. The Canadian field-naturalist. Natural history; Sciences naturelles. rf Wiggirt***-*-'- Control 29 May 12 June 26 June Treatment Date 10 July 24 July Figure 3. Final root and shoot mass of mature Pale Swallow-wort plants clipped on various dates. Values are means + SE. Clipping date had a significant effect on mean shoot mass (Kruskal-Wallis test, H = , df = 5, P < ) but there was no difference in mean root mass among treatments (Kruskal-Wallis test, H = , df = 5, P = ). Ranked means that were significantly different (P < ) according to Games and Howell's (1976
. The Canadian field-naturalist. Natural history; Sciences naturelles. rf Wiggirt***-*-'- Control 29 May 12 June 26 June Treatment Date 10 July 24 July Figure 3. Final root and shoot mass of mature Pale Swallow-wort plants clipped on various dates. Values are means + SE. Clipping date had a significant effect on mean shoot mass (Kruskal-Wallis test, H = , df = 5, P < ) but there was no difference in mean root mass among treatments (Kruskal-Wallis test, H = , df = 5, P = ). Ranked means that were significantly different (P < ) according to Games and Howell's (1976) multiple com- parisons test are assigned different letters. did differ from both 10 and 24 July treatments. The 10 and 24 July treatment plants were not significantly different from one another but they did differ signifi- cantly from all other treatment groups. Seed production was greatly affected by clipping treatments (Table 1). Experimentally cut plants showed a significant decline in their reproductive output in com- parison to uncut controls (Kruskal-Wallis, H = df = 5, P < ). The Games-Howell post-hoc test revealed that the clipping treatments were not signifi- cantly different from one another. No fruit produc- tion was observed until 26 June, and those plants that produced seeds despite having been clipped (29 May and 12 June cutting treatments) did so by 24 July and 7 August, respectively. Plants cut on or after 26 June failed to produce any seeds. Response of seedlings to differentially timed above- ground tissue loss Seedlings in the six treatments did not differ sig- nificantly in initial height (ANOVA, F 5144 = , P = ). The timing of clipping had a significant effect on their final height (Kruskal-Wallis, H = df = 5, P < ). The Games-Howell post-hoc test revealed that plants that were cut on 30 May were able to compensate in height as they were not significantly different in height from the uncut controls (Figure 4). Plant
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