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Monday, July 16, 2007

The Canadian Beaver - pest or benefactor

Beaver nibbling twigs -Kelowna BC
It's no wonder the beaver gets a bad press. The first time someone is aware that beavers have returned to their ancestral home is when a favorite fruit tree is cut down or a road is washed away because of a dammed culvert. The results of returning beavers are often visible, immediate and in your face. The benefits they bring are, unfortunately, often invisible, happen over generations and are hard to quantify unless you are  a scientist with access to long term records. However for all their subtlety the benefits from beavers are profound.

The beaver is an aquatic rodent as large as a medium sized dog. He is a odd beast compared to other mammals in that he continues growing all his life. He lives in a lodge which he constructs by piling up branches in a pond. He plasters the upper layer of branches with mud which, in the winter, freezes to the consistency of reinforced concrete. A small hole is left in the top for ventilation. When he has a suitable pile of sticks, he eats out underwater entrances and a den above the water line.

Where naturally occurring ponds are rare, or where pond locations are already occupied, the beaver will build a dam across a stream to create a pond and it is this habit that makes him so useful. In large rivers or lakes, he may excavate a burrow in the bank and become almost invisible

Beaver cut stump - Chilcoten BC
A main food of beavers is the under-bark of a wide range of copicing trees such as willow, cotton wood, poplar, aspen and alder and it is the wood of these trees that he uses for both dam and lodge. Beavers will also eat a wide variety of water plants and their roots.  Once the beavers have created a pond, these types of plants flourish and provide more food for beavers and other animals. A beaver will also eat windfall apples (or apples from a tree he has just felled).

Some botanists believe that the reason willows, alders and poplars are such good copicers is because they evolved with beavers. In beaver country a tree that sends copious branches from a stump each year has a distinct evolutionary advantage, over a tree that dies when it is cut down. In turn, this sort of tree is of great benefit to the beaver since it produces tender young food each year and a new supply of dam repair material.
Beavers were introduced into Tierra del Fuego in the 40's where the trees hadn't evolve with the beavers and there, beavers are considered an invasive pest. The local people aren't aware of the long term benefits of beaver dams and all they see is a treeless area around each dam covered with shrubs and grass.

Beaver eaten skunk Cabbage - Prince Rupert
Beaver knawed cedar tree - Prince Rupert
If really desperate a beavers will turn to some hard woods and even some evergreens but this is often just before they leave for a more favorable greener pastures. In lakes beavers can get by without a supply of suitable trees if there are sufficient water plants available. For instance in Morse Pond in Prince Rupert, BC, beavers are eating Lilly pad leaves,  skunk cabbage and undoubtedly many types of aquatic vegetation not visible on the surface of the pond. Except for some gnawing on a cedar tree by their lodge, there is no sign of them cutting down the very scarce deciduous trees in the area. Almost all the trees surrounding Morse Pond are evergreens which are distasteful to beavers.

Beavers produce around three kits each year and the kits stay with the parents for a second year and participate in the work of maintaining the dam and lodge.  In the third year young leave the home pond and look for a suitable site to build their own home. Given a decade or so without disturbance, a whole water-shed can have beaver dams in first, second and even third order tributaries.

In North America, historically, beavers lived from the Arctic circle down to Mexico. They manage very well in areas where their ponds are frozen over for months of the year and also in very warm areas.

Beaver populations are self limiting. They are completely tied to water and so their population is limited by the availability of suitable sites. Beaver families are very territorial and will drive out strange beavers. Typically, when beavers come back to an area, their population overshoots slightly and then falls back to the carrying capacity of the area.

So what good do beaver do. It is hard to know where to start.

Beavers mitigate floods.
Beaver dams have a small amount of free board (the part of the dam above the water) and as a storm wave moves down a stream system, the dams fill up to the top and then slowly release their water. This is especially so with the floods that seem to come, all to often , after a drought.

Beaver dams are somewhat leaky so with a long period of low rainfall, the level in the beaver dam is likely to be low. The lower the water level in the beaver dams, the greater the mitigating effect on flood peaks.

