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Bibliometric Analysis for Papers on Topics Related to Ecosystems Research
January 5, 2006

This is a bibliometric analysis of the papers prepared by intramural and extramural researchers of the U.S. Environmental Protection Agency (EPA) on topics related to ecosystems research. For this analysis, 1,455 papers were reviewed. These 1,455 papers, published from 1995 to 2005, were cited 13,317 times in the journals covered by Thomson’s Web of Science.1 Of these 1,455 papers, 1,245 (86%) have been cited at least once in a journal.

The analysis was completed using Thomson's Essential Science Indicators (ESI) and Journal Citation Reports (JCR) as benchmarks. ESI provides access to a unique and comprehensive compilation of essential science performance statistics and science trends data derived from Thomson’s databases. The chief indicators of output, or productivity, are journal article publication counts. For influence and impact measures, ESI employs both total citation counts and cites per paper scores. The former reveals gross influence while the latter shows weighted influence, also called impact. JCR presents quantifiable statistical data that provide a systematic, objective way to evaluate the world’s leading journals and their impact and influence in the global research community.

Summary of Analysis

Nearly one-fifth of the ecosystems publications are highly cited papers. A review of the citations indicates that 283 (19.4%) of the ecosystem papers qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. Twenty-nine (2.0%) of the ecosystem papers qualify as highly cited when using the criteria for the top 1%. Three (0.2%) of these papers qualify as very highly cited (in the top 0.1%). None of the papers meet the highest threshold (the top 0.01%) for highly cited papers.

The ecosystems papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, in 15 of the 19 fields in which the EPA ecosystems papers were published, the ratio of actual to expected cites is greater than 1, indicating that the ecosystems papers are more highly cited than the average papers in those fields.

Nearly one-fifth of the ecosystem papers are published in very high impact journals. Two hundred eighty-one(281) of 1,455 papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 19.3% of EPA’s ecosystem papers. Nearly one-fifth of the ecosystem papers are published in the top 10% of journals ranked by JCR Immediacy Factor. Two-hundred eighty-eight (288) of the 1,455 papers appear in the top 10% of journals, representing 19.8% of EPA's ecosystem papers.

Twenty-eight of the ecosystems publications qualified as hot papers. ESI establishes citation thresholds for hot papers, which are selected from the highly cited papers in different fields, but the time frame for citing and cited papers is much shorter—papers must be cited within 2 years of publication and the citations must occur in a 2-month time period. Using the current hot paper thresholds established by ESI as a benchmark, 28 of the ecosystems papers, representing 1.92% of the ecosystems publications, were identified as hot papers in the analysis.

The authors of the ecosystems papers cite themselves less than the average self-citation rate. Eighthundred thirty-four(834) of the 13,317 cites are author self-cites. This 6.26% author self-citation rate is well below the accepted range of 10-30% author self-citation rate.

Highly Cited Ecosystem Publications

The 1,455 ecosystem papers reviewed for this analysis covered 19 of the 22 ESI fields of research. The distribution of the papers among these 19 fields and the number of citations by field are presented in Table 1.

Table 1. Ecosystem Papers by ESI Fields

No. of Citations

ESI Field

No. of EPA Ecosystem Papers

Average Cites/Paper

7,986

Environment/Ecology

954

8.37

1,144

Engineering

148

7.73

870

Multidisciplinary

19

45.79

741

Biology & Biochemistry

49

15.12

536

Microbiology

35

15.31

524

Geosciences

53

9.89

484

Plant & Animal Science

56

8.64

437

Chemistry

43

10.16

182

Agricultural Sciences

28

6.50

165

Pharmacology & Toxicology

19

8.68

67

Clinical Medicine

4

16.75

41

Mathematics

22

1.86

31

Economics & Business

4

7.75

30

Physics

7

4.28

26

Molecular Biology & Genetics

3

8.67

26

Computer Science

8

3.25

21

Immunology

1

21.00

6

Social Sciences

1

6.00

0

Materials Science

1

0.00

Total =

13,317

 

Total =

1,455

9.15

There were 283 (19.4% of the papers analyzed) highly cited EPA ecosystems papers in 14 of the 19 fields—Environment/Ecology, Multidisciplinary, Engineering, Biology & Biochemistry, Plant & Animal Science, Microbiology, Geosciences, Chemistry, Agricultural Sciences, Pharmacology & Toxicology, Economics & Business, Clinical Medicine, Mathematics, and Computer Science—when using the ESI criteria for the top 10% of papers. Table 2 shows the number of EPA papers in those 14 fields that met the top 10% threshold in ESI.

