Assessing Synergistic Effects on NPP from a Refined Vegetation Perspective: Ecological Projects and Climate in Heilongjiang

Net Primary Productivity (NPP) serves as a key indicator of ecosystem health and productivity. However, most existing research focuses on primary land cover types, overlooking the dynamic response processes of NPP in refined vegetation types to multiple climate drivers. Furthermore, it lacks systematic analysis of the feedback mechanisms through which China’s Five-Year Plan (FYP) ecological projects regulate climate stress. This study, based on refined vegetation classification, systematically analyzes the dynamic changes in NPP in Heilongjiang Province from the 10th to the 13th FYP periods (2001–2020), with a focus on refined vegetation types. Results show that between 2001 and 2020, mixed-leaved forest emerged as the core driver of regional NPP change during the 12th FYP (NPP increase of +58.4 gC·m−2·a−1). Although deciduous needle-leaved forest (DNF) showed the highest cumulative increase (+64 gC·m−2·a−1), it experienced significant degradation (p < 0.01) in 57%–62% of its area during the 12th and 13th FYP periods. The dominant climate driver shifted from precipitation (positively correlated in 74% of the area during the 10th–11th FYPs) to drought stress dominated by vapor pressure deficit (VPD) (positive correlation increasing to 54%). Ecological projects mitigated the negative impact of temperature, reducing the area with negative correlations by 13%. Overall, the ecological policies of the FYP exerted a weak negative influence. However, forest vegetation was strongly regulated by VPD (SV = −0.61~0.59), while grasslands and croplands exhibited high sensitivity to temperature. These findings underscore the contrasting climate policy responses among plant functional groups, highlighting the urgent need for differentiated ecological management strategies.