## 4 Discussion  
### Do EVI and NDVI Correlate with Canopy Height?  
In this section, we explore the first objective that EVI, due to its assumed sensitivity to canopy structure and density, would demonstrate stronger positive correlations with CHM compared to NDVI--an expectation challenged by our findings. Of the two VIs, NDVI exhibited higher static correlations with CHM30 (a joint measure of height and cover) (Table 1) across all classes. This corroborates the findings from [PERSON] et al. [106] where several VIs were compared over wetland sites in the US.  
To address the second sub objective--supported by the different performance of NDVI and EVI across the examined classes--we found that the most notable divergent response between the VIs was in the upland forest class (Table 1) where NDVI showed a significantly stronger correlation with mean canopy height (r 0.58, \(p\) < 0.01) than EVI (r 0.22, \(p\) > 0.05). This finding indicates NDVI increases either as woody biomass grows taller, or when the gaps between taller woody vegetation fill in.  
Of the landcovers examined, EVI only showed a highly significant correlation with shrubs (r = 0.59, \(p\) < 0.01), which was almost as high as NDVI (r = 0.63, \(p\) < 0.01), indicating that EVI was less responsive to canopy structure variations in tall tree (primarily confer) environments. Shadow effects are expected to influence the spectral response of NDVI and EVI in taller vegetation areas, with inclusion of the blue band making EVI more susceptible to visible light variations caused by shadows (as reported by [PERSON] et al. [107]). While inclusion of the blue band in EVI helps mitigate against saturation [34; 35], the vegetation canopy cover in the PAD rarely approaches saturation in either VI, suggesting that for total foliage variations within northern environment tall woody vegetation classes, the benefits of EVI do not exceed NDVI.  
Figure 10: Landsat-derived LST changes and trend lines (through all raw data points) from 2000 to 2018. “All land” = all no-permanent water areas; “EVI+” = all areas of TS greening trend; “NDVI+ minus EVI+” = NDVI greening after masking areas of EVI greening. The box represents the interquartile range of LST for each year and the center line is the median.  
Furthermore, woody vegetation generally exhibits lower reflectance in visible bands compared to herbaceous species [108], which could contribute to the lower EVI sensitivity to height and cover variations observed in taller forest vegetation classes. [PERSON] et al. [109] reported a negative correlation between IKONOS-derived EVI and forest cover measures of effective LAI. High susceptibility of EVI to the effects of shadows, viewing and illumination geometry were also reported by [PERSON] et al. [110], [PERSON] et al. [111], [PERSON] et al. [112], [PERSON], [PERSON] and [PERSON] [106] and [PERSON] et al. [113].  
This contrast in shadow sensitivity between NDVI and EVI underscores the importance of selecting appropriate indices based on specific environmental conditions and the physical characteristics of the vegetation. However, both NDVI and EVI demonstrated their strongest correlations with canopy cover in shrub swamps (Table 1, r = 0.65 and r = 0.59, respectively). The high correlation between canopy cover and VI likely reflects the dense and uniform vegetation typical of shrub swamps, where both indices are effective in capturing the biomass and structure due to limited soil and water interference that influence spectral response.