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Beaver in the Sierra Nevada
(詳細はNorth American beaver (''Castor canadensis'') had a historic range that overlapped the Sierra Nevada in California. Before the European colonization of the Americas, beaver were distributed from the arctic tundra to the deserts of northern Mexico. The California Golden beaver subspecies (''Castor canadensis subauratus'') was prevalent in the Sacramento and San Joaquin River watersheds, including their tributaries in the Sierra Nevada. Recent evidence indicates that beaver were native to the High Sierra until their extirpation in the nineteenth century.
Until recently, beavers were considered non-native pests. Beavers and their dams are still being removed by wildlife managers in the Sierra Nevada despite evidence of being native mammals and of their beneficial effects on biodiversity for fish and other species in mountain wetland ecosystems.
==Historical range and distribution==
In 1916, Harold Bryant wrote in ''California Fish and Game'', "The beaver of our mountain districts has been entirely exterminated and there are but a few hundred survivors to be found along the Sacramento, Colorado and San Joaquin Rivers." Earlier, in 1906, Frank Stephens wrote in "California Mammals" that Castor canadensis' historic range was from the "Pacific slope from Alaska to central California east to and including the Sierra Nevada and Cascade Mountains" and adds "In most parts of California the presence of beavers is only made known by the stumps of the trees and saplings that they have cut." McIntyre hypothesized that beaver were trapped out of the Sierra early in the nineteenth century by trappers before records could be kept.〔 Other early twentieth century naturalists (Grinnell, Tappe, etc.) questioned whether the California Golden beaver dwelt above of elevation in the Sierra. Recently novel physical evidence has demonstrated that beaver were native to the Sierra until at least the mid-nineteenth century, via radiocarbon dating of buried beaver dam wood uncovered by deep channel incision in two locations in Red Clover Creek in the Feather River watershed. That report was supported by a summary of indirect evidence of beaver including reliable observer accounts of beaver in multiple watersheds from the northern to the southern Sierra Nevada, including its eastern slope.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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