# An Object- and Shapelet-Based Method for Mapping Planted Forest Dynamics from Landsat Time Series
## 3 Results
### Planting Year Characterization  
The expansion of the planted forests in the NHAR over the past three decades (1991-2020) is depicted in the planting year map (Figure 10a). All the forests planted before 1992 were marked as 1991. Three sites were purposely selected to display the map in detail. The planted forests in Figure 10b were mainly established during the period 2000-2010 (especially in 2005), and they have become an ecological protective screen to effectively block the invasion of the Mu Us desert. As shown in Figure 10c, economic forests, such as apricot (_Armeniaac sibirica_ L.), were cultivated in the irrigated areas to increase rural incomes and improve the environment ([PERSON] et al., 2015). The years that these planted forests were established were not uniform, but they were mainly planted after 1998. Figure 10d shows that the site, as a water conservation area (rainfed agricultural system), has carried out continuous planting initiatives since the 1990s, with remarkable achievements around 2005 and 2012. The annual planting area (1991-2020) (in Figure 10e) derived from the planting year map reveals that 93.1% of the planted forests in the 2020 NHAR forest map were established after 2000. The planted forest began to increase in 2000, reached a peak in 2005, and remained at a high level until 2014. A decline occurred after 2015; however, it can be explained by the fact that the young forest canopy was not close enough to be detected in the classification process. The statistics of the afforestation area for each year from the NHAR Statistical Yearbook are described in Figure 10e as well. In general, during the past three decades, the annual afforestation area in the NHAR began to increase around 2000 and remained stable after 2005 with a high level. Therefore, the trend of the planting area in the Landsat data is generally consistent with the official statistics, indicating the Chinese government began to implement forestry eco-engineering programs, such as GPP and Three Northern Protected Forest Program (TNSFP), for improving the ecosystems and promoting economics since 2000 in the study region ([PERSON] et al., 2009; [PERSON] et al., 2010). The inconsistency happened in 2002-2004, with a significant increase in the afforestation area but with little change in the annual planting area derived from the planting year map, which may be due to the lower rate of survival of trees in the early days ([PERSON] et al., 2009; [PERSON] et al., 2010). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Land Cover**} & \multicolumn{4}{c}{**Classified Data**} & \multirow{2}{*}{**Total**} & \multirow{2}{*}{**Producer Accuracy (PA)**} \\ \cline{3-3} \cline{5-6}  & & **Natural Forest** & & & **Planted Forest** & **Non-Forest** \\ \hline \multirow{3}{*}{Referenced Data} & Natural forest & 89 & 2 & 9 & 100 & 89.0\% \\  & Planted forest & 2 & 81 & 17 & 100 & 81.0\% \\  & Non-forest & 3 & 5 & 92 & 100 & 92.0\% \\ \hline Total & 94 & 88 & 118 & 300 & \\ \hline User Accuracy (UA) & 94.7\% & 92.0\% & 78.0\% & \\ \hline \multicolumn{3}{c}{Overall Accuracy = 87.3\%, Kappa = 0.82.} \\ \end{tabular}
\end{table} 
Table 2: Confusion matrix of the NHAR natural/planted forest maps in 2020. The planting year labels of the planted forest samples (including 100 samples in Table 2 and 100 random samples) were assigned with the help of the Landsat time series and high-resolution images. Excluding the samples that were not correctly classified in Table 2, a total of 181 planted forest samples were available for the planting year assessment. Figure 11 shows a comparison of the mapped versus observed years of the planted trees. The overall RMSE of the two data sources is 2.46 years. Additionally, the regression line shows an apparent correlation (R\({}^{2}\) = 0.81) between them. It reveals a slight underestimation of the planting year of trees before 2000 but an overestimation for the younger forests, particularly around 2010, when the dispersion is comparably large. Figure 10: **(a)** The 2020 NHAR planting year map.