Impact of the interaction between drought and wildfires on the gross primary productivity (GPP) of boreal forest exhibit time-scale dependence on time scales

Changes in forest gross primary productivity (GPP) are essential for understanding the dynamics of the global carbon cycle and impacts of climate change. Given the increasing frequency of droughts and wildfires due to climate change, assessing their impact on GPP in boreal forests has become increasingly important. This study utilized remote sensing data, including GPP data, the standardized precipitation-evapotranspiration index (SPEI), and burned area data from 2001 to 2022, and employed trend analysis, Pearson correlation analysis, and Shapley Additive Explanations (SHAP values) to examine the spatiotemporal characteristics of GPP in boreal forests and their response mechanisms to drought and wildfires. The results were as follows. (1). GPP in boreal forests exhibited a spatial pattern of being higher in the south and lower in the north, with approximately 54.14 % of the area exhibiting an increasing trend in GPP and approximately 41.0 % showing a decreasing trend. (2) Areas with a declining GPP highly overlapped with regions that experienced intense drought. The SPEI primarily showed a negative correlation with GPP; however, the proportion of positively correlated areas increased with longer SPEI time scales. (3) Wildfires generally exerted a negative impact on vegetation GPP, as burned areas typically decreased in productivity compared to unburned regions; however, most affected areas demonstrated a basic recovery in GPP within five years. (4) Shrublands, grasslands, and savannas exhibited a higher GPP sensitivity to drought and wildfires, whereas forest communities demonstrated greater ecological resilience. (5) The interaction between drought and wildfires exacerbated negative impacts on GPP over short-term time scales; however, a gradual weakening influence was observed over medium- to long-term timescales. This study offers novel insights into and a theoretical foundation for assessing and understanding the impacts of drought and wildfires on the GPP of boreal forests.