NPP Grassland: NPP Estimates from Biomass Dynamics for 31 Sites, 1948-1994

Field measurements of biomass and associated environmental data were compiled for multiple study sites in major grassland types worldwide. When sufficient biomass data were available, we compared NPP estimated by six different algorithms for 31 grassland sites to examine potential bias associated with the algorithms (Scurlock et al. 2002). This data set includes monthly grassland biomass data and NPP estimates produced by the different algorithms.

The data consisted of monthly measurements of biomass components including aboveground live material, standing dead, litter, belowground biomass, and belowground dead material. However, many of the sites did not collect all of the components. There are 1477 field measurements of some component of NPP, all sites having at least aboveground biomass measurements. Of the 31 sites, 20 also measured standing dead and litter or total live plus dead material. In addition, 17 sites measured total belowground biomass, and six of these sites provided separate measurements of live and dead root components. The study sites had from 1 to 29 years of biomass data with an average of 3 years per site. Five ecoregions were represented, including cold desert steppe, temperate dry steppe, humid savanna, humid temperate, and savanna.

The selection of study sites was based on the availability of complete and consistent information on NPP or at least partial NPP, together with the dynamics of live biomass and dead matter for at least the growing season (Scurlock et al. 2002). Site-description metadata, such as latitude, longitude, elevation, and information on vegetation type (biome), soil type, and land-use history were also desirable for inclusion for study sites in the compilation.

In addition, we included study sites that had at least one reference from the peer-reviewed literature. Quality assurance included mapping the points in geographical space to confirm that they coincided with landforms and checking data ranges for outlying values. For consistency, only measurements from long-term natural or ungrazed treatments were used in the analysis of Scurlock et al. (2002), although measurements are available for manipulated study sites from the ORNL DAAC's NPP Web site (see below). One of the 31 sites (i.e., Kurukshetra, India) appears to be an outlier because it has an ANPP that is 3 to 7 times that of the other grassland sites. The high NPP may be a consequence of some undocumented factor such as a previous history of fertilization at the study site. Because Kurukshetra meets all other criteria for inclusion, it is included here; however, users may choose to exclude it from their specific application.

We processed the original grassland biomass observations for each site to generate data sets that had common variable names, units of measure, and organization. For example, we assumed that the variables described in the original literature as outstanding dead, recent dead, dead were equivalent, representing plant matter which was produced and had died within the current year, and that the variables old dead and litterusually represent the accumulation of previous years' production. Some sites lacked desired information, such as the day of the month that measurements were recorded, or required decisions to assemble the data, such as combining aboveground and belowground measurements when the components were measured on different days. When possible in these cases, we examined the original literature or contacted the authors to confirm our data processing decisions.

Aboveground and belowground components were processed separately, and, if measurements for both components were available, ANPP and BNPP were summed to provide total NPP for the site. In the summary of annual NPP, sites with fewer than five biomass measurements for a year were dropped to ensure that the entire growing season was represented (assuming most sites measured biomass on an approximately monthly schedule).

Climatological data for each study site (precipitation, mean monthly maximum temperature, mean monthly minimum temperature) were obtained from the original literature or the original authors, if available. Alternatively, we obtained the climate data from the nearest weather station (<10 km distant, and at similar elevation) if available from existing collections such as the National Climatic Data Center (Asheville, NC, U.S.A.) or the Carbon Dioxide Information and Analysis Center (CDIAC, Oak Ridge National Laboratory, Oak Ridge, TN, U.S.A.) see the individual sites' site descriptions for details and specific sources of climate data.

References for the source of site data and NPP estimates for specific years, biomass, climate, and other associated environmental variables for the 31 detailed study sites are available on the Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC) NPP Web site (http://www.daac.ornl.gov/NPP/npp_home.html). Many of the sites have data for multiple treatments as well as ancillary information such as site photographs and graphs of biomass dynamics and climate.

