Leaf biomechanical property is a composite metric to quantify both force (or work) needed to punch, tensile, or shear a laminar surface. As a plant defense strategy adopted by plants in response to external disturbances, their connection with leaf-litter decomposition through afterlife effects has not been systematically evaluated to date. Here, we determined 37 functional traits (including 12 leaf biomechanical traits, through three standard tests and expressed them in mass or area basis), as controller over leaf-litter decomposition dynamics, across 186 plant species from diverse functional types in a botanical garden in Southwest China. Biomachanical traits exhibited high environmental plasticity and co-varied substantially with chemical and structural traits. Quantified as per area, they outperformed mass-based ones as predictors in forecasting decomposition rate. Incorporating all traits into multidimensional space identified the “force to punch” the most important contributor for plant specialisation along the first PCA axis (also identified as leaf economic spectrum), which constrained the pace of decomposition. Given the independently effect (p < 0.001) of leaf's intrinsic resistance property on decomposition, leaf mass per area, a surrogate for leaf physical strength (or toughness), cannot sufficiently substitute biomechanical traits. We also found, since tensile force in leaves with parallel veins may underrepresent leaf-litter decomposition rates and overlap with other biomechanical properties, exploring punch force and shearing work as key biomechanical traits offers a promising research avenue for improved understanding leaf traits' influence on decomposability.