Product-Dependent Productivity Trends and Drought-Related GPP Anomalies in Planted and Natural Forests of Subtropical China

Natural and planted forests contribute substantially to regional gross primary productivity (GPP) in subtropical China, yet their long-term productivity trajectories and drought-related GPP responses remain uncertain, particularly across different satellite products. Using two satellite GPP products (MUSES and eLUE), meteorological records, and the Standardized Precipitation Evapotranspiration Index (SPEI), we compared long-term productivity trends in stable natural (796,468 km2) and planted forests (341,696 km2) and evaluated their responses during and after the 2016 summer drought relative to a 2001–2015 baseline. Both forest types experienced significant warming alongside sustained GPP increases; however, trend magnitudes differed across products, with eLUE indicating faster growth in planted forests and MUSES showing identical rates. Despite severe meteorological drought in summer 2016, both products indicated predominantly positive GPP anomalies, with SPEI explaining less than 1.5% of spatial anomaly variation. In the post-drought period (September–October), mean GPP anomalies declined across products, but the resulting status was highly product dependent: MUSES showed stronger negative anomaly changes in planted forests and below-baseline status, whereas eLUE indicated comparable anomaly changes between forest types and persistent above-baseline GPP. In conclusion, these findings highlight product-dependent interpretations of drought-related GPP responses, without establishing universal differences in drought resistance between forest types. These event-specific findings emphasize the need to distinguish meteorological drought exposure, short-term GPP anomaly changes, and productivity relative to historical seasonal baselines, without equating these indicators with long-term ecosystem resilience or recovery.