## 4 Discussion
[71] proposed a comprehensive methodological approach to both quantitatively and qualitatively estimating emission and sequestration of greenhouse gases by plants and highlighted the potential of green spaces to mitigate climate change impacts. The results of research revealed that highest weakened carbon sequestration occurs in the Zagros Mountains Forest steppe ecosystem, indicating remarkable changes in the ecosystem NPP values, and carbon sequestration and storage decreased owing to the loss of forest cover. [PERSON] et al. [72] in China and [PERSON] et al. [73] in India investigated the NPP changes in different biomes, too, and suggested that forest and farming biomes accounted for the greatest NPP fluctuations. In Iran, restoring forest ecosystems and preventing further damage or loss tothem through compatible cropping patterns, avoiding deforestation, and fire management planning could help rise carbon capture and sequestration and to some extent modulate increasing climate change trend. Environmental degradation and land use alterations have been driven by Iran's economic growth which in turn considerably influenced ecological processes, including carbon sequestration. However, the relationship between NPP and the level of anthropogenic activities in Iran is very difficult to understand because most of Iran's production activities are concentrated in the central provinces such as Tehran and Isfahan, while these provinces have high reliance of other regions on imports of raw materials and do not exploit local natural resources. Drought is a serious environmental threat across Iran, mainly due to the climate change; however, its effects are exacerbated by rapid population growth, inappropriate population distributions, land overharvesting, and poor water management [74]. The results also showed that, at the 95% confidence level, only in 27.27% of the pixels the correlation between NPP and VHI is statistically significant. Figure 7 shows the average percentage of correlation between NPP and agricultural drought in different ecosystems. Various values indicate that the effect of droughts on NPP depends on the ecosystem type. These correlations could be associated with the differences in drought intensity, drought duration and vegetation type. [PERSON] et al. [75] and [PERSON] et al. [76] discovered that the positive correlation between NPP and SPEI was more robust in the ecosystems located in arid and semi-arid climatic regions. Similarly, in the current study, the highest correlation was observed in the Zagros Mountains forest steppe (Figure 7), an ecosystem located in a semi-arid climate with the highest amount of rainfall in winter and spring. On the contrary, the weakest correlation was spotted in the Registan-North Pakistan sandy desert with cold desert climate. This ecosystem encompasses a small area in Iran; hence, caution must be exercised in making claims based on the findings. [PERSON] et al. [76] and [PERSON] et al. [77] exploited SPEI to examine the association between NPP and droughts. A problem with using SPEI is that this index may overestimate the impact of droughts in arid and semi-arid regions [13]. This is especially undesirable in Iran, with over two thirds of its area being located in arid and semi-arid climates. [PERSON] et al. [78] also assert that soil moisture is more important than drought stress in ecosystem production. This important variable, however, is not taken into account by SPEI. Figure 7: Correlation percentage between NPP with agricultural droughts in different ecosystems.