You will see beaver cut branches here and there.
Wooden bridge across the Otter River

Keep going (20 minutes to half an hour from the gate at the start of the path) until you come to a well trodden place on the side of the river.  If you sit on the edge of the river and look upstream you will see a bed of bull rushes and on the East side of the river, a small beach.  The beavers often haul out there.  If you look a little way down stream, you will see a pile of branches up against the far bank.  This is where their burrow* is located.

* When first introduced to a new area, beavers often make burrows in the river bank for raising their young.  Later, when they dam feeder streams, they construct a lodge in the pond they have created for their nest.

In larger rivers, beavers make burrows in the bank. 

At present (Sept 2016), the adult pair at this location have five kits.  Generally when beavers are introduced to a new area, their population expands at about 25% per year.  This only requires one surviving kit every two years.  Clearly the potential for an increase in population is much greater.  The kits stay with the parents for an additional year and help them to look after the next batch of kits.When the adults are building dams, lodges and food stores, they help with this too.  They become sexually mature around the end of the second year and the parents drive them out.

A second place you can see beavers is from the middle of the wooden bridge.  You may need a pair of field glasses.  Look upstream to where there is a wee beach.  They often haul out there.

Before I start, have a look at these beavers.  This footage was shot by Sylvia Meller, wild life photographer extrordinaire.  I had gone to England with no thought that I would be able to go and see the beavers of Devon and didn't have a camera with me.  Spot the dummy.  However these pictures are far better than anything I could have shot.  Look up other works by Sylvia.  They are great.

The territoriality of beavers, the fact that they drive out their young after they have reached maturity,  has an interesting consequence.  Once the available location in rivers and streams are occupied, the population overshoots slightly each year and then falls back to its carrying capacity.  Unlike many other animals, you can't have a population explosion of beavers.

A caution
The beavers in the Otter catchment are becoming habituated.  That is to say, they are becoming used to humans.  Like any mammal they learn and as long as they aren't harmed by humans, they will show their natural behavior in full view.  This presents a magnificent opportunity for school trips with all the ecological opportunities any teacher could ask for.  Beavers are shy creatures but can become very tame.  Just one caution though.  They are a trifle touchy when protecting their kits.  Best to keep your favorite dog on a leash when watching beavers.  In the water, a beaver has all the advantages and you may have a vet bill if your dog threatens their young.

These beavers, thought are wary of humans so if you want a great experience, sit still where your silhouette is broken up (beside or in front of a tree), talk quietly and whisper to your kids.  They will usually catch the mood and whisper back. Using a flash light will often scare the beavers and they won't come out again for a while. 

Helping the Beavers
Beavers do so much good for the environment and for an individual farm that you may desire to encourage them to create a pond on your farm or in the head waters of your catchment.  The only way you can increase the beaver population is by making new areas attractive to them.  The best way is to truncheoning in a new forest of deciduous trees on the banks of a stream).  Tiny seeps that hardly deserve the name of a stream can be occupied by beavers if the habitat is provided for them.

Dam Building
I just read a web site (which shall remain nameless) that stated that the European beaver Castor fiber unlike the America beaver Castor canadensis does not build dams.  I hate to rain on your parade guys but  European beavers definitely make dams and be thankful that they do.  Almost all the massive benefits that beavers bring to a catchment depend on the fact that they do make dams and thus create ponds. In a new area, beavers tend to build their burrows on the banks of the main river but once these locations are taken up, they will move into the secondary streams where they build dams to make ponds for their safety.  Let's catalog the benefits from beavers.

Water flow regulation
Beavers store water on the land in a number of ways.  This is particularly important in the catchment of the Otter.  The underlying strata is mainly sandstone and water doesn't infiltrate the aquifer quickly, unlike outwash plains such as the ones found East of the Rockie Mountains in the USA or to the East of the Alps in the south island of New Zealand.  In the Otterton, most of the water from high rainfall events shoots down to the sea in a day or two.  Of course, if these are unusually high rainfall events, they cause flooding.  So how do beavers store water.

