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NPP Grassland: Hays, USA, 1970, R1
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Revision date: October 23, 2014

Summary:

This data set contains three ASCII files (.txt format). Two files contain above- and below-ground biomass and productivity data for a mixed prairie grassland, one file for an ungrazed treatment and the other for a moderately grazed treatment. The study site (38.87 N, - 99.38 W, Elevation 714 m) is located in the central Great Plains near the city of Hays, Kansas, about 400-km west of Kansas City. The third file contains monthly and annual climate data for the period 1891-1994 obtained from a weather station (38.87 N, -99.38 W, Elevation 613 m) located at the Hays grassland study site.

Dynamics of above-ground living and dead plant biomass were monitored by the harvest technique at roughly 2-week intervals during the growing season of 1970. Total below-ground biomass was sampled at the same intervals by manual coring within the harvested plots to a depth sufficient to include at least 90% of the root mass. Data were collected as part of a coordinated study over 1-3 years at ten grassland sites of the central and western United States, under the US Grassland Biome Project of the International Biological Program (IBP).

Annual above-ground net primary production (ANPP) was estimated conservatively by summing peak biomass of individual species. These values were 363 g/m2/year for ungrazed and 372 g/m2/year for grazed grassland plots. Annual below-ground net primary production (BNPP) was estimated as the sum of positive increments in total root biomass (including root crowns); 1,062 g/m2/year for ungrazed and 855 g/m2/year for grazed grassland plots.

Revision Notes:Only the documentation for this data set has been modified. The files have been checked for accuracy and are identical to those originally published in 1998.

Additional Documentation

The Net Primary Productivity (NPP) data collection contains field measurements of biomass, estimated NPP, and climate data for terrestrial grassland, tropical forest, temperate forest, boreal forest, and tundra sites worldwide. Data were compiled from the published literature for intensively studied and well-documented individual field sites and from a number of previously compiled multi-site, multi-biome data sets of georeferenced NPP estimates. The principal compilation effort (Olson et al., 2001) was sponsored by the NASA Terrestrial Ecology Program. For more information, please visit the NPP web site at http://daac.ornl.gov/NPP/npp_home.html.

Data Citation:

Cite this data set as follows:

Hulett, G.K., and G.W. Tomanek. 2014. NPP Grassland: Hays, USA, 1970, R1 . Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, USA. doi:10.3334/ORNLDAAC/208.

This data set was originally published as:
Hulett, G.K., and G.W. Tomanek. 1998. NPP Grassland: Hays, U.S.A., 1970. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.

Table of Contents:

 

1. Data Set Overview:

Project: Net Primary Productivity (NPP)

Productivity of a mixed prairie grassland was monitored at the Hays, Kansas (38.87 N, -99.38 W, Elevation 714 m) during 1970. The study site is located in the central Great Plains about 400-km west of Kansas City. The Fort Hays branch station was established in 1906.

Dynamics of above-ground plant biomass were monitored at roughly 2-week intervals during the growing season. Data on above-ground live biomass and standing dead matter are available for two replications of a moderately grazed and an "ungrazed" (relatively undisturbed) treatment. Total below-ground biomass was also sampled.

Annual above-ground net primary production (ANPP) was estimated conservatively by summing peak biomass of individual species, and annual below-ground net primary production (BNPP) was estimated as the sum of positive increments in total root biomass (including root crowns).

Table 1. Annual above-ground net primary production at Hays, 1970 (g/m2/year)

YEAR UNGRAZED GRAZED
1970 363 372

Table 2. Annual below-ground net primary production at Hays, 1970 (g/m2/year)

YEAR UNGRAZED GRAZED
19701,062 855

Source: Sims and Singh (1978b), Table 4, p. 583. BNPP for the ungrazed grassland is also reported in Esser (2013) and in Scurlock and Olson (2013).

Note: Productivity values are also reported in Olson et al. (2013a; b), but do not agree with the values given above because different calculation methods and conversion factors were used.

Climate data are available for the period 1867-1994 from a weather station (38.87 N, -99.38 W, Elevation 613 m) located at the Hays grassland study site.

