Ecological Archives E089-070-D1

Elsa E. Cleland, Chris M. Clark, Scott L. Collins, Joseph E. Fargione, Laura Gough, Katherine L. Gross, Daniel G. Milchunas, Steven C. Pennings, William D. Bowman, Ingrid C. Burke, William K. Lauenroth, G. Philip Robertson, Juliet C. Simpson, David Tilman, and Katharine N. Suding. 2008. Species responses to nitrogen fertilization in herbaceous plant communities, and associated species traits. Ecology 89:1175.

A. Data set identity:

Title: Species responses to nitrogen fertilization in herbaceous plant communities, and associated species traits.

B. Data set identification code

Suggested Data Set Identity Code: Fertsyntraitsall_Jan27_2008.txt

C. Data set description


This synthetic data set contains plant species relative abundance measures from 35 nitrogen (N) fertilization experiments conducted at 10 sites across North America. The data set encompasses the fertilization responses of 575 taxa from 1159 experimental plots. The methodology varied among experiments, in particular with regard to the type and amount of N added, plot size, species composition measure (biomass harvest, pin count, or percent cover), additional experimental manipulations, and experimental duration. At each site, each species has been classified according to a number of easily identified categorical functional traits, including life history, life form, the number of cotyledons, height relative to the canopy, potential for clonal growth, and nativity to the United States. Additional data are available for many sites, indicated by references to publications and web sites. Analyses of these data have shown that N enrichment significantly alters community composition in ways that are predictable on the basis of plant functional traits as well as environmental context. This data set could be used to answer a variety of questions about how plant community composition and structure respond to environmental changes.

D. Key words: database; fertilization; functional trait; nitrogen; plant community; synthesis.


Elsa E. Cleland1, 13, Chris M. Clark2, 14, Scott L. Collins3, Joseph E. Fargione4, Laura Gough5, Katherine L. Gross6, Daniel G. Milchunas7, Steven C. Pennings8, William D. Bowman9, Ingrid C. Burke10, William K. Lauenroth10, G. Philip Robertson6, Juliet C. Simpson11, David Tilman2, and Katharine N. Suding12

1National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, California 93101 USA

2Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota 55108 USA; Present address: School of Life Sciences, Arizona State University, Tempe, Arizona 85287 USA

3Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131 USA

4The Nature Conservancy Midwestern Resource Office, 1101 West River Parkway Suite 200, Minneapolis, Minnesota 55415 USA

5Department of Biology, University of Texas, Arlington, Texas 76019 USA

6W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, Michigan 49060 USA

7Forest, Rangeland, and Watershed Stewardship Department and Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado 80523 USA

8Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204 USA

9Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309 USA

10Graduate Degree Program in Ecology, Natural Resources Ecology Laboratory, Department of Forest, Rangeland, and Watershed Stewardship, Colorado State University, Fort Collins, Colorado 80523 USA

11Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106 USA; Present address: Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912

12Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697 USA

13Corresponding author: Elsa E. Cleland (

Research Origin Descriptors

Representatives from various Long Term Ecological Research (LTER) sites first came together in 1996 to synthesize data from nitrogen (N) fertilization experiments in order to ask questions about productivity–diversity relationships; they conducted two meta-analyses on subsets of the current database (Gough et al. 2000, Gross et al. 2000). They found that N fertilization usually increased productivity and decreased diversity, but there was considerable variation in these responses among locations. Subsequently, the PDT-Net (Productivity Diversity and Traits Network) research group was initiated to ask whether plant functional traits play a role in the relationship between productivity and diversity, and in particular to ask whether experimental increases in productivity via fertilization affect species differently depending on their functional traits. The database was expanded to include species functional trait information, as well as to include data from more locations. Currently, PDT-Net consists of the following researchers, who can answer questions pertaining to data from particular sites:

Chris M. Clark (representing the CDR data set,

Elsa E. Cleland (representing the JRGCE data set,

Scott L. Collins (representing the KNZ and SEV data sets,

Joeseph E. Fargione (familiar with the CDR and SEV data sets,

Laura Gough (representing the ARC data set,

Katherine L. Gross (representing the KBS data set,

Daniel G. Milchunas (now retired, has represented the SGS data set, new contact W.K. Lauenroth

