# Parallel Seasonal Patterns of Photosynthesis, Fluorescence, and Reflectance Indices in Boreal Trees
## 3 Results
### Seasonal Patterns of Photosynthesis and Remote Metrics
For the broad-leaf deciduous species, the spring transition was very rapid, with sampling periods limited to before budburst and following early leaf expansion. _L. laricina_ showed more gradual spring activation than the broad-leaf deciduous species. Maximum photosynthetic rates varied greatly during the growing season for broad-leaf species, but were regularly above 10 umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) until the start of the fall transition, while _L. laricina_ had more consistent photosynthetic rates (ca. 10 umol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)) during the growing season. During the fall transition, photosynthetic rates for broad-leaf species decreased more quickly than for _L. laricina_, with near-zero rates by the end of September and mid-October, respectively. For evergreens, except for declines during periods of snow, the NDVI was relatively constant through the year (ca. 0.8), but dropped slightly in spring during a brief period of decreased tree density following repotting (Figure 3b). For deciduous species, canopy-level NDVI values increased abruptly in spring and decreased abruptly in the fall (Figure 3g). Maximum values of the NDVI (ca. 0.85) were seen in the early summer, when trees were flush with foliage. Prior to the rapid spring transition, when trees lacked foliage and mostly bare soil was being sampled, NDVI values were approximately half (ca. 0.4) the summer maximum. Similar values were seen in late-fall following senescence, when canopies had no green foliage. Snow caused marked declines in the NDVI, and minimum values of the NDVI (ca. 0.1-0.2) occurred in the winter months when snow was present. Seasonal patterns of the PRI varied for deciduous and evergreens species. For evergreens, seasonal PRI patterns closely followed temperature and increased gradually from winter minima (ca. \(-\)0.2: _P. mariana_ and _P. glauca_; and ca. \(-\)0.27: _P. banksiana_) to near-growing season maxima (ca. \(-\)0.03 and ca. \(-\)0.06, respectively), following the spring transition (Figure 3c). The PRI for _P. banksiana_ increased slightly (ca. \(-\)0.04) towards the end of the summer, prior to the fall transition. Through the fall, PRI values decreased gradually to winter minima (ca. \(-\)0.2: _P. mariana_ and _P. glauca_; and ca. \(-\)0.27: _P. banksiana_). Over the winter period, spikes in the PRI corresponded with periods of snow. PRI values for deciduous species had less overall variation than was seen with evergreens (Figure 3h), but still showed indications of seasonal changes associated with spring leaf development and fall senescence. Prior to the growing season, PRI values were slightly higher for the broad-leaf deciduous species (ca. \(-\)0.8) compared to _L. laricina_ (ca. \(-\)0.14). Following the spring transition, PRI values increased sharply to maximum growing season values (ca. \(-\)0.03). The fall senescence period saw a gradual decrease in the PRI. During leaf senescence, when leaves visibly yellowed, values slightly dropped below those prior to the spring transition (ca. \(-\)0.16), then increased slightly after leaf-fall. For evergreens, the CCI showed strong seasonal variation that roughly coincided with changes in temperature (Figure 3d). Winter values of the CCI were lower for _P. banksiana_ (ca. \(-\)0.25) than the spruce species (ca. \(-\)0.1), and _P. banksiana_ trees were visibly stressed during this period, showing a red-yellow needle coloring. During the spring transition, the CCI increased sharply for all evergreen species. The maximum CCI occurred in early summer for _P. mariana_ and _P. glauca_ (ca. 0.2), which coincided with the later stages of budburst, when new branches were nearly fully elongated and developed. The maximum CCI for _P. banksiana_ (ca. 0.2) was seen later in the summer, during a period when needles were elongating following vertical shoot growth. The CCI gradually decreased during the fall transition for both spruce species. This decrease was more rapid for _P. banksiana_ than for _P. mariana_ and _P. glauca_.