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Without beaver dams in the catchment, heavy rainfall causes floods downstream

First, of course, are the ponds they create with their dams.  Depending on the topography of the particular area where they build their dams, they can store considerable water.  Beaver dams are somewhat leaky so some water is leaked downstream and water also seeps downward into the underlying strata. holding the water on the land allows time for the water to infiltrate the 'reluctant' aquifer.  

Secondly, the ponds raise the water table in the surrounding land.  Water tables intersect streams at the surface of the water in the stream.  As the water rises in a beaver dam, the surrounding water table rises as well.  In particularly propitious cases, a field which had to be irrigated, now doesn't need it since the field crops can access the underlying water table.  Water then leaks back into the stream, down steam from the beaver dam.
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Much of the water stored by beavers is in the surrounding water table

Thirdly, the dams simply roughen the macro contours along a stream.  Even if all the dams are full when a rainfall event occurs, just having all these dams in place slows down the water flow to the sea.  All these effects lower peak flows and raise low flows.

Check out this rather neat cartoon

And fourthly on a long term basis, beaver ponds catch bed load, suspended sediment, wood chips, scats of various animals, spawned-out salmon and so forth creating a deeper and deeper sponge.  Over time, this water retaining sponge increases.  The effect of the beavers dam to regulate water flow increases over the years.

Incidentally, by catching sediment and bed load, beaver dams extend the life of downstream hydro electric dams and help maintain their capacity.  If a hydro dam becomes filled with sediment, it's water storage capacity decreases and hence its function as an energy storage device.  Also be evening out flow, there are less instances where water has to be wasted over the spill way.  More water is available for generation or irrigation.

Beavers sometimes abandon a site in which case, over time, the dam breaches and the beaver pond becomes a wetland with all the benefits this brings.  Wet lands are rich ecological environments, slow stream flows, catch sediment, hold water and in short, still fulfill many of the beneficial functions of beaver ponds.  Generally, after a while, as the deciduous trees move in from the edge of the wet land, a new colony of beavers will establish themselves in the same area and create a new pond above the wetland.  The deep, water storing sponge grows and grows.

Fora and Fauna
A beaver dam, obviously, gives rise to a location with dependable deep (a few meters) water.  Where before you had a stream, riparian zone and surrounding fields or towns, now you have a new environment.  In addition, you have more dependable stream flows between beaver dams than in streams where there are no beaver dams, with none of the exceedingly low flows which kill fish and other wild life or floods which destroy people's structures.

In the pond, animals such as water voles and muskrat can prosper.  Water birds find shelter from predators in the middle of the pond  and will nest in the reed beds that develop along the margins of a beaver pond.  A whole range of invertebrates, which only prosper in still water can grow and form part of the food chain for larger animals.  Dragon flies, which are excellent predators of flying insects such as mosquitoes and biting flies can lay their eggs and increase their populations..

A detritus cycle develops in the pond based on the bits of cellulose (water log wood chips, leaves, twigs etc) that the pond catches.  This cellulose based detritus feeds a wide variety of fauna. 

A beaver pond becomes the 'go to' area to sit and watch wild life.

Benefits to Salmonids
Here is where the beaver pond really comes into its own.  Many of the salmonids lay their eggs in redds.  These are gravelly areas in a stream.  Factors that decrease the success of hatching include floods which wash out the eggs from the redds,  low water which doesn't provide enough oxygen to the eggs and silting  which smothers the eggs.  Beaver ponds ensure an even  flow of clear water.  This is especially important today with increased silt* from farming.  Beaver ponds catch this silt and protect the redds.

* Incidentally  Otterton was once a sea port.  Poor farming practices and the use of the plow allowed masses of soil from the hinterland to flow into the ocean and fill the estuary.  It is now a 15 minute walk from the flour mill to the sea.  This situation exists all over the UK and in other countries as well.  If you have ever visited Pompey in Italy, you may have seen the boat houses where the people took shelter from the volcano and were cooked where they lay.  The boat houses are now a considerable distance from the sea.