By widening the flood plain, beavers greatly increase the amount of water a stream bed can hold, further reducing flood peaks. Beaver dams also 'roughen' the stream bed, slowing down the water. This further reduces flood peaks down stream.

Water is not only stored in the pond itself but in the surrounding land.  Water tables intersect streams at their surfaces.  A beaver dam raises the water table in the surrounding land, storing yet more water to slowly leak back into the stream, downstream.

Check this out

In terms of human perception, we tend not to notice when something doesn't happen. We notice, when a flood washes away our house. We don't notice when the house isn't washed away. Only a hydrologist with access to rainfall and weir records over an extended period  would realize that a similar or more intense rainfall event than the one that destroyed property before the beaver returned was a non event with beavers back in the catchment.

Beavers increase the summer flow in streams and rivers.
Due to the effects described above and some others in following paragraphs, stream flow is increased in the summer when it is most needed for farming, drinking, lawn watering and so forth. In some places in the dry South West of the USA, streams which haven't flowed in the summer in living memory started to flow after beavers had returned to their head waters (link). In black and white cases like this, the effect of beaver dams is pretty obvious but who but a hydrologist would notice that the streams flowed more this summer than 10 summers ago when there weren't any beavers in the catchment. Once more, the effects of beavers, while profound, are hard to perceive without historical records of flow rates and rainfall events.

The water holding capacity of the stream is further increased by the excavations beavers do around their pond. They use mud to plaster both dam and lodge and they even dig canals so that they can float logs to their pond. This along with the dam itself, creates a series of wider areas in the stream at each beaver pond and increases water infiltration into the soil, ground water level around the dam, water holding capacity in the river and the size of the eventually formed wetland.

Beavers increase ground water recharge.
If all the water that drains off a catchment into it's streams is unimpeded, it flows down to the sea as fast as the slope and stream characteristics allow. A very rapid wasting of valuable water occurs.  This is especially so if there is a rainy season or a spring  snow pack melt. Some estimates suggest that well over 95% of the water falling in the Canterbury region in New Zealand flows straight down to the sea. Beaver dams increase the amount of water a stream can hold within its banks and hold it on the land for extended periods. The wetted area of the stream is increased. The combined effects of greater wetted area and longer contact between water and soil increases infiltration. Water which seeps into the ground, slowly seeps back into the stream, evening out stream flow over the year.

Better still, water flowing through soils is purified.

Beaver ponds also reduce the hydrological gradient (gradient of the surface of the water table) above the dams by raising the water level in the stream. This further slows the draining of the water from the water shed. All these effect ensure that more water goes down into the ground where it slowly flows back into the streams. The water table is also raised, benefiting anyone with a well. A beaver dam will raise the water table under adjacent land greatly increasing the amount of stored water way above what is in the actual dam. More infiltration results in more flow shifted from the winter to the summer and water in the ground is protected from evaporation ensuring more net flow. In building alluvial plains such as Canterbury in New Zealand where steams fill their beds and then change course, the effect of beaver dams would be especially strong with water flowing out into the adjoining alluvium. On a small scale, this is the same as the land to the East of the Rocky Mountains in the USA and Canada which were produced by a similar process. Farmers on the plains of the USA could benefit greatly from becoming fanatical about protecting beavers above and on their farms.

Beavers ponds clean the stream's water.
Fast running streams keep sediment in suspension. Ponds slow the water so that the sediment can settle out. Besides looking nicer, a stream of clear water is better for a wide range of aquatic animals. Sunlight reaches the bottom and a variety of water plants can grow, attached to bottom rocks and water logged wood. Attached water plants are both food and shelter for even more aquatic organisms. Clear water in downstream rivers is less expensive to process for a city water supply when sediment doesn't have to be settled out of it first and clear water is preferred by trout and salmon.

