Bet-Hedging Strategies in Heracleum mantegazzianum Sommier & Levier (Apiaceae) Populations of the European Northeast Russia

This study investigates the mechanisms enabling Heracleum mantegazzianum Sommier & Levier to sustain stable population dynamics in the middle taiga subzone of European Northeast Russia without maintaining a persistent soil seed bank. Our analysis of mericarp (“seed”) viability in the soil bank, seedling recruitment patterns, and juvenile plant development demonstrates that while populations accumulate substantial quantities of empty seed coats, viable mericarp density never exceeds 2000 units/m2. The extended natural stratification period (six months) facilitates nearly complete germination of the previous year’s seed cohort during spring, resulting in the formation of only a transient seed bank under these climatic conditions. Field observations reveal remarkably consistent juvenile plant densities averaging 200 individuals/m2, maintained through three synergistic factors: reliable annual seed production, rapid spring seedling establishment, and the facultative retention of second-year plants in a juvenile growth stage. The ecological strategy of juvenile plants combines efficient seasonal light capture during spring and autumn with summer dormancy, allowing them to persist under conditions of intense intraspecific competition. H. mantegazzianum implements a sophisticated bet-hedging strategy characterized by minimal reproductive allocation (<0.01% population contribution), preservation of dormant underground meristems, and phenotypic plasticity of juvenile individuals. These integrated adaptations collectively ensure population stability despite environmental fluctuations and the evolutionary trade-off of lacking long-term seed banking capacity.