In addition to grasslands, the global database NPP from the ORNL DAAC includes forest sites based upon field observations (Scurlock and Olson 2002) to address the need for a high quality data to parameterize, calibrate, and validate terrestrial biosphere models (Olson et al. 2001). NPP estimates in the database draw primarily on the published estimates of NPP. While this analysis of grassland methods demonstrated a potential bias of estimated NPP depending biome type and on which method was used, users are encouraged to review site information to decide which NPP estimates are appropriate for a particular application.

Cite this data set as follows:

Scurlock, J. M. O., K. R. Johnson, and R. J. Olson. 2003. NPP Grassland: NPP Estimates from Biomass Dynamics for 31 Sites, 1948-1994. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.

Scurlock, J. M. O., K. Johnson, and R. J. Olson. 2002. Estimating net primary production from worldwide extant grassland biomass dynamics measurements. Global Change Biology 8:736-748.

Scurlock, J. M. O., and R. J. Olson. 2002. Terrestrial Net Primary Productivity--A brief history and a new worldwide database. Environmental Reviews 10:91-109.

Olson, R. J ., K. Johnson, D. Zheng, and J. M. O. Scurlock. 2001. Global and Regional Ecosystem Modeling: Databases of Model Drivers and Validation Measurements. ORNL/TM-2001/196. Oak Ridge National Laboratory, Oak Ridge, Tennessee.

The following two files are included in the grasslands NPP data set. Missing or unavailable values are represented by -9999. Variables, units of measure, and example data records are provided below.

File: Grassland NPP_biomass_months (contains 1490 biomass field measurements)

Example data records from the Grassland NPP_biomass_months data file:

SITE,TREATMNT,YEAR,MONTH,DAY,JDATE,AGBMASS,AGTOTCLP,CROWN,BGTOTMAT,
STDEAD,LITTER,BGBMASS,BGDEAD,AGTOTMAT
bcn,lngtrm,1972,3,30,90,67.7,-9999,-9999,-9999,-9999,-9999,-9999,-9999,574.4
bcn,lngtrm,1972,6,2,154,198.4,-9999,-9999,-9999,-9999,-9999,-9999,-9999,570.7

 File:   Grassland NPP_site_summary (contains location, climate, and vegetation characteristics for 31 sites, along with NPP estimates by five methods).

The methods referenced in the Grassland NPP_site_summary. See Table 1 of Scurlock et al. 2002 for specific details.

Method	Description
1	Peak live biomass
2	Peak standing crop (live plus standing dead matter)
3	Maximum minus minimum live biomass
4	Sum of positive increments in live biomass
5	Sum of positive increments in live and dead plus litter

Example data records from the Grassland NPP_site_summary data file:

Site,Name,Country,Rainfall,Temperature,Elevation,Latitude, Longitude,C3_C4,Vegetation,Ecoregion,ECORGN_Bailey,
Reference,Start,End,N_years,N_trtmt,Ny_x_Nt,AGbiomass/litter, Bgbiomass,ANPP_lit,BNPP_lit,TNPP_lit,NYR,
MAX_MON,ANPP1, ANPP2,ANPP3,ANPP4,ANPP5,ANPP6,BNPP1,BNPP2,BNPP3,BNPP4,BNPP5,NPP1,
NPP2,NPP3,NPP4,NPP5
bcn,Beacon Hill,U.K.,858,11,205,50.92, -0.85,C3,chalk grassland,Humid temperate,Humid temperate broadleaf
forest(243),Williamson(1976),1972,1973,1,1,1, monthly,N/A,691, -9999,-9999,1,8,355,574,287,287,333,287,
-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999
bdk,Badkhyz,Turkmenistan,310,12.6,700,35.68,62,C3,desert steppe, Temperate dry steppe,Temperate dry steppe (343),
Gilmanov et al. (1997),1948,1982,34,1,34,monthly,N/A,100, -9999,-9999,17,5,54,-9999,50,50,-9999,-9999,-9999,
-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999

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