Monitoring Plant Diversity and Water Resource Recovery Following the Restoration of Degraded Mountain Areas

This study examined long-term changes in floristic composition and hydrological conditions following reforestation in the Yangju Forest Watershed Experimental Catchment, Republic of Korea. The analysis integrated repeated floristic surveys spanning approximately 50 years’ hydrological record from the same experimental catchment. Floristic surveys conducted at 9, 19, 26, 40, and 50 years after reforestation were analyzed using taxonomic and functional-group richness, Sørensen similarity, and zeta diversity, while streamflow records from 1984–2019 were evaluated using flow-duration curves (FDCs) and hydrological indices. Floristic richness increased from 54 taxa in the 1980s to 122 taxa in the 2020s (2.3-fold), with family- and genus-level richness increasing approximately 1.7- and 2.1-fold, respectively. Floristic similarity was highest between adjacent survey periods, whereas the greatest compositional turnover occurred between the 1980s and 2020s. Life-form and root-system representation increased over time, and wetland indicator species appeared approximately 25 years after reforestation. Hydrological change was characterized by increased runoff duration, a decreased flow-duration index, and a progressive increase in the dormant-season runoff ratio. Across four overlapping survey periods, plant species richness, the weighted root-system richness index (R), and wetland indicator species richness showed concurrent temporal patterns with hydrological variables, including fewer relatively low-discharge days and higher drought-flow discharge (Q355) and dormant-season runoff ratios. These long-term records reveal concurrent trajectories of floristic development and increasing streamflow persistence during five decades of forest development, demonstrating the value of integrating repeated floristic observations with long-term hydrological monitoring to evaluate forest restoration.