The NPP Database Dictionary defines the common terms, codes, and conventions used in the database. Data in the NPP Database may have been reformatted to achieve consistency in format and definitions of variables. Some of the processing or conversions that are often necessary to have common definitions include: expressing biomass as dry weight, expressing NPP as carbon equivalents, and distinguishing above-ground, below-ground, and total plant components. Missing numeric values are assigned a code of "-999.9."
Since the data were collected by research workers using a variety of methods, secondary users of these data are encouraged to consult the general scientific literature as well as the published study site descriptions in order to more fully understand the data from each site. The NPP Database Dictionary attempts to standardize the terms and abbreviations used by field workers and modellers, but may not include the full range of synonyms used for plant biomass and production parameters.
All the terms used throughout the NPP Database are defined, although they sometimes differ from biome to biome. The following list was prepared principally with reference to grasslands.