Ecophysiological responses of naturally regonerntod seedlings to natural and man-made disturbance and their application for silviculture

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Leaf morphology and anatomy of 4 successional dcciduous broadleaved tree seedlings grown under various light levels were examined in relation to their photosynthetic capacity. The successional growth sites of seedlings of birch (Betula schmidtir), oak (Quercus serrata), Keyaki (Zelkova serrata) and maple (Acer tenuifolium) are respectively sunny open, open or gap, gap and shade environment in a forest. Before the bud break, seedlings were transplanted from a small gap or under forest canopy to open nursery. Birch was also transplanted from open site to the nursery. A positive correlation between leaf thickness and the maximum photosynthetic rate of all species was found. For the seedlings grown under shade in the preceding year, oak, Keyaki and maple leaves bore one palisade parenchyma layr even though their leaves unfolded under full sunlight in the nursery. In contrast, leaves expanded under full sunlight in previous year had two palisade parenchyma layrs except for maple where only one layr formed irrespective of growth light environment. Chlorophyll b content of all leaves developed under shade was higher then those grown in the open. In an open, stomatal density was high while the size of bundle sheath extension compartment (area divided by the extension of vascular bundle sheathes) was small. The ecological relationship among leaf morphology, anatomy and its gas exchange capacity in seral tree seedlings is discussed with special reference to the timing of leaf primordial differentiation.