 

2. Data Description:

Spatial Coverage

Site: Hays, Kansas, USA

Site Boundaries: (All latitude and longitude given in decimal degrees)

Site (Region) Westernmost Longitude Easternmost Longitude Northernmost Latitude Southernmost Latitude Elevation (m)
Hays, Kansas, USA -99.38-99.3838.8738.87714

Spatial Resolution

Sampling in each treatment area generally involved two replications with 20 plots per replication. Exceptions were one replication with 10 plots on two sampling occasions in the recently grazed treatment area. Harvest plots ranged in size from 0.25 to 0.5 m2; these plots were usually square or rectangular in shape.

Temporal Coverage

Biomass measurements were made from 1970/01/16 through 1970/11/15 at the ungrazed site and from 1970/01/16 through 1970/12/18 at the grazed site. Precipitation data are available from 1867/01/01 through 1994/12/31. Temperature data are from 1893/01/01 through 1994/12/31.

Temporal Resolution

Biomass measurements were made at roughly 2-week intervals during the growing season. All NPP estimates are based on plant dry matter accumulation, expressed as g/m2year. Climate data are expressed as monthly and annual precipitation amounts (mm) and monthly and annual average maximum/minimum temperatures (degrees C). Monthly and annual climatic means are available for the 1867-1994 period (precipitation) and 1893-1994 period (temperature).

Data File Information

Table 3. Data files and descriptions

FILE NAMETEMPORAL COVERAGE FILE CONTENTS
hys1_npp.txt 1970/01/16 - 1970/11/15 Above- and below-ground biomass and NPP data for an ungrazed grassland at Hays, Kansas, USA
hys2_npp.txt 1970/01/16 - 1970/12/18 Above- and below-ground biomass and NPP data for a moderately grazed grassland at Hays, Kansas, USA
hys_cli.txt 1867/01/01 - 1994/12/31 Monthly and annual climate data from the weather station at the Hays, Kansas, USA grassland site.

NPP Data. Biomass estimates for the Hays site are in two files, one for each treatment (Table 3). The data sets are ASCII files (.txt format). The first 18 lines are metadata; data records begin on line 19. The variable values are delimited by semicolons. The values -9, -99, -99.9, and -999.9 are used to denote missing values. All NPP units are in g/m2/year (dry matter weight). Below-ground depth is reported in cm.

Table 4. Column headings in NPP files

COLUMN HEADINGS DEFINITION UNITS
Site Site where data were gathered (code refers to site identification) Text
Treatmt Long term management of site (code refers to treatment described in metadata in data file)
Year Year in which data were collected Numeric
Mn Month in which data were collected
Dy Day on which data were collected
Jdate Date in Julian year
Tyear Date in decimal year (year plus the Julian date divided by 365)
nrep Number of replicates
nplots Number of sampling plots
AGbiomass Mean above-ground standing crop of living biomass; each value is the mean of two replicates g/m2
AGbm_SE Standard error for above-ground living biomass measurement
Olddead Mean above-ground stnding crop of old dead biomass (i.e., carry-over material from the previous year); each value is the mean of two replicates
Oldd_SE Standard error for above-ground old dead biomass measurement
Newdead Mean above-ground standing crop of new dead biomass (i.e., material produced and senesced during the current growing season); each value is the mean of two replicates
Newd_SE Standard error for above-ground new dead biomass measurement
AGTotclip Mean total above-ground standing crop biomass (living + dead); each value is the mean of two replicates
Total_SE Standard error for total above-ground biomass measurement
BGtop30 Mean below-ground standing crop biomass in top 30 cm sample; each value is the mean of two replicates
BGtotal Mean total below-ground stnding crop biomass; each value is the mean of two replicates
BGdepth Maximum below-ground sampling depth cm

Note: All values are from Sims et al. (1978), Appendix III.

