Regeneration and coexistence of two subalpine conifer species in relation to dwarf bamboo in the understorey

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<jats:p><jats:bold>Abstract. </jats:bold> Microhabitats for seedling establishment and gap regeneration in subalpine forests of northern Japan were studied for two conifers, <jats:italic>Abies sachalinensis</jats:italic> and <jats:italic>Picea glehnii</jats:italic>. The abundance of understorey dwarf bamboo (<jats:italic>Sasa</jats:italic> spp.) was different for the four plots examined. Two types of micro‐habitats were recognized for the two conifers: ground and elevated woody substrates (fallen logs and buttresses). <jats:italic>Picea</jats:italic> regenerated mostly on elevated sites, while <jats:italic>Abies</jats:italic> regenerated on both ground and elevated sites. The densities of <jats:italic>Picea</jats:italic> were independent of those of <jats:italic>Sasa</jats:italic>, but <jats:italic>Abies</jats:italic> densities decreased with increasing abundance of <jats:italic>Sasa</jats:italic> because <jats:italic>Sasa</jats:italic> reduced regeneration on the ground. Density of <jats:italic>Abies</jats:italic> on elevated sites was higher than that of <jats:italic>Picea</jats:italic>, irrespective of <jats:italic>Sasa</jats:italic> and of the density of adult trees. There was no significant difference in growth in sapling trunk height between the two conifers, but <jats:italic>Picea</jats:italic> grew more slowly under the canopy than <jats:italic>Abies</jats:italic> and was aggregated into gaps. Thus, in forests with less <jats:italic>Sasa</jats:italic>, the recruitment capacity of <jats:italic>Abies</jats:italic> was greater than that of <jats:italic>Picea</jats:italic>. The long life span of <jats:italic>Picea</jats:italic> compensated for its low density on elevated sites. Examination of a dynamic system model showed that <jats:italic>Picea</jats:italic> was excluded by <jats:italic>Abies</jats:italic> in forests without <jats:italic>Sasa</jats:italic> because regeneration on the ground is more advantageous than on elevated sites, but the two conifers could coexist in forests with <jats:italic>Sasa</jats:italic> because of the increased relative success of regeneration on elevated sites by <jats:italic>Picea</jats:italic> saplings.</jats:p>

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