Dispersal patterns of Quercus serrata acorns by wood mice in and around canopy gaps in a temperate forest

The hypothesis of directed dispersal presumes that seeds can arrive at favorable sites for establishment more frequently than expected by chance as a result of seed dispersal by particular agents. Canopy gaps are generally favorable sites for seed establishment and survival. To test this hypothesis, the pattern of seed dispersal by wood mice in and around canopy gaps was investigated in broad-leaved deciduous forest. The study was conducted in a temperate deciduous forest in the northern part of the Kanto region of central Japan. A total of 360 magnet-equipped Quercus serrata acorns were placed on forest floors in and around two canopy gaps in the autumn of 1994, and were tracked with a magnetic locator the following spring. Of the 160 acorns detected, 16 (10%) were sound, and the remaining 144 (90%) had lost their germination ability due to predation by wood mice. Furthermore, of the 160 acorns detected, 82 (51%) were transported to destinations close to wood debris or tree bases; 132 (83%) were hoarded at nest-related sites, with 69 (43%) being hoarded at sites that met both criteria (i.e., nest-related sites close to wood debris or tree bases). This tendency of transporting seeds to woody structures was common to the three seed source categories (within canopy gaps, at the edge of canopy gaps, and about 10 m beyond the edge of canopy gaps). At one of the two gaps, transportation of acorns toward canopy gap by wood mice from the edge and the outside of the canopy gap were observed. This seed transport in the direction of canopy gaps was attributed to the preference of wood mice for various types of woody debris for refuge and/or habitat. Survival ratio of acorns hoarded close to wood structure was significantly lower than those of acorns hoarded at the destinations discontiguous with wood structure. Light levels at the acorn storage sites were not increased by dispersal. However, light levels at the acorn destinations under a thicket of fallen branches, and beside trunks or limbs of fallen trees were higher than, and equivalent to, those of areas distant from wood debris, respectively. This may be because most of such debris was in canopy gaps. These results do not clearly support the directed dispersal hypothesis for seed dispersal by wood mice; however, these results still suggest the possibility of it.