Promotion of species co-existence in old-growth coniferous forest through interplay of life-history strategy and tree competition

Question: Does the interplay of life-history strategy and tree competition promote tree species co-existence? Using a growth dynamics model, we investigated mechanisms of co-existence among major tree species in a sub-alpine old-growth coniferous forest. Location: Sub-alpine old-growth coniferous forest at 18501920 m a.s.l. in the Ontake Forest Reserve of central Japan. Methods: We investigated the growth and mortality rates of trees >= 5.0 cm stem DBH and recruitment processes in a 2-ha study plot, and developed a model for individual growth that incorporated both intra and interspecific competition and analysed the direction and degree of competitive effect. Results: Four species, Picea Jezoensis var, hondoensis, Tsuga diversifolia, Abies mariesii and Abies veitchii co-occurred as dominant species in the canopy layer. P. Jezoensis var. hondoensis and T. diversifolia had low stem densities and bell shaped DBH distributions. In contrast, A. mariesii and A. veitchii had high stem densities and inverse J-shaped DBH distributions. The growth of the species with inverse J-shaped DBH distributions (Abies spp.) was governed by the abundances of the species with bell shaped DBH distributions (Picea and Tsuga). However, Picea and Tsuga were inferior to Abies spp. in terms of recruitment rate (the number of juveniles that grow up to 5.0 cm DBH per year). Therefore, it was suggested that there was a trade-off between recruitment pattern and interspecific competition for species co-existence. Conclusions: Picea and Tsuga, with inferior recruitment, coexisted with Abies spp., with superior recruitment, by suppressing the growth of potential successors of Abies spp. The interplay of life-history strategies (recruitment and longevity) and interspecific competition therefore plays an important role in promoting species co-existence in this sub-alpine old-growth coniferous forest.