Effects on riparian trees and vegetation North American beaver

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.