Steven C. Pennings (representing the SBC and GCE data sets,

Katharine N. Suding (representing the NWT data set,

Across all of the sites in this data set, N fertilization almost always increased primary productivity and decreased species diversity (Suding et al. 2005), as was found by the earlier synthesis (Gough et al. 2000). Rare species were more likely to be lost following fertilization, as were species with a few key functional traits. In particular, perennials, N-fixers and native species were more susceptible to local extinction following fertilization (Suding et al. 2005). Although species richness within experimental plots (alpha diversity) tended to decline, there was variation in the direction and magnitude of the response of species richness at larger scales. Beta diversity (species turnover among plots) sometimes increased with N fertilization, while gamma diversity tended to decline, mirroring the alpha diversity response (Chalcraft et al. 2008 ). Widespread species generally responded the same way to fertilization regardless of where they were found, but some coastal marsh species increased at some sites while decreasing at others, depending on environmental and community context (Pennings et al. 2005). A structural equation model showed that the degree of diversity decline was related to environmental context, with greater species loss in communities with a lower soil cation exchange capacity, colder regional temperature, and larger production increase following N addition (Clark et al. 2007).

Data set description

This synthetic data set has undergone several revisions. The metadata presented here correspond to the data file named: Fertsyntraitsall_Jan27_2008.txt. This version of the data set should be cited when data are utilized for any analysis. Future versions will be renamed according to the date of the revision. Column headings are indicated in bold in the following text.

Column headings and descriptions:

Site: Each Site represents the area around a field station that has hosted long term research. The three letter abbreviations correspond to each Site as described in the Methods section.

Experiment: Within some Sites fertilization experiments were conducted in several community types, or in concert with other environmental manipulations. Abbreviations for each Experiment as well as descriptions of the communities or manipulations are described within each Site in the Methods section.

Abbreviation: A three letter acronym followed by a number acts as an abbreviation for the unique Site and Experiment combination, for use in figures and tables.

Year: The year in which the data were collected.

Fert: Fertilization treatment.

            1: fertilized plots

            0: unfertilized plots

Block: Many experiments used randomized block experimental designs. This Block number can be used to identify appropriate pairs of control and fertilized plots that are located in close proximity.  Block numbers are only provided when there is one plot per unique combination of Block and Fert.

PlotID: Each replicate within a block is given a distinct numerical label – thus plots do not have unique IDs, rather the combination of Fert, Block and PlotID is needed to identify individual plots within an Experiment.

Other: Other experimental manipulations including phosphorus (P) additions, water additions, burning, mowing, or soil disturbance treatments.

Species_code: The original species code assigned in the raw data for each data set.

USDA_symbol: The abbreviation used for each species in the USDA PLANTS database

( These symbols were first used in the Soil Conservation Service’s National List of Scientific Plant Names (NLSPN), and are currently used in the PLANTS database to keep track of individual species and synonyms.

Rawabund: The raw abundance value in the original data set. Methods for measuring abundance differ among the experiments and include biomass harvests, percent cover estimation, or pin hits. See Methods section for methods corresponding to each Experiment.

Rawabundmetric: The method and metric used in the measurement of raw abundance in the Rawabund column.

Relabund: The relative abundance of a species in a particular plot, it is calculated based on the raw abundance values in the Rawabund column (relative abundance of speciesA = raw abundance of species A divided by the total abundance of all species in the plot). Relative abundance is thus always a fraction, and the relative abundances of all species in a plot always sum to 1.0. Relative abundance calculations excluded litter, bare ground, and non-vascular plants.

Plotsize: This indicates the size of the plot in square meters in which species composition and relative abundance were measured. This is important because species richness does not scale in a linear manner with area, and thus plot diversity should not be directly measured across experiments with different plot sizes.

Scientific_name: The scientific name of the taxa abbreviated in the Species_code column. Taxa were generally identified to the species level but some taxa were identified to the genus level and some taxa identified only by their functional group such as "unknown grass.” Note that due to changes in taxonomy, the same species may have different scientific names at different Sites, here we preserved the scientific name that is used at a particular site to allow easy comparison with other data sets at that site. Within Sites there are not multiple scientific names for one species. The USDA_symbol for each species has been provided as a way to resolve these synonymies if desired in future analyses.

Family: The family in which the species is nested.

