Effects of burying depth and seed size on seedling establishment of Japanese chestnuts, Castanea crenata

The extent to which caching depth and nut size affect seedling establishment of Japanese chestnuts, Castanea crenata Sieb. et Zucc., were investigated by burying the nuts of three different size-classes at different depths (0 cm on litter; 0, 5, 10, 20 and 30 cm beneath litter) in a nursery. Seedling emergence, seedling mass and height were usually reduced by deep burial, particularly for small nuts. With increasing burial depth and decreasing nut size, the biomass allocation to stems (particularly below ground stems) increased, while allocation to roots (part below cotyledons including hypocotyl) decreased. Such morphological changes would amortize the limited seed reserve to facilitate emergence. Seedling emergence, seedling mass and height were greatest at 5 cm burial depth, but no seedlings emerged when nuts were sown on litter, suggesting that animal caching in shallow burial (scatter hoarding) favors chestnuts regeneration. At the optimal burial depth (5 cm), there was little difference in the seedling height among nut size-classes which showed that nut size has little effect on their competitive abilities with neighboring herbs in the early successional habitats where the chestnuts usually regenerate. The fact that most of the larder- or nest-hoarded nuts (depth ≥ 10 cm) were consumed by wood mice (Apodemus spp.) in the fields suggests that large nuts would not always have distinct advantages over small nuts.