Twenty-nine (2.0%) of the papers analyzed qualified as highly cited when using the ESI criteria for the top 1% of papers. These papers were categorized in five fields—Environment/Ecology, Multidisciplinary, Biology & Biochemistry, Engineering, and Plant & Animal Science. Table 3 shows the 29 papers by field that met the top 1% threshold in ESI. There were three (0.2% of the papers analyzed) very highly cited EPA ecosystems papers in two fields—Environment/ Ecology and Engineering. These three papers met the top 0.1% threshold in ESI. None of the ecosystems papers met the highest threshold for highly cited papers (i.e., the top 0.01% threshold) in ESI.

Table 2. Number of Highly Cited Ecosystems Papers by Field (top 10%)

No. of Citations

ESI Field

No. of Papers

Average Cites/Paper

% of EPA Papers in Field

4,457

Environment/Ecology

164

27.18

17.19%

853

Multidisciplinary

14

60.93

73.68%

739

Engineering

48

15.40

32.43%

514

Biology & Biochemistry

8

64.25

16.33%

348

Plant & Animal Science

14

24.86

26.92%

258

Microbiology

6

43.00

17.14%

227

Geosciences

9

25.22

16.98%

215

Chemistry

6

35.83

13.95%

101

Agricultural Sciences

5

20.20

17.86%

85

Pharmacology & Toxicology

2

42.50

10.52%

27

Economics & Business

1

27.00

25.00%

49

Clinical Medicine

2

24.50

50.00%

13

Mathematics

3

4.33

13.64%

3

Computer Science

1

3.00

12.50%

Total =

7,889

 

Total =

283

27.88

 

Table 3. Number of Highly Cited Ecosystems Papers by Field (top 1%)

No. of Citations

ESI Field

No. of Papers

Average Cites/Paper

% of EPA Papers in Field

1,140

Environment/Ecology

16

71.25

1.68%

463

Multidisciplinary

3

154.33

15.79%

355

Biology & Biochemistry

2

177.50

4.08%

301

Engineering

5

60.20

3.38%

146

Plant & Animal Science

3

48.67

5.36%

Total =

2,405

 

Total =

29

 

 

The citations for the highly cited papers in the top 1% are presented in Tables 4 through 8. The citations for the very highly cited papers are listed in Table 9.

Table 4. Highly Cited Ecosystems Papers in the Field of Environment/Ecology(top 1%)

No. of Cites

First Author

Paper

181

Sakai AK

The population biology of invasive species. Annual Review of Ecology and Systematics 2001;32:305-332.

172

Huston MA

Local processes and regional patterns: appropriate scales for understanding variation in the diversity of plants and animals. Oikos 1999;86(2):393-401.

156

Burkholder JM

Pfiesteria piscicida and other Pfiesteria-like dinoflagellates: behavior, impacts, and environmental controls. Limnology and Oceanography 1997;42(5):1052-1075.

111

Morel FMM

The chemical cycle and bioaccumulation of mercury. Annual Review of Ecology Evolution and Systematics 1998;29:543-566.

91

Oberdorster G

Pulmonary effects of inhaled ultrafine particles. International Archives of Occupational and Environmental Health 2001;74(1):1-8.

74

Moran MA

Carbon loss and optical property changes during long-term photochemical and biological degradation of estuarine dissolved organic matter. Limnology and Oceanography 2000;45(6):1254-1264.

65

Chase TN

Simulated impacts of historical land cover changes on global climate in northern winter. Climate Dynamics 2000;16(2-3):93-105.

49

Phillips DL

Incorporating concentration dependence in stable isotope mixing models. Oecologia 2002;130(1):114-125.

46

Law BE

Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation. Agricultural and Forest Meteorology 2002;113(1-4):97-120.

39

Davidson C

Spatial tests of the pesticide drift, habitat destruction, UV-B, and climate-change hypotheses for California amphibian declines. Conservation Biology 2002;16(6):1588-1601.

34

Ollinger SV

Regional variation in foliar chemistry and N cycling among forests of diverse history and composition. Ecology 2002;83(2):339-355.

