Early Growth Responses of <i>Larix kaempferi</i> (Lamb.) Carr. Seedling to Short-Term Extreme Climate Events in Summer

Extreme climate events such as heat waves, drought, and heavy rainfall are occurring more frequently and are more intense due to ongoing climate change. This study evaluated the early growth performance of one-year-old Larix kaempferi (Lamb.) Carr. seedlings under open-field extreme climate conditions including experimental warming and different precipitation regimes. We recorded the survival rate, root collar diameter, height, biomass, shoot-to-root ratio, and seedling quality index using nine treatments (three temperature levels, i.e., control, warming by 3 °C and by 6 °C, × three precipitation levels, i.e., control, drought, and heavy rainfall) in July and August 2020. The survival rate of seedlings did not differ between treatments, showing high values exceeding 94% across treatments. The measured shoot height was largest under warming by 3 °C and high rainfall, indicating that moderate warming increased seedling height growth in a moist environment. Heavy rainfall decreased stem volume by 21% and 25% under control and warming by 6 °C treatments, respectively. However, drought manipulation using rain-out shelters did not decrease the growth performance. Overall, extreme climate events did not affect the survival rate, biomass, shoot-to-root ratio, and seedling quality index of L. kaempferi. We thus conclude that, regarding growth responses, L. kaempferi seedlings may be resistant to short-term extreme warming and drought events during summer