<p>Inspired by the thermal annealing concept in materials science, this study presents an eco-friendly thermal modification strategy to upgrade fast-growing poplar into high-performance structural glulam columns, addressing its inherent humidity sensitivity and mechanical deficiencies. The axial compression behavior and damage evolution of full-scale modified columns were systematically investigated under varied slenderness ratios (<i>λ</i> = 10.66–53.29) and humidity conditions (60% and 90% relative humidity). Results demonstrate that thermal modification significantly enhances dimensional stability and reduces moisture uptake, leading to remarkable improvements in load-bearing capacity (up to 33.7% under high humidity) and stiffness. Notably, the failure mode of slender columns shifts from instability-driven buckling to material strength-dominated crushing after modification. Integrated acoustic emission and digital image correlation analyses reveal that tensile microcracks prevail (~ 70% of events) and damage evolves through four distinct stages. A sensitivity analysis of the critical acoustic emission classification threshold confirms the robustness of this finding. A novel stability correction coefficient is introduced to quantify the thermo-hygro-mechanical coupling effects, with predictive equations established and validated using coefficient of determination, mean absolute error and root mean square error metrics. Comparative analysis with other engineered timber systems shows that the proposed modification achieves comparable or superior performance gains to conventional reinforcement methods while maintaining eco-friendly characteristics. This work validates the feasibility of using thermally upgraded fast-growing poplar in sustainable timber construction, providing both mechanistic insights and practical design tools for humidity-resilient glulam structures.</p>