Effects of mixedwood canopies on conifer advance regeneration in a subalpine old-growth forest in central Japan

We investigated the effects of mixed conifer-deciduous canopies on the spatial patterns and growth of understorey saplings of dominant subalpine evergreen conifers. The distributions of Abies mariesii and of Abies veitchii saplings were significantly clumped at the microsites north of canopy trees of the deciduous Betula ermanii. Because irradiance comes from the south, such microsites experienced more light during the leafless period of B. ermanii, which improved the growth of Abies saplings. Moreover, the shading intensity of B. ermanii was less than that of conifers even in the season when the canopy was entirely closed. Therefore, the light conditions of such microsites appear to have a favourable influence on the growth and survival of Abies saplings, determining the spatial location of shade-tolerant Abies saplings in the understorey. Consequently, this study suggests that deciduous-canopy trees favour the advance regeneration of shade-tolerant conifers by providing the preferable growing microsites in the understorey of a mixedwood subalpine forest.