33

Wiens JA

Riverine landscapes: taking landscape ecology into the water. Freshwater Biology 2002;47(4):501-515.

29

Law BE

Changes in carbon storage and fluxes in a chronosequence of ponderosa pine. Global Change Biology 2003;9(4):510-524.

20

Cohen WB

An improved strategy for regression of biophysical variables and Landsat ETM+ data. Remote Sensing of Environment 2003;84(4):561-571.

20

Mazdai A

Polybrominated diphenyl ethers in maternal and fetal blood samples. Environmental Health Perspectives 2003;111(9):1249-1252.

20

Gray MJ

Effects of agricultural cultivation on demographicsof Southern High Plains amphibians. Conservation Biology 2004;18(5):1368-1377.

Table 5. Highly Cited Ecosystems Papers in the Field of Multidisciplinary (top 1%)

No. of Cites

First Author

Paper

185

Matson PA

Agricultural intensification and ecosystem properties. Science 1997;277(5325):504-509.

184

Stoddard JL

Regional trends in aquatic recovery from acidification in North America and Europe. Nature 1999;401(6753):575-578.

94

Wolfenbarger LL

Biotechnology and ecology – the ecological risks and benefits of genetically engineered plants. Science 2000;290(5499):2088-2093.

Table 6. Highly Cited Ecosystems Papers in the Field of
Biology & Biochemistry (top 1%)

No. of Cites

First Author

Paper

245

Aber J

Nitrogen saturation in temperate forest ecosystems – hypotheses revisited. Bioscience 1998;48(11):921-934.

110

Driscoll CT

Acidic deposition in the northeastern U.S.: sources and inputs, ecosystem effects, and management strategies. Bioscience 2001;51(3):180-198.

Table 7. Highly Cited Ecosystems Papers in the Field of Engineering (top 1%)

No. of Cites

First Author

Paper

130

Mason RP

Uptake, toxicity, and trophic transfer of mercury in a coastal diatom. Environmental Science & Technology 1996;30(6):1835-1845.

50

Amyot M

Production and loss of dissolved gaseous mercury in coastal seawater. Environmental Science & Technology 1997;31(12):3606-3611.

47

Reuter JE

Concentrations, sources, and fate of the gasoline oxygenate methyl tert-butyl ether (MTBE) in a multiple use lake. Environmental Science & Technology 1998;32(23):3666-3672.

46

Douglas EM

Trends in floods and low flows in the United States: impact of spatial correlation. Journal of Hydrology 2000;240(1-2):90-105.

28

Schneider AR

Recent declines in PAH, PCB, and toxaphene levels in the northern Great Lakes as determined from high resolution sediment cores. Environmental Science & Technology 2001;35(19):3809-3815.

Table 8. Highly Cited Ecosystem Ecosystems Papers in the Field of
Plant & Animal Science (top 1%)

No. of Cites

First Author

Paper

75

Zak DR

Elevated atmospheric CO 2, fine roots and the response of soil microorganisms: a review and hypothesis. New Phytologist 2000;147(1):201-222.

51

Burkholder JM

Overview and present status of the toxic Pfiesteria complex (Dinophyceae). Phycologia 2001;40(3):186-214.

20

Andersen CP

Source-sink balance and carbon allocation below ground in plants exposed to ozone. New Phytologist 2003;157(2):213-228.

Table 9. Very Highly Cited Ecosystems Papers (Top 0.1%)

Field

No. of Cites

First Author

Paper

Environment/Ecology

181

Sakai AK

The population biology of invasive species. Annual Review of Ecology and Systematics 2001;32:305-332.

 

172

Huston MA

Local processes and regional patterns: appropriate scales for understanding variation in the diversity of plants and animals. Oikos 1999;86(2):393-401.

Engineering

130

Mason RP

Uptake, toxicity, and trophic transfer of mercury in a coastal diatom. Environmental Science & Technology 1996;30(6):1835-1845.

Ratio of Actual Cites to Expected Citation Rates

The expected citation rate is the average number of cites that a paper published in the same journal in the same year and of the same document type (article, review, editorial, etc.) has received from the year of publication to the present. Using the ESI average citation rates for papers published by field as the benchmark, in 15 of the 19 fields in which the EPA ecosystems papers were published, the ratio of actual to expected cites is greater than 1, indicating that the EPA papers are more highly cited than the average papers in those fields (see Table 10).

