Ecology North American beaver

1 ecology

1.1 effects on stream flows , water quality
1.2 effects on bird abundance , diversity
1.3 effects on trout , salmon
1.4 effects on riparian trees , vegetation
1.5 beavers , stream restoration

ecology

the beaver trapped out , extirpated in north america because fur , castoreum highly sought after. beaver furs used make clothing , beaver hats. in united states, extensive trapping began in 17th century, more 10,000 beaver per year taken fur trade in connecticut , massachusetts between 1620 , 1630. 1630 1640, around 80,000 beavers taken annually hudson river , western new york. 1670 onwards, hudson s bay company sent 2 or 3 trading ships bay every year take furs england canada. archaeological , historical evidence suggests beaver ponds created moth-hole habitats in deciduous forest dominated eastern north america. nonforest habitat attracted both native american , colonial hunters abundant fish, waterfowl, , large game attracted riparian clearings created these aquatic mammals. first colonial farmers attracted fertile, flat bottomlands created accumulated silt , organic matter in beaver ponds.

as eastern beaver populations depleted, english, french, , american trappers pushed west. of westward expansion , exploration of north america driven quest animal s fur. before 1849 california gold rush, earlier, 19th-century california fur rush drove earliest american settlement in state. during 30 years (1806–1838) of era of mountain man, west missouri california , canada mexico thoroughly explored , beaver brought brink of extinction.

with protection in late 19th , 20th centuries, current beaver population has rebounded estimated 10 15 million; fraction of estimated 100 200 million north american beavers before days of fur trade.

these animals considered pests in parts of range because dams can cause flooding, or because habit of felling trees can pose danger people, in charlotte, north carolina s park road park. because persistent in repairing damage dam, historically relocated or exterminated. nonlethal methods of containing beaver-related flooding have been developed. 1 such flow device has been used both canadian , u.s. governments, called beaver deceivers or levelers, invented , pioneered wildlife biologist skip lisle.

the beaver keystone species, increasing biodiversity in territory through creation of ponds , wetlands. wetlands formed , riparian habitats enlarged, aquatic plants colonize newly available watery habitat. insect, invertebrate, fish, mammal, , bird diversities expanded.

effects on stream flows , water quality

beaver ponds increase stream flows in seasonally dry streams storing run-off in rainy season, raises groundwater tables via percolation beaver ponds. in recent study using 12 serial aerial photo mosaics 1948 2002, impact of return of beavers on openwater area in east-central alberta, canada, found mammals associated 9-fold increase in openwater area. beavers returned area in 1954 after long absence since extirpation fur trade in 19th century. during drought years, beavers present, 60% more open water available same areas during previous drought periods when beavers absent. authors concluded beavers have dramatic influence on creation , maintenance of wetlands during extreme drought.

from streams in maryland coastal plain lake tahoe, beaver ponds have been shown remove sediment , pollutants, including total suspended solids, total nitrogen, phosphates, carbon, , silicates, improving stream water quality. in addition, fecal coliform , streptococci bacteria excreted streams grazing cattle reduced beaver ponds, slowing currents lead settling of bacteria in bottom sediments.

the term beaver fever misnomer coined american press in 1970s, following findings parasite giardia lamblia, causes giardiasis, putatively carried beavers. further research has shown many animals , birds carry parasite, , major source of water contamination humans. recent concerns point domestic animals significant vector of giardia, young calves in dairy herds testing high 100% positive giardia. new zealand has giardia outbreaks, no beavers, whereas norway has plenty of beavers, had no giardia outbreaks until (in southern part of norway densely populated humans no beaver).

effects on bird abundance , diversity

canada goose nest on beaver lodge

beavers waterfowl creating increased areas of water, , in northerly latitudes, thaw areas of open water, allowing earlier nesting season. in study of wyoming streams , rivers, watercourses beavers had 75-fold more ducks without.

trumpeter swans (cygnus buccinator) , canada geese (branta canadensis) depend on beaver lodges nesting sites. canada s small trumpeter swan population observed not nest on large lakes, preferring instead nest on smaller lakes , ponds associated beaver activity.

beavers may benefit birds frequenting ponds in several additional ways. removal of pondside trees beavers increases density , height of grass–forb–shrub layer, enhances waterfowl nesting cover adjacent ponds. both forest gaps trees had been felled beavers , gradual edge described complex transition pond forest intermixed grasses, forbs, saplings, , shrubs associated greater migratory bird species richness , abundance. coppicing of waterside willows , cottonwoods beavers leads dense shoot production provides important cover birds , insects on feed. widening of riparian terrace alongside streams associated beaver dams , has been shown increase riparian bird abundance , diversity, impact may important in semiarid climates.

