# Patterns of Arctic Tundra Greenness Based on Spatially Downscaled Solar-Induced Fluorescence
## 3 Results  
For the overall trend in Arctic tundra greenness from 2007 to 2013, the spatial patterns of the annual maximum NDVI trend for the GIMMS NDVI3g and MOD13Q1 were similar for almost all parts of the study area (Figure 2a,b). The tundra was greening in the North Slope of Alaska and most parts of central Siberia, and browning in the High-Arctic Canadian Archipelago, western Alaska (Yukon-Kuskokwim Delta), and eastern Siberia (high latitude area of Kolyma Lowland and Yana-Indigirka Lowland) according to the trends of NDVImax_g and NDVImax_m (Figure 2a,b). The spatial pattern of the SIFmax trend was very different from NDVImax_g and NDVImax_m. Most parts of the Arctic tundra region below 75\({}^{\circ}\) N showed browning trends (Figure 2c) according to the trend of SIFmax from 2007 to 2013. The magnitude of browning was higher in northwest Alaska, western Russia, and eastern and \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Site ID \({}^{\star}\)** & **Site Name** & \begin{tabular}{c} **IGBP \({}^{\star\star}\)** \\ **Classification** \\ \end{tabular} & **V Vegetation Type** & **Latitude** & **Longitude** & \begin{tabular}{c} **Data** \\ **Period** \\ \end{tabular} & **References** \\ \hline RU-Sam & Samoylov & Grasslands & \begin{tabular}{c} Erect dwarf-shrub \\ tundra \\ \end{tabular} & 72.37 & 126.50 & 2007–2013 & [PERSON], et al. [43] \\ RU-Tks & Tksi & Grasslands & \
\begin{tabular}{c} Nortussock sedge, \\ dwarf-shrub, moss \\ \end{tabular} & 71.59 & 128.89 & 2010–2013 & [PERSON], et al. [44] \\ RU-Cok & Chokurdakh &
\begin{tabular}{c} Open \\ shurlands \\ \end{tabular} & Low-shrub tundra & 70.83 & 147.49 & 2007–2013 & [PERSON], et al. [45] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of eddy-covariance tower information for the research. central Siberia than in other study regions. However, the vegetation showed greening for some regions, such as western Alaska, south of the High-Arctic Canadian Archipelago, and the Yamal peninsula of Russia. Additionally, the NDVImax_g of the Arctic tundra showed successive declines from 2010 for the North American Arctic tundra and the entire Arctic tundra region (Figure 3a). While the trend for NDVImax_m of Arctic tundra showed the opposite direction with increases (slope: 0.0085) from 2010 (Figure 3a). For the third greenness index, the negative SIF trend of Arctic tundra was obvious (-0.0098 mW/m\({}^{2}\)/sr/nm/year) from 2007 (Figure 3b). The average of the SIFmax for the entire Arctic tundra area changed from 0.3696 mW/m\({}^{2}\)/sr/nm (2007) to 0.2899 mW/m\({}^{2}\)/sr/nm (2013). The SIF of two separate continents (North America and Eurasia Arctic) had a similar time-series pattern to the Arctic tundra area. The annual GPP of three flux sites showed overall declines (Figure 3c), and the temporal pattern (2007-2009) between the SIF and the annual GPP was similar. The maximum value of the monthly GPP showed a decline for the RU-Sam site (Figure 3d). Figure 2: Spatial patterns of the Arctic tundra greenness (annual maximum value) trend from 2007 to 2013. (**a**) GIMMS NDVI3g, (**b**) MOD13Q1, and (**c**) SIF (unit: mW/m\({}^{2}\)/sr/nm/year). The green colors represent the tundra greening, while the yellow, brown, and red colors represent the tundra browning. In terms of Arctic tundra greenness in the area of the EC tower flux measurements, the two NDVI remote sensing indices showed similar trends. The SIFmax data only included three of the EC flux sites, and showed overall negative trends. Two sites, Samoylov and Tiksi of Russia, had a similar temporal pattern with the ground data. When comparing the EC-observed GPP with the NDVI and SIF, the \(p\)-value was lower than 0.05 for three flux sites (Figure 4). The coefficient of determination (R\({}^{2}\)) between SIF/NDVI and GPP was calculated for each flux site.