## 3 Results and Discussion
### NDVI Trends
#### 3.1.3 Spatial Pattern of NDVI Trends  
The three indicators, the annual mean, minimum and standard deviation of NDVI, were calculated for each pixel to represent vegetation productivity, minimum apparent coverage and seasonality, respectively, and their trends from 1982 to 2011 are shown (Figure 3). Dark gray represents non-vegetated area, and was identified by a 30-year average NDVI less than 0.1. This sparsely \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Month**} & \multirow{2}{*}{**Mean NDVI**} & \multicolumn{2}{c}{**Overall Trend**} & \multicolumn{2}{c}{**Trend Before TP**} & \multicolumn{2}{c}{**Trend After TP**} \\  & & \(\mathbf{(\lambda 40^{-5} NDVI\cdot yr^{-1})}\) & **TP** & \(\mathbf{(\lambda 40^{-5} NDVI\cdot yr^{-1})}\) & \(\mathbf{(\lambda 10^{-5} NDVI\cdot yr^{-1})}\) & **AIC** \\ \hline
1 & 0.27 & \(-\)24.0 & 1999 & 65 & \(-\)172 & \(-\)0.95 \\
2 & 0.26 & 14.4 & 1987 & 531 & \(-\)35 & 0.19 \\
3 & 0.28 & 40.0 & 2001 & 119 & \(-\)162 & 0.25 \\
4 & 0.34 & 166.9 * & 1998 & 246 & 61 & 1.87 \\
5 & 0.50 & 134.7 * & 1990 & 400 & 71 * & \(-\)1.36 \\
6 & 0.56 & 15.1 & 1984 & 2201 & \(-\)27 & \(-\)8.59 * \\
7 & 0.63 & 53.3 * & 1988 & 399 & 6 & \(-\)4.08 * \\
8 & 0.64 & 62.3 * & 2007 & \(-\)3 & 1088 & \(-\)13.1 * \\
9 & 0.59 & 105.6 * & 2003 & 82 & 203 & 2.02 \\
10 & 0.43 & 85.8 & 2000 & 28 & 204 & 2.21 \\
11 & 0.33 & 61.8 & 2009 & 93 & \(-\)1566 & \(-\)1.24 \\
12 & 0.29 & \(-\)16.4 & 2008 & 0.8 & \(-\)466 & 2.01 \\ \hline \hline \end{tabular}
* indicates a significant TP in terms of AIC.  
\end{table} 
Table 1: Trends and TPs of NDVI for entire study area, in each month from 1982 to 2011.  
vegetated area constitutes 22.5% of the study area, and is mainly located in southern Xinjiang (desert) and northern Tibet (ice/snow cover). From 1982 to 2011, annual mean NDVI increased significantly over 33% of the vegetated area (Figure 3a), most of these pixels were observed in central and southern China, mainly located in the following three regions: subtropical evergreen broadleaf forest, warm temperate deciduous broadleaf forest and tropical monsoon and rain forest. The annual NDVI declined sharply in the Yangtze and Pearl River deltas, because of rapid urban expansion over the past 30 years [37, 65]. Also, the regions where annual mean NDVI decreased significantly (\(\approx\)8% of vegetated area in the country) were mainly observed in northeastern China; this decrease is likely to be related to agricultural reclamation [65], consistent with the findings of [PERSON] _et al._[66] NDVI tended to decrease significantly in forest- dominated regions of the northeast China. A small proportion (\(\approx\)9%) of the vegetated area had a significant trend in minimal vegetation cover (Figure 3b; about 60% trending positive and 40% negative); these pixels were mostly located in subtropical evergreen broadleaf forest. There were areas with a significant positive trend in minimum annual NDVI (at a rate greater than 0.0035 yr\({}^{-1}\)) in Jiangxi, Hunan and Hubei provinces There was a negative trend area in southwestern China, where extreme drought occurred in the late 2000s [67]. Figure 3: Trends of (**a**) annual mean; (**b**) annual minimum and (**c**) annual standard deviation of NDVI in study area. White pixels represent no data, light gray pixels indicate an insignificant trend, and dark gray pixels are masked with threshold of 30-year mean NDVI \(<\) 0.1. About 24% of China's vegetated land showed a significant trend in vegetation seasonality (indicated by the annual standard deviation of NDVI, Figure 3c). In terms of seasonality, the areas with positive and negative trends accounted for about 21% and 3% of the vegetated area, respectively; northern China (north of 35 ) had positive trends; most regions (cold temperate deciduous coniferous  
Figure 3: _Cont._  
forest, temperate coniferous and broadleaf mixed forest, and warm temperate deciduous broadleaf forest) had increasing trends.