Table 10. Ratio of Average Cites to Expected Cites for Ecosystems Papers by Field

ESI Field

Total Cites

Expected Cite Rate

Ratio

Environment/Ecology

7,986

5,379.63

1.48

Engineering

1,144

369.46

3.10

Multidisciplinary

870

70.71

12.30

Biology & Biochemistry

741

518.15

1.43

Microbiology

536

319.39

1.68

Geosciences

524

289.37

1.81

Plant & Animal Science

484

234.84

2.06

Chemistry

437

319.87

1.37

Agricultural Sciences

182

110.53

1.65

Pharmacology & Toxicology

165

110.98

1.49

Clinical Medicine

67

39.95

1.68

Mathematics

41

27.63

1.48

Economics & Business

31

8.06

3.85

Physics

30

50.02

0.60

Molecular Biology & Genetics

26

47.29

0.55

Computer Science

26

19.23

1.35

Immunology

21

21.11

0.99

Social Sciences

6

4.30

1.40

Materials Science

0

5.66

0.00

JCR Benchmarks

The Impact Factor is a well known metric in citation analysis. It is a measure of the frequency with which the average article in a journal has been cited in a particular year. The Impact Factor helps evaluate a journal’s relative importance, especially when compared to others in the same field. The Impact Factor is calculated by dividing the number of citations in the current year to articles published in the 2 previous years by the total number of articles published in the 2 previous years.

Table 11 indicates the number of ecosystems papers published in the top 10% of journals, based on the JCR Impact Factor. Two hundred eighy-one (281) of 1,455 papers were published in the top 10% of journals, representing 19.3% of EPA’s ecosystems papers.

Table 11. Ecosystem Papers in Top 10% of Journals by JCR Impact Factor

EPA Ecosystems Papers in that Journal

Journal

Impact Factor (IF)

JCR IF Rank

37

Environmental Science & Technology

3.557

540

37

Ecological Applications

3.287

623

19

Applied and Environmental Microbiology

3.810

470

19

Bioscience

3.041

730

19

Limnology and Oceanography

3.024

737

12

Ecology

4.104

394

12

Remote Sensing of Environment

3.185

666

10

Environmental Health Perspectives

3.929

439

10

Conservation Biology

3.672

504

10

Ecosystems

3.283

624

8

Journal of Chromatography A

3.359

602

7

Nature

32.182

9

7

Science

31.853

10

7

Analytical Chemistry

5.450

243

7

Global Change Biology

4.333

358

7

Ecology Letters

3.914

445

6

Journal of Climate

3.500

558

6

New Phytologist

3.355

603

4

Annual Review of Ecology Evolution and Systematics

9.429

102

4

Ecological Monographs

5.016

282

3

Molecular Ecology

4.375

351

3

Electrophoresis

3.743

482

3

Toxicological Sciences

3.391

591

2

Evolution

3.719

490

2

Proceedings of the Royal Society of London Series B-Biological Sciences

3.653

509

2

Plant Cell and Environment

3.634

517

1

JAMA-Journal of the American Medical Association

24.831

15

1

Lancet

21.713

20

1

Gastroenterology

13.092

61

1

Proceedings of the National Academy of Sciences of the United States of America

10.452

88

1

Reviews of Geophysics

8.667

114

1

Molecular Biology of the Cell

7.517

151

1

Plant Physiology

5.881

214

1

Emerging Infectious Diseases

5.643

230

1

Biochemistry

4.008

421

1

Environmental Microbiology

3.995

427

1

Epidemiology

3.840

459

1

Drug Metabolism and Disposition

3.836

461

1

Geochimica et Cosmochimica Acta

3.811

468

1

Mutation Research-Reviews in Mutation Research

3.667

506

1

Climate Dynamics

3.497

561

1

Journal of Experimental Botany

3.366

597

1

Journal of Applied Ecology

3.266

629

1

American Journal of Public Health

3.241

642

Total = 281

 

Immediacy Index

The journal Immediacy Index is a measure of how quickly the average article in a journal is cited. It indicates how often articles published in a journal are cited within the year they are published. The Immediacy Index is calculated by dividing the number of citations to articles published in a given year by the number of articles published in that year.

