Question: In the population dynamics of four understorey shrub species (Hp, Hydrangea paniculata Sieb. et Zucc.; Lu, Lindera umbellata Thunb. var. membranacea (Maxim.) Momiyama; Ms, Magnolia salicifolia (Sieb. et Zucc.) Maxim.; Vf, Viburnum furcatum Blume ex Maxim.), (1) What is the relative importance of seedling regeneration versus vegetative growth? (2) Can these shrubs persist stably for a long time in the understorey? (3) What kind of variation in demographic features is observed among these shrubs?
Location: 780m a.s.l., north-eastern Japan.
Methods: Population dynamics were analyzed by using stage-classified matrix models. Models were mainly constructed from five years stem-census data, including current-year seedlings and sprouts.
Results: Current-year sprouts emerged every year in every species. Current-year seedlings emerged every year in Lu and Vf, but densities were very low. In every species, population growth rate (λ) was close to the equilibrium value 1.0 and no statistical difference was found among species. The stable stage-distribution predicted from the matrix model was similar to the observed distribution for Lu, Ms and Vf, but much different for Hp. Elasticity matrix was also similar among Lu, Ms and Vf, but was quite different for Hp.
Conclusions: Lu, Ms and Vf were considered as climax shrubs that can regenerate and maintain their population stably in the understorey, even if canopy gaps form infrequently. Hp is a pioneer shrub that require more frequent formation of canopy gaps for long-term persistence in the understorey.
Abbreviations: Hp = Hydrangea paniculata; Lu = Lindera umbellata var. membranacea; Ms = Magnolia salicifolia; SL = Current-year seedling; SP = Current-year sprout; Vf = Viburnum furcatum.