## 3 Analyses and Results
### Spatial Differences between the HJ-1-Based Forest Map, GlobCover, and MCD12Q1  
The forest cover percentages from the three datasets (HJ-1 2010, GlobCover 2009, and MCD12Q1 2009) were calculated using a 1500-m resolution aggregated grid (Figure 7); Figure 8 presents a comparison of these datasets represented as pixel frequencies of different forest cover percentages. The histogram reveals that there are approximately three to six times more pixels in the HJ-1 2010 dataset than in the MCD12Q1 2009 and GlobCover 2009 datasets with forest percentages of less than 10%. This is attributed to the fact that HJ-1 imagery at 30-m resolution can be used to identify small patches of forest, but the MCD12Q1 imagery at 500-m resolution and GlobCover imagery at 300-m resolution tend to miss small forest patches. With forest percentages of 90-100%, the pixel counts of the three datasets are all much greater than other forest percentage levels, especially the MCD12Q1 2009 dataset, which accounts for approximately 50% of the total number of pixels contributing to this percentage level. For the percentage ranges of 0-10%, 10-20%, 20-30%, 40-50%, 60-70%, and 80-90%, the order of pixel counts is MCD12Q1 2009 \(<\) GlobCover 2009 \(<\) HJ-1 2010. The GlobCover 2009 has the largest number of pixel counts within the percentage of 30-40%, 50-60%, 70-80%. Figure 7: Forest cover percentage maps from HJ-1 2010 **(a)**, GlobCover 2009 **(b)** and MCD12Q1 2009 **(c)** at a resolution of 1500 m.  
To compare the spatial difference at the pixel level, the difference for each of two forest percentage map groupings was calculated (Figures 9 and 10). For the two groupings, more than 75% of the grid cells fall within 0-100% discrepancies across the entire study area except for the northern Daxing'an Mountains, Hulun Buir region, Sanjiang Plain, and Songliao Plain. Approximately 50% of the pixels in the region fall within 0-30% discrepancies, mostly in the Songliao Plain. This indicates that the estimated forest area based on the HJ-1 2010 classification map is higher than that in the MCD12Q1 2009 and GlobCover 2009 datasets, especially for small forest patches. This is because 30-m HJ-1 images can extract small forest patches, whereas MODIS (500-m) and MERIS (300-m) images cannot. For the HJ-1 and GlobCover grouping, approximately 8% of the grid cells fall within\(-\)30%\(-\)\(-\)100% of the discrepancies, primarily in the northern Daxing'an Mountain and across the Sanjiang Plain (Figure 9a). In the northern Daxing'an Mountain, the GlobCover map contains larger forest areas than the HJ-1 map, where extensive rivers and wetlands are dispersed across the valleys, as reflected by the shape features of the forest percentage difference between the HJ-1 map and GlobCover map. In the Sanjiang Plain, a large amount of cropland was previously classified as forest. The field samples collected for those intricate regions support the results of the HJ-1 classification (Figures 11 and 12). Figure 8: Pixel frequency of different forest percentage from the HJ-1 2010, GlobCover 2009 and MCD12Q1 2009 datasets. Figure 9: Comparison maps of forest percentage at a spatial resolution of 1500 m between HJ-1 2010 and GlobCover 2009 (**a**) and HJ-1 2010 and MCD12Q1 (**b**); red indicates larger HJ-1 2010 data values, whereas green indicates larger of the other data values. Figure 11: False color image of HJ-1 and a field photo collected from the Daxing’an Mountains. (**a**) Daxing’an Mountains; (**b**) rivers and wetlands. Figure 10: Pixel frequency at various levels of percentage difference between HJ-1 2010 and GlobCover 2009, HJ-1 2010 and MCD12Q1 2009. For the HJ-1 and MCD12Q1 grouping, approximately 4% of the grid cells fall within \(-\)30%--100% of the discrepancies, primarily in the northern Daxing'an Mountains and across the southwestern Songliao Plain. The MODIS derived map (Figure 5c) shows that there is a relatively large shrub area in the southwestern Songliao Plain, but in the HJ-1-derived map the shrub patches are much smaller and more fragmented.