Seedling Establishment of Subalpine Stone Pine ( Pinus pumila ) by Nutcracker (Nucifraga) Seed Dispersal on Mt. Yumori, Northern Japan

Seedling establishment of Japanese stone pine, Pinus pumila, primarily depends on seed dispersal by Japanese nutcrackers (Nucifraga caryocatactes var. japonica). To assess how this mode of seed dispersal affects regeneration and habitat expansion of P. pumila, we made field observations concerning foraging behavior of nutcrackers, past annual production of pine cones, and age structure of established pine seedlings. Nutcrackers used various microsites for feeding and removing the pine seeds, especially on bare ground or around rocks. The pine seedlings occurred mainly in open patches sparsely covered with dwarf woody shrubs in wind-exposed sites, suggested that the nutcrackers preferred such open patches for caching. Age structure of the seedlings (<20 yr old) showed a clumped age distribution. Most of the younger pine seedlings (<10 yr old) grew as clusters, averaging four to five in number per cluster. Past cone production, estimated using a cone scar technique, varied annually, with some remarkable poo...