Document Type

Thesis - Open Access

Award Date

1987

Degree Name

Master of Science (MS)

Department

Wildlife and Fisheries Science

Abstract

Habitat utilization and lodge site selection by beaver (Castor canadensis) were investigated during 1985 and 1986 along the Big Sioux River in eastern South Dakota. Because livestock grazing has affected the number and size of trees available for beaver use, the study area was portioned into grazed, ungrazed, and farmed habitat. Diameter at breast height (DBH) of trees in grazed areas was greater (p < 0.01) than in ungrazed or farmed areas. Almost half (48%) of the trees in ungrazed areas were small (DBH < 7.5 cm), while a majority (58%) of the trees in grazed areas had large diameters (DBH > 30 cm). Beaver activity was evident on 286 of 2410 (11.8%) trees (DBH > 2.5 cm) and 756 of 7,794 (9.7%) stems (DBH < 2.5cm) sampled. A greater proportion (p < 0.01) of trees were cut by beavers in ungrazed than in grazed areas. Beaver did not select tree species for cutting according to availability (p < 0.01). Green ash (Fraxinus pennsylvanica) was selected for cutting while both boxelder (Acer negundo) and hawthorn (Crataegus mollis) were selected against. Sandbar willow (Salix exigua) stems were important for food and building materials. Trees cut by beaver were significantly smaller in diameter (p < 0.01) than uncut trees. Mean distance from water of cut trees was also less (p < 0.01) than for uncut trees. Over half (52%) of the trees damaged by beaver were not killed and either resprouted or remained alive and standing. Of 8 variables examined at lodge sites, analysis indicated that the 2 most important factors in beaver lodge site selection were riverbank slope and horizontal cover density between 0.9 m and 1.8 m above ground (read from 10 m). Mean slope of the riverbank at lodge sites (40.7 degrees) was greater (p < 0.01) than at control sites (26.7 degrees), while mean horizontal cover density between 0.9 m and 1.8 m (read from 10 m) was also greater (p < 0.01) at lodge sites (53%) than at control sites (28%). Ungrazed habitat was selected by beaver for lodge sites, and grazed areas were selected against. Although 40% of the study area was ungrazed, 27 of 33 (82%) active lodges were located in these areas. Ungrazed areas along the Big Sioux River are important for beaver populations and selection for these areas by beaver reflects habitat quality.

Library of Congress Subject Headings

Beavers -- Habitat
American beaver -- South Dakota
Big Sioux River (S.D. and Iowa)

Description

Includes bibliographical references (pages 53-58)

Format

application/pdf

Number of Pages

70

Publisher

South Dakota State University

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