Multi-decadal dynamics of ecosystem service interactions in boreal forests (NE China): trade-off synergy strength,...

Quantifying long-term trade-offs and synergies among forest ecosystem services (ESs) is essential for adaptive management, yet the strength and drivers of these interactions over long timescales remain poorly understood. Seven key ESs in the Great Khingan Mountains (GKM), northeast China, were assessed from 1990 to 2024 using multi-source remote sensing data, including water yield (WY), soil conservation (SC), habitat quality (HQ), leisure and recreation (LR), carbon fixation and oxygen release (CF), climate regulation (CR), and net primary productivity (NPP). A Trade-off-Synergy Strength (TSS) metric was developed to characterize both the direction and composite magnitude of pairwise ES co-change. SHAP, and self-organizing maps were integrated to identify dominant drivers and ES bundles. Results showed that SC, CF, CR, and NPP generally increased, whereas WY declined; HQ decreased markedly during 2020-2024, and LR peaked in 2015 before declining. ES interactions were mainly synergy-dominated, although LR-related pairs exhibited persistent trade-offs. Climatic variables accounted for 52.1% of the mean absolute SHAP contribution to TSS variation, while topographic factors mainly shaped ES bundle organization. Under the climatic-change conditions examined in the GKM, SHAP-based analyses suggested that positive TSS responses were generally associated with radiation, precipitation, and temperature growth rates ranging from -8.00 to 5.59 MJ·m^-2·yr^-1, -0.74 to 0.03 mm·yr^-1, and -3.22 to 1.74 °C·yr^-1, respectively. These findings provide scientific support for climate-adaptive forest management.