Regeneration in Heracleum mantegazzianum – response to removal of vegetative and generative parts

Response of Heracleum mantegazzianum to removal of leaves and flowers was studied in the Křivoklát Protected Landscape Area, central Bohemia, Czech Republic. In June 1993, i.e. at the peak of flowering period, plants were subjected to the following treatments: A. removal of all umbels and leaves, B. removal of all umbels, C. removal of the terminal umbel, and D. control. Regeneration was assessed at the end of August. By that time, the plants defoliated in June (treatment A) compensated for 12.4 % of the leaf area, and the seed production of plants of A and B treatments reached on average 5.75 and 2.88 %, respectively, of the number of flowers present in June. Removal of the terminal umbel did not decrease the total fecundity. Regeneration in plants of the treatments A and B occurred through (a) new branches on the plant's main stem, and/or (b) new shoots from the stem base. The plants subjected both to defoliation and umbel removal (treatment A) produced more new shoots from the stem base than plants that were only deflorated (treatment B) but their fruitlet (= one-seed portion of the fruit) weight was significantly reduced. Frequency distributions of fruitlet weights in all treatments were bimodal due to a certain portion of very small fruitlets produced. Stem branches had a high proportion of these small fruitlets but, when large fruitlets were analysed separately, those coming from regenerating branches were heavier than those produced on control plants.