Seed germination and initial seedling survival of the subalpine tree species, Picea jezoensis, on different forest floor substrates under elevated temperature

The Korean Peninsula is the southern limit of the distribution of Picea jezoensis (Siebold et Zucc.) Carrière, where it occurs only on isolated subalpine mountain tops in South Korea. Global warming is altering habitat environments, threatening the survival of P. jezoensis. This study investigated the seed germination, seedling establishment, and seedling mortality of P. jezoensis on different forest floor substrates (woody debris [WD], litter, and soil from a P. jezoensis habitat on Mt. Gyebang), together with horticultural sand, under control (mimicking habitat condition: day 22.3 °C/night 9.4 °C) and elevated (26.6 °C/13.7 °C) air temperatures to determine the effects of an increase in temperature on P. jezoensis regeneration. Seed germination did not differ significantly between the control and elevated temperature conditions on all substrates. Yet, seedling mortality increased by more than 1.4 times under elevated temperature compared to controls on all substrates. Among the four substrates, WD and litter respectively exhibited the lowest (15.6%) and highest (50%) seedling mortality for P. jezoensis under control conditions, with respective significant increases of 53% and 77% seedling mortality under elevated temperature (p < 0.05). Picea jezoensis on soil and sand had levels of mortality that were intermediate between WD and litter under control conditions and P. jezoensis did not show significant changes in seedling development between the control and elevated temperature conditions on soil and sand. P. jezoensis began to show differences in survival among substrates from the post-germination stage orwards, with most seedling mortality occurring within 30 days of seedling emergence. WD seemed to be the most favorable substrate under the control condition. Nevertheless, seedling establishment, survival and development on WD decreased to a percentage similar to those on soil and sand under elevated temperature, implying that the role of WD as a dominant rooting substrate for P. jezoensis regeneration may not remain the same under an elevated temperature condition. Global warming has a great potential to increase initial seedling mortality, adversely affecting the regeneration of this subalpine species.