## 3 Results and Discussion  
On average, the mean NDVI was found to maintain higher values than the mean EVI throughout the entire period for all the NTE types except for alpine and boreal barren/sparsely vegetated lands, and boreal forest (Figure 2). This general difference between the VIs found in this study supports similar findings of the related literature [16, 21-23]. Relative to the MODIS NDVI, the MODIS EVI is reported to show improved sensitivity in high biomass regions as well as an improved vegetation monitoring capability through a reduction in atmospheric impacts on the canopy background signal. The temporally averaged values of the VI time series for each NTE as shown in Table 1 can be used as a proxy to identify temporal variability in timing of onset of greenness (start of growing season) and end of growing season (onset of leaf senescence), the dates at which the VI values stay above and below the long-term mean VI level, respectively. Mean MODIS VI values were the same for alpine barren/sparsely vegetated lands, and boreal forest, while the mean NDVI value was lower than the mean EVI value for boreal barren/sparsely vegetated lands (Figure 2). The standard deviation (SD) values of the seasonal NDVI were consistently higher than those of the seasonal EVI, thus indicating the relatively high variability of the seasonal NDVI data for the NTEs in Turkey (Figure 2 and Table 1). Both VIs, on average, exhibited a unimodal growing season, with peaks in spring and summer for all the NTEs except for alpine and boreal barren/sparsely vegetated lands, and boreal and Mediterranean forest. The EVI showed a bimodal growing season, with peaks in both winter and summer for alpine and boreal barren/sparsely vegetated lands, and boreal forest, while the NDVI showed a peak in winter for Mediterranean forest only (Figure 2). Being consistent with our findings, [PERSON] et al. [16] and [PERSON] et al. [37] found both MODIS VIs to have a similar multi-temporal response over a range of LC types, with the NDVI having higher values. In terms of potential natural LC types, biogeochemical zones, seasons, and years, the mean VIs for the seven-year period had a similar pattern of changes in that both VIs had values in the decreasing order of forest \(>\) shrubland/woodland \(>\) grassland \(>\) barren/sparsely vegetated land \(>\) snow/ice for potential natural LC; Mediterranean \(>\) warm temperate \(>\) cool temperate \(>\) boreal \(>\) alpine \(>\) (sub)nival for biogeochemical zones; summer \(>\) spring \(>\) autumn \(\geq\) winter; and 2001 and 2003 \(\geq\) 2002 \(>\) 2000 and 2004 to 2006 (Table 2). In terms of interannual variability among the LC types and biogeochemical zones, the seasonal VIs were strongly correlated in the decreasing order of barren/sparsely vegetated land grassland \(>\) shrubland/woodland \(>\) forests; and (sub)nival \(>\) warm temperate \(>\) alpine \(>\) cool temperate \(>\) boreal = Mediterranean, respectively (Table 3). The VIs had the following decreasing order of correlations: summer \(>\) spring \(>\) autumn \(>\) winter; barren/sparsely vegetated land \(>\) grassland \(>\) shrubland/woodland \(>\) forests; and (sub)nival \(>\) warm temperate \(>\) alpine \(>\) cool temperate \(>\) boreal = Mediterranean. The summer, spring and autumn VIs were more strongly correlated for grassland than the other LC types, while the winter VIs were more strongly correlated for shrubland/woodland than the other LC types (Table 3). In terms of the biogeochemical regimes, the spring, autumn, summer and winter VIs were most correlated for warm temperate, alpine, cool temperate, and winter, respectively (Table 3). The most pronounced differences between the MODIS VIs were observed in Mediterranean forest during winter, boreal forest during spring and winter, and cool temperate zone during winter.