Environmental conditions for seed germination and seedling growth of Cinnamomum camphora (Lauraceae): the possibility of regeneration in an abandoned deciduous broad-leaved forest, eastern Japan

Cinnamomum camphora is an evergreen broad-leaved tree distributed throughout southeastern China, Taiwan, and southern Japan. This tree has been widely cultivated and utilized by humans since ancient times; therefore, its natural distribution and regeneration are ambiguous. We established a mowing zone and a control zone in an abandoned deciduous broad-leaved forest in eastern Japan. In the mowing zone, an evergreen dwarf bamboo, Pleioblastus chino, and evergreen broad-leaved trees such as Quercus myrsinifolia and Eurya japonica were cut at ground level. We set nine study sites (1x1m quadrats) on the forest floor of these zones, and measured the fraction of absorbed photosynthetically active radiation (fAPAR), soil moisture content, and soil temperature. Overall, 120 seeds of C. camphora were sown at a depth of 1cm on each site, and seed germination and the survival and growth of seedlings were monitored over 4years. Seed germination ratios at the sites were negatively affected by fAPAR and soil moisture content and positively affected by daily fluctuation of soil temperature. Seedling survival ratios and heights were negatively affected by fAPAR and positively affected by soil moisture content; no seedlings survived at the control site, and the height of seedlings was significantly higher under the canopy gap. Seeds of C. camphora could germinate in an abandoned secondary forest in eastern Japan, but the dominance of P. chino largely prevented the establishment of seedlings; the presence of a canopy gap, along with consecutive mowing, was considered to be indispensable for regeneration.