Beavers produce rich "bottom land".
If you have ever read a western novel, it's likely you came across one of the characters talking about the rich bottom land east of the Rockies (Rocky Mountains). Much of this bounty was created by the beaver. Over the 11,000 or so years since the continental glaciers left the land and for far longer south of the maximum extent of the ice sheet, beavers have been building layer upon layer of dams across the primary, secondary and tertiary streams which drain East through the Great Lakes or South down the Mississippi. Sediment from the young, steep, sediment-producing Rockies has been caught by generations of beaver dams, layered with wood chips, water-log leaves, insect exoskeletons and beaver and ungulate dung to make the rich dark soil that so much agriculture is based on. When the first farm-settlers arrived in North America, the beaver was already gone, trapped almost to extinction by the trappers who sent the pelts back to England to make top hats. The farmers had no inkling of where all this rich dark soil came from and why it was often terraced as you walked along the stream. A terrace, of course, was the filled in area behind a location where generation after generation of beavers had built their dams. With the beaver gone, the mud and stick dam was soon clad with grass and shrubs and effectively disguised.

Beavers Sequester Carbon
Anywhere beavers settle they sequester carbon and this is especially so on streams with high bed load (large amounts of sediment moving down the stream or river). Such streams are ones which start in steep, fast growing mountains such as the Rockies of the USA or the Southern Alps of New Zealand. Not only does the beaver build his dam and lodge from wood but in the quiet pond, leaves, wood chips, twigs and so forth become water logged and sink to the bottom. During spring snow melt or winter rains, more mineral material is carried by the stream, settles in the beaver pond and buries this load of cellulostic material. Half of the dry weight of wood is carbon so this represents a considerable amount of sequestering. A short distance below the bottom of a beaver pond, the oxygen is used up as the water seeps down and the environment is anaerobic. Wood is almost completely refractory under anaerobic conditions.

It doesn't end there. If the beavers abandon a site, it becomes a wetland with all the wetland plants growing where the pond once was. Such plants grow, die and fall into the marsh, also to be preserved as peat. Eventually trees colonize the area, and another family of beavers colonize the site. Typically they build their dam on the site of the former dam, raising the water level and flooding the marsh. The layer of sequestered carbon gets deeper and deeper and forms a larger and larger sponge to hold water and slowly release it. The effect of the beavers increases with each successive colonization.

Beavers increase ecological diversity. While coniferous forests are pretty barren places, deciduous forest create quite a few ecological niches for a variety of animals and plants. With the introduction of beavers, the situation is further improved. Beaver open up an area around their ponds, in rare cases going as far as a hundred meters from the stream to get their favorite food and building material. In the cleared area the sun reaches the ground allowing grass, herbage and bushes to grow. This sort of area becomes the favorite haunt of grazing and browsing animals such as deer. The pond which results from the damming of the stream, provides many niches not available in running water. Sedges, bull rushes and various water weeds grow in the shallow parts of the pond providing more places for everything from dragon fly larvae to trout to ducks. A stream that would otherwise dry up will now flows all year providing water for all the surrounding terrestrial animals and a stable habitat for fish. Animals such as moose will graze in the pond and deer graze along the margins. Some of their dung will be dropped away from the stream where they lay up. In this way, nutrients are kept on the land and even moved up-slope rather than only being flushed down to the sea. Salmon coming up the streams, eaten by bears and other predators also add to the upward transfer of nutrients. With beavers in the head waters of a stream the water is kept clear and attractive for salmon and trout.

If the pond silts up and becomes too shallow or the beavers exhaust the trees in the local area, they sometimes abandon a site. Eventually without the constant repair by the beavers, the dam will breach and the water will begin to drain out. The marshy area left above the dam will be colonized by sedges and other water loving plants and you have a wetland with all their well known benefits to the ecology. Flood peaks are still ameliorated by the wetland and nutrients and silt are still removed from the water. Wetlands also provide many ecological niches not found in either running water or in ponds.

