Annals of Botany 77: 529-538, 1996
© 1996 Annals of Botany Company
Allometry and Competition between Saplings of Picea jezoensis and Abies sachalinensis in a Sub-boreal Coniferous Forest, northern Japan
Department of Biology, Tokyo Metropolitan University, Tokyo, 192-03, Japan
March 30, 1995 ; December 7, 1995
The crown shape and the mode of competition between saplings (<2m in height) of the two conifers,Picea jezoensis andAbies sachalinensis, of a sub-boreal forest, northern Japan, were investigated based on the diffusion model. A model for individual sapling growth considering both inter- and intraspecific competition was developed. The effect of species-specific crown shape on the sapling growth and competition of the two species were examined.Picea jezoensisandAbies sachalinensissaplings had deep conic and shallow flat crowns, respectively.Picea jezoensishad more foliage mass thanAbies sachalinensisof the same sapling mass. It was suggested that thePicea jezoensissapling has a high cost for assimilation–respiration balance under dark conditions of closed canopies, whereas theAbies sachalinensissapling maintains effective assimilation even under suppressed conditions. Widely spaced saplings, such as gap successors, ofPicea jezoensishad a greater relative growth rate (a0) than widely spacedAbies sachalinensis. The crown shape of saplings of the two species shows different adaptations for efficient persistence in the sub-boreal forest.
Saplings ofPicea jezoensisandAbies sachalinensiswere not uniformly distributed, but aggregated in different sites as the saplings grew, indicating habitat segregation between the two species at the sapling stage. Intraspecific sapling competition was one-sided in each of the two conifers. Interspecific sapling competition was one-sided in the direction only fromAbies sachalinensistoPicea jezoensis. Therefore, asymmetric competition prevailed at the sapling stage of the two species. These results contrast with weak symmetric competition or the almost absence of competition between trees (
2m in height) of the two species (Kubota and Hara,Annals of Botany76: 503–512, 1995). The mode of competition changed with the life-history stage from the sapling (intense and asymmetric) to the tree (weak and symmetric or almost absent).
In conclusion (1) asymmetric and intense competition between saplings brought about habitat segregation between the dominant species,Picea jezoensisandAbies sachalinensis, in the early stage of life-history; (2) therefore, the coexistence ofPicea jezoensisandAbies sachalinensisof the sub-boreal forest was determined by the boundary conditions for the growth dynamics of the trees, as segregation of establishment sites resulting from asymmetric and intense competition between saplings; (3) then the species composition of the forest was maintained by weak symmetric competition or the almost absence of competition between trees.
Crown shape; growth dynamics; species coexistence; habitat segregation; diffusion model