## 4 Results and Analysis  
### Analysis of Variance in Forest Canopy Vertical Stratification  
In forest canopies, vertical temperature and VPD stratification vary with forest type and season. Figure 2A,B show the differences in the daily average vertical temperature from day of year (DOY) 210 to 365 at the DHS site (EBF) in 2005, and from DOY 182 to 365 in 2003 at the TMK site (DNF).  
Variances in air temperature occur in forest canopies during the growing season. In most cases, the air temperature in the tree layer is higher than that in the grass layer, with an average temperature difference of approximately 0.4 \({}^{\circ}\)C at the DHS site. In the DNF vegetation type at the TMK site, the mean temperature difference was approximately 0 \({}^{\circ}\)C before DOY 240. From DOY 240 to 280, the temperature of the tree layer was 0.5 \({}^{\circ}\)C higher than that of the grass layer. However, during the non-growing season after DOY 290, the temperature differences of the forest layer ranged from 0.5 \({}^{\circ}\)C to 1.5 \({}^{\circ}\)C, which means that the temperatures in the tree layer were higher than those in the grass layer.  
Similarly, the VPD of the tree layer in the forest canopy was higher than that of the grass layer. VPD varies with air temperature. During the summer to autumn period (DOY 180 to 300), the daily average VPD of the tree layer was approximately 120 Pa higher than that of the grass layer at the DHS site, and approximately 70 Pa higher than that at the TMK site. With the decrease in temperature during the winter period (DOY 300 to 365), the VPD of the tree layer was 50 Pa higher than that of the grass layer at the DHS site, and 25 Pa higher than that at the TMK site, which was not as great as the difference during the summer period. Figure 2B,D shows that Tdif and VPDdif have a robust linear relationship in months during the growing season.  
In a forest canopy, overstory incident PAR is much higher than that in the understory layer because the incident energy in the understory is affected by sky conditions and the overstory forest structure parameters. At the TMK site, the understory incident PAR was approximately 10% of the overstory incident PAR during the growing season when the LAI of the overstory was high (LAI = 5). However, when the overstory LAI was low during the winter period (DOY 300 to 365), the understory incident PAR was 30% of the overstory incident energy (Figure 3A). However, in EBFs such as those at the DHS site, the overstory LAI did not intensely change throughout the year. Figure 3B shows that the incident PAR of the shrub layer at the DHS site was 40% that of the tree layer, and the incident PAR of the grass layer was 20% that of the tree layer. After DOY 250, the incident PAR of the overstory layer was steadier than that in the summer period (before DOY 250) because there were fewer cloudy days; thus, the incident PAR of the grass layer was approximately 15% that of the overstory layer.  
The vertical forest structure parameters also influence the amount of understory incident PAR. Table 3 indicates that the total amount of incident PAR in the understory layer was underestimated by 2% to 3% at these two sites.  
Figure 2: Seasonal patterns in the vertical variance in temperature and vapor pressure deficit (VPD) at the DHS and TMK sites. In the subplots **(A,C)**, the blue bars (VPDdif in Pa) are the biases between the tree layer VPD and the grass layer VPD. The red line (Tdif in \({}^{\circ}\)C) is the bias between the air temperatures of the top and grass layers. The green dotted line is the 0 \({}^{\circ}\)C line, indicating no difference between the temperatures of the tree and grass layers. Subplots (**B,D**) show the relationships between Tdif and VPDdif at the two sites. The dot colors are clustered by month.