# Parallel Seasonal Patterns of Photosynthesis, Fluorescence, and Reflectance Indices in Boreal Trees
## 3 Results
### Correlations  
Correlations between photosynthetic activity and optical metrics, including F\({}_{\text{S}}\) and reflectance indices (NDVI, PRI, and CCI), are shown in Figure 4, and summarized in Table 1a for evergreen species, and Table 1b for deciduous species. For evergreens, _P. mariana_ and _P. glauca_ showed weak correlations between the NDVI and photosynthetic activity, while _P. banksiana_ showing a moderate correlation (Figure 4a). Deciduous species showed strong correlations (Figure 4e). For evergreens, the PRI showed strong correlations with photosynthetic rate (Figure 4b), while in broad-leaf deciduous species, the PRI showed moderate correlations, and in _L. laricina_, a strong correlation was found (Figure 4f). Strong correlations emerged between the CCI and photosynthetic rate for all evergreen and deciduous species (Figure 4c,g). F\({}_{\text{S}}\) had strong correlations with photosynthetic rate for all evergreen species (Figure 4d), but moderate correlations were seen for broad-leaf deciduous species, and no significant correlation was seen for _L. laricina_ (Figure 4h). The slopes of the regressions between both the NDVI and PRI and photosynthetic rate were significantly different for evergreen and deciduous species (_p_\(<\) 0.0001), indicating functionally distinct behavior of these indices in the two vegetation types. The regression slopes between both the CCI and F\({}_{\text{S}}\) and photosynthetic rate in evergreen and deciduous species were not significantly different (_p_\(>\) 0.05). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Species** & **n** & **NDVI** & **PRI** & **CCI** & **F\({}_{\text{S}}\)** \\ \hline a) & _P. mariana_ & 17 & (10) & 0.318 * & 0.905 *** & 0.945 *** & 0.891 *** \\  & _P. banksiana_ & 21 & (13) & 0.556 *** & 0.853 *** & 0.928 *** & 0.908 *** \\  & _P. glauca_ & 17 & (10) & 0.199 & 0.950 *** & 0.914 *** & 0.922 *** \\ b) & _L. laricina_ & 16 & (9) & 0.861 *** & 0.796 *** & 0.896 *** & 0.307 \\  & _P. tremuloides_ & 14 & (8) & 0.937 *** & 0.505 ** & 0.881 *** & 0.674 * \\  & _P. balsamifera_ & 14 & (8) & 0.828 *** & 0.595 ** & 0.824 *** & 0.692 * \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Linear correlation coefficients (\(r^{2}\)) between canopy-level optical indices (normalized difference vegetation index (NDVI), photochemical reflectance index (PRI), chlorophyll/caroenoid index (CCI), and steady-state fluorescence (Fs)) and photosynthetic rate for evergreen (**a**) and deciduous (**b**) species. Data points from the spring transition in 2016 for _P. glauca_ and _P. mariana_ were excluded from analyses. The sample size for F\({}_{\text{S}}\) was smaller than for reflectance indices, and is indicated in parentheses. Annual correlations between F\({}_{\text{S}}\) and reflectance indices (NDVI, PRI, and CCI) are shown in Figure 5, and summarized in Table 2a for evergreen species, and Table 2b for deciduous species. For the NDVI, weak correlations with F\({}_{\text{S}}\) were seen in all evergreens (Figure 5a), except for _P. bansiana_, which yielded a good correlation, but with a very small range of NDVI values compared to deciduous species that had moderate correlations (Figure 5d). The PRI had strong correlations with F\({}_{\text{S}}\) for all evergreen species (Figure 5b), and moderate correlations for two deciduous species (Figure 5e). The CCI had strong correlations with F\({}_{\text{S}}\) for all evergreen species (Figure 5c), and moderate correlations for deciduous species (Figure 5f). The slopes of the regressions between both the NDVI and PRI and F\({}_{\text{S}}\) were significantly different in deciduous and evergreen species (_p_ < 0.0001, and \(p\) < 0.05), again indicating functionally distinct behavior of the NDVI and PRI in the two vegetation types. The regression slopes between the CCI and F\({}_{\text{S}}\) in deciduous and evergreens were not significantly different (_p_ > 0.05).