Question: Is light available for subcanopy individuals of Fagus crenata spatiotemporally heterogeneous across patches with closed canopies of different foliage phenologies and gaps? Is local abundance of Sasa influenced by the composition of the canopy layer? If so, does the Sasa layer also affect the amount of light available to small F. crenata saplings? Is variation in F. crenata population structure consistent with the hypothesis that light is important?

Location: Mt. Kurikoma, Japan 780 m a.s.l.

Methods: Population structure of subcanopy individuals of Fagus crenata and importance of Sasa were examined in five patch types. The patch-types were Fc (F. crenata only in the crown), Qm (Quercus mongolica var. grosseserrata only in the crown), Mo (Magnolia obovata only in the crown), Fc′ (periphery of F. crenata) and Gap. Seasonal changes in light availability above and below the Sasa layer was examined by using hemispherical photographs and quantum sensors.

Results: Subcanopy individuals of F. crenata began unfolding their leaves approximately one month earlier than canopy trees of Q. mongolica var. grosseserrata and M. obovata, but a few days later than those of adult F. crenata. Accumulated photosynthetic photon flux density above the Sasa layer was greatest in Qm and Mo, and lowest in Fc. Importance of Sasa was highest in Gap. Maximum height and the number of subcanopy individuals of F. crenata were greatest in Qm, followed by Mo, and lowest in Fc.

Conclusions: Differences in canopy layer composition probably influence the regeneration of F. crenata both directly through their foliage phenologies, and also indirectly by determining the importance of Sasa.

Nomenclature: Ohwi & Kitagawa (1983).

Abbreviations: PPFD = Photosynthetic Photon Flux Density; RPPFD = Relative PPFD.