The area will eventually become a meadow as it is colonized by a variety of grasses and as the water continues to drain out and silt is trapped. The meadow provides forage for grazing animals. Beaver meadows of this type are called "Vegas". And while this is going on, trees will be recolonizing the meadow from the edges. Eventually the meadow will disappear and becomes once more a riverine forest, flatter, higher and wider than it was before. At some time in this succession, the beavers will come back and, using the new tree growth, start another colony. The cycle repeats, and another layer of soil is added. Over the centuries, the water holding soil-sponge gets deeper and deeper and the positive effect of the beaver's work increases. No wonder that the First People called the beaver 'the sacred centre of the earth'. In legends of the first nation, the beaver provided the salmon. Another example of the first people understanding a relationship that we are only now beginning to 'discover'.

Beavers remove nutrients from the water. In our agricultural society with increasing levels of nutrients leaching into our water-ways, this characteristic of beaver dams is particularly important. Nutrient removal depends on the detritus cycle. Cellulose from wood chips, uneaten twigs, falling leaves and even the lodge and the dam of the beavers is actually poly-glucose, a natural 'plastic' made of chains of sugar molecules. No multi cellular animal produces the enzyme, cellulase, which can split off these sugar molecules for food. Many bacteria do however. We all know about the rumen of a cow or the gut of a termite that contain bacteria which can break down cellulose. Similar bacteria exist in streams and ponds. They colonize these various bits of cellulose and start to break them down for energy. However they can no more live on pure sugar than you or I can. They are hungry for Nitrates, Phosphates and all the other 'ates' that they use to build their bodies. They scavenge them from the water. These bacteria are equivalent to photosynthetic single celled algae in so far as they form the base of a food chain. The difference is that their source of energy is chemical (the sugar of the cellulose) rather than photic (the energy of the sun). They form the base of the detritus cycle just as the photosynthetic organism form the base of their photosynthetic pyramid of life. Another difference is that they live, attached to the cellulose particles they utilize rather than living in the water column as many single celled algae do. Various detritovours as diverse as worms, insect larvae and even ducks eat this rich source of protein and pass the remaining cellulose, somewhat diminished, through their gut to be recolonized and re-ingested. Once again, nutrients passing down a stream are caught, utilized and often redistributed up-slope in the water-shed by the animals which move away from the stream. Some of the detritus in the pond is buried, especially in spring when larger quantities of sediment are shed from the mountains, and this forms the rich legendary soil of bottom land. Without the beavers, detritus is washed straight down the stream. In the long term, even the dam and lodge of the beaver dam become part of the detritus cycle and part of the newly created bottom land.

Beavers improve salmon recruitment
With Coho at the very least, and probably with other salmon, beaver dams greatly increase the survival of juvenile salmon resulting in vastly improved recruitment into the sea.

When adult salmon migrate up-river, they represent a large pulse of nutrients moving landward from the sea. Many salmon are taken before spawning and some after spawning by a wide range of predators and scavengers.

The classic amount of nutrients transferred from one tropic level to the next is 10%, meaning 10% of the consumed nutrient (fish in this case) becomes 'bear' and that some 90% of the nutrients of the consumed fish are spread, within a day or two, over the surrounding land in the form of dung. The spawning runs, in their pristine state were so large that the predators could only consume a tiny part of the bounty. Large quantities of spent fish, stayed in the river and were swept downstream. In a stream system without lakes or beaver dams, the uneaten bodies of the adult salmon, are fairly rapidly swept down to the sea. Salmon biologists have realized the dynamics of the system for some time and in streams with lakes but with much reduced spawning runs they actually fertilized the lakes to increase the supply of food to the salmon fingerings. In pre-European times, the adult salmon were the source of nutrients to feed the young salmon. LinkLinkLink
LinkBeaver ponds with their rich supply of cellulose are the ideal venues to capture mineralised nutrients from the disintegrating salmon and the ideal mechanism to keep dead salmon from being washed downstream. Floating salmon carcases collect along the shore of the pond or by the dam and salmon which have disintegrated to the point where their air spaces have being breached, sink to the bottom of the pond. A wide variety of fauna eats up the dead salmon and rooted plants, floating plants and phytoplankton take up mineralized nutrients. The significance of all this activity is that nutrients are captured in various forms in the web of life both in the stream and in the surrounding land. The surrounding land slowly gives back some of its nutrients which the beaver dams captured. All this provides more food for the salmon larvae and fingerling after they have used up their yoke.

