Canopy tree competition and species coexistence in anAbies veitchiiandA. mariesiimixed subalpine forest, central Japan

The mode of competition in a crowded subalpine mixed forest of Abies veitchii Lindley and A. mariesii Masters, central Japan, was investigated by using spatial and non-spatial competition models for stem diameter (d.b.h.) and tree height growth. (1) Size distribution of tree height became bimodal as the stand developed, where the relative abundance (in terms of tree number and basal area) of A. mariesii increased in the lower vertical layer but both species kept almost constant relative abundances in the upper layer; (2) there was little difference in the growth patterns (size-dependent mean absolute growth rate and variance in absolute growth rate) of d.b.h. and tree height for canopy trees ≤ 1.3 m in height between A. veitchii and A. mariesii; (3) for small saplings ≤ 1.3 m in height, the growth pattern was somewhat different between the two Abies species: the variance and/or the mean of relative height growth rates of A. mariesii saplings were significantly greater than those of A. veitchii saplings under relatively dark conditions (5-20 % relative light intensity); (4) mortality rate of small trees of A. mariesii was lower than that of A. veitchii; (5) A. veitchii underwent symmetric competition, whilst A. mariesii gave little indication of competition in individual growth. It is concluded that the vertical community structure of this mixed forest was induced by difference in the mortality rate of small trees between the two species but not by the growth patterns of canopy trees or competitive interactions between canopy trees. The coexistence of A. veitchii and A. mariesii was governed by the mortality and recruitment rates of small saplings but not by the growth patterns of canopy trees or competitive interactions between canopy trees.