Gap formation, microsite variation and the conifer seedling occurrence in a subalpine old‐growth forest, central Japan

To evaluate the effects of canopy gaps and forest floor microsites (soil, fallen logs, root‐mounds, buttresses and stumps) on regeneration of subalpine forests, the gap regeneration and seedling occurrence of conifers ( Abies mariesii, Abies veitchii, Picea jezoensis var. hondoensis and Tsuga diversifolia ) were studied in two stands of a subalpine old‐growth forest, central Japan. The percentage of gap area to total surveyed area was 11.2–11.3% in the stands. Gap regeneration was not common for P. jezoensis var. hondoensis and T. diversifolia . In contrast, gap regeneration by advanced regeneration was relatively common for Abies . Seedling occurrence of P. jezoensis var. hondoensis and T. diversifolia was restricted on elevated surfaces such as stumps and root‐mounds, while Abies seedlings could occur on soil as well as on elevated surfaces. Rotten stumps were the most favorable microsites for conifer seedling occurrence, which covered small area in the forest floor. Although canopy gaps were not always favorable for seedling occurrence, all conifer seedlings were larger under canopy gaps than under closed canopy. Canopy gaps and forest floor microsites clearly affected seedling occurrence and growth of conifers. This suggests that regeneration of conifers is related to the difference of growth advantage under canopy gaps and favorable microsites for seedling occurrence.