Once the eggs have hatched, the tiny salmon are prone to predation from the water and from the air.  The beaver pond provides water which is too deep for wading birds and creates many many niches in the front wall of the dam and in amongst the branches of the lodge and in the  food store of branches.

In areas where the streams freeze in winter, the beaver pond provides water deep enough not to freeze.  Check out this beautiful Youtube video of beavers repairing their lodge in the winter.

Nutrient flow
Most of the time, nutrients flow from the land to the sea.  Beaver dams help reverse this one way flow.  Spent salmon are caught in beaver ponds instead of being washed down to the sea and enrich the pond.  The adult salmon provide the nutrients for their soon-to-hatch young.  Animals which feed in the pond, spread their dung upslope.  Altogether there is a flow of nutrients upstream associated with beaver dams.

Education about beavers
I have heard  fisheries biologists, who should know better, and anglers argue that a beaver dam stops the upstream migration of adult salmon. It is not for nothing that the Atlantic salmon was name Salmo salar .  In Latin it means 'the leaper'.  For a sex crazed Atlantic Salmon that can jump great waterfalls in a single bound and which is heading upstream for its once in a life time act of procreation, a beaver dam is just a little morning warm up.
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Atlantic salmon leaping a tall water fall in a single bound

I think where the confusion arises, is that Salmon will rest in the plunge pool below a beaver dam for a while before continuing upstream.  Sometimes they wait for a wee freshet from a rainfall event to point the way.  Not a bad adaptation when you consider that the stream above the beaver pond will be fuller following a rain.

It is interesting that anglers, who quite correctly have been removing tires, old car bodies and other junk from their streams, also remove fallen trees.  You can see one such case along the Otter.  If you look at the opposite bank as you walk up the stream, you will see the butt of a tree that has been chain sawed off.  Have a look at this web site on 'big wood'. 

Benefits of large wood in streams. Illustration © The Nature Conservancy (Erica Sloniker)
"Big Wood" is of great benefit to salmonids

Pacific Salmon Migration
Incidentally, with the decrease of ice in the Arctic Ocean, Pacific salmon have been found for the first time in streams flowing into the Arctic Ocean and even as far as Greenland.  Since we are not going to mitigate the melting of the Arctic, this migration is bound to continue.  It wouldn't be too surprising to find, some decades hence, some strange salmon swimming upstream in British rivers.

For the purist, this will be anathema.  Of interest, though, are the wide variety of life styles of the Pacific Salmon (also mentioned in the above link).  They range from the pinks and chum which tend to spawn in streams near the mouth of rivers and to swim (at night) down to the ocean as soon as they are hatched to  Sockeye, who in contrast will swim down a small stream until they come to a river and then turn upstream and find a lake to reside in for a variable number of years.  Some Sockeye will even begin to treat the lake as an ocean and form a landlocked population.  In which case, on the Pacific coast they are called Kokanee.  I understand that Salmo salar also can form landlocked populations.

Benefits to the Riparian Zone
It is vital for the health of a stream that there is a riparian zone.  Such stream verges shade the water, keeping it cool and of even temperature.  The roots of the growing trees and bushes intercept excess nutrients in the ground water flowing toward the stream from farms.  The trees, bushes and grasses bind the bank together so it doesn't slump and pollute the stream and riparian zones provide not only habitat for wild life but also corridors along which they can migrate.
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A riparian zone is hugely important for the health of a river. 

At first glance, you might suspect that the cutting down of a tree by a beaver is  negative.  The opposite is true.  Virtually all deciduous northern hemisphere trees coppice*.  Not surprising since they evolved with beavers.   A beaver cut tree sends out a plethora of branches.  This has a number of effects.  The tree is now protected from becoming uprooted by a storm and exposing raw earth to the stream.  Light can now reach the under-story so that shrubs and grasses prosper.  Their root masses further stabilize the bank.  The young vegetation is lower where it can be accessed by, for instance, deer and the flush of new vegetation is food and shelter for a variety of animals and birds.  Of course, the new branches supply both food and building material for the beavers.

