Changes in Composition of Ground Water, Soil Fertility, and Forest Growth Produced by the Construction and Removal of Beaver Dams

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Abstract
The residual effects of flooding and subsequent drainage were investigated on several typical beaver flowages in Marinette County, Wisconsin. The extremely low negative oxidation-reduction potential of the surface and ground water samples indicated that the removal of the dam drains the flowage only superficially, but not internally. The analyses of submerged soils revealed several unfavorable changes produced by impounded water, namely: saturation of soil with H2S, ac-cumulation of ferrous Fe, and fixation of P. Greenhouse trials showed that prolonged inundation destroys mycorrhizal fungi. The lack of these microorganisms appears to be one cf the obstacles retarding the re-invasion of forest trees on drained flowages. The detn. of annual increment on strip sample plots proved that a rise of the ground water table depresses the growth of forest stands on neighboring lowlands. The beneficial effect of a raised ground water table on upland stands was found to be insignificant. The lowering of the ground water due to drainage creates a danger of drought injury to both upland and lowland stands. The advisability of dynamiting the dam is questioned, and systematic observations of water courses and measures preventing beaver settlements in undesired locations are suggested.

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