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

日本40%以上的林地由单一种植的针叶树种植园组成。许多天然林相互隔离，由于种植园比例高，被单一种植园包围。引导天然林型林分的发展可能是这些种植园生态系统适当恢复的一部分。然而，人们对如何实现这一目标的了解相当有限。本研究的目的是：1)掌握人工林种子库的现状；2)为林冠管理促进苗木生长，促进人工林生态恢复奠定基础。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分年龄相关。因此，柳杉的正常轮伐期可能太短，无法保持最大的潜在物种多样性。人工林苗木的种类组成与月桂林相近。在月桂林的主要组成树种中，人工林的苗木密度显著低于月桂林。与冠层结构有关的幼苗的生态生理特性测定了生长在林隙和林下的幼苗的叶片对PPFD突然增加的光合成诱导反应。诱导期与相对初始气孔导度在PPFD增加前达到最大值相关。林隙与林下植被的关系相似。利用树体大小、树干距树干距离和树冠距树冠深度，建立了杉木树冠内叶面积分布的经验模型。通过对冠层结构的模拟，建立了预测PPFD空间变异的模型。通过模拟模型分析了间伐对人工林苗木光合势的影响。

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.