Browse selection by beaver: Effects on riparian forest composition
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Authors: C. A. Johnston, and R. J. Naiman
Date: 1990
Journal: Canadian Journal of Forest Research
Volume: 20
Number:
Pages: 1036-1043
Summary of Methods: During the summer of 1985, the effects of browsing by beaver were studied at two beaver ponds in Minnesota (46° 50’ N, 92° 11’ W). Pond one (colonized from 1980-1985) was located on a first-order stream while pond two (colonized for two years in the late 1970s, abandoned, and then recolonized in 1985) was on a second-order stream. Transects stretching from the pond edge to the end of beaver herbivory were established to set up to 66 plots at each pond. The plots included browsed and unbrowsed areas. Along with stem density and frequency, stumps eaten by beaver, and stems of all woody species were measured for diameter at stump height. This information was then used to calculate basal area, species composition, and to compare post browsed stands to pre-browsed conditions. In addition, pre- and post- colonization changes were calculated using the comparisons between browsed and unbrowsed plots.
Article Summary / Main Points: During colonization, beavers utilized 42% of the aboveground tree biomass around pond one (colonized from 1980-85) and 24% from around pond two (recolonized in 1985). Trembling aspen in the greater than five cm class were selected preferentially (>60 %) by beavers at both ponds. Pond one had a lower stem density and basal area for all woody species ≥ five cm after colonization. Pond two showed little differences in steam density and basal area between pre-recolonization and during colonization. Beavers can utilize large amounts of woody biomass in northern forests and alter stand characteristics given enough time.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: 91B Wisconsin and Minnesota Sandy Outwash 93A Superior Stony and Rocky Loamy Plains and Hills, Western Part
Agrovoc Control Words: Riparian zones Rangelands Wildlife
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: beaver, castor canadensis, trembling aspen, populus tremuloides, species composition, selective herbivory, biomass, beaver ponds, stem diameter
Annotation: This study took place in a boreal forest; therefore, biomass removal and species composition changes by beavers would be different in other less forested rangelands. Having only measured these stands one time reduces the ability to understand long-term trends of beaver herbivory. As time increases, herbivory can alter both abiotic and biotic factors and how those factors change over time is important to understand. In addition, the inclusion of an abandoned pond could have helped in demonstrating the effects of beavers on aspen stands.
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