Cot: Cotyledon number

MC: Monocot

DC: Dicot

Dur: Duration of life-history

A: annual

B: biennial

P: perennial

LF: Life Form

F: forb

G: graminoid (including grasses, sedges and rushes)

S: woody or shrub

Note: This data set includes only communities that are dominated by herbaceous vegetation and thus mature trees are not represented in the data set. Tree seedlings found in the experimental plots were thus given the “S” designation.

DLF: Detailed Life Form

C3: graminoid with C3 type photosynthesis,

C4: graminoid with C4 type photosynthesis

DW: deciduous woody shrub or immature tree

EW: evergreen woody shrub or immature tree

L: forb (usually a legume) with the potential for nitrogen fixation

NL: non-leguminous forb that does not fix nitrogen

HT: Height, as average canopy position.

B: bottom 1/3 of the canopy

M: middle 1/3 of the canopy

U: upper 1/3 of the canopy.

Note: These height definitions are based on the canopy position only under control conditions; a species might have a different relative position in the canopy under fertilized conditions and this has not been taken into account. These height definitions are coded in the context of a particular experiment at a particular site; thus, a species might occupy different canopy positions in different experiments depending on which other species were present.

CLO: Clonal growth potential.

O: Non-clonal

C: Caespitose strategy for clonal growth (for instance bunch-grasses)

R: Rhizomotous strategy of clonal growth (such as grasses that create “runners” along the ground).

ORIGIN: Nativity status, either “NATIVE” to the United States or “NON-NATIVE,” as indicated by the USDA PLANTS database (

Variety: The species’ variety if provided.

Notes: Additional information about the species or traits.


The methods are described separately for each site below, and a summary table of site characteristics is included following the individual site descriptions. We included data sets where species composition data were available for both control and fertilized plots, only when the original investigators gave permission to publish the data. Species composition was measured using a variety of techniques, but these were standardized by calculating a relative abundance metric which allows all of the data sets to be directly compared. One exception exists for questions relating to species richness; different plot sizes were used at each site so species richness values should not be directly compared across sites, response ratios can be utilized instead. In general, plot sizes were small when biomass harvests were used to measure species composition, and larger when percent cover or pin hit measures were used. For the LTER sites, additional location, climate, and vegetation information is often available on individual LTER websites, found through

ARC: Arctic LTER located in the northern foothills of the Brooks Range, Alaska (68º 38’N, 149º 36’W, elevation 760 m), contains five experiments conducted in distinct tundra community types at two locations in the vicinity of the LTER site (Toolik Lake corresponding to the “Toolik” suffix in the experiment code, and the Sagavinirktok River toposequence corresponding to the “Sag” suffix in the experiment code). 10 g/ m2 added as NH4NO3; experiment began 1985 at the two Sag communities, 1989 at DHToolik and MATToolik, and 1997 at MNATToolik; relative abundance was calculated from percent cover measures based on 1-m2 plots; the data here are from 1998 (except the Moist Non-Acidic Tundra Toolik community where the data were collected in 2001). Biomass data are available for control plots in all experiments, and for fertilized plots for DHToolik (conducted in 1996, published in Gough et al. 2002) and MNATToolik (conducted in 2000, published in Gough and Hobbie 2003). Data for some experiments are available from the ARC LTER data archive (, or contact L. Gough for original data.

Experiments and references:

DHToolik = Dry heath community, Toolik Lake site (Gough et al. 2002)

DHSag = Dry heath community, Sag River site (Shaver et al. 1996)

MATToolik = Moist acidic tundra community, Toolik Lake site (Hobbie et al. 2005)

MNATToolik = Moist non-acidic tundra community, Toolik Lake site (Gough and Hobbie 2003)

MTSag = Moist tussock tundra community, Sag River site (Shaver et al. 1996)

CAR: Carpinteria salt marsh is located in southern California (34°24' N, 119°31'30'' W), and is part of the University of California Natural Reserve System. The marsh slope is very gradual, rising <1 m in elevation over a horizontal distance of 230 m inland from the mean high water intercept. This site contains six experiments conducted in distinct community types; data were collected by S. C. Pennings and J. C. Simpson. 420 g/ m2 fertilizer (84 g/ m2 N) was added in the first year (1999) and 820 g/ m2 fertilizer (164 g/ m2 N) was added in subsequent years in the form of pellets, 20:10:5 NPK, derived from ureaformaldehyde and ammoniated phosphate. Relative abundance was calculated from percent cover measured on 0.25-m2 plots. The data here are from 1999–2005. Biomass data were not collected. The results of this experiment have not been published, but Pennings and Callaway (1992) describe the site. Contact S. C. Pennings for original data.