It wouldn't be much of a surprise if salmon juveniles themselves eat the cellulose detritus, digesting off the protein rich coat of micro and mia fauna and excrete the diminished particle of cellulose to be re-colonized. Whether or not they do feed at this first trophic level, they certainly feed at the next level and undoubtedly ingest considerable amounts of cellulose in the gut of their prey. Chitin from the exoskeletons of any arthropods consumed is excreted by the salmon to also become part of the detritus cycle.

The detritus cycle is not the whole story. Beaver ponds are widened areas in the stream. As such they have a larger sun-collecting area than the undammed stream. Given a supply of nutrients, they increase the amount of photosynthesis going on in the stream by both rooted plants and phytoplankton and hence the potential supply of food for the juvenile fish and the removal of nutrients from the water.

The beaver dams also provide quiet areas for juvenile salmon to grow and provides areas deep enough to protect the juvenile salmon from wading birds. The larger a smolt is when it reaches the sea, the greater its chance of survival. Not only do beaver ponds provide feed for the young salmon but also eliminate the need to constantly fight the current and burn up energy which is needed for growth.

I have occasionally seen suggestions that the beaver dams are barriers to the upstream migration of salmon. People who suggest this have clearly never seen salmon vaulting a waterfall. A beaver dam is just a hop, skip and a jump for a sex crazed salmon heading upstream for its once in a lifetime act of procreation. When you consider it from an evolutionary point of view, this isn't surprising. Beavers and salmon have evolved together for Milena and it is hardly surprising that a fish which evolved with the beaver dams in every possible place in the watershed where one could be built, not only isn't disadvantaged by beaver dams but has adapted to benefit from them.

Actually the above paragraph is a little unfair. A beaver dam without enough water immediately downstream can form a barrier to salmon. The salmon need enough of a plunge pool to get up some speed to leap the dams. This can be a problem early in spring before snow melt and spring rains swell the streams. It can also be a problem with a new dam if it is built in a location such that there is no depth of water just downstream. As soon as a stream fills up enough to give the salmon a fair run at it, beaver dams are no more than a little early morning exercise for migrating salmon. In addition, a new dam will usually develop a plunge pool after a few freshets. Once again, evolution and history are the best place to look for an answer to the question of beaver stopping salmon migration. Historically, salmon runs were at least two orders of magnitude larger than they are today in most North American streams. At that time, beavers had colonized every even marginally suitable location. It is abundantly clear that even if sometimes an individual beaver dam can stop the upstream movement of salmon, over all, beaver dams are not detrimental to salmon. Both the weight of evidence and simple logic is that they are highly beneficial.

Incidentally, it is interesting to note that from 1818, following an agreement that gave the USA rights to the Columbia watershed, the Hudson Bay company had a policy of extirpating the beaver in the Columbia catchment to discourage American trappers. As the beaver disappeared,so did the salmon.

This happened long before there were any of the other influences extant that we associate with the decline of the salmon runs such as logging, farming and large man made dams.

LinkBeavers increase power generation
Hydroelectric dams have two purposes. The first is to create enough head to generate electricity. The greater the head, the more electricity that can be generated from a given quantity of water. The second purpose is to store water so that power can, be generated, to a large extent, when it is needed. the greatest reducer of gross power generation is a seasonal water flow. If lots of water flows during a rainy season or during snow melt, often much of the water must be allowed to flow over the spillway without going through the generators. To capture this water, larger more expensive dams must be built. A river with beavers in all the up slope catchment streams feeds the water to its river more evenly, transferring water from the wet to the dry season. This increases the total amount of electricity which can be generated from the same amount of river flow and allows the same power to be generated from smaller dams.