as trees drowned rising beaver impoundments, become ideal nesting sites woodpeckers, carve cavities attract many other bird species, including flycatchers (empidonax spp.), tree swallows (tachycineta bicolor), tits (paridae spp.), wood ducks (aix sponsa), goldeneyes (bucephala spp.), mergansers (mergus spp.), owls (tytonidae, strigidae) , american kestrels (falco sparverius). piscivores, including herons (ardea spp.), grebes (podicipedidae), cormorants (phalacrocorax ssp.), american bitterns (botaurus lentiginosa), great egret (ardea alba), snowy egret (egretta thula), mergansers, , belted kingfishers (megaceryle alcyon), use beaver ponds fishing. hooded mergansers (lophodytes cucullatus), green heron (butorides virescens), great blue heron (ardea herodias) , belted kingfisher appeared more in new york wetlands beaver active @ sites no beaver activity.

by perennializing streams in arid deserts, beavers can create habitat increases abundance , diversity of riparian-dependent species. example, such upper san pedro river in southeastern arizona, reintroduced beavers have created willow , pool habitat has extended range of endangered southwestern willow flycatcher (empidonax trailii extimus) southernmost verifiable nest recorded in 2005.

effects on trout , salmon

salmon (oncorhynchus nerka) jumping beaver dam

beaver ponds have been shown have beneficial effect on trout , salmon populations. many authors believe decline of salmonid fishes related decline in beaver populations. research in stillaguamish river basin in washington found extensive loss of beaver ponds resulted in 89% reduction in coho salmon (oncorhynchus kisutch) smolt summer production , equally detrimental 86% reduction in critical winter habitat carrying capacity. study found beaver ponds increased smolt salmon production 80 times more placement of large woody debris. swales , leving had shown on coldwater river in british columbia off-channel beaver ponds preferentially populated coho salmon on other salmonids , provided overwintering protection, protection high summer snowmelt flows , summer coho rearing habitat. presence of beaver dams has been shown increase either number of fish, size, or both, in study of brook trout (salvelinus fontinalis), rainbow trout (oncorhynchus mykiss) , brown trout (salmo trutta) in sagehen creek, flows little truckee river @ altitude of 5,800 feet in northern sierra nevada. these findings consistent study of small streams in sweden, found brown trout larger in beaver ponds compared in riffle sections, , beaver ponds provide habitat larger trout in small streams during periods of drought. similarly, brook trout, coho salmon, , sockeye salmon (oncorhynchus nerka) larger in beaver ponds in unimpounded stream sections in colorado , alaska. in recent study on headwater appalachian stream, brook trout larger in beaver ponds.

contrary popular myth, beaver dams not pose barriers trout , salmon migration, although may restricted seasonally during periods of low stream flows. in meta-review of studies claiming beaver dams act fish passage barriers, kemp et al. found 78% of these claims not supported data. in 2013 study of radiotelemetry-tagged bonneville cutthroat trout (oncorhynchus clarki utah) , brook trout (salvelinus fontinalis) in utah, both of these fish species crossed beaver dams in both directions, including dams 2 metres (6.6 ft) high. rainbow, brown, , brook trout have been shown cross many 14 consecutive beaver dams. both adults , juveniles of coho salmon, steelhead trout, sea run cutthroat (oncorhyncus clarki clarki), dolly varden trout (salvelinus malma malma), , sockeye salmon able cross beaver dams. in southeast alaska, coho jumped dams high 2 meters, found above beaver dams , had highest densities in streams beaver. in oregon coastal streams, beaver dams ephemeral , wash out in high winter flows rebuilt every summer. migration of adult atlantic salmon (salmo salar) may limited beaver dams, presence of juveniles upstream dams suggests dams penetrated parr. downstream migration of atlantic salmon smolts unaffected beaver dams, in periods of low flows. two-year-old atlantic salmon parr in beaver ponds in eastern canada showed faster summer growth in length , mass , in better condition parr upstream or downstream pond.

