Population dynamics of four understorey shrub species during a 7-yr periodin a primary beech forest

Shrubs persist in the understorey layer of forests throughout their lives, while tall trees remain there only during the juvenile stage and then grow into the canopy layer. Thus demographic parameters (recruitment-, mortality -, and growth-rates) of shrub species are expected to differ from those of tall tree species. We investigated aspects of the demography four dominant deciduous-shrub species ( Viburnum furcatum, Lindera umbellata var. membran acea, Magnolia salicifolia, and Hydrangea paniculata) in Fagus crenata fore sts at the beginning and at the end of a 7-yr period in a 1-ha permanent pl ot. For each species, the number of stems changed little (within +/- 10%) d uring the study period, while total basal area increased markedly (11.7 - 3 3.8%), because (1) new stems continuously recruited by vegetative growth re placed the substantial number of dead stems, and (2) vegetative steins grew vigorously, probably due to nutrient support from parents The results indi cate that these four understorey shrub species have high ability to maintai n their population size in the shaded forest understorey. While in each spe cies more than half of the dead stems were standing dead, a substantial pro portion of the dead stems (9.0 - 38.5%) showed signs of mechanical damage, such as stem breakage and suppression by fallen branches or trees. Snow pre ssure that resulted in decumbent stems was also an important mortality agen t for V furcatum (20.7%) and L. umbellata var. membranacea (5.6%.). Probabi lity of damage was constant across all DBH-classes for all study species. I n each species, newly recruited steins and dead stems were spatially aggreg ated, largely due to habits of vegetative growth and mechanical damage, res pectively. This study revealed that several demographic traits, resulting f rom recruitment by vegetative growth and death by mechanical damage, were s hrub-species specific and markedly different from those of tall tree specie s.