Regeneration characteristics of Quercus communities in Sado Island.

摘要本研究旨在从林分结构估算的齿栎和水杨栎群落的更新过程、开花至成苗过程中的限制因素、木鼠的种子传播捕食者的功能以及幼苗的安全地点等方面，阐明萨都岛栎群落的更新特征。再生过程：研究林分水杨高度和胸径的频率分布格局分别为j形和钟形。从这一格局看，水杨林分的幼树数量较少，在遭到大面积采伐等干扰后，林分的同步更新似乎无法持续更新。在林分结构和更新过程上有相同的趋势。限制因素：扩散前昆虫的危害是影响齿刺木再生过程的最关键的限制因素。由于雌花产量无波动，因此齿刺小蜂种群无法逃脱昆虫的捕食压力。木鼠的作用：佐渡岛栓皮栎种子的主要传播捕食者为斑姬鼠。木鼠分散橡子曾经是分散囤积的，但所有贮藏的橡子都被提前到明年春天。安全地点：冬季（11 - 4月）5年以上水杨幼苗数与rPPFD呈显著相关。冬季光照强度增加的落叶树冠下或林缘下，水杨幼苗能够生根生长。上述结果对佐渡岛栎树群落的管理具有重要的指导意义，但橡子生产和扩散的时空波动对其更新特性的影响必须长期持续监测。

The purpose of this study was to clarify the regeneration characteristics of Quercus communities (Q.dentata and Q. salicina) in Sado Island from the view points of the regeneration process estimated from the stand structure, the limiting factors in regeneration process from flowering to seedling establishment, the function of seed dispersing predator of wood mouse, and the safe site of seedling.1. Regeneration process : The frequency distribution patterns of height and diameter at breast height of Q. salicina in study stand show the J-shape and bell-shape, respectively. From this patterns, there were few saplings in the Q. salicina stand and it seem to be failed to continuous regeneration after simultaneous regeneration following the large-scale disturbance like clear cutting. Q. dentata stand had the same tendency about stand structure and regeneration process.2. Limiting factor : Pre-dispersal insect damage was the most critical limiting factor in the regeneration process of Q. dentata. As there was no fluctuation of female flower production, Q. dentata population could not escape the insect predation pressure.3. Function of wood mouse : In Sado Island, Apodemus speciosus was main seed dispersing predator of Quercus acorns. Dispersing acorns by wood mouse were once scatter-hoarded, but all caching acorns were predated until next spring.4. Safe site : There was significant correlation between the number of over five years old Q. salicina seedling and the rPPFD in winter season (from November to April). Q. salicina seedling was able to establish and grow under the deciduous tree canopy or forest margin where light intensity would be increase in winter season.Though above results are very important and useful to manage the Quercus communities in Sado Island, time and space fluctuation of acorn production and dispersion, that would be effective on the regeneration characteristics, must be continuously monitored for long time.