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

在日本，以锯缘栎类为主的落叶灌木林广泛分布于城市、农场和山村。从1950年的S到1970年，针叶林在那里得到了广泛的应用。但最近，充分利用本土阔叶树种进行自然繁殖的新趋势在人们中兴起。母树法和防护林法具有许多优点，例如易于实施、能够缩短更新期等。为了检验这些自然繁殖方法在锯缘栎上的适用性，开展了各种基础研究和技术试验。冠层树几乎每两年结一次好种子，每隔6年或8年就丰收一次。在树木结实较多的年份，提供较多的成熟种子。大部分种子正好落在树冠下或树冠附近，主要收集在地面上的低点。种子掉落之后是落叶，也是以同样的方式收集叶子来覆盖种子。因此，种子可以避免干燥伤害。苗木在当年生长期表现出较高的叶片光合作用能力，60%~70%的幼树表现出较强的光合作用能力，没有观察到光合作用的光抑制现象。当年生幼苗即使在夏季非雨季也能保持较高的白天气孔导度，这可能与其根系发育显著有关。第二年，杂草和灌木开始长得茂密，抑制了幼苗的某些部分。然而，如果能人为地限制毛竹的旺盛生长，锯缘栎更新最终是成功的。使用反铲清除竹草等地下系统是非常有效的。虽然用这种重型机械压实土壤，但对苗木的光合作用和生长反应的影响微乎其微。

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.