## 3 Results  
The annual NPP distribution pattern in different ecosystems for the interval ranging from 2000 to 2020 was calculated. The results showed that the degree of carbon sequestration in Iran, which varies to 1.38 kg\({}^{\text{s}}\)C/m\({}^{2}\), is a function of geographical longitude and latitude (Figure 3). In fact, the northern parts of the country registered a higher amount of carbon sequestration in comparison with the southern regions. There is also a decrease in the amount of carbon sequestration in the direction from west to east, with the exception of a cluster in the northern regions, where a high degree of carbon sequestration was detected due to the existence of the Hypcanian coniferous forest ecosystem on the edge of the Caspian Sea. Almost no carbon sequestration was recorded in the central parts of Iran, which is home to the ecosystem of the Central Persian desert basins and is characterized by lack of rainfall and poor vegetation. Ecosystems which recorded an average carbon sequestration above 100 g\({}^{\text{s}}\)C/m\({}^{2}\) are located in the north of Iran, whereas those registering an average carbon sequestration of fewer than 100 g\({}^{\text{s}}\)C/m\({}^{2}\) are mainly located in the central and eastern parts of the country. The highest amount of carbon sequestration was detected in Caspian Hyrcanian mixed forests, Azerbaijan shrub desert and steppe, and Elburz Range forest steppe, which is located in the north of Iran, with average carbon sequestration rates of 492.90, 329.51 and 225.99 g\({}^{\text{s}}\)C/m\({}^{2}\), respectively. Conversely, Arabian Desert and East Sahero-Arabian xeric shrulands and Tigris-Euphrates alluvial salt marsh, located in southwestern Iran, were the ecosystems that recorded the lowest rate of carbon sequestration (0.20 and 12.60 g\({}^{\text{s}}\)C/m\({}^{2}\), respectively). We also calculated the coefficient of variation (CV) for different ecosystems. Arabian Desert and East Sahero-Arabian xeric shrulands (CV = 5.99) and Tigris-Euphrates alluvial salt marsh (CV = 1.87) in southwestern Iran were the two ecosystems registering the  
Figure 3: The spatial distribution of median net primary productivity in Iran, 2000–2020. highest variability, which indicates instability in the amount of photosynthesis in these ecosystems. On the other hand, the lowest CVs were recorded for the Middle East steppe and the Badghyz and Karabil semi-desert ecosystem (with CV indices of 0.19 and 0.20, respectively). This indicates that vegetation photosynthesis in the studied period was relatively stable in these regions during the studied period. Moran's I was calculated in light of the values of each pixel to understand whether carbon sequestration followed a clustered or dispersed pattern. Given that the value obtained for spatial Moran (0.9701) was higher than the expected value (\(-0/00001\)) and the \(p\)-value was equal to 0.000, the spatially clustered pattern of carbon sequestration in Iran was confirmed. Figure 4 demonstrates the available trends of carbon sequestration for each pixel obtained through conducting Mann-Kendall with a confidence level of 95%. Overall, 65.8% of the pixels in Iran indicates a statistically insignificant trend, while 34.2% of them demonstrates a significant increasing and decreasing trends. As Figure 4 suggests, some parts of western, northwestern, northeastern, and central Iran possess a significant rising trend. The highest increasing trend obtained through the Z score (0.94) was observed in the Eastern Anatolian Mountain steppe. Additionally, the increasing trend of carbon sequestration was detected around mega cities such as Tehran, Isfahan, and Mashhad, which is attributed to planting trees in the surrounding areas of these cities. The highest increasing rates were observed in the Eastern Anatolian Mountain steppe (91.1%) and mountainous Zagros forests (62.26%). Figure 4 further shows that northern and southwestern parts of Iran recorded a significant decreasing trend.