Caching of Japanese Stone Pine Seeds by Nutcrackers at the Shiretoko Peninsula, Hokkaido

Abstract

In early September of 1982 clumps of seedlings of Japanese stone pine Pinus pumila germinated from caches were observed on the slopes cut along the road (Route 334), between the Shiretoko Pass and Utoro (Fig. 1, Photos 1-3), at 750 to 400 m above sea level. At 3 caching sites, 8 species of woody seedlings were growing (Figs. 2-5). Most seedlings of the pine and a maple Acer tschonoskii were in clumps, and to a lesser extent seedlings of Todo-fir Abies sachalinensis were also in clumps. The number of seedlings was up to 23 per clump in the pine, 40 in the maple, and 6 in the fir. They were 1 to 3 years old.The clumping of seedlings appeared to be caused by animals. The disseminules of the pine are wingless, but those of the maple and the fir are winged (Fig. 6, Table 1). The mature cones of the pine are easily removed from the branchlets, but they remain closed and do not release their seeds. Although several species of small mammals and birds store the seeds of the pine (Table, 2), the main disseminator appeared to be the Nutcrackers Nucifraga caryocatactes, because the distances between seed sources situated in the alpine zone and caching sites in the subalpine zone are not close, and the caches exist on the bare parts of upper slopes.These caching sites are suitable both for the Nutcrackers to retrieve seeds cached and for the bushy pines to establish themselves in less competition with tall trees. The Nutcrackers are the best planters of the pine for the bare slopes cut along the mountain roads in alpine and subalpine zones. The large, winged, nut-like disseminules, such as of the maple and the fir, at first appear to be dispersed by wind. However, they may also be originated from the caches by the Nutcrackers. In the dispersal of seeds of trees and shrubs, ornithochoryl, especially synzoochoryl and endozoochoryl, seems to play an important role.