Table 12 indicates the number of EPA papers published in the top 10% of journals, based on the JCR Immediacy Index. Two hundred eighty-eight (288) of the 1,455 papers appear in the top 10% of journals, representing 19.8% of EPA’s ecosystems papers.

Table 12. Ecosystems Papers in Top 10% of Journals by JCR Immediacy Index

EPA Ecosystems Papers in that Journal

Journal

Immediacy Index (II)

JCR II Rank

37

Ecological Applications

0.747

466

37

Environmental Science & Technology

0.623

617

32

Hydrobiologia

0.681

532

19

Bioscience

0.863

356

17

Journal of Geophysical Research

0.617

630

13

Freshwater Biology

0.664

558

12

Ecology

0.590

676

10

Ecosystems

2.048

76

10

Environmental Health Perspectives

1.202

202

10

Conservation Biology

0.744

468

8

Climatic Change

1.235

195

7

Science

7.379

3

7

Nature

6.089

5

7

Analytical Chemistry

0.885

346

7

Ecology Letters

0.754

459

6

New Phytologist

0.876

349

5

Ecotoxicology

1.450

151

3

Ambio

1.435

156

3

Aquatic Sciences

0.800

413

3

Molecular Ecology

0.674

545

3

Aerosol Science and Technology

0.595

668

3

Electrophoresis

0.575

697

2

Natural Resources Journal

1.034

262

2

Plant Cell and Environment

0.605

653

1

JAMA – Journal of the American Medical Association

5.499

9

1

Lancet

5.017

12

1

Gastroenterology

2.529

51

1

Proceedings of the National Academy of Sciences of the United States of America

1.923

89

1

Reviews of Geophysics

1.714

110

1

Molecular Biology of the Cell

1.641

119

1

Journal of Paleolimnology

1.581

132

1

Emerging Infectious Diseases

1.350

169

1

Ecology Law Quarterly

1.174

213

1

Mutation Research-Reviews in Mutation Research

1.125

224

1

Hydrology and Earth System Sciences

1.069

242

1

Plant Physiology

0.961

296

1

Bulletin of the American Meteorological Society

0.895

341

1

Epidemiology

0.864

354

1

Marine Geology

0.842

373

1

American Journal of Botany

0.768

445

1

Biochemistry

0.737

477

1

American Journal of Public Health

0.723

489

1

Journal of Applied Ecology

0.718

493

1

Geochimica et Cosmochimica Acta

0.680

535

1

Environmental Microbiology

0.677

539

1

Tellus Series B-Chemical and Physical Meteorology

0.610

646

1

Drug Metabolism and Disposition

0.590

676

1

Journal of Physical Oceanography

0.565

718

1

Theoretical and Applied Climatology

0.564

718

Total = 288

 

Hot Papers

ESI establishes citation thresholds for hot papers, which are selected from the highly cited papers in different fields, but the time frame for citing and cited papers is much shorter—papers must be cited within 2 years of publication and the citations must occur in a 2-month time period. Papers are assigned to 2-month periods and thresholds are set for each period and field to select 0.1% of papers. There were no hot papers identified for the current 2-month period (i.e., September-October 2005), but there were 28 hot papers identified from previous periods.

Using the current hot paper thresholds established by ESI as a benchmark, 28 hot papers, representing 1.92% of the ecosystems papers, were identified in the fields of Environment/Ecology, Engineering, Plant & Animal Science, Mathematics, and Multidisciplinary. The hot papers are listed in Table 13.

Table 13. Hot Papers Identified Using Current ESI Thresholds

Field

ESI Hot Papers Threshold

No. of Cites in 2-Month Period

Paper

Environment/ Ecology

6

8 cites in April-May 2002

Watts JM, et al. Thermal, mixing, and oxygen regimes of the Salton Sea, California, 1997-1999. Hydrobiologia 2001;466(1-3):159-176.

 

8

8 cites in May-June 2000

Polsky C, et al. The Mid-Atlantic Region and its climate: past, present, and future. Climate Research 2000;14(3):161-173.

 

7

8 cites in May-June 2003

Sakai AK, et al. The population biology of invasive species. Annual Review of Ecology and Systematics 2001;32:305-332.

 

7

7 cites in September-October 2004

Brooks JR, et al. Hydraulic redistribution of soil water during summer drought in two contrasting Pacific Northwest coniferous forests. Tree Physiology 2002;22(15-16):1107-1117.

 

7

