Dynamics of major conifer and deciduous broad-leaved tree species in an old-growth Chamaecyparis obtusa forest, central Japan

摘要

Dynamics of major conifer and deciduous broad-leaved tree (DBL) species in an old-growth (ca. 300 years old) Chamaccyparis obtusa (Sieb. et Zucc.) Endlicher forest was monitored using stem mapping method for 10 years (1988-1998) in a 4 ha permanent plot of the Akasawa Forest Reserve in central Japan. The plot was dominated by C obtusa, followed by Thujopsis dolabrata Sieb. et Zucc. and Chamaecyparis pisifera (Sieb. et Zucc.) Endlicher, which are evergreen conifers, and DBL species such as Quercus mongolica Fischer ex Turez., Magnolia obovata Thumb., and Betula grossa Sieb. et Zucc.. We focused the dynamics of steins greater than or equal to5 cm dbh (diameter at 1.3 m above ground) of these six major tree species. Out of 1443 stems ha(-1) of these species which were alive in 1988, 154 were dead and 67 new stems recruited during 10 years. The recruitment rate was lower than the mortality rate for the conifers, but the reverse was almost true for the DBL species; the rates of recruitment and mortality of C obtusa were 0.05 and 0.27% yr(-1), respectively, and those of T dolabrata were 0.53 and 1.48% yr(-1), respectively. The recruitment rate of conifers was clearly lower than that of DBL species. The basal area of the total six major tree species was 64.2 m(2) ha(-1) at the beginning and increased to 65.9 m(2) ha(-1) in 1998. The gain rate of basal area was higher than the loss rate for each of the conifers and the DBL species. The gain rate of M, obovata (2.26% yr(-1)) and the loss rate of T dolabrata (0.77% yr(-1)) were highest among major tree species. The mortality of stems was size dependent for all major tree species, which implies that smaller stems had higher mortality. Standing dead was first, especially for DBL species, and stem broken was next dominant state of the stem mortality. The recruitment and mortality of some species related to forest floor conditions or canopy gaps. The DBL species significantly recruited and died under canopy gaps, The mortality of some species depended on the local density of understory stems. These results clearly indicate that this old-growth forest has not still reached a equilibrium state.