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Fig. 1.   Plot of total (a) and above-stump (b) woody biomass versus cumulative growing season NDVI. The growing season is defined as the period when NDVI is greater than 0.1 because values below this threshold tend to be associated with marginally vegetated regions, senescing vegetation, and bare soils. Data from 171 of the 205 provinces (Sweden twice), where forest area is greater than 15% of the land area, are shown. The wood volume data sources from which biomass was computed are inventory yearbooks (Finland, Norway, and Sweden) and reports (10-12). Outlier 1 is British Columbia (Canada) and outliers 2 are data from Washington, Oregon, and (northern) California. These represent 16% of North American forest area. The data, without the outliers, were regressed to obtain a statistically significant relation between biomass and greenness levels by using the following specification: (1/y) = a + b*Lat + c*[(1/x)/Lat²] + e, where Lat is latitude of the inventory province centroid (degrees), x is growing season NDVI total, averaged over the 5-year inventory period, and y is either above-stump or total woody biomass per ha of the province, e is a normally distributed random error, and a, b, and c are regression coefficients. The value of these coefficients is estimated by using ordinary least squares. For total biomass, a = 0.0377 (±0.00977), b = 0.0006 (±0.00011), c = 3809.65 (±902.51); adjusted r² = 0.43. For above-stump biomass, a = 0.0557 (±0.0136), b = 0.000854 (±0.000153), c = 5548.05 (±1274.17); adjusted r² = 0.49. Values in parentheses are standard errors. Using t tests, we reject the null hypothesis that the individual regression coefficients are equal to zero (P < 0.001).

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