. The Canadian field-naturalist. 158 The Canadian Field-Naturalist Vol. 87 26 24 22 20 18 a> a ^* a> O 14 c 12 u q! 10 lllllll Scirpus volidus and Scirpus ( Hordeum jubatum and Glycer I I I § 1966 1967 1966 1967 1966 1967 1966 1967 2 3 Zone. 1966 1967 1966 1967 1966 1967 1966 1967 2 3 Zones Figure 3. Percentage coverage of residual vegetation on islands A and C, May 25, 1966 and 1967. Zones 1 and 2 on Island A and Zones 2 and 3 on Island C were sprayed during July 1966. erage of each species increased throughout the summer. Application of herbicide in mid-July of 1966 reduced the coverag
. The Canadian field-naturalist. 158 The Canadian Field-Naturalist Vol. 87 26 24 22 20 18 a> a ^* a> O 14 c 12 u q! 10 lllllll Scirpus volidus and Scirpus ( Hordeum jubatum and Glycer I I I § 1966 1967 1966 1967 1966 1967 1966 1967 2 3 Zone. 1966 1967 1966 1967 1966 1967 1966 1967 2 3 Zones Figure 3. Percentage coverage of residual vegetation on islands A and C, May 25, 1966 and 1967. Zones 1 and 2 on Island A and Zones 2 and 3 on Island C were sprayed during July 1966. erage of each species increased throughout the summer. Application of herbicide in mid-July of 1966 reduced the coverage of broad-leaved forms by 85 %, relative to the untreated zones, in August 1966 (Figure 4). Nettles were ef- fectively eliminated; grasses increased by 219% on the same areas 1 year after treatment. Weekly application of 2,4-D ester through- out the summer of 1967 reduced the coverage of nettles and thistles in August from an aver- age of about 30% to about 3% 1 year later (Figure 5). By contrast, the coverage of grasses in August increased from an average of about 11% to about 27%. The overall effect was to decrease plant coverage in 1967. The effect on nettles and thistles of herbi- cide apphcation in mid-July 1966 and weekly throughout June, July, and August of 1967, was much more dramatic (Figure 6). The single treatment in 1966 reduced the coverage of these genera by August, and the multiple treatment in 1967 virtually eliminated them. Again, the coverage of grasses increased re- markably from an average of about 10% in August 1966 to about 41% in August 1967. Thus, all treatments with 2,4-D ester reduced the coverage of broad-leaved forms, virtually eliminating some such as nettles, but allowing grasses to expand their distribution and increase their coverage. The impact of these changes in coverage of old and new growth of vegetation, on nesting waterfowl, would depend on the relative at- tractiveness of these various plants to the Please note that these images
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