Sample NPP Data Record <hys1_npp.txt>

Site;Treatmnt;Year;Mo;Dy;Jdate;Tyear;nrep;nplots;AGbiomass;AGbm_SE;Olddead;Oldd_SE;Newdead;Newd_SE;
AGTotclip; Totcl_SE;nrep_BG;nplot_BG;BGtop30;BGtotal;BGdepth
hys;ungrazed;1970;01;16; 16;1970.044; 2; 20; 0.0; 0.0; 228.4; 39.2; 0.0; 0.0; 228.4; 39.2; -9;-99;-999.9;-999.9; -99.9
hys;ungrazed;1970;01;26; 26;1970.071; -9;-99;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9; 1; 10;2818.7;2818.7; 15.0
..
hys;ungrazed;1970;11;01;305;1970.836; -9;-99;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9; 1; 10;3689.6;3689.6; 15.0
hys;ungrazed;1970;11;15;319;1970.874; 2; 20; 0.0; 0.0; 0.0; 0.0; 197.1; 10.2; 197.1; 10.2; -9;-99;-999.9;-999.9; -99.9


Sample NPP Data Record <hys2_npp.txt>

Site;Treatmnt;Year;Mo;Dy;Jdate;Tyear;nrep;nplots;AGbiomass;AGbm_SE;Olddead;Oldd_SE;Newdead;Newd_SE;
AGTotclip; Totcl_SE;nrep_BG;nplot_BG;BGtop30;BGtotal;BGdepth
hys;rcntgrzd;1970;01;16; 16;1970.044; 2; 20; 0.0; 0.0; 125.1; 24.6; 0.0; 0.0; 125.1; 24.6; -9;-99;-999.9;-999.9; -99.9
hys;rcntgrzd;1970;01;26; 26;1970.071; -9;-99;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9;-999.9; 1; 10;3155.9;3155.9; 15.0
..
hys;rcntgrzd;1970;11;18;322;1970.882; 2; 20; 0.1; 0.1; 0.0; 0.0; 120.4; 11.5; 120.5; 11.5; -9;-99;-999.9;-999.9; -99.9
hys;rcntgrzd;1970;12;18;352;1970.964; 1; 10; 0.9; 0.9; 0.0; 0.0; 146.6; 22.4; 147.5; 22.5; -9;-99;-999.9;-999.9; -99.9

Climate Data. The data set is an ASCII file (.txt format). The first 18 lines are metadata; data records begin on line 19. The variable values are delimited by semicolons. Monthly and annual precipitation data are provided for each year 1867 through 1994. Monthly and annual maximum and minimum temperature are provided for each year 1893 through 1994. Monthly and annual means are provided for the respective periods. There are no missing values.

COLUMN HEADINGS DEFINITION
Site Unique 3-character code for each site based on the first three consonants in the site name (e.g., hys for Hays)
Temp
(Temporal)
Indicates whether the values in that row are either long-term (i.e, mulit-year) or annual data for the specified parameter.

For multi-year, the values are:
  mean=mean values (monthly and annual) calculated for the years of data as noted in the documentation
  numb=number of years of data included in a reported mean value
  stdv=standard deviation of a mean value

Annual data: 19XX=monthly and annual parameter values for the specified year (e.g., 1972)
Parm Parameter, indicates the meteorological data reported in that row.
  prec-total precipitation for the month or year
  tmax=maximum temperature for the month or year reported in degrees C
  tmin=minimum temperature for the month or year reported in degrees C

 

Description of specific Temp and Parm data values:

Long-term data:

site;mean;prec;
Multi-year mean of total precipitation for each month [Jan, Feb, Mar, …, Dec] and mean of total annual precipitation across all years [Year] (mm)

site;mean;tmax;
Multi-year mean of maximum temperature for each month [Jan, Feb, Mar, …, Dec] and mean of annual maximum temperature across all years [Year] (C)

site;mean;tmin;
Multi-year mean of minimum temperature for each month [Jan, Feb, Mar, …, Dec] and mean of annual minimum temperature across all years [Year] (C)

… site; numb and stdv; repeat for prec, tmax, and tmin;

Annual data:

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

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

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

… site;19XX;(prec, tmax, and tmin); repeat for reported years.

Annual data missing value note: If a monthly parm value is missing, the parm value for [Year] is also set to missing (-999.9).