Beavers increase hydro lake life
Streams, especially from steep mountains, contain suspended sediment and push a bed load of coarser material along the bottom of their beds. In the most extreme cases, you get braided rivers as soon as the stream leaves the foot hills of the mountains and begins to deposit its load, jump its banks and establish new pathways. Any stream carries some mineral material. When a stream reaches a pond or lake, its velocity slows and this material settles out of the water. In the case of bed load, consisting of coarse material, this material settles out immediately forming a delta. Finer material travels further to settle out all over the bottom of the lake or pond. With beaver dams distributed through the catchment of a hydro dam, this material is intercepted before it reaches the hydro reservoir. The beavers, when their pond gets too shallow, either abandon the site or build the dam higher. An abandon site turns into a wetland which still settles out sediment, forms a meadow and eventually a forest. Beavers come back and build another dam with the new trees and another layer of sediment is captured. Over the Milena, beaver dams can fill up valleys with deep rich water holding soil and their value to downstream facilities, including generating reservoirs increases.

Beavers attract tourists.
People find it simply amazing just to view the works of this furry little rodent. Add to the experience an explanation of all the benefits that the beaver brings to the environment and the increasingly ecologically aware public find beavers fascinating. It is hard to beat a beaver dam as a station on an ecological walk or bird watching tour. A trailer park or camping ground fortunate enough to have a beaver dam on site has an attraction that their competitors can't rival. The ambiance, the feel good factor towards the business is really enhanced by the experience of seeing the camp living in harmony with the beaver.

Beaver Damage

How, though, do we deal with the beavers that are washing away a road or cutting down fruit trees on the side of the orchard near the stream. There are solutions to all of these problems, some of them expensive, most not. Wide deep box culvert have been tried but are expensive and don't always work. A relatively cheap fence can be put between the beavers and the fruit trees or each vulnerable tree can be ringed by wire mesh. Beavers hate to be separated from their stream which is their safe refuge. If a beaver does get up-slope of a fence he will become truly frantic until he finds a way around or through the fence. A little experimentation and observation will show the type and extent of fence needed to keep the beavers from doing damage. Go to for more information on living in harmony with beavers and how to build beaver deceivers.

Prehistoric man and Beavers
There is some speculation based on logic but limited archaeological evidence that early man gained considerably from the beaver.  I'm not talking about the obvious effects which are detailed elsewhere in this blog but more immediate benefits.

Beaver fell more trees than they need which they will  use if there is a breach in the dam or if it is necessary to raise or reinforce it during high rainfall events.  When you only have a Flint axe to cut down trees, how much easier to go and pick up what you need from around a beaver pond.  Even the branches which have already being incorporated into a dam can be pulled out and used.  This is so not only for wood for construction making handles (from well cured wood) but even fire wood.  The disassembly of a beaver dam would provide wood for the winter for an Indian Tepee, especially if collected in spring and allowed to dry.

A beaver dam also provides a convenient bridge to cross a stream dry shod.

Cattails grow in the shallows of beaver dams and the wetlands left over if the beavers desert the location.  They are a source of flour from the pollen and from the starchy roots, fire drills from the dried stems and a source fresh cooking vegetables from the center of young shoots.

Of course the beaver itself provides a very welcome easily captured meal and an unsurpassed fur for winter clothing and bedding.

A beaver dam is also a convenient place to sit and fish with fairly deep water right beside the fisherman and during the salmon migration, the salmon will have to jump the dam and can be caught in a hand net.  Perhaps that is where the game of Lacrosse started

Attracting Beavers

And what about encouraging beavers. The best thing you can do is to plant any of the wide variety of copicing deciduous trees over a wide swath on both sides of your stream. The beavers will do the rest. In early spring, cut down a copicing type tree. (almost any deciduous tree of Europe or North America). Cut it into arm length truncheons, sharpen the lower end . Pound these truncheons into the ground along your stream. For smaller branches, of a size that can be cut with a pair of pruning shears, use a steel bar to punch a hole in the ground and pop them in. Heel in the soil around them. As long as the ground has a bit of water in it, most of the truncheons and small branches will take root and grow into trees. Willow is unbelievable. I have seen willow mulch; willow branches which went through a mulcher and were then spread on the garden, break out in a lawn of little willow trees and poplars will even copice from roots left in the ground. In cattle country, cattle must be kept away from the stream in an area where you want beavers to establish.

