Structure and dynamics of a Castanopsis cuspidata var. sieboldii population in an old-growth, evergreen, broad-leaved forest: The importance of sprout regeneration

摘要

The population structure and dynamics of Castanopsis cuspidata var. sieboldii were studied to evaluate vegetative and sapling regeneration in an old-growth, evergreen broad-leaved forest exposed to low-severity typhoon disturbances by annual typhoons on the Tsushima Islands in Japan. The density of individuals ≥5 cm d.b.h. was 38.0 ha~(-1) in 1990; 7.9% were multiple-stemmed individuals. Over the 7-year study period (1990―1997), the number of individuals decreased, although the number of stems increased. Over 30% of apparently dead individuals were reconstituted by sprouting stems. Compared with sprout regeneration, sapling regeneration rarely occurred and was only observed in canopy gaps. Most individuals had at least one sprout shoot (H ≥30 cm, d.b.h. <5 cm), and the number and size of sprout shoots increased as the size of the individuals increased. During the study period, larger individuals with stem breakage tended to produce sprout stems. The density of saplings was 1074 ha~(-1) and they were more abundant in canopy gaps than under closed canopies, but large saplings were very rare even in canopy gaps. The population of C. cuspidata var. sieboldii consisted primarily of single-stemmed individuals with a few multiple-stemmed individuals providing a sprout bank. Larger individuals responded to the low severity typhoon disturbances and formed sprout stems. Although many saplings were observed, regeneration occurred more often by sprout formation than by growth of saplings. Thus, sprout regeneration is an important mode of regeneration, which allows this pioneer-like species to maintain its population in this forest.