*Sprout from a stump

When a beaver pushes an unpeeled branch into his dam, it will often sprout and the roots grow down into the dam, greatly strengthening it.  A beaver dam can turn into a hedge.
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Vegetation will often grow on a beaver dam, making it stronger

 Often, though, the beaver will first eat the bark before using the branch as building material.  As the beaver pond matures, many forms of vegetation such as Bull Rushes, Lilly Pads, pond weeds and so forth will take up residence in the pond.  More and more, they form the food of the beavers and bark becomes a smaller part of their diet.  It's a pretty neat adaptation.  In a new location, beavers can use their building material for food until the pond vegetation develops.
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Ponds develop a wide variety of vegetation which beavers and other wildlife utilize

Stream Hydrology and Ecology
The river Otter is an ideal location to have the first English introduction of beavers.  It has been well researched in terms of the relation between stream flow and rain fall events, the frequency of flood and low water events, knowledge of the flora and fauna of the stream, especially the trout and salmon and the flora and fauna around the stream.  If our talks with residents is anything to go on, there is a great interest in the re-introduction of this long missing native of Britain.   The Otter is about 32km long with many small feeder streams.  It is surrounded mainly with farm land and has a couple of villages along its length that are periodically flooded.

No major effects of the beavers will be seen until they decide to move into the feeder streams and build dams.  Because the Otter is so well researched, it will be an ideal case study to document the effect of the return of the beavers.

How to get a beaver pond on your farm.
Now is a great time for the people living in the catchment to prepare the areas they want beavers to settle.  It is very easy to establish a food and building supply for beavers and since they are in small numbers to date, there will be time for a wee forest to develop before the beavers discover the location.  Truncheoning is the answer. No need to plant expensive seedlings.

Find an appropriate deciduous tree.  Beavers most appreciate willows but aspens, poplars,  birch and many others will do.  Avoid evergreens.  Sometimes beavers will utilize them but they much prefer deciduous trees.

Fell the chosen tree, cutting it at, say, knee height.  It will sprout and before you know it, you will have the tree back in all its glory.  cut the entire tree into pieces about as long as your fore-arm.  Small twigs can be cut with pruning sheers, large ones with your chain saw.  Large logs, I usually split in four and sharpen the bottom end with an ax.  Wrist diameter pieces, simply sharpen.  Small twigs, leave as they are.  You can leave the cut pieces in the shade for a couple of days and some people recommend doing this.  I have usually used the pieces the same day.

Head for your chosen site with an iron bar and an ax or sledge hammer.  You need a  location in which there is some moisture in the ground. After a good rain is not a bad time to do this so in England that means almost any time.

Pound the larger pieces into the ground.  If the ground is hard, the iron bar can be jammed into the same hole a few times, rotating it around after each thump before pounding in your truncheon.  For the smaller pieces, simply make a hole about a third of the length of the truncheon with the iron bar, drop in the twig and soon you will have  a forest to make the most discriminating beaver happy.

Mitigating beaver damage.
Since we have taken over the habitat of the beavers, we will not be pleased if they cause a road to wash away, flood a favorite field or cut down our fruit tree.  Mind you, before you use the following measures, ask yourself if a flooded field might possibly be of benefit to your farm.  There are many benefits to having a pond and/or wetland on your farm.    However, suppose you have decided that you don't want a field or building flooded.  The answer is simple.  You simply install a beaver deceiver.
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Note the outlet.  It's height determines the water level in the pond

Get a piece of that corrugated flexible black plastic pipe which is long enough to reach into the pond, over the dam with its outlet at the level you want to keep the pond at.  Dig away enough branches during the day to lower the water level to where you consider appropriate.  Lay in the pipe.  Pound in a stake on either side of the pipe on top of the dam.  Nail on a cross piece touching the top of the pipe.  The beavers will repair the damage you have made that night.  then get a piece of wire weld mesh with a hole size of  abut 10cm and a bar diameter of six or eight millimeters.  The mesh they use for cement reinforcing is ideal.  Form this into a cylinder, cut out one or two cross bars at one end and pound it into the bottom of the pond at the intake of the pipe.  If you like, you can put a lid on it and pound it in so that it is completely covered by the water.