DisSal = Low marsh zone, dominated by mixtures of Distichlis and Salicornia

JaumSal = Low marsh zone, dominated by mixtures of Jaumea and Salicornia

SalCus = Low marsh zone, Salicornia dominated

HighMar = Upper extent of the Salicornia zone, high species diversity

ArthSal = Mid-High marsh zone, dominated by mixtures of Arthrocnemum and Salicornia

MonArth = High marsh zone, dominated by mixtures of Monanthochloe and Arthrocnemum

CDR: Cedar Creek Natural History Area LTER lies at the prairie-forest boundary in central southern Minnesota (45°40' N, 93°20' W, mean elevation 270m). This site contains four experiments, three conducted in old-fields of different ages since agricultural abandonment and one conducted in undisturbed native oak savannah. Data were originally collected by many researchers working with D. Tilman. Beginning in 1982, 9.52 g N/ m2 was added annually in the form of NH4NO3, with half added in mid-May and half in late-June. The data included here are from 1999–2001. Relative abundance was calculated from biomass harvests from 0.3-m2 plots. Tilman (1987) describes the experimental methods, sites, and measurements in greater detail. The raw data, including additional years, can be found in the CDR LTER data archive (Experiment E001 found at


A = Field A, Old field abandoned in 1968

B = Field B, Old field abandoned in 1957

C = Field C, Old field abandoned in 1934

D = Field D, Native oak savannah

GCE: Georgia Coastal Ecosystems LTER, is located on the central Georgia coast (31°43' N, 81°37' W). This site contains five experiments conducted in distinct community types along a tidal gradient on Sapelo Island. 1560 g/ m2 N per year was added as pelletized 29:3:4 NPK, experiment lasted two years (1996 and 1997), only 1997 data is included here. Relative abundance was measured with a biomass harvest using 0.25 m2 plots. Pennings et al. (2002) describes the experimental methods, communities, and measurements. Contact S. C. Pennings for original data.


BorJun = High marsh zone, dominated by mixtures of Borrichia and Juncus

SpaJun = Mid marsh zone, dominated by mixtures of Spartina and Juncus

SpaBor = Mid marsh zone, dominated by mixtures of Spartina and Borrichia

SpaSal = Low marsh zone, dominated by mixtures of Spartina and Salicornia

SpaDis = Low marsh zone, dominated by mixtures of Spartina and Distichlis

JRG: The Jasper Ridge Biological Preserve is associated with Stanford University, located in the inland foothills of central coastal California. It hosts a diversity of habitat types, but these data are from the Jasper Ridge Global Change Experiment, located in an area of predominantly annual grassland on sandstone soils (37°24' N, 122°14' W, 120 m elevation). This site contains two experiments (actually factorial N + water treatments which are a subset of the larger global change experiment). Data for this experiment were originally collected by many researchers working with H. A. Mooney and C. B. Field, in particular E. S. Zavaleta. 7 g/ m2 N was added as calcium nitrate, experiment began in 1998, relative abundance was calculated from pin counts within a 0.5 m2 plot (the closest 5 individuals to 10 pins placed in standardized locations were identified, for a total of 50 identifications per plot). The experiment was initiated in 1998 and the data here are from 1999–2002. Biomass data were also collected. Zavaleta et al. (2003) describes the methods, treatments, and species composition measurements. More information about this site can be found at: Contact E. E. Cleland for original data.


Water = Annual grassland, water addition treatment increased ambient precipitation by 50%

Nowater = Annual grassland, no supplemental water addition

KBS: Kellogg Biological Station LTER, is located in southwest Michigan in the eastern portion of the U.S. cornbelt, 50 km east of Lake Michigan in the SW corner of the state (42° 24' N, 85° 24' W, elevation 288 m). This site contains two experiments in old fields that are annually tilled versus un-tilled. 12.3 g N/ m2 added as NH4NO3, experiment began in 1989 and is ongoing, the data here are from 1992–2001. Relative abundance is based on a biomass harvest in 1 m2 plots. (Note that before 1992 plot size varied over time 1989 = 0.2 m2, 1990–1991 = 0.3 m2, hence these data were not included). Huberty et al. (1998) describes the methods, experiments and measurements in more detail. Original data are available from Kay Gross, and other data sets from the “Early successional community” experimental plots are available in the KBS LTER data archive (, data set KBS019-004).


