(1) Background: Understanding how forest management practices regulate hydrological cycles is critical for sustainable water resource management and addressing global water crises. However, the effects of light-felling (selective thinning) on hydrological processes in temperate mixed forests remain poorly understood. This study comprehensively evaluated the impacts of light-felling intensity levels on three hydrological layers (canopy, litter, and soil) in mid-rotation Korean pine (Pinus koraiensis) forests managed under the “planting conifer and preserving broadleaved trees” (PCPBT) system on Changbai Mountain, China. (2) Methods: Hydrological processes—including canopy interception, throughfall, stemflow, litter interception, soil water absorption, runoff, and evapotranspiration—were measured across five light-felling intensity levels (control, low, medium, heavy, and clear-cutting) during the growing season. The stand structure and precipitation characteristics were analyzed to elucidate the driving mechanisms. (3) Results: (1) Low and heavy light-felling significantly increased the canopy interception by 18.9%~57.0% (p < 0.05), while medium-intensity light-felling reduced it by 20.6%. The throughfall was significantly decreased 10.7% at low intensity but increased 5.3% at medium intensity. The stemflow rates declined by 15.8%~42.7% across all treatments. (2) The litter interception was reduced by 22.1% under heavy-intensity light-felling (p < 0.05). (3) The soil runoff rates decreased by 56.3%, 16.1%, and 6.5% under the low, heavy, and clear-cutting intensity levels, respectively, although increased by 27.1% under medium-intensity activity (p < 0.05). (4) The monthly hydrological dynamics shifted from bimodal (control) to unimodal patterns under most treatments. (5) The canopy processes were primarily driven by precipitation, while litter interception was influenced by throughfall and tree diversity. The soil processes correlated strongly with throughfall. (4) Conclusions: Low and heavy light-felling led to enhanced canopy interception and reduced soil runoff and mitigated flood risks, whereas medium-intensity light-felling supports water supply during droughts by increasing the throughfall and runoff. These findings provide critical insights for balancing carbon sequestration and hydrological regulation in forest management.

Korean pine (Pinus koraiensis) nut-timber plantations are important for both timber and seed production, yet optimal water and fertilizer management for mature cone-bearing stands remains poorly understood. A two-year field experiment was conducted to evaluate the effects of three fertilization levels (F1, F2, and F3, corresponding to N:P₂O₅:K₂O application rates of 50:75:25, 100:150:50, and 150:225:75 kg ha⁻¹, respectively) and three soil moisture regimes corresponding to 80%, 60%, and 40% of field capacity (W1, W2, and W3, respectively) on tree growth, cone yield, and soil physicochemical properties in approximately 35-year-old Korean pine plantations established on Albeluvisol at Maoer Mountain, northeastern China. Tree growth and cone yield generally followed the order F2 > F3 > F1 and W2 > W1 > W3, with F2W2 (N:P₂O₅:K₂O = 100:150:50kg ha⁻¹ and 60% of field capacity) consistently producing the best performance. Compared with the control (CK, no fertilizer application, rainfed under natural ambient conditions), F2W2 increased height, diameter, and crown width increments by 46.2%, 71.4%, and 65.6%, respectively, in 2023. Per-tree cone number, total cone mass, and total pine nut mass increased progressively across years, reaching increases of 88.5%, 100.6%, and 132.4%, respectively, in 2024. In contrast, thousand-seed weight showed relatively small changes and a delayed water–fertilizer interaction. Water–fertilizer coupling significantly altered soil physicochemical properties by reducing soil pH under the optimal treatment, while also regulating inorganic nitrogen availability and soil nutrient distribution. Nitrate nitrogen was highest under W2, whereas ammonium nitrogen peaked under W1. Total nitrogen was highest under F3W1, while available phosphorus and potassium accumulated under high fertilization combined with non-optimal soil moisture, but were lowest under F2W2, indicating enhanced nutrient uptake under the optimal treatment. Cluster analysis showed that nitrate nitrogen was positively associated with growth and yield variables. Overall, F2W2 provided the most favorable balance between stand productivity and soil nutrient status, representing an effective water–fertilizer management strategy for mature Korean pine nut-timber plantations on Albeluvisol. These findings provide a scientific basis for precision water and nutrient management in northeastern China.