## 2 Methods
### Data Collection
#### 2.2.2 Spectral Sampling  
To link spectral reflectance with functional composition and species diversity, sampling of spectral reflectance was performed at APEX and SPRUCE in the same plots where vegetation cover data were collected. Spectral reflectance measurements were taken at APEX using an Analytical Spectral Devices Fieldspec Pro that measured reflectance in 1-nm bandwidths between 300 and 2500 nm (Figure 3). Data were collected during peak growing season on 29 June 2016. Scans were performed during a 1-h window on each side of solar noon, which occurred at approximately 12:30 p.m. local time. The sun at the time of data collection was at an azimuth angle of approximately 151\({}^{\circ}\) east of north. Three scans were performed at each plot at the same location to acquire a local average. The instrument was positioned 1 m above the peat surface, and captured a field of view of 44 cm in diameter (Equation (1)) [65]. \[GFOV=2*height*tan\frac{(25^{\circ})}{2} \tag{1}\]  
Data were processed such that water and atmospheric absorption bands that had a relative reflectance of greater than one or less than zero were automatically excluded, as well as areas that exhibited noise from the instrument. This resulted in three regions of the electromagnetic spectrum being included in the analysis (Figure 3). Thirteen plots were sampled for vegetation and spectral reflectance among the three APEX water table manipulation treatments: five plots in the control treatment and four plots each of the lowered and raised plots. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **SPRUCE** & \multicolumn{2}{c}{**APEX**} \\ \hline PFT & Species & PFT & Species \\ \hline Forb & _Drosera rotundifolia_ & Equisetum & _Equisetum fluviatile_ \\ Forb & _Maianthemum trifolium_ & Forb & _Galium trifidum_ \\ Graminoid & _Carex magellanica_ & Forb & _Potamogeton gramineus_ \\ Graminoid & _Carex oligosperma_ & Graminoid & _Calamagrostis canadensis_ \\ Graminoid & _Carex trisperma_ & Graminoid & _Carex loilacea_ \\ Graminoid & _Eriophorum vaginatum_ & Graminoid & _Carex utriculata_ \\ Graminoid & _Eriophorum virginicum_ & Moss & _Sphagnum spp._ \\ Shrub & _Andromeda polifolia_ & Shrub & _Potentilla palustris_ \\ Shrub & _Chameadaphne calyculata_ & & \\ Shrub & _Kalmia polifolia_ & & \\ Shrub & _Rhododend_ & & \\ _greenlandcium_ & & & \\ Shrub & _Vaccinium angustifolium_ & & \\ Shrub & _Vaccinium oxycocos_ & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of vascular plant species present at both study sites and plant functional type groupings used in analysis. Spectral data were collected at SPRUCE on 22 September 2016 under clear sky conditions beginning at 1:00 p.m. local time. The sun at the time of data collection was at an azimuth angle of 178\({}^{\circ}\) east. Although it was past peak growing season, senescence had only just begun at the site, and experimentally warmed plots were still near peak growing conditions. Data collection was performed using a PP Systems UniSpec-DC spectroradiometer that detected incoming and reflected solar radiation in 3-4 nm bandwidths between 310 and 1100 nm (Figure 3). Three scans were performed above each vegetation plot in the same sampling location to acquire a local average. Details on data collection and processing are provided in [PERSON] et al. 2018 [PERSON] et al. 2018 [PERSON] et al. (2018). Reflectance was calculated for the average of the three scans following the methods of [PERSON] et al. (2014) [PERSON] et al. (2014) and [PERSON] et al. (2016 & 2018) [PERSON] et al. (2016, 2018) [PERSON] et al. (2018). Bands at the beginning and end of the spectrum were eliminated due to noise, resulting in a data range of 400-1000 nm used in the analysis (Figure 3). Data for SPRUCE chamber number 4 (+4.5 \({}^{\circ}\)C, elevated CO\({}_{2}\)) were also excluded because reflectance data for that plot presented as a significant outlier, with values that were far outside of the typical reflectance distribution collected at the other plots.