Tilled = Abandoned old field, annual disturbed by tilling

Untilled = Abandoned old field, undisturbed

KNZ: The Konza Prairie Biological Station is a 3487 ha preserve associated with Kansas State University and the Nature Conservancy located about 10 miles south of Manhattan, Kansas (39°05'N, 96°35'W, 320-444 m elevation). Vegetation is primarily unplowed mesic tallgrass prairie some of which is grazed by bison and some areas are grazed by cattle. Data from the Konza Prairie LTER comes from eight experiments in ungrazed areas. Four are from a factorial burning, mowing, nitrogen and phosphorus fertilization experiment, where additional P treatments are coded as blocks (none added block = 1, P added block=2). This experiment was conducted in tallgrass prairie, data are from 1999. Collins et al. (1998) describes the methods, community, and measurements. The other four experiments are from a factorial N × water addition experiment conducted in upland vs. lowland prairie sites; data are from 2003. The species composition data are unpublished. Details on the irrigation methods and net primary production responses to irrigation can be found in Knapp et al. (2001). All eight experiments added 10 g N / m2 as NH4NO3 annually. In the UnburnUnmow, UnburnMowed, BurnedMowed, and BurnUnmowed experiments species composition and abundance were measured visually using a modified Daubenmire scale (see Collins and Smith 2007) in two 5-m2 circular subsamples per replicate and cover values from the two subsamples were averaged for each replicate. In the UplandWater, UplandNoWater, LowlandWater and LowlandNoWater experiments, treatments were applied to 2 × 2 m plots, and species composition was measured by visual estimation in a central 1 m2 plot per replicate. S. L. Collins is the contact for all original data from KNZ in this database.


UnburnUnmow = Tall-grass prairie, unmanipulated

UnburnMowed = Tall-grass prairie, mowed

BurnedMowed = Tall-grass prairie, burned and mowed

BurnUnmowed = Tall-grass prairie, burned


UplandWater = Upland prairie, added water

UplandNoWater = Upland prairie

LowlandWater = Lowland prairie, added water

LowlandNoWater = Lowland prairie

NWT: Niwot Ridge LTER is located approximately 35 km west of Boulder, Colorado (40°03' N, 105°36' W). This site contains two experiments in dry and wet alpine tunrdra meadow communities, at approximately 3500 m elevation. Data were originally collected by T. A. Theodose and W. D. Bowman. N was added as urea slow-release pellets, the amount varied among years, 25 g/ m2 was added in 1990, none in 1991, 10 g/ m2 1992–2000. Relative abundance was calculated based on pin hits in 1 m2 plots using a point frame - 100 total hits. Note, a factorial P addition is indicated using blocking (1=none, 2=P added), in previous PDT-net analyses the plots receiving P addition were excluded. Data for the wet meadow are from 1990–1996, data for the dry meadow are from 1990–2000 with 1997 and 1999 missing. Biomass data were also collected. Theodose and Bowman (1997) describe the methods, sites, and measurements in more detail. Original data can be found in the NWT LTER data archive (


DryBowman = Dry alpine tundra meadow

WetBowman = Wet alpine tundra meadow

SEV: The Sevilleta LTER is located in a 92,060 ha area of native desert grassland, shrubland, woodland and riparian vegetation managed by the US Fish and Wildlife Service, approximately 80 kilometers south of Albuquerque, NM (34°10’N, 106°55’W, 1433 to 2743 m elevation). Data from the Sevilleta LTER come from one experiment conducted in native desert grassland. In this experiment N was added at 10 g N / m2 as NH4NO3 annually. A total of 20 plots (5 × 10 m) were randomly assigned to controls or fertilized treatments. Within each plot 4 1- m2 subplots were measured for species composition. Relative abundance was calculated based on percent cover measures in the1 m2 subplots. Percent cover was measured seasonally, and the maximum cover for each species was taken to subsequently calculate relative abundance. This experiment was established by N. C. Johnson, E. B. Allen, and M. Allen in 1995 (see Johnson et al. 2003). The data here are from 2004, the year when species composition measurements began. Aboveground net primary production (ANPP) has been estimated in each replicate since 2004 using a non-destructive allometric method in each of the four species composition subplots yielding ANPP values by species. The species composition and ANPP data have not been published, but a manuscript is in preparation at this time. Contact S. L. Collins for original data.


