Net primary production estimates compiled by the combined efforts of the Global Primary Production Data Initiative, covering 2523 individual sites and 5164 half-degree grid cells

Net primary production (NPP) data from existing field measurements are being compiled for approximately 100 study sites covering several major world ecosystem types. These data are used by global change modelers to develop and validate models of vegetation-soil-atmosphere interactions within the global carbon cycle and to help calibrate remote sensing of vegetation worldwide Under the auspices of the Global Primary Production Data Initiative (GPPDI), NPP estimates were compiled for 2,523 sites and 5,164 half-degree grid cells, by investigators based at the Environmental Sciences Division, Oak Ridge National Laboratory (ORNL), Tennessee, USA and the Department of Geography, University of Maryland, USA. The GPPDI database includes NPP measurements collected over a long time period by manyinvestigators using a variety of methods. Progress in modeling the global carbon cycle was previously inhibited by the lack of adequate observational data for model parameterization and validation, such as NPP and its individual components from field measurements. To address this problem, the GPPDI was set up as a Focus 1 activity of the IGBP Data and Information System, a coordinated international program to improve worldwide estimates of terrestrial NPP for parameterization, calibration, and validation of NPP models at various scales. Under the auspices of the GPPDI, NPP estimates were compiled for 2,523 sites and 5,164 half-degree grid cells, by investigators based at the Environmental Sciences Division, Oak Ridge National Laboratory (ORNL), Tennesseee, U.S.A. and the Department of Geography, University of Maryland, U.S.A. Together, these data represent a more comprehensive database of NPP measurements than has previously existed. The GPPDI database includes NPP measurements collected over a long time period by many investigators using a variety of methods. The minimum requirements for data to be included were as follows: 1. the use of one or more accepted methods to estimate aboveground or belowground NPP, 2. geographical location for the study site, 3. definition of biome or vegetation type, and 4. citable reference to peer-reviewed publication, symposium or workshop proceedings, book chapter, or technical memorandum. The point measurements of NPP were categorized as either Class A, representing intensively studied or well-documented study sites (e.g., with site-specific climate, soils information, etc.), Class B, representing more numerous"extensive" sites with less documentation and site-specific information available, or Class C, representing regional collections of half-degree latitude-longitude grid cells