the importance of winter habitat salmonids afforded beaver ponds may important (and underappreciated) in streams without deep pools or ice cover makes contact bottom of shallow streams. enos mills wrote in 1913, 1 dry winter stream...ran low , froze bottom, , trout in survived in deep holes of beaver ponds. cutthroat trout , bull trout noted overwinter in montana beaver ponds, brook trout congregated in winter in new brunswick , wyoming beaver ponds, , coho salmon in oregon beaver ponds. in 2011, meta-analysis of studies of beaver impacts on salmonids found beaver net benefit salmon , trout populations improving habitat (building ponds) both rearing , overwintering , conclusion based on half time on scientific data. in contrast, cited negative impact of beavers on fishes barriers migration, although conclusion based on scientific data 22% of time. found when beaver dams present barriers, these short-lived, dams overtopped, blown out, or circumvented storm surges.

by creating additional channel network complexity, including ponds , marshes laterally separated main channel, beavers may play role in creation , maintenance of fish biodiversity. in off-mainstem channels restored beaver on middle section of utah s provo river, native fish species persist when have been extirpated in mainstem channel competition introduced non-native fish. efforts restore salmonid habitat in western united states have focused on establishing large woody debris in streams slow flows , create pools young salmonids. research in washington found average summer smolt production per beaver dam ranges 527 1,174 fish, whereas summer smolt production pool formed instream large woody debris 6–15 individuals, suggesting re-establishment of beaver populations 80 times more effective.

recently, beaver have been discovered living in brackish water in estuarine tidal marshes chinook salmon (oncorhynchus tshawytscha) densities 5 times higher in beaver ponds in neighboring areas.

effects on riparian trees , vegetation

tree felled beaver (c. c. canadensis), diameter 20 cm

conventional wisdom has held beavers girdle , fell trees , diminish riparian trees , vegetation, opposite appears true when studies conducted longer-term. in 1987, beier reported beavers had caused local extinction of quaking aspen (populus tremuloides) , black cottonwood (populus trichocarpa) on 4–5% of stream reaches on lower truckee river in sierra nevada mountains; willow (salix spp.) responded regrowing vigorously in reaches. further speculated without control of beaver populations, aspen , cottonwood go extinct on truckee river. not have aspen , cottonwood survived ongoing beaver colonization, recent study of ten sierra nevada streams in lake tahoe basin using aerial multispectral videography has shown deciduous, thick herbaceous, , thin herbaceous vegetation more highly concentrated near beaver dams, whereas coniferous trees decreased. these findings consistent of pollock, reported in bridge creek, stream in semiarid eastern oregon, width of riparian vegetation on stream banks increased several-fold beaver dams watered dry terraces adjacent stream. in second study of riparian vegetation based on observations of bridge creek on 17-year period, although portions of study reach periodically abandoned beaver following heavy utilization of streamside vegetation, within few years, dense stands of woody plants of greater diversity occupied larger portion of floodplain. although black cottonwood , thinleaf alder did not resprout after beaver cutting, grew seeds landing on freshly exposed alluvial deposits subsequent beaver activity. therefore, beaver appear increase riparian vegetation given enough years aggrade sediments , pond heights sufficiently create widened, well-watered riparian zones, in areas of low summer rainfall.

the surface of beaver ponds typically @ or near bank-full, small increases in stream flows cause pond overflow banks. thus, high stream flows spread water , nutrients beyond stream banks wide riparian zones when beaver dams present.

finally, beaver ponds may serve critical firebreaks in fire-prone areas.

beavers , stream restoration

in 1930s, u.s. government put 600 beavers work alongside civilian conservation corps in projects stop soil erosion streams in oregon, washington, wyoming, , utah. @ time, each beaver, initial cost $5, completed work worth estimated $300. in 2014, review of beaver dams stream restoration tools proposed ecosystem approach using riparian plants , beaver dams accelerate repair of incised, degraded streams versus physical manipulation of streams.

the province of alberta published booklet providing information on using beaver stream restoration.

utah published beaver management plan includes reestablishing beavers in ten streams per year purpose of watershed restoration each year 2010 through 2020.

in pilot study in washington, lands council reintroducing beavers upper methow river valley in eastern cascades evaluate projections if 10,000 miles of suitable habitat repopulated, 650 trillion gallons of spring runoff held release in arid autumn season. beavers exterminated in methow watershed 1900s fur trappers. project developed in response 2003 washington department of ecology proposal spend as $10 billion on construction of several dams on columbia river tributaries retain storm-season runoff. of january, 2016, 240 beavers released upper methow river @ 51 sites had built 176 beaver ponds, storing millions of gallons of water in semiarid east region. 1 beaver passive integrated transponder tagged , released in upper part of methow valley, swam mouth of methow river, okanogan river canada–us border, journey of 120 miles (190 km).