## 3 Results
The highest declining trend with a Z score of \(-0.86\) was observed in the Caspian Hyrcanian mixed forests ecosystem. The minimum trend change (\(-82\) g*C/m\({}^{2}\)) was also observed in this ecosystem. On the contrary, the highest mean of positive trend (12.29 g*C/m\({}^{2}\)) was detected in the Azerbaijan shrub desert and steppe, while the maximum trend change (53.41 g*C/m\({}^{2}\)) was registered for the Zagros Mountains forest steppe. Table 2 displays the percentage and area of trend changes for each ecosystem (kg/m\({}^{2}\)/year) categorized into four classes: extreme negative trend (\(-83\) to \(-30\)), slight negative trend (\(-30\) to \(0\)), extreme positive trend (\(0\) to \(30\)), and slight positive trend (\(30\) to \(53\)). Caspian Hyrcanian mixed forests had the largest area with negative trend covering (12,598.61774 km\({}^{2}\) equal to 24%), whereas the smallest area with negative trend was \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**ECO\_NAME** & **MIN** & **MAX** & **RANGE** & **MEAN** \\
**(g*C/m\({}^{2}\))** & **(g*C/m\({}^{2}\))** & **(g*C/m\({}^{2}\))** & **(g*C/m\({}^{2}\))** & **STD 1** \\ \hline Caspian Hyrcanian mixed forests & \(-80.73\) & \(52.19\) & \(132.9\) & \(-12.25\) & \(16.43\) \\ Tigris–Euphrates alluvial salt marsh & \(-16.39\) & \(11.58\) & \(27.98\) & \(-3.09\) & \(4.73\) \\ Arabian Desert and East Sahero-Arabian seric shrublands & \(-8.66\) & \(0.56\) & \(9.22\) & \(-0.62\) & \(1.48\) \\ Kopt Dag semi-desert & \(-15.93\) & \(12.14\) & \(28.08\) & \(-0.61\) & \(8.59\) \\ Caspian lowland desert & \(-23.81\) & \(25.39\) & \(49.21\) & \(-0.02\) & \(10.97\) \\ Registan–North Pakistan sandy desert & \(-6.21\) & \(2.34\) & \(8.55\) & \(0.90\) & \(2.04\) \\ South Iran Nubo-Sindian desert and semi-desert & \(-22.70\) & \(37.69\) & \(60.40\) & \(1.88\) & \(5.6\) \\ Kuh Rud and Eastern Iran montane woodlands & \(-21.60\) & \(33.95\) & \(55.56\) & \(3.382\) & \(2.37\) \\ Badghyz and Karabil semi-desert & \(-4.30\) & \(9.92\) & \(14.22\) & \(3.99\) & \(1.34\) \\ Mesopotamia shrub desert & \(-3.04\) & \(10.82\) & \(13.86\) & \(4.39\) & \(2.30\) \\ Central Persian desert basins & \(-34.84\) & \(44.67\) & \(79.51\) & \(4.73\) & \(4.41\) \\ Lake & \(-9.90\) & \(18.45\) & \(28.35\) & \(5.41\) & \(4.20\) \\ Elburz Range forest steppe & \(-38.08\) & \(53.15\) & \(91.24\) & \(5.59\) & \(6.28\) \\ Zagros Mountains forest steppe & \(-59.83\) & \(53.41\) & \(113.25\) & \(6.10\) & \(4.19\) \\ Kopet Dag woodlands and forest steppe & \(-13.26\) & \(24.57\) & \(37.84\) & \(6.19\) & \(2.69\) \\ Middle East steppe & \(7.72\) & \(7.72\) & \(0\) & \(7.72\) & \(0\) \\ Eastern Anatolian montane steppe & \(-78.40\) & \(51.93\) & \(130.33\) & \(8.58\) & \(4.86\) \\ Azerbaijan shrub desert and steppe & \(-44.71\) & \(40.42\) & \(85.14\) & \(12.29\) & \(5.79\) \\ \hline \hline \end{tabular} \({}^{1}\) Standard Deviation.  
\end{table} 
Table 1: Statistical calculations NPP of slope change in different ecosystems. Figure 5: [PERSON]’s slope of NPP. recorded for the Badghyz and Karabil semi-desert ecosystem with an area smaller than 1 km\({}^{2}\) (0.037%). On the other hand, the Zagros Mountains forest steppe with an area of 149421/1033 (42%) and Kuh Rud and Eastern Iran mountain woodlands with an area covering less than 1 km\({}^{2}\) (0.0005%), respectively, were the largest and smallest regions with positive trend. Considering the association between carbon sequestration and agricultural droughts, the regions where a significant positive correlation was observed between NPP and VHI are illustrated in Figure 6. The strongest correlations were detected in the north, northeast, and southwest, while the weakest correlations were recorded in the central parts of Iran. As observed, save for two ecosystems (i.e., Middle East steppe and Baluchistan xeric woodlands), positive correlations between NPP and VHI were observed for the entire country.