Desertgrass = Native desert grassland

SGS: The Shortgrass Steppe LTER is located on a 6000 ha tract of shortgrass steppe in the piedmont of north central Colorado (40°49' N, 104°46' W, elevation 1650 m). The data from SGS are from a multi-factorial experiment designed to evaluate how nitrogen and water interact to influence net primary production, plant species composition, and biogeochemical processes. The full experiment consists of 2 blocks, with 4, 0.4-ha treatment plots of a control (no-water or N), increased water (about 600 mm each year), increased nitrogen (6 g N/ m2 yearly 1997-2000, 3 g N/ m2 per year 2001-present, in the form of NH4NO3), and a water plus nitrogen treatment. These plots also contain warming chambers for a full factorial with heating (data not included). Relative abundance is based on percent basal cover measured in 50 randomly located, 0.1 m2 plots per treatment/block combination. Cover was estimated using classes (<5%; 5–14%; 15–24%; 25–39%, 40–59%, 60–100%). The species composition data here are from 2000, species composition and biomass data are collected in alternate years and results are not yet published from this experiment. Contact W. K. Lauenroth for original data.


Water = Short-grass steppe community with experimental water addition, which added approximately 600 mm of precipitation each year.

Nowater = Short-grass steppe community without supplementary water

Table 1. Summary of site characteristics.



Data-use policy

The data sets compiled here are primarily publicly available data from participating sites in the Long Term Ecological Research network – – and permission to use these data has been granted by the principle investigators at the LTER sites. Data from the Jasper Ridge Global Change Experiment are from the only non-LTER site, and permission to use these data has been granted by Christopher Field and Hal Mooney. Data from SGS have not been previously released into the public domain due to ongoing research; to utilize data from SGS please contact William Lauenroth or Ingrid Burke. The PDT-Net researchers have spent substantial time organizing these data into a common format for the purpose of synthesis, and encourage others to utilize this database for complementary analyses and publications. Those wishing to use these data for analyses that result in publication should carefully read this meta-data document, consult previous manuscripts utilizing this database to avoid replication of effort, and cite the data set as follows:

Cleland, E.E., C.M. Clark, S.L. Collins, J.E. Fargione, L. Gough, K.L. Gross, D.G. Milchunas, S.C. Pennings, W.D. Bowman, I.C. Burke, W.K. Lauenroth, G.P. Robertson, J.C. Simpson, D. Tilman and K.N. Suding (2007). Species responses to nitrogen fertilization in herbaceous plant communities, and associated species traits. (To be submitted as a data publication to Ecology)


Chalcraft, D. R., S. B. Cox, C. M. Clark, E. E. Cleland, K. N. Suding, E. Weiher, and D. Pennington. 2008. Nitrogen enrichment studies often overestimate plant species loss at large spatial scales: the importance of beta diversity. Ecology 89: in press.

Clark, C. M., E. E. Cleland, S. L. Collins, J. E. Fargione, L. Gough, K. L. Gross, S. C. Pennings, K. N. Suding and J. B. Grace. 2007. Environmental and plant community determinants of species loss following nitrogen enrichment. Ecology Letters 10:596–607.

Collins, S. L., A. K. Knapp, J. M. Briggs, J. M. Blair, and E. M. Steinauer. 1998. Modulation of diversity by grazing and mowing in native tallgrass prairie. Science 280:745–747.

Collins, S. L., and M. D. Smith. 2006. Scale-dependent interaction of fire and grazing on community heterogeneity in tallgrass prairie. Ecology 87:2058–2067.

Gough, L. and S. E. Hobbie. 2003. Responses of moist non-acidic arctic tundra to altered environment: productivity, biomass, and species richness. Oikos 102:204–216.

Gough, L., C. W. Osenberg, K. L. Gross, and S. L. Collins. 2000. Fertilization effects on species density and primary productivity in herbaceous plant communities. Oikos 89:428–439.

Gough, L., P. A. Wookey, and G. R. Shaver. 2002. Dry heath arctic tundra responses to long-term nutrient and light manipulation. Arctic, Antarctic and Alpine Research 34:211–218.

