. The Canadian field-naturalist. 426 The Canadian Field-Naturalist Vol. 90 f 4 ,\X~. J Figure 1 A. Enlarged print of 35-mm High Speed Ektachrome aerial photograph of flowage 300, 20 May 1971. The larger flowage area in early spring required photography from a higher altitude and thus a smaller scale for complete coverage. The lack of detail in the surrounding uplands was due to scattered shadows cast by the leafless hardwood crowns of the light-toned forest floor litter. Water levels were high, flooding extensive areas of trees and shrubs along the flowage margin. Emergent vegetation was spars
. The Canadian field-naturalist. 426 The Canadian Field-Naturalist Vol. 90 f 4 ,\X~. J Figure 1 A. Enlarged print of 35-mm High Speed Ektachrome aerial photograph of flowage 300, 20 May 1971. The larger flowage area in early spring required photography from a higher altitude and thus a smaller scale for complete coverage. The lack of detail in the surrounding uplands was due to scattered shadows cast by the leafless hardwood crowns of the light-toned forest floor litter. Water levels were high, flooding extensive areas of trees and shrubs along the flowage margin. Emergent vegetation was sparse and confined to the shallow water. Four active dams were present. The main lodge was visible near the dam in the main pool. identified on the 10 study flowages. Vegetation differences from spring to summer were easily quantified. Differences from midsummer to fall could not be quantified from the aerial photo- graphs alone. Changes in gross flowage area could be detected at any season. In flowages where the beaver were able to maintain water levels throughout the year, changes in vege- tation were qualitative as the season progressed. In those flowages with widely variable water levels, quantitative changes outweighed the qualitative differences resulting from seasonal plant succession. Sharp pictures were obtained at various air- speeds (129-160 km/h) even as low as 152 m above the flowage. Delineation of the flowage shoreline was possible even in dense stands of willows (Salix spp). and alders {Alnus spp.). Water standing in newly flooded areas was clearly visible through the still living tree and shrub crowns. Airspeeds as slow as possible were preferable for photographer comfort, care being taken not to yaw the aircraft. Operating the hand-held camera became difficult only in accelerated steep banks. The mapping technique permitted successive measurements of the vege- tative cover throughout the open-water season. After the initial location of the control points, it. Plea
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