Light energy gain and carbon balance of the seedlings of Quercus serrata in natural reproduction sites by the shelterwood method

在日本，以锯齿栎为主的落叶矮林广泛分布在城市、农田和山村周围。在20世纪50年代至70年代期间，这里的针叶林受到了积极的影响。但近年来，充分利用乡土阔叶树种进行自然繁殖的新潮流在人们中逐渐兴起。母株法和防护林法具有许多优点，例如，易于执行，使更新周期缩短等，进行了各种基础研究和技术试验，以检查这些自然繁殖方法的适用性锯叶栎。冠层乔木几乎每两年产生一次好种子，每6 ~ 8年产生一次大种子。结果表明，在结实较多的年份，成熟种子的供应量较大。大部分种子落在树冠下或树冠周围，主要集中在地面的低洼处。种子落下之后是叶子落下，并且也以相同的方式收集叶子以覆盖种子。因此，种子可以避免干燥伤害。幼苗在当年期已表现出较高的光合能力，占幼树的60 - 70%，未观察到光合作用的光抑制。当年生幼苗即使在夏季非降雨期也能保持较高的气孔导度，这可能是由于根系发达所致。第二年，杂草和灌木开始生长，并抑制了幼苗的某些部分。但若能人为地限制竹草的旺盛生长，锯缘青冈的更新最终还是会成功的。使用反铲是非常有效的清除地下系统的竹草等，虽然土壤被压实使用这种重型机械，光合性能和幼苗的生长反应的影响是微不足道的。

Deciduous coppice forests dominated by Quercus serrata are widely distributed around cities and farm and mountain villages in Japan. Afforestation by conifers was actively made there during 1950's to 1970'. But recently the new trend towards natural reproduction by making full use of native broad-leaved tree species have been growing among people. The mother tree method and the shelterwood method have a number of advantages ; e.g. easily performed, enable to shorten the regeneration period and so on. Various fundamental studies and technical tests were carried out in order to examine applicability of these natural reproduction methods for Q.serrata. The canopy trees produced good seed crop almost every two years, bumper seed crop at intervals of 6 or 8 years. Larger number of mature seeds were supplied at years when the trees bore more seeds. Most of seeds fell right under tree crowns or near around them and collected mainly at low spots on the ground surface. The seed fall was followed by leaf fall and the leaves also collected in the same manner to cover seeds. So seeds could avoid desiccation damage. Seedlings showed , already at current year stage, high photosynthetic ability in leaves, 60 to 70 % of young trees, and the photoinhibition of photosynthesis was not observed. Daytime stomatal conductance of current year seedlings was kept relatively high even in non rain fall periods in summer, probably due to marked development of their root system. At the following year weeds and shrubs started to grow thick and suppressed certain parts of the seedlings. It appeared, however, that the regeneration of Q.serrata would succeed finally, if vigorous growth of bamboo grasses could be restricted artificially. Use of backhoe was extremely effective for removing under-ground system of bamboo grasses etc. Although soils were compacted by using such heavy machinery, the influence on photosynthetic performance and growth reaction of the seedlings was negligible.