# Forest Resistance and Resilience to 2002 Drought in Northern China
## 3 Results
### Spatial Distribution of Ecosystem Stability of the Forests to Drought in 2002
#### 3.3.1 The Resistance during Drought in 2002  
Generally, the range of R\({}_{\text{EVI}}\) and R\({}_{\text{GPP}}\) was similar, which was [1.16, 84.38] and [1.00, 76.58], respectively. The range of R\({}_{\text{MTE-GPP}}\) was the smallest, between 1.25 and 45.17 (Figure 5a, outliers were excluded). This difference was due to the higher magnitude of MTE-GPP in 2001, which resulted in a relatively sharp decrease in the drought year 2002. The spatial distribution of resistance generated from EVI (R\({}_{\text{EVI}}\)) and GPP (R\({}_{\text{GPP}}\)) showed  
Figure 4: Interannual variations of standardized monthly EVI (orange line), GPP (red line), and MTE-GPP (blue line) during 2001–2006.  
Figure 3: The ratio of forest areas under different water balance conditions in 2002. DNF stands for the stable deciduous needleleaf forest pixels, and DBF stands for the stable deciduous broadleaf forest pixels.  
similar pattern (Figure 6a vs. Figure 7a), albeit the R\({}_{\text{TEVI}}\) were generally higher than the R\({}_{\text{GTP}}\). More than that, the spatial distribution of R\({}_{\text{MTTE-GPP}}\) was distinctly different from that of R\({}_{\text{TEVI}}\) and R\({}_{\text{GPP}}\) (Figure 8a). In the north area, the high values of R\({}_{\text{MTTE-GPP}}\) was not only higher, but also more spatial-clustered than the other two spatial distributions. Meanwhile, many pixels illustrated opposite results between R\({}_{\text{MTTE-GPP}}\) and R\({}_{\text{TEVI}}\) with R\({}_{\text{GPP}}\). The pixels with R\({}_{\text{TEVI}}\) and R\({}_{\text{GPP}}\) higher than 100 often had a R\({}_{\text{TEVI}}\) value lower than 20 in both the east and the south of the study area. The results implicated different response regimes of MODIS-EVI, MODIS-GPP, and MTE-GPP to drought.  
Figure 5: Boxplot of (**a**) resistance during 2002; (**b**) resilience one year after 2002 drought; (**c**) resilience two years after 2002 drought; and (**d**) resilience four years after 2002 drought. Outliers were removed. The blue box stands for values of stable DNF. The pink box stands for values of stable DBF.  
Figure 6: Spatial distribution of (**a**) resistance to drought in 2002; (**b**) resilience 1-year after 2002 drought; (**c**) resilience 2-years after 2002 drought; and (**d**) resilience 4-years after 2002 drought, calculated from EVI.  
and MTE-GPP were 0.58, 0.57, and 0.65, respectively, which implied similar recovery levels of canopy and gross photosynthesis.  
The spatial distribution of resilience 2-years after the 2002 drought was different from the 1-year after resilience. Rs calculated from EVI, GPP, and MTE-GPP all illustrated higher recovery, especially in the northeast of the study area (Figures 6c, 7c and 8c). These changes supported the perspective that forests generally need more than one year to recover from annual droughts.  
When it came to the fourth year (2006) after the 2002 drought, the overall mean growing season SPEI12 was exactly at the 25 th percentile, which was the threshold of normal year and moderate drought. The changes of the resilience were unevenly distributed as \(\text{R}_{\text{EVI-4}}\), \(\text{R}_{\text{GPP-4}}\), and \(\text{R}_{\text{SMTE-GPP-4}}\) shown (Figures 6d, 7d and 8d). Some areas showed continuously increasing resilience, while some others' resilience decreased. The inconsistency might be due to the spatial heterogeneity of hydrothermal conditions. These results called for further comparison considering the water balance condition pixel-by-pixel.