| Summary: | Soil erosion after harvesting of forest plantations can create infertile colluvial soil, therefore, seedlings used for site reforestation should be equipped against nutrient-poor edaphic conditions. The oak genus is a suitable candidate for such reforestation efforts. Oak is an ectomycorrhizal (ECM) tree genus known to grow under infertile environments. In this study, the initial stage of tree growth in three species of oak seedlings inoculated with a spore suspension of ECM fungus was monitored to evaluate the acceleration of seedling growth and nutrient uptake. I selected <i>Quercus acuta</i> Thunb., <i>Quercus glauca</i> Thunb., and <i>Quercus salicina</i> Blume, as these are common, evergreen, broad-leaved woody species commonly found in Southwestern Japan. The seedlings were inoculated with <i>Boletus reticulatus</i> and planted in infertile colluvial soils collected from a site that had undergone soil erosion. I also compared the ecophysiological characteristics of the potted seedlings planted in colluvial soil and normal forest soil. After six months of cultivation, <i>Q. glauca</i> with the ECM showed the highest growth rate in the fertile forest soil and had leaves with a higher nutrient content. In contrast, root dry mass increased slightly in <i>Q. acuta</i> and <i>Q. salicina</i> planted in colluvial soil. In all species, the seedling’s ECM colonization rate in colluvial soil was lower than that in forest soil, yet the increase in nutrient uptake in the former was not obvious. The contents of K and Ca in the roots of <i>Q. acuta</i> and <i>Q. salicina</i> increased with <i>B. reticulatus</i> infection. I concluded that the inoculation with a <i>B. reticulatus</i> spore suspension effectively accelerated the growths in all three <i>Quercus</i> species. <i>Q. glauca</i> favored a fertile environment, and <i>Q. acuta</i> and <i>Q. salicina</i> suitably acclimated to both soil types. Thus, these species were selected as potential future candidates for reforestation in such eroded sites.
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