Growth response of goldenrod, Solidago canadensis (Asteraceae), to periodic defoliation

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Abstract
Intensive grazing by Trirhabda spp. on the goldenrod, Solidago canadensis L., was simulated by manual defoliation experiments to estimate quantitatively the effects of various levels of grazing. Mean stem length per clump, measured as the sum of the lengths of the main stem and branches below the inflorescence, and the number of stems per clump were significantly reduced toward the end of the growing season. Inflorescence development was either retarded or prevented. By spring of the year following treatment, plants receiving repeated defoliation had both lower mean leaf biomass per stem and mean stem length and fewer stems per clump. There was also some clump mortality. These results corroborate the observation that repeated defoliation of Solidago canadensis during an outbreak of beetles of the genus Trirhabda is followed by a major reduction in goldenrod in old-field communities.