We assessed the naturalness of rivers based on the riparian vegetation index throughout the national territory of South Korea as a preparatory process for restoration to improve the ecological quality of rivers. The riparian vegetation index was obtained by incorporating the diversity of species and community, vegetation profile, and ratios of the number of species and areas occupied by exotic, obligate upland, and annual plants. The evaluation was conducted based on both the riparian vegetation index and each vegetation component. The result of the evaluation based on the riparian vegetation index showed that more than 70% of the river reaches were graded as less than “moderate” and exotic and obligate upland plants were more common than endemic aquatic plants. The reaches recorded as “very good” and “good” grades were usually restricted around the upstream of the north and central-eastern parts, whereas reaches of the other areas showed “poor” naturalness (less than “moderate”). The vegetation components selected for the evaluation showed a significant correlation with each other as well as the riparian vegetation index. The degree of contribution of each vegetation component showed that the vegetation profile played the most significant role, followed by species diversity, community diversity, and the ratio of area occupied by annual plants. The riparian vegetation index revealed a significant correlation with the indices based on other taxa such as benthic invertebrates, periphytic algae, and fish, habitat conditions in the waterway, and water quality based on biochemical oxygen demand (BOD). The diagnostic evaluation results imply that most reaches need ecological restoration. The reference information was prepared by incorporating the vegetation condition with the highest score in each reach in the diagnostic evaluation. The river reach was divided into five reaches of upper and lower valley streams, upstream, midstream, and downstream. Information on the reference vegetation for restoration was prepared with the stand profile including both horizontal and vertical arrangements of riparian vegetation and species composition classified by the reach divided into five types. The levels of restoration were determined based on the diagnostic evaluation results. The lower the naturalness grade, the higher the level of restorative treatment was recommended.

During a survey of diseased plants on Wando Island, Korea from May to June 2020, a severe leaf spot disease was observed in the upper leaves of Japanese bay tree (Machilus thunbergii). Early symptoms were light blackish spots on the leaf surface and enlargement of older spots. Dry leaf spots surrounded with deep black margins were common throughout the plants. Symptomatic leaf samples were collected, and the causal pathogen was isolated on potato dextrose agar (PDA). Three fungal isolates (CMML20-1, CMML20-3, and CMML20-4) were cultured on PDA for morphological characterization at 25 °C in the darkness. Fungal colonies were circular, fast-growing, olivaceous to dark grey, and with abundant aerial mycelium. Sporulation was induced in 14 h-10 h light-dark conditions, and the conidia were single-celled, thin-walled with a smooth surface, ellipsoid with round apices, and measuring 17.5–20.5 (avg. 17.5) μm × 7.5–10.0 (7.9) μm. The morphological characteristics resembled those typical for Neofusicoccum parvum. Molecular identification was confirmed by partially sequencing the internal transcribed spacer (ITS) region and the translation elongation factor 1-α (EF1-α) genes. Pathogenicity tests were conducted on detached leaves and whole plants of M. thunbergii. High disease prevalence was observed, and Koch postulates were fulfilled. This is the first worldwide report of N. parvum causing leaf spots on Machilus thunbergii.

This study was conducted to determine the effect of thinning on the ecosystem respiration in a red pine forest in southern Korea. We measured the ecosystem respiration and its component respirations from soil, stem, leaf, and coarse woody debris (CWD) in thinned and control stands during 2010. The forest was thinned in October 2009. The total respiration was 8.37 and 8.82 Mg C ha⁻¹ year⁻¹ in the thinned and control stands, respectively. Estimated annual soil, leaf, stem, and CWD respirations in the thinned stand were 5.55, 1.41, 0.90, and 0.51 Mg C ha⁻¹ year⁻¹, accounting for 66, 17, 11, and 6%, respectively. Estimated annual soil, leaf, and stem respirations in the control stand were 5.54, 2.09, and 1.19 Mg C ha⁻¹ year⁻¹, accounting for 63, 24, and 13%, respectively. The organic C storage in tree biomass (149.24 vs. 198.61 Mg C ha⁻¹), input from litterfall (6.79 vs. 7.92 Mg dw ha⁻¹ year⁻¹) and total tree biomass increment (7.67 vs. 9.28 Mg C ha⁻¹ year⁻¹) were all significantly lower (P < 0.05) in the thinned stand than in the control stand. However, the individual tree increment was higher in the thinned stand than in the control stand (9.35 vs. 8.24 kg C year⁻¹). Organic C output through the loss rate of litter mass was significantly higher (55 vs. 50%, P < 0.05) in the thinned stand than in the control stand. These results indicate that ecosystem respiration was slightly increased by thinning, whereas tree biomass C dynamics, and organic C input and output through litter production and decomposition were decreased by thinning. Further long-term study and analyses will be required to define overall C cycling in red pine forests.

Annual tree rings of Pinus densiflora, Quercus variabilis, Larix leptolepis, and Cryptomeria japonica were analyzed to examine the correlations of annual ring growth of these species with environmental variables. In all four species, annual ring area was increased over time and affected by integration of climate changes and atmospheric pollutants in the forest ecosystem. C. japonica ring growth was larger than that of other species. The annual growth rings of P. densiflora and C. japonica increased with increasing temperature (p < 0.05). The significant impacts of NO₂ concentration on annual ring growth of C. japonica (p < 0.05) might reflect the nitrogen deposition. The relation of CO₂ concentration with annual ring growth of C. japonica (p < 0.001) could suggest that annual ring growth of C. japonica decreased with increasing CO₂ concentration, probably due to stomatal closure. The effects of SO₂ concentration on annual ring area of P. densiflora, L. leptolepis, and C. japonica (p < 0.05) along with the correlation of O₃ concentration with ring growth of P. densiflora (p < 0.05) could be due to acid deposition. The relationships of precipitation pH with annual ring growth of P. densiflora (p < 0.05) and Q. variabilis (p < 0.01) might reflect the change of nutrient cycles in the forest ecosystem. Therefore, annual ring growths of four tree species depended on environmental factors in the study area. Integrated effects of climate change and atmosphere pollutants on tree growth in the study might reflect the problem of acidification in the forest ecosystem.

Urban trees grow in diverse environments where site conditions and human management may influence their growth patterns. However, few allometric equations (AEs) have been developed for urban trees, and the effects of environmental variations across urban land use categories on tree biomass remain largely unexplored. Therefore, this study developed urban land-use-specific AEs for major urban tree species in South Korea. We selected eight major urban tree species groups (at genus level), harvested 201 trees, and non-destructively measured the stem volumes of 1995 trees using a laser dendrometer. Species-specific and generalized AEs to estimate stem volume were developed under three urban land use categories: street trees, urban parks, and others. The results indicated that differences in stem volume across urban land use categories varied by species, with street trees generally showing smaller stem volumes. Furthermore, due to the high variation in stem volume within species, sampling designs that encompass diverse size distributions are necessary when developing AEs for urban trees. Our findings indicate that various factors in urban environments influence tree volume and considering these differences is essential for improving biomass estimation accuracy.