Homo industrialis (that's us) is a control freak. We insist on putting our houses on flood plains and then get the Army Core of Engineers to canal the Mississippi so that our houses don't flood. We put shrimp ponds in the middle of mangrove forests and wonder why we get storm surge damage. We build houses in the low lands of New Orleans despite sure and certain knowledge that the land is sinking, sea level is rising, storms are getting worse and at some time in the future it will be flooded. We have behaved the same way with wetlands and drained them wherever we found them for their rich agricultural soils. Realization has dawned on us very slowly how valuable wetlands are for the good of the whole country. We are finally realising that the beaver provides an inexpensive way of reestablishing wetlands.

Every generation sees the country as it is when they are born and only has that vision as a basis of comparison. There is little collective memory of what it was like 2, 3 or 4 generations ago to compare with the present. And worse still, the first farmers in North America, had no chance to see the beavers. They had been eliminated by the time most farmers arrived to homestead.

With the beaver, we have the chance to restore wetlands all around our countries and with almost no cost. The price is the flooding of some land, which will then go out of agricultural production. We may also have to install a "beaver deceiver" or two in individual locations to keep a road from being washed away. We may even have to move bits of some roads or paths to go around a beaver pond instead of through it. Part of the problem is that the good that beavers do is long term, and hard to see with our senses while the problems they cause are visible but really insignificant.

Perhaps it would be more accurate to say that the positive results from beavers are easy to see but it is hard to make the connection between what we see who caused the change. If a river flows less in the winter, mitigating floods, and more in the summer when the water is most needed, how many of us will make the connection that this is caused by beavers returning to the head-waters of the river. If the river runs clear and steadily instead of silty and pulsating, how many of us will realize that the resulting increased salmon runs are due to the beaver. If our rivers have less nutrients washing down stream, how many of us will realize that the reduced eutrophication of our lakes and estuaries and the recovery of our coral reefs are due to the return of the beaver. And yet destruction by the beaver is evident. A pathway in a trailer park gets flooded. Instead of building a new path the owner gets The Parks Board to destroy the beaver dam. A fruit tree is cut down. Instead of putting some cheap chicken wire around vulnerable trees, we shoot the beaver. Our view of life is very myopic.

After the Beaver Returns

The reintroduction of the beaver to a catchment will bring huge benefits but the real question is what will we do with the bounty. Our rivers will flow with more net water, clearer water, a bigger proportion of the net water in the dry period and with less entrained nutrients. Then what do we do. Since there is more available water, do we allow more extraction by agriculture. Since the water is less polluted, do we allow agriculture and industry to leak more waste into the water shed. If so, we will rapidly get right back to the situation that existed before the return of the beaver. On the other hand, we might decide to keep water extraction at it's present levels and to allow the same (or even less) pollution to escape agriculture and industry. If we follow this latter path, we will have a much improved environment to enjoy. And just a little warning. If we do allow more pollution and more water extraction after the return of the Beaver, we might make the environment so bad that the beaver will die out. Just imagine what our environment would be like then with the new levels of river abuse and without the beaver to mitigate the damage we cause.

Further Reading
For a most amazing account of the result of bringing back the beaver to an area, read Three Against the Wilderness by Eric Collier.


William Hughes-Games said...

Since writing this article, New Scientist has come out with an article on the beaver. See Aug 25, 2007 Page 42. It appears that early man had a much closer relationship with beavers than previously thought. They obtained building material, good hunting, good fishing, good foraging, inspiration for coppicing (and possibly trees adapted to coppicing) and paths across streams.

Anonymous said...

Hi, very interesting post, greetings from Greece!