Gross, K. L., M. R. Willig, L. Gough, R. Inouye, and S. Cox. 2000. Patterns of species diversity and productivity at different spatial scales in herbaceous plant communities. Oikos 89:417–427.

Hobbie, S. E., L. Gough, and G. R. Shaver. 2005. Species compositional differences on different-aged glacial landscapes drive contrasting responses of tundra to nutrient addition. Journal of Ecology 93: 770–782.

Huberty, L. E., K. L. Gross, and C. J. Miller. 1998. Effects of nitrogen addition on successional dynamics and species diversity in Michigan old-fields. Journal of Ecology 86:794–803.

Johnson, N. C., D. L. Rowland, L. Corkidi, L. M. Egerton-Warburton, and E. B. Allen. 2003. Nitrogen enrichment alters mycorrhizal allocation at five mesic to semi-arid grasslands. Ecology 84:1895–1908.

Knapp, A. K., J. M. Briggs, and J. K. Koelliker. 2001. Frequency and extent of water limitation to primary production in a mesic temperate grassland. Ecosystems 4:19–28.

Pennings, S. C., and R. M. Callaway. 1992. Salt marsh plant zonation: the relative importance of competition and physical factors. Ecology 73:681–690.

Pennings, S. C., C. M. Clark, E. E. Cleland, S. L. Collins, L. Gough, K. L. Gross, D. G. Milchunas and K. N. Suding. 2005. Do individual plant species show predictable responses to nitrogen addition across multiple experiments? Oikos 110:547–555.

Pennings, S. C., L. E. Stanton, and J. S. Brewer. 2002. Nutrient effects on the composition of salt marsh plant communities along the southern Atlantic and Gulf Coasts of the United States. Estuaries 25: 1164–1173.

Shaver, G. R., J. A. Laundre, A. E. Giblin, and K. J. Nadelhoffer. 1996. Changes in live plant biomass, primary production, and species composition along a riverside toposequence in Arctic Alaska, U.S.A. Arctic and Alpine Research 28:363–379.

Suding, K. N., S. L. Collins, L. Gough, C.M. Clark, E. E. Cleland, K. L. Gross, D. G. Milchunas, and S. Pennings. 2005. Functional- and abundance-based mechansisms explain diversity loss due to N fertilization. Proceedings of the National Academy of Sciences 102:4387–4392.

Theodose, T. A., and W. D. Bowman. 1997. Nutrient availability, plant abundance, and species diversity in two alpine tundra communities. Ecology 78:1861–1872.

Tilman, D. 1987. Secondary succession and the pattern of plant dominance along experimental nitrogen gradients. Ecological Monographs 57:189–214.

Zavaleta, E. S., M. R. Shaw, N. R. Chiariello, B. D. Thomas, E. E. Cleland, C. B. Field, and H. A. Mooney. 2003. Grassland responses to three years of elevated temperature, CO2, precipitation, and N deposition. Ecological Monographs 73:585–604.


We are grateful to the many researchers who originally collected these data or contributed to the trait compilations. In particular, we wish to thank Gus Shaver for maintaining the ARC plots, Chris Field, Hal Mooney, and Erika Zavaleta for their work in JRG, Carol Baker for her work at KBS, John Blair for sharing data from KNZ, Terry Theodose for collecting data at NWT, and Karen Wetherill for her work at SEV. Significant funding for the collection of these data was provided by the National Science Foundation (NSF) through the LTER network grant numbers: DEB-9810222 (ARC), DEB-0080382 (CDR), OCE-0620959 (GCE), DEB – 0423627 and DEB – 9810220 (KBS), DEB – 0423662 and DEB – 9810218 (NWT), DEB – 0080529 & DEB – 8811906 (SEV), and DEB – 0217631 (SGS). Support for data collection in the Jasper Ridge Global Change Experiment was provided by NSF, the David and Lucile Packard Foundation, the Morgan Family Foundation and the Jasper Ridge Biological Preserve. Collaboration among PDT-Net members has been supported by LTER cross-site synthesis grants. This work was conducted while E.E.C. was a postdoctoral associate at the National Center for Ecological Analysis and Synthesis, a Center funded by NSF (DEB-0553768), the University of California, Santa Barbara, and the State of California.

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