Articles Earth systems science-the integrated analysis of the atmosphere, oceans, cryosphere, and biosphere as a functioning system-had its origins in the early 1980s. A few years earlier, the introduction of the now famous atmospheric "Keeling curve" for carbon dioxide (CO 2 ), measured at Mauna Loa, Hawaii, had shown definitively for the first time that humans were progressively changing Earth's total atmosphere (Keeling et al. 1976). Atmospheric scientists had recently completed the first primitive global models of atmospheric circulation. Ocean and cryospheric scientists were taking measurements of ocean temperature and ice sheet area, which, although not global, were certainly regional in scope. Unfortunately, however, ecologists (including the senior author) had no background in addressing ecology at global scales. Before the 1980s, biology focused on the organism level, and ecological studies, at best, embraced a 0.1-hectare (ha) field plot. No global ecological measurement was even considered, so analyzing seasonal trends in atmospheric CO 2 concentrations was the only option for assessing global biospheric activity. In early discussions, ecologists considered measuring vegetation density, canopy height, plant biomass, species classes, and other common ecological variables. Only slowly, by realizing that true global measurements could only be made using satellite remote sensing, did ecologists begin to develop a conceptual basis for computing a satellite-based estimate of net primary production (NPP).From a theoretical standpoint, NPP marks the first visible step of carbon accumulation; it quantifies the conversion of atmospheric CO 2 into plant biomass. The earliest attempts to evaluate ecosystem processes such as NPP at a global scale were made by geographers, and the famous estimates by Lieth and Whittaker (1975) Three activities that first evolved in the early 1980s proved to be the foundations of global-scale terrestrial ecology. First,

Rangeland extent is an important factor for evaluating critical indicators of rangeland sustainability. Rangeland areal extent was determined for the coterminous United States in a geospatial framework by evaluating spatially explicit data from the Landscape Fire and Resource Management Planning Tools (LANDFIRE) project describing historic and current vegetative composition, average height, and average cover through the viewpoints of the Natural Resources Inventory (NRI) administered by the Natural Resources Conservation Service and the Forest Inventory and Analysis (FIA) program administered by the US Forest Service. Three types of rangelands were differentiated using the NRI definition encompassing rangelands, afforested rangelands, and transitory rangelands. Limitations in the FIA definition permitted characterization of only two rangeland types: rangeland and rangeland vegetation with a small patch size. These classes were similar to those from the NRI definition but differed in tree canopy cover threshold requirements. Estimated rangeland area resulting from the NRI-and FIA-LANDFIRE models were 268 and 207 Mha, respectively. In addition, the NRI-LANDFIRE model identified 19 Mha of afforested rangelands due principally to encroachment and increased density by species classified as trees belonging to the genera Quercus, Prosopis, and Juniperus. The biggest discrepancies between acreage estimates derived from NRI-and FIA-LANDFIRE models occurred in oak, pinyon-juniper, and mesquite woodlands. The differences in area estimates between the NRI and FIA perspectives demonstrate the need for development of unified, objective methods for determining rangeland extent that can be applied consistently to all rangelands regardless of ownership or jurisdiction. While the models and geospatial information developed here are useful for national-scale estimates of rangeland extent, they are subject to the limitations of the LANDFIRE data products. ResumenLa extensión de los pastizales es un importante factor para evaluar indicadores críticos de la sustentabilidad de estas aéreas. La extensión aérea de los pastizales se determinó por los colindantes de Estados Unidos (US) en un marco geoespacial para evaluar espacialmente los datos explícitos del proyecto LANDFIRE describiendo su composición botánica histórica y actual, altura promedio, y cobertura promedio mediante el uso los criterios desarrollados por el Natural Resources Inventory (NRI) administrado por el Natural Resources Conservation Service y el Forest Inventory and Analysis Program (FIA) administrado por el US Forest Service. Tres tipos de pastizales se evaluaron usando la definición del NRI abarcando: pastizales, pastizales forestados y pastizales transitorios. Limitaciones en la definición de la FIA solo permiten la caracterización de dos tipos de pastizales: pastizales y vegetación con pequeñ as areas de pastizal. Estas clases fueron similares a aquellas de la definición de NRI pero difirieron en los requerimientos de la cubierta aérea de los árboles. Las areas de...

The potential effects of climate change on net primary productivity (NPP) of U.S. rangelands were evaluated using estimated climate regimes from the A1B, A2 and B2 global change scenarios imposed on the biogeochemical cycling model, Biome-BGC from 2001 to 2100. Temperature, precipitation, vapor pressure deficit, day length, solar radiation, CO 2 enrichment and nitrogen deposition were evaluated as drivers of NPP. Across all three scenarios, rangeland NPP increased by 0.26 % year −1 (7 kg C ha) but increases were not apparent until after 2030 and significant regional variation in NPP was revealed. The Desert Southwest and Southwest assessment regions exhibited declines in NPP of about 7 % by 2100, while the Northern and Southern Great Plains, Interior West and Eastern Prairies all experienced increases over 25 %. Grasslands dominated by warm season (C4 photosynthetic pathway) species showed the greatest response to temperature while cool season (C3 photosynthetic pathway) dominated regions responded most strongly to CO 2 enrichment. Modeled NPP responses compared favorably with experimental results from CO 2 manipulation experiments and to NPP estimates from the Moderate Resolution Imaging Spectroradiometer (MODIS). Collectively, these results indicate significant and asymmetric changes in NPP for U.S. rangelands may be expected.