Remember, you don't want to siphon all the water out of the dam.  The object is to hold as much water on the land for as long as possible.

If your favorite fruit tree is within about a hundred yards of a beaver colony, put a layer of chain link, wire weld or chicken wire around the trunk.  Problem solved.
A simple way of protecting a special tree.

To finish, lets summarize a few beaver facts

1/  Beavers do not eat fish or any other animal.  The only eat vegetation. As the pond develops, they eat less bark and more water plants.

2/  Beavers. once they start building dams, reduce flood peaks and increase low water flows.

3/  Beavers greatly increase ecological diversity

4/  Beavers enhance salmon and trout populations

5/  Salmon and trout pass upstream and downstream over beaver dams.

6/  Beavers are not responsible for Guardia in streams.  New Zealand doesn't have a single beaver and some of her rivers contain Guardia.

7/  Beavers improve riparian zones by felling trees in the riparian zone.  A felled tree will coppice from the stump and be less vulnerable to wind.  It is good to get sun to the understory of the Riparian zone.

8/  Flooding of some feature such as a dwelling or orchard is easily mitigated with a beaver deceiver.

9/  Damage to a favorite tree is easily mitigated

10/  Beaver dams reduce the concentration of nitrates and phosphates in a stream through the agency of the detritus cycle.

11/  Beaver dams in the catchment of a hydro electric dam increase the amount of electricity the hydro dam can generate, the amount of water that can be used and extend the life of the hydro-electric dam by intercepting bed load and sediment.

The future
The people in the Otter River catchment are very fortunate to be the first place in England to see the return of the beaver.  If we are to believe the scientists, the weather is going to become much more erratic and this doesn't only mean more severe rain fall events.  It also means more protracted periods of drought.

No need for a leap of faith.  We already see some of the results with weather patterns getting frozen in one place instead of moving eastward in a regular progression.  A commonly expressed theory is that it is caused by changes in the jet stream.  Whatever the cause, it depends on  which weather pattern lands on top of you as to whether you experience protracted drought or protracted rain.

In addition, climate zones are moving northward at over a kilometer a year and are likely to take some rather severe lurches northward in the future.   Already, some locations in southern England are defined as sub tropical.

It is a bit of a race against time, whether the beavers can occupy the feeder streams in time to mitigate the effects of climate change which are already beginning to manifest themselves.  At least, the Otter Catchment may be ahead of the game.  The rest of England will be playing catch up but will fortunately have the example of the Otter Catchment to draw on.

When first built, before they have time to settle and before roots  grow down into them, a beaver dam can be washed away by an exceptionally severe flood.  When there are beaver dams  all the way up and down the catchment they protect each other, the flood peaks are reduced and all the dams are likely to survive.  Once well established, a beaver dam is unlikely to be shifted by anything nature can throw at it.

As I mentioned, in all of this, the rest of England is going to be playing catch up.  Hopefully, a really intense research program will document the effects of beaver dams as they become established throughout the Otter catchment.  This will be the body of work that other catchments can point to to convince the uninformed of the benefit of the return of the beaver.

In the end it depends on the people in the Otter catchment.  If they establish favorable habitats for the Beavers and avoid harming them, the beavers will return the favor with interest.

Check out this great poster.

1 comment:

Heidi Perryman said...

William! Really nice post on the complex benefits of beavers. There was a fantastic article two days ago on BBC Earth about the Devon beavers, and a ridiculous article yesterday from Sir Git who has laid a bounty for them! Wish everyone was as informed about beavers as you!

Heidi Perryman
Worth A Dam