## 3 Results and Discussion

\begin{tabular}{l c c c c c c c} \hline \hline  & \multicolumn{2}{c}{Regression coefficients} & \multirow{2}{*}{\(r^{2}\)} \\ Natural terrestrial ecosystem types & & & & & & & & & \\ \cline{2-9}  & Raw NDVI & & & & & & & \\ \hline (Sub)nival snow/ice & 0.0087 & 0.919 & 93.1 & 2.26 & 0.00911 & 0.904 & 90.9 & 2.00 \\ Alpine barren/sparsely vegetated & 0.0145 & 0.912 & 92.5 & 2.08 & 0.0469 & 0.719 & 73.2 & 2.03 \\ Boreal barren/sparsely vegetated & 0.0130 & 0.910 & 92.3 & 2.17 & 0.0828 & 0.485 & 52.9 & 2.30 \\ Boreal forest & 0.0161 & 0.929 & 94.1 & 3.24 & 0.156 & 0.308 & 32.7 & 2.81 \\ Cool Temperate barren/sparsely vegetated & 0.0424 & 0.818 & 82.7 & 4.97 & 0.0121 & 0.927 & 94.4 & 19.92 \\ Cool Temperate grassland & 0.0603 & 0.789 & 79.8 & 4.58 & 0.0231 & 0.875 & 90.0 & 12.37 \\ Cool Temperate shrubland/woodland & 0.0215 & 0.929 The positive VI trends can indicate increased VI levels observed over the course of growing season, an increased capacity to fix carbon via photosynthesis, increased vegetation density and canopy cover, and progressive succession and may even reflect positive side effects of climate warming in the northern and/or high-altitude NTEs [38-43]. The highest seasonal indices of both VIs occurred consistently during the summer and spring except for Mediterranean forest in the winter according to \begin{table}
\begin{tabular}{c c c c c c c c c} \hline _Natural terrestrial_ & \multicolumn{3}{c}{_Components_} & \multicolumn{3}{c}{_Seasonal Indices_} & \multicolumn{3}{c}{_Accuracy measurements_} \\ _ecosystem types_ & Trend & Seasonal & W & Sp & Su & A & MAPE & MAD & MSD \\ \hline (Sub)nival snow/ice & 0.1125 - & A & -0.0991 & -0.0903 & 0.1494 & 0.0401 & 672.52 & 0.013 & 0.0001 \\ Alpine barren/sparsely & 0.1682 - & A & -0.1437 & -0.1203 & 0.2213 & 0.0428 & 29.40 & 0.016 & 0.0005 \\ vegetated & 0.00012*t & A & -0.1233 & -0.0973 & 0.1871 & 0.0336 & 18.71 & 0.013 & 0.0003 \\ Boreal barren/sparsely & 0.0044*t & A & -0.1666 & -0.1097 & 0.2416 & 0.0348 & 10.15 & 0.017 & 0.0006 \\ Boreal forest & 0.2408 - & A & -0.0065*t & A & -0.0852 & 0.0651 & 0.0453 & -0.0252 & 11.72 & 0.019 & 0.0007 \\ Cool Temperate & 0.2785 + & M & 0.5975 & 1.1402 & 1.1892 & 1.0729 & 9.47 & 0.020 & 0.0007 \\ Cool Temperate grassland & 0.3004 + & A & -0.1230 & 0.0267 & 0.0920 & 0.0042 & 7.36 & 0.019 & 0.0005 \\ shrubland/woodland & 0.00018*t & A & -0.1412 & -0.0286 & 0.1422 & 0.0276 & 6.31 & 0.018 & 0.0006 \\ Cool Temperate forest & 0.2560 + & M & 0.7975 & 1.2783 & 1.0589 & 0.8652 & 6.58 & 0.014 & 0.0004 \\ barren/sparsely vegetated & 0.00033*t & A & -0.0132 & 0.0716 & -0.0187 & -0.0396 & 3.14 & 0.012 & 0.0002 \\ Warm Temperate grassland & A & -0.0388 & 0.0698 & 0.0077 & -0.0387 & 3.74 & 0.016 & 0.0004 \\ Warm Temperate forest & 0.5199 - & A & -0.0959 & 0.0148 & 0.0561 & 0.0248 & 3.52 & 0.016 & 0.0004 \\ Mediterranean & 0.3196 + & M & 0.9953 & 1.2961 & 0.8493 & 0.8590 & 3.47 & 0.011 & 0.0002 \\ barren/sparsely vegetated & 0.00072*t & M & 1.0528 & 1.1615 & 0.9077 & 0.8779 & 3.23 & 0.014 & 0.0003 \\ Mediterranean & 0.3953 + & A & 0.0540 & 0.1093 & -0.0127 & -0.1506 & 17.50 & 0.053 & 0.0044 \\ shrubland/woodland & 0.00367*t & A & 0.0403 & 0.0277 & -0.0468 & -0.0211 & 2.05 & 0.011 & 0.0001 \\ Mediterranean forest & A & 0.0403 & 0.0277 & -0.0468 & -0.0211 & 2.05 & 0.011 & 0.0001 \\ \hline \end{tabular}  
* A: Additive; M: Multiplicative; t: temporal index of 1 to 28 for the period of 2000 to 2007 in the recurrent seasonal order of Winter (W), Spring (Sp), Summer (Su), and Autumn (A), respectively.  
\end{table} 
Table 5: Decomposition of MODIS NDVI time series into trend and seasonal components for natural terrestrial ecosystems in Turkey. the NDVI, thus indicating the higher VI values in the summer and spring, on average, than the rest for the NTEs (Tables 5 and 6).