The studies on the inducing development of natural-forest-type stands from conifer plantations

日本40%以上的林地是单一的针叶树种植园。许多天然林相互隔离，由于人工林比例高，被单一种植的人工林包围。诱导天然林类型的林分的发展可能是适当恢复这些种植园生态系统的一部分。然而，如何实现这一目标的知识非常有限。本研究的目的是：1）掌握人工林苗木库的实际状况，2）为促进苗木生长的林冠管理，为人工林的生态恢复提供基础研究。人工林苗木多样性和密度：人工林木本植物物种丰富度与林龄相关。因此，柳杉的正常轮伐期可能太短，无法保存最大的潜在物种多样性。人工林幼苗的种类组成与相邻的月桂林相似。在部分主要组成树种中，人工林的幼苗密度显著低于月桂林。幼苗生理生态特性与冠层结构的关系研究了生长在林隙和林下的幼苗叶片对PPFD突然增加的光合诱导反应。诱导期与PPFD增加前相对初始气孔导度最大值相关。林隙与林下植被的关系相似。利用树体大小、距树干的距离和距树冠表面的深度，建立了一个估算日本雪松树冠内叶片空间分布的经验模型。通过对冠层结构的模拟，建立了PPFD空间变异的预测模型。利用模拟模型分析了疏伐对种植园苗木光合势的影响。

More than forty percent of the forested land in Japan comprises monoculture conifer plantations. Many natural forests are isolated from each other, and are surrounded by monoculture plantations due to high proportion of plantations. Inducing development of natural-forest-type stands may be part of appropriate rehabilitation for ecosystems in these plantations. However, the knowledge of how to achieve it is quite limited. The objectives of this study are 1) to grasp the actual state of the seedling-bank in plantations, and 2) to make basic researches for the canopy management to promote the growth of seedlings, for an ecological rehabilitations of the plantations.The diversity and density of seedlings in plantations : The species richness of woody plants in plantations was correlated with stand age. The normal rotation period of Cryptomeria japonica may therefore be too short to conserve the maximum potential species diversity. The species composition of seedlings in plantations was similar to that in bordering laurel forest. The seedling density in plantations was significantly lower than that in laurel forests in some major component species of laurel forests. Eco-physiological property of seedlings related with canopy structurePhotosynthetic induction responses to a sudden increase in PPFD were measured in leaves of seedlings growing in a gap and understory of canopy. The induction period was correlated with relative initial stomatal conductance to maximum values before increase in PPFD. The relationships was similar between gap and the understory. An empirical model was constructed for estimating the spatial foliage distribution within crowns of Japanese cedars, using tree size, distance from stem and depth from crown surface. The model predicting the spatial variance of PPFD was also developed through simulating the canopy structure. The effect of line-thinning on the photosynthetic potential of seedlings in plantation was analyzed by the simulation models.