## 4 Discussion
### Impact of CDHEs on Carbon Dynamics  
We utilized the interaction module of GD to assess the precise effect of CDHEs on forest carbon dynamics. The results indicated that CDHEs had reduced forest NPP, inhibiting forest carbon sequestration efficiency. This finding aligned with conclusions from [PERSON] et al. [12], [PERSON] et al. [11], and [PERSON] et al. [30]. [PERSON] et al. [2] demonstrated that extreme drought and heat negatively impact vegetation carbon fluxes and ecosystem productivity. When temperatures exceed the tolerance range of vegetation, enzyme denaturation may accelerate, thereby suppressing growth [2; 71; 72]. Drought reduced carbon sequestration capacity by affecting ecosystem photosynthesis and respiration, fundamentally altering the functionality and structure of terrestrial ecosystems and potentially transforming them into carbon sources [2; 73]. Our study found that drought events more significantly explained the carbon dynamics in Nanjing forests than heat events. In contrast, heat events played a more significant role in carbon dynamics in Shaoguan. This variability may stem from the complexity of environmental factors affecting vegetation photosynthesis during CDHEs. Differences in study scope, duration, and modeling approaches contribute to varying assessments of the impact of heat and drought on VNPP. Some studies have emphasized that latitude is an essential factor that should not be ignored in assessing global or regional CDHEs [74]. This is due to the amount of heat the sun radiates at different latitudes, complicating the correlation between CDHEs. There is a difference in latitude between Nanjing and Shaoguan. This regional thermal difference further leads to differences in the ability of forest ecosystems at different latitudes to adapt to CDHEs [74]. We observed a two-month lagged effect of drought and heat events on forest vegetation types, indicating that forests have a specific capacity for recovery from extreme weather conditions. This finding aligns with previous research results [75; 76]. Forest vegetation has efficient water regulation mechanisms, flexible leaf stomatal control, and strong water absorption from deep root systems [12]. [PERSON] et al. [12] suggested that vegetation may adjust parameters such as photosynthetic rate and water use efficiency in reaction to environmental pressures following extreme climate events, potentially leading to delayed forest responses. Therefore, it shows resistance in the face of CDHEs. Table 4 indicates that CDHEs have a more substantial impact on forest NPP than single extreme events. Previous studies showed that heat can trigger heat stress in vegetation, which damages photosynthetic enzymes and inhibits the process of photosynthesis. When drought coincides with heat, it creates a low-humidity environment that exacerbates the adverse effects of heat stress and further reduces the trend of decreasing photosynthetic efficiency [12; 77]. This study revealed a pattern of synergistic or nonlinear enhancement of CDHEs, suggesting that CDHEs have a more severe impact on forest carbon dynamics than a single event, consistent with prior research findings [2; 78]. The results emphasized the importance of quantifying the effects of CDHEs on forest carbon dynamics. Finally, using the photosynthesis equation and the optimal response time, we obtained the change in forest carbon sequestration due to each CDHE in the two regions. The results show that CDHEs lead to a decrease in forest carbon sequestration. With the increase in the intensity of CDHEs, the reduction in forest carbon sequestration also increased. Therefore, in the context of global warming, increased attention must be paid to CDHEs to enhance the carbon sequestration potential of forest ecosystems. We should develop targeted coping strategies based on forests in different regions. For example, adjusting the planting structure of some forest vegetation, as well as timely irrigation and fertilization, will enhance the adaptability of forests to CDHEs.