## 3 Results
### Mapping the Spatiotemporal Patterns of FCO\({}_{2}\) and Exploring Their Topographical Effects  
Based on the optimal RF, we finally map the spatiotemporal patterns of FCO\({}_{2}\) with 500 m pixel size. We further calculated the mean of FCO\({}_{2}\) during the dry season, autumn, and winter to understand the spatial patterns of the FCO\({}_{2}\) across the forested watershed as shown in Figure 8. Generally, the distribution of FCO\({}_{2}\) shows a similar spatial pattern among different periods, while the FCO\({}_{2}\) varied across the watershed. Like what we observed at the two monitoring areas, the regional mean FCO\({}_{2}\) in autumn (8.7 g C m\({}^{-2}\) day\({}^{-1}\)) is higher than that in winter (7.2 g C m\({}^{-2}\) day\({}^{-1}\)) (Figure 8b,c). In autumn, most areas are occupied by the high FCO\({}_{2}\) values (>8 g C m\({}^{-2}\) day\({}^{-1}\)) and these areas are mainly distributed in the northwest and center of the watershed (Figure 8b). In contrast, the simulated FCO\({}_{2}\) values are comparatively low in winter (<6 g C m\({}^{-2}\) day\({}^{-1}\)) in most areas of the watershed (Figure 8c).  
Moreover, the FCO\({}_{2}\) maps show that the topography has a clear effect on the spatial distribution of FCO\({}_{2}\) values. To demonstrate it, we further counted the FCO\({}_{2}\) of different elevations, slopes, and aspects to investigate how topography influences the spatial distribution of FCO\({}_{2}\). The elevations were divided into 10 levels with 100 intervals (Figure 9a), the slopes were divided into 9 grades at 5-degree intervals (Figure 9b), as well as the aspects were separated as the shady slope (0-45\({}^{\circ}\) and 315-360\({}^{\circ}\)), semi-shady slope (225-315\({}^{\circ}\)), semi-sunny slope (45-135\({}^{\circ}\)), and sunny slope (135-225\({}^{\circ}\)) (Figure 9c). It obviously shows that the pattern of topographic effects on FCO\({}_{2}\) is similar when measured at different periods (i.e., dry season, autumn, and winter) (Figure 9a-c). However, the effect of a specific topographic factor on FCO\({}_{2}\) varies distinctly. For example, a large number of the FCO\({}_{2}\), higher than  
Figure 8: The average spatial patterns of FCO\({}_{2}\) in the whole dry season (**a**), autumn (**b**), and winter (**c**). The spatial distribution of the FCO\({}_{2}\) map is based on the mean values obtained from the two areas.  
9 g C m\({}^{-2}\) day\({}^{-1}\), are mainly occurred in the relatively high altitude areas, while the low values (<8 g C m\({}^{-2}\) day\({}^{-1}\)) are found below 300 m (Figure 9a). In other words, the FCO\({}_{2}\) in high-altitude areas is higher than that in low-altitude areas. For slopes, the high FCO\({}_{2}\) values are mainly concentrated on slopes of 10-25 degrees (Figure 9b). Besides, no matter what season, the value of FCO\({}_{2}\) on the sunny slope is always higher than that on the shady slope, and the order of FCO\({}_{2}\) value in different aspects is: sunny slope > semi-sunny slope > semi-shady slope > shady slope (Figure 9c).  
Figure 9: FCO\({}_{2}\) changes are associated with elevation (**a**), slope (**b**), and aspect (**c**). The grey error bars indicate the corresponding standard deviations.