## 2 Methods
### Data Collection  
#### 2.2.1 Vegetation Cover Sampling  
Species and PFT cover were measured differently at the two study sites owing to differences in their respective data collection protocols (Table 1). In particular, non-vascular plants at APEX (which accounted for less than 10% of total cover) were recorded where present, whereas, at SPRUCE, mosses carpeted the soil surface and were therefore considered to have 100% cover across the site and were not included in the sampling protocol. At APEX, species cover was recorded using a point bar vegetation survey method [64]. Species were recorded along two perpendicular transects positioned across a series of replicate plots in each treatment. A metal frame was positioned above the canopy 1 m above the surface of the peat. A laser pointer was inserted into 10 evenly spaced holes in the metal frame along the transect. Species and height above the ground were recorded for all interceptions of the laser beam. This was repeated for each \"hit\" from the canopy to the surface of the peat. If the target was not photosynthetic it was recorded as either \"standing dead\", indicating that it was non-photosynthetic biomass but still standing, or as \"litter\", indicating it was part of the match forming at the surface of the peat. For the lowered and raised treatments, four replicate plots were sampled, and in the control treatment five replicates were sampled. Each species was categorized by PFT, and percent cover for each type was calculated based on the percentage of hits of each PFT relative to the entire sample (see Table 2 for species list). In addition, we calculated the leaf area index (LAI) for each point along each transect as the number of living layers of vegetation present between the canopy and the soil surface [25].  
\begin{table}
\begin{tabular}{c c c} \hline  & **APEX** & **SPRUCE** \\ \hline Peatland type & Rich fen & Ombrotophic bog \\ \hline Location & Alaska, USA & Minnesota, USA \\ \hline \multirow{3}{*}{Experimental design} & Water table manipulation with & Regression-based factorial \\  & 120 m\({}^{2}\) control, lowered and raised & between increasing temperature \\  & treatments & and CO\({}_{2}\) level \\ \hline Vegetation sampling & Point bar laser survey method & 2 m\({}^{2}\) sampling frame method \\ \hline Spectral reflectance & ASD Fieldspec Pro & Unispec DC \\ \hline \end{tabular}
\end{table}
Table 1: Description of two study sites, data types, and differing data collection methods between sites.  
Vegetation cover at SPRUCE was sampled in mid-July across the range of temperature and carbon dioxide treatments. Three 2-m\({}^{2}\) plots were sampled in each of the 13 chambers for a total of 33 plots in the final analysis. Each plot was sampled using a 1- x 2-m frame that was set onto PVC pipes installed in the experiment to facilitate repeated data collection in the exact same area. The frame was divided into 50 cells 20 x 20 cm in size. The presence of all species was recorded within each cell of the grid, and species were later grouped into PFTs (Table 2). If a species or PFT was present in half of the cells it was considered to occupy 50% of the plot. Our sampling method at SPRUCE did not allow for the calculation of the LAI.