Interannual variation in global-scale net primary production: Testing model estimates

Testing estimates of year‐to‐year variation in global net primary production (NPP) poses some challenges. Large‐scale, multiyear records of production are not readily available for natural systems but are for agricultural systems. We use records of agricultural yields at selected sites to test NPP estimates produced by CASA, a global‐scale production model driven by both meteorological data and the satellite‐derived normalized difference vegetation index (NDVI). We also test estimates produced by the Miami model, which has underlain several analyses of biosphere response to interannual changes in climate. In addition, we test estimates against tree ring data for one boreal site for which data from both coniferous and deciduous species were available. The agricultural tests demonstrate that CASA can reasonably estimate interannual variation in production. The Miami model estimates variation more poorly. However, differences in NDVI‐processing algorithms substantially affect CASA's estimates of interannual variation. Of the four versions tested, the FASIR NDVI most closely reproduced yield data and showed the least correlation with changes in equatorial crossing time of the National Oceanic and Atmospheric Administration satellites. One issue raised is the source of the positive trends evident in CASA's NDVI‐based estimates of global NPP. The existence of these trends is consistent with potential stimulation of terrestrial production by factors such as CO2 enrichment, N fertilization, or temperature warming, but the magnitude of the global trends seen is significantly greater than suggested by constraints imposed by atmospheric fluxes

Cost of Removing and Assembling Biomass from Rangeland Encroaching Eastern Redcedar Trees for Industrial Use

Eastern redcedar trees have encroached on Great Plains grasslands and are spreading at a glacial pace, reducing forage production, destroying native ecosystems, and producing human health harming allergens. The study was conducted to determine the expected cost to deliver a flow of feedstock to an optimal factory location for a business designed to use eastern redcedar biomass harvested from grasslands. Proportion of trees available for removal, quantity of feedstock required, harvest costs, and tree growth rate are critical factors. Assuring investors that a flow of eastern redcedar trees for industrial use would be attainable for 20 years at a reasonable cost may be challenging. © 2017 The Society for Range ManagementThe Rangelands archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information