Tree Shelters-Induced Microclimate Enhances Early Growth and Photosynthetic Performance in <i>Larix kaempferi</i>

Tree shelters are widely used to improve seedling establishment; however, their effects on microclimate and physiological responses remain insufficiently understood in Korea. This study investigated the effects of tree shelters differing in color and height (blue: 60, 75, and 120 cm; white: 120 cm) on microclimate, growth, and photosynthetic responses of Larix kaempferi seedlings during the early establishment period. Tree shelters created warmer and more humid internal conditions, with daily maximum air temperature averaging 34.65 ± 0.26 °C and reaching up to 44.23 °C. Relative humidity averaged 91.63 ± 0.40%, while vapor pressure deficit decreased to 0.18–0.24 kPa compared with the control. Shelter treatments also modified light conditions, with white shelter transmitting more light and blue shelters reducing total irradiance and red:far-red ratios. Survival rate remained relatively high in the shelter treatments, averaging 84.17%, although it did not exceed that of the control (91.67%). Shelter treatments promoted height growth, with mean height reaching 68.44 cm, but limited diameter growth, resulting in higher (height-to-diameter) H/D ratios. Photosynthetic performance was enhanced in both taller blue and white shelters, as indicated by higher maximum photosynthetic rate, apparent quantum yield, and carboxylation efficiency, suggesting improved light-use efficiency and CO2 assimilation responsiveness under taller shelter conditions. White shelter showed relatively lower H/D ratio than the blue shelter treatments (77.08 ± 2.28 vs. 104.27 ± 1.85), suggesting greater structural stability. Overall, tree shelters enhanced early growth and photosynthetic performance of L. kaempferi seedlings, but long-term monitoring across diverse site conditions is needed because this study was conducted as a short-term experiment during one growing season. Further evaluation of shelter specifications and removal timing will also be necessary to optimize shelter design and assess practical applicability in open-field reforestation sites.