Sample Climate Data Record

Site;Temp;Parm; Jan; Feb; Mar; Apr; May; June; July; Aug; Sept; Oct; Nov; Dec; Year
hys ;prec;mean; 11.92; 19.92; 31.48; 55.68; 85.22; 92.65; 84.86; 76.72; 58.93; 36.60; 22.18; 17.63; 591.63
hys ;tmax;mean; 4.90; 7.50; 12.89; 19.22; 24.05; 30.04; 33.60; 32.75; 27.94; 21.44; 12.72; 6.44; 34.33
hys ;tmin;mean; -9.45; -7.72; -2.65; 3.65; 9.36; 15.08; 17.95; 17.16; 11.78; 4.71; -3.07; -7.67; -10.53
hys ;prec;numb; 128.00; 128.00; 128.00; 123.00; 128.00; 128.00; 128.00; 128.00; 128.00; 128.00; 128.00; 128.00; 128.00
hys ;tmax;numb; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00
hys ;tmin;numb; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00; 102.00
hys ;prec;stdv; 13.83; 20.79; 36.30; 37.76; 49.60; 60.57; 56.26; 43.92; 47.42; 31.39; 24.04; 20.09; 160.49
hys ;tmax;stdv; 3.79; 3.95; 3.81; 2.22; 2.05; 2.62; 2.31; 2.27; 2.16; 2.56; 2.42; 2.99; 2.06
hys ;tmin;stdv; 2.61; 2.75; 2.30; 1.74; 1.75; 1.51; 1.26; 1.32; 1.68; 1.69; 1.71; 2.40; 2.37
hys ;prec;1867; 20.57; 71.63; 13.21; 49.53; 109.22; 93.47; 109.47; 16.51; 19.56; 0.00; 3.30; 18.80; 525.27
hys ;prec;1868; 4.83; 60.71; 28.45; 15.24; 57.66; 35.31; 22.35; 118.36; 6.35; 28.70; 102.36; 16.00; 496.32
..
Where,
Temp (temporal) - specific year or long-term statistic:
  mean = mean based on all years
  numb = number of years
  stdv = standard deviation based on all years
Parm (parameter):
  prec = precipitation for month or year (mm)
  tmax = mean maximum temperature for month or year (C)
  tmin = mean minimum temperature for month or year (C)

 

3. Data Application and Derivation:

Grassland monthly biomass dynamics data are provided for comparison with model output and estimation of NPP. Climate data are provided for use in driving ecosystem/NPP models.

Data at Hays were collected as part of a coordinated study over 1-3 years at ten grassland sites of the central and western United States, under the US Grassland Biome Project of the International Biological Program (IBP). The aim of the US/IBP Grassland Biome program was to study the whole US grassland system, particularly the seasonal biomass and energy dynamics of grasslands across multiple trophic levels (Sims et al., 1978). The ten sites for which net primary productivity (NPP) data are reported encompassed six major grassland types, ranging from latitude 30 to 48 N and longitude -96 to -123 W, and from 390 m to 2,340 m in elevation. Mean annual precipitation for the ten sites ranged from 228 mm to 930 mm, and mean annual temperature from 2.7 degrees C to 15.2 degrees C.

 

4. Quality Assessment:

Under the US Grassland Biome Project, above- and below-ground net productivity at the participating grassland sites was measured and calculated using comparable methods.

Sources of Error

Annual ANPP determined by the summation of peak live weights of individual species, as in this study, can yield a conservative estimate because material produced, senesced and detached before the peak live weight of a given species occurs is unaccounted for. The presence of different growth forms in the variety of vegetation types grasslands complicates the study of crowns and estimation of crown biomass production. Difficulties and inaccuracies involved in the estimation of root production arise primarily because of insufficient information on the periods of greatest root growth and decomposition, and the unaccounted losses of organic root secretions, sloughing of root hairs, root caps, and cortical layers, translocation of organic material to the soil and to the fungal components of mycorrhizal roots, death and decay of fine roots, and consumption of fine roots by soil. Estimates of root production should therefore be viewed with the constraints imposed by the procedures used.

