3.2 Neighborhood eco-effect
We derived the spatial distributions of both the largest correlation coefficients for quantitatively characterizing the optimal EP responses of the LEP, AEP, and HEP ecosystems to the snow-onset SP (Supplementary Fig. 4A, in the form of trends) over the NH (Fig. 3) and their related response directions (Fig. 4). For the case of snow-end SP, the spatial maps of both the largest correlation coefficients (Fig. 5) and the related response directions (Fig. 6) were also derived. In both of these two scenarios, the 0.5°×0.5° geo-grids performing with statistically significant EP-SP correlations, somehow, were locally clustered but globally scattered across the continents.
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The statistics of area ratios for the geo-grids, which performed with the statistically strongest EP responses of the LEP, AEP, and HEP ecosystems to the snow-onset and -end SP of both the same geo-grid and all of the surrounding geo-grids, compared to the whole NH were obtained (Fig. 2d–f, respectively). For the EP of any kind of the ecosystems, the ratio of their responses to the SP of the same geo-grids could not compare with the ratio sum for the geo-grids around, even could not compete with that for any of the geo-grids around. The same inference was available for the NA (Supplementary Fig. 5) and NE (Supplementary Fig. 6) as well. This eco-effect suggested that the productivity of the Arctic circumpolar ecosystems was more sensitive to the SP anomalies of their neighboring sites. As regards to the ratios of the EP responses to the snow-onset and -end SP, the statistics (Supplementary Fig. 7) showed that for the three kinds of ecosystems, snow-onset rather than -end SP decided their productivity for all of the NH, NA, and NE study areas. This inference is consistent with the previous finding (Vaganov et al., 1999), albeit the NA area showed a minor difference.