Decoupling of structural and functional forest recovery: heterogeneity in post-fire normalized difference vegetation index (NDVI) and net primary productivity (NPP) trajectories across China (2000–2015)

Forest fires are major disturbances that reshape ecosystem structure and function, yet post-fire trajectories of vegetation greenness and productivity often diverge. The spatial patterns and drivers of this structural–functional decoupling remain insufficiently understood. Here, we quantified differences between normalized recovery trends of normalized difference vegetation index (NDVI) and net primary productivity (NPP) in China's forests during the first five years following single-burn events (2001–2015) using a metric termed ΔnSlope (defined as the difference between normalized NDVI and NPP recovery slopes). By applying a sensitivity threshold of 0.5 standard deviations to distinguish significant decoupling from background noise, we found that 53.93% of the burned areas exhibited significant structural–functional decoupling. Specifically, functional recovery (NPP) significantly outpaced structural recovery (NDVI) in 29.60% of the total burned area. Spatially, NPP‑lead decoupling was most pronounced in northeastern forests and the North China–Inner Mongolia ecotone, while synchronous or NDVI‑lead patterns occurred in southwestern regions. Using a random forest model on the continuous dataset, we identified that fire-year precipitation was the strongest positive driver of synchrony, whereas post-fire drought stress amplified divergence. Topography and soil properties further modulated heterogeneity, with higher elevation, steeper slopes, and sandy soils increasing decoupling by constraining resource availability. These findings reveal substantial spatial variability in post-fire ecosystem recovery across China and highlight the dominant role of water availability in shaping structural–functional dynamics. The results provide a scientific basis for region-specific forest restoration and resilience management under a changing climate. • A novel ΔnSlope metric quantifies post-fire NDVI and NPP recovery decoupling. • Functional recovery (NPP) generally outpaced structural recovery (NDVI) in China. • Moisture availability dominates recovery; post-fire drought intensified divergence. • The framework guides region-specific forest restoration and resilience monitoring.