 

5. Data Acquisition Materials and Methods:

Site Information

The Hays study site (38.87 N, -99.38 W) is situated in the central Great Plains, near the city of Hays, Kansas, about 400-km west of Kansas City. The Fort Hays branch station was established in 1906.

The Hays study site is located in a mixed prairie (modified Bailey ecoregion temperate dry steppe/humid prairie, #332/251) at an elevation of 714 m. This central Great Plains site has a mixture of cool- and warm-season grasses and forbs. It is dominated by the warm-season bluestem bunchgrasses Andropogon scoparius and A. gerardi; the midgrass Bouteloua curtipendula is also well-represented. The warm-season shortgrasses, Bouteloua gracilis and Buchloe dactyloides, are especially important on mixed-grass prairies like Hays when grazed by large herbivores. The Hays site also has a large proportion of forb species; for example, Psoralea tenuiflora can become a significant contributor to the standing crop during the summer period. The total number of vegetation species recorded at Hays in this study was 74.

The soil type at Hays is loamy Mollisol. One of the special characteristics of the soils at Hays, which may be relevant to root development and vegetation characteristics, is the shallow limestone bedrock at the study sites.

Methods

The experimental design included two treatments: ungrazed (i.e. long-term absence of grazing by large domestic herbivores) and moderately grazed grasslands. The ungrazed treatment area had been protected from grazing by an enclosure for over 60 years at the time of this study. The grazed treatment refers to grazing during the previous growing seasons, since no domestic animals were allowed on the areas sampled during the current year. Sampling in each treatment area generally involved two replications with 20 plots per replication. Exceptions were one replication with 10 plots on two sampling occasions in the recently grazed treatment area.

Intra-seasonal dynamics of the various above- and below-ground primary producer compartments were studied at Hays. The experimental design included two replications of ungrazed (i.e., long-term absence of grazing by large domestic herbivores by enclosure) and recently-grazed treatments. Structural characteristics studied included quantities of cool- and warm-season plants at each plot, and magnitude and seasonality of primary producer compartments. These latter measurements included seasonal above-ground live biomass, above-ground dead matter (recent plus old dead), total above-ground standing crop (living plus dead biomass), below-ground biomass by depth (root and crown inclusive), and total below-ground biomass. Litter decomposition and below-ground root turnover were also separately measured but the data are not included in this data set.

Above-ground biomass was measured by the harvest technique, over successive 2-week intervals during the growing season. The aerial plant material was clipped from harvest plots at the soil surface. Above-ground plant biomass was separated into several compartments, including perennial live, current (annual) live, recent dead, and old dead. Recent and old dead were primarily determined on the basis of color and the experience of the field and laboratory workers; recent dead was the material produced and senesced during the current growing season, while old dead was carry-over material from the previous year. Live and dead compartment material was further separated by species. Litter material was hand-picked from the harvest plots. All material was oven-dried at c. 60 degrees C. Aerial materials were presented on a dry matter basis while litter weights were converted to an ash-free basis. Perennial and current live were summed to obtain total live material, and likewise recent dead and old dead were summed to give total dead material.

Below-ground biomass was sampled by coring within the harvested plots to a depth sufficient to include at least 90% of the root mass. At Hays, the sampling was limited to 0-15 cm because of the limiting depth of the soil profile (i.e., the shallow limestone bedrock). Soil cores were obtained with a hydraulic coring device and washed over a 32-mesh screen. No separation of roots and crowns was made. All material was oven-dried at c. 60 degrees C, weighed, and then ashed. Further details for specific sampling procedures for Hays appear in Hulett and Tomanek (1971) and Sims et al. (1978).

Intra-seasonal biomass dynamics data are provided in this data set. Annual ANPP or shoot production was determined by the summation of peak live weights of individual species. Net root production was estimated from the summation of the significant positive increases in root biomass by depth. Annual BNPP was estimated as the sum of total root biomass (including crown biomass). Data analysis and results are discussed by Sims and Singh (1978b).

Climate data

Monthly and annual climate data for the period 1867-1994 were calculated from daily observations obtained from a weather station (38.87 N, -99.38 W, Elevation 613 m) located at the Hays grassland study site. Mean annual precipitation was 591.63 mm, approximately 75% of which fell between April and September. Mean annual maximum temperature was 34.33 degrees C and mean annual minimum temperature was -10.53 degrees C based on a 1867-1994 climatic record at Hays. The length of thermal potential growing season (defined as the number of consecutive days with a 15-day running-mean air temperature at or above 4.4 degrees C) during the NPP study was 226 days.

The climate data accompanying this NPP data set was compiled from daily observations of Tmax, Tmin, and precip amount.

For a given month, the maximum value of the daily Tmax for that month and the minimum value of the Tmin for that month is provided. For the year, the maximum value of the monthly Tmax is the annual Tmax and for the year the minimum value of the monthly Tmin values is the annual Tmin. Daily precipitation amount is summed to yield a monthly precipitation amount and the monthly precipitation is summed to provide an annual precipitation amount.

The multi-year mean monthly Tmax is the average of the Tmax values for that month for each year of the record. For example the mean monthly Tmax for April is the mean of each April’s Tmax for the observation period of record. Mean monthly Tmin and Mean monthly precip amount are calculated similarly.

6. Data Access:

This data is available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Data Archive Center:

Contact for Data Center Access Information:
E-mail: uso@daac.ornl.gov
Telephone: +1 (865) 241-3952

7. References:

Hulett, G.K., and G.W. Tomanek. 1971. Herbage Dynamics on a Mixed Prairie Grassland Near Hays, Kansas. US/IBP Grassland Biome Technical Report, No. 108. Colorado State University, Fort Collins, Colorado.

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

Sims, P.L., J.S. Singh, and W.K. Lauenroth. 1978. The structure and function of ten western North American grasslands. I. Abiotic and vegetational characteristics. Journal of Ecology 66: 251-285.

Additional Sources of Information:

Esser, G. 2013. NPP Multi-Biome: Global Osnabruck Data, 1937-1981. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, USA. doi:10.3334/ORNLDAAC/214

Lewis, J.K. 1971. Grassland Biome: a synthesis of structure and function, 1970. In: N. R. French (ed.). Preliminary Analysis of Structure and Function in Grasslands, pp. 317-87. Range Science Department Science Series No. 10. Colorado State University, Fort Collins, Colorado.

Olson, R.J., J.M.O. Scurlock, S.D. Prince, D.L. Zheng, and K.R. Johnson (eds.). 2013a. NPP Multi-Biome: Global Primary Production Data Initiative Products, R2. Data set. Available on-line [http://daac.ornl.gov] from the Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, USA. doi:10.3334/ORNLDAAC/617

Olson, R.J., J.M.O. Scurlock, S.D. Prince, D.L. Zheng, and K.R. Johnson (eds.). 2013b. NPP Multi-Biome: NPP and Driver Data for Ecosystem Model-Data Intercomparison, R2. Data set. Available on-line [http://daac.ornl.gov] from the Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, USA. doi:10.3334/ORNLDAAC/615

Scurlock, J.M.O., and R.J. Olson. 2002. Terrestrial net primary productivity - A brief history and a new worldwide database. Environ. Rev. 10(2): 91-109. doi:10.1139/a02-002

Scurlock, J.M.O., and R.J. Olson. 2013. NPP Multi-Biome: Grassland, Boreal Forest, and Tropical Forest Sites, 1939-1996, R1. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, USA. doi:10.3334/ORNLDAAC/653

Scurlock, J.M.O., K. Johnson, and R.J. Olson. 2002. Estimating net primary productivity from grassland biomass dynamics measurements. Global Change Biology 8(8): 736-753. DOI: 10.1046/j.1365-2486.2002.00512.x

Sims, P.L. and J.S. Singh. 1978a. The structure and function of ten western North American grasslands. II. Intra-seasonal dynamics in primary producer compartments. Journal of Ecology 66: 547-572.

Sims, P.L. and J.S. Singh. 1978b. The structure and function of ten western North American grasslands. III. Net primary production, turnover and efficiencies of energy capture and water use. Journal of Ecology 66: 573-597.