All the terms used throughout the ORNL DAAC NPP Database (principally associated with sites in the grassland biome) are defined below.

Since the field measurements 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 (see References) in order to more fully understand the data from each site.

Net primary productivity (based on field measurements of biomass)

NPP

estimated net primary productivity (g/m2/year)

ANPP

estimated above-ground net primary productivity (g/m2/month or g/m2/year)

BNPP

estimated below-ground net primary productivity (g/m2/month or g/m2/year)

CumANPP

Cumulative ANPP during the course of a year or 12-month period (g/m2 since start of measurement interval)

Notes: NPP may be estimated for above-ground only (ANPP), below ground (BNPP) or above plus below ground. Unless otherwise specified, the term "NPP" implies that some attempt has been made to include an estimate or guess of below-ground production as well as above-ground production. Units are g/m2/[measurement interval], where the measurement interval may be the interval between successive monthly samples, or may be an interval over which NPP has been summed (quarter-year or year).

NPP for grasslands is expressed in g/m2/year (oven-dry matter). For the purposes of modelling carbon fluxes, NPP may sometimes be expressed in gC/m2/year, where 1.0 gramme carbon is equivalent to 2.2 grammes oven-dry organic matter (organic matter = 45% carbon by weight)

Above-ground matter (sometimes described as shoot matter)

AGbiomass

above-ground live biomass (g/m2)

Note: this is probably the most consistently measured and therefore the most comparable parameter between different study sites

Stdead

standing dead plant matter, not yet fallen (g/m2)

litter

dead plant matter lying on ground (g/m2)

AGTotdead

Stdead+ litter (i.e. total dead plant matter) (g/m2)

AGTotclip

AGbiomass+ Stdead (i.e. total plant matter which might be clipped without any sorting) (g/m2)

Note: this is sometimes described rather ambiguously as "standing crop"

AGTotmatter

AGTotclip + litter (i.e. total live + dead plant matter) (g/m2)

AGr

relative rate of decomposition for above-ground dead matter (g/g/month)
Note: usually a function of available water for decomposer organisms and micro-organisms, as well as a function of temperature. Strictly speaking, AGr decreases as decomposition proceeds, while the proportion of resistant material remaining increases. However, simple field measurements of decomposition usually determine an average initial rate over 1-2 months.

Below-ground matter (sometimes described as root matter)

BGbiomass

below-ground live biomass (g/m2) *

BGdead

below ground dead matter (g/m2) *

BGTotmatter

BGbiomass + BGdead (i.e. total below-ground plant matter) (g/m2) *

* Note: any or all of the above may include perennating organs such as rhizomes, although these may be measured as a separate category. "Crown biomass" may also be reported separately; the crown refers to the stump left behind at ground level after clipping, from which new shoots will grow. Since the crown remains attached to the roots, crown biomass is usually included with below-ground biomass - however, in some cases it may be added to the above-ground biomass category. If crown biomass is considered important, refer to the original literature or data originator for details.

BGr

relative rate of decomposition for below-ground dead matter (g/g/month)

Note: usually a function of available water for decomposer organisms and micro-organisms, as well as a function of temperature. Strictly speaking, BGr decreases as decomposition proceeds, while the proportion of resistant material remaining increases. However, simple field measurements of decomposition usually determine an average initial rate over 1-2 months.

Nutrient determination

N-AGbio

Nitrogen content of above-ground live biomass (g N/m2)

P-AGbio

Phosphorus content of above-ground live biomass (g P/m2)

S-AGbio

Sulphur content of above-ground live biomass (g S/m2)

Climate data

These are represented by a parameter field (4 characters) followed by either a temporal field indicating year (19XX) or a long-term statistic (mean, stdv, numb), where stdv = standard deviation; numb = number of years contributing to the statistics.

Prec 19XX

Total precipitation for each month [Jan, Feb, Mar,.....Dec] and total for the year [Year] for year 19XX (mm)

Prec mean Long-term

average precipitation for each month [Jan, Feb, Mar,.....Dec] and long-term average annual total [Year] (mm)

Tmin 19XX

Minimum temperature for each month [Jan, Feb, Mar,.....Dec] and minimum for the year [Year] for year 19XX (C)

Tmax 19XX

Maximum temperature for each month [Jan, Feb, Mar,.....Dec] and maximum for the year [Year] for year 19XX (C)

Tmin mean

Long-term average minimum temperature for each month [Jan, Feb, Mar,.....Dec] and long-term average annual minimum temperature [Year] (C)

Tmax mean

Long-term average maximum temperature for each month [Jan, Feb, Mar,.....Dec] and long-term average annual maximum temperature [Year] (C)

Time and basic site description

date

Date (Year, month, day), e.g. 1995, 06, 01

Juliandate

Day of the year (1 to 365)

Tyear

Date expressed as 19XX.FFF where 19XX = year and .FFF = (Julian date/365)

Note: this is a convenient way of displaying the time base for measurements extending over many years, since a measured parameter can be plotted directly against the parameter [tyear].

site

Unique 3-character code for each site, based on the first three consonants in the site name (e.g. NRB for Nairobi)

treatment

8-character code indicating the long-term site management or experimental treatment; used to differentiate between multiple data sets collected at the same site.