3.1.1. Sensitivity of annual forest GPP
On average, decreasing ASWC to 50 mm from 200 mm had
only a moderate influence (5–20% change) on annual forest GPP
estimates within all level 1 ecoregions across the U.S.A. (Fig. 1a).
Ecoregions containing forests that showed N20% variation in
GPP with a large reduction in ASWC were predominately in the
south, central and western parts of the country and included: 6
(Northwestern forested mountains); 9 (Great Plains); 10 (North
American Deserts); 11 (Mediterranean California); and 13
(Temperate Sierras) (Figs. 1a and 2). Ecoregions with a large
proportion of forested pixels showing b5% variation in GPP
values from the standard ASWC of 200 mm included: 9 (Great
Plains), 13 (Temperate Sierras) and 15 (Tropical Wet Forests)
(Fig. 1a).