Exotic species plantations are increasing for timber production and other economic benefits. However, evaluation of species adaptation to local climates requires long-term research and the information is still limited. This study was conducted to understand the growth response of three exotic tree species, Abies firma, Cryptomeria japonica, and Chamaecyparis obtusa, to regional moisture conditions during the dry spring and wet summer in plantations located in south-central Korea. We examined the growth response of A. firma, C. japonica, and C. obtusa to monthly precipitation and drought indices from 1950 to 1998 using tree-ring analysis. The radial growth of A. firma showed a significantly positive relationship with precipitation and drought indices in spring (p < 0.05). Water stress in spring was the main limitation to radial growth in A. firma. In contrast, C. japonica and C. obtusa, with indeterminate growth, had negative correlations with precipitation and drought indices in summer (p < 0.05). Abnormally high summer precipitation may interrupt photosynthesis by reducing sunshine duration and evaporation, negatively affecting the growth of C. japonica and C. obtusa. The different responses of these species to monthly precipitation and drought indices imply that regional precipitation patterns should be carefully considered in species selection for the establishment of exotic species plantations.

Relict and peripheral tree populations may combine reduced within-population variation with strong among-population divergence, complicating conservation decisions. We combined a de novo draft genome assembly of Platycladus orientalis (~ 8.73 Gbp; N50 = 248,484 bp) with genotyping-by-sequencing data comprising 38,820 single-nucleotide polymorphisms from 95 individuals in seven Korean stands. Nucleotide diversity was higher in the Danyang–Jecheon limestone corridor (π = 0.245–0.274) than in the isolated Andong, Yeongyang, and Daegu populations (π = 0.156–0.216). The isolated populations were strongly differentiated from one another (pairwise FST = 0.396–0.431), whereas differentiation within the corridor was lower but heterogeneous (FST = 0.117–0.223). Hierarchical analysis of molecular variance attributed 29.26% of variation to differences among populations (ΦST = 0.293). No repeated or near-identical multilocus genotypes were detected. Rarefied private allelic richness among common variants was greater at the corridor-group level than in the isolated group (0.1214 vs. 0.0415 per locus), although rare variants were underestimated. FIS declined strongly under stricter depth and missing-data filters, indicating a substantial technical component in baseline heterozygote deficits. Contemporary effective population size estimates were highly heterogeneous and imprecise, ranging from 2.0 in Danyang Seokmun to 202.8 in Daegu, while Danyang Hasi-ri was unbounded. Exploratory Mantel tests suggested nominal geographic and climatic associations, but none remained significant after multiple-test correction. Adult–seedling FST values were ≤ 0.035 in three focal stands. These results support treating the isolated stands as candidate conservation units and the limestone corridor as a management-relevant diversity reservoir, while gene flow or seed transfer should be evaluated through a risk-assessed framework.

Direct seeding is considered a versatile and cost-effective approach to forest regeneration; however, its broader application is limited by low seedling survival rates and species-specific regeneration requirements, which often necessitate site preparation. We investigated the emergence, survival, and growth of Korean ash (Fraxinus chinensis subsp. rhynchophylla (Hance) A.E.Murray) seedlings regenerated by direct seeding over six years following two site preparation treatments—scarification and mixing—to determine appropriate site preparation methods for direct seeding and to assess the effects of site preparation treatments on soil, understory vegetation, and seedling growth. Additionally, the seed germination, shoot and root lengths, and biomass of the seedlings were investigated over 50 days in a growth chamber using soils from each site preparation treatment to examine early-stage growth responses. Both scarification and mixing treatments enhanced seed germination and seedling establishment. Seedling emergence rates were similar between the treatments; however, the seedling mortality and the height and coverage of competing understory vegetation were significantly greater at the scarification treatment than at the mixing treatment during the first year (p < 0.05). Both treatments reduced minimum winter soil temperatures during the first two years, with frost heaving identified as a primary cause of early seedling mortality. From the second year onward, seedling growth was significantly greater in the mixing treatment (p < 0.05), which also more effectively suppressed competing vegetation. A shallow depth mixing treatment (<5 cm) is recommended for direct seeding of Korean ash, as it reduces frost heaving damage and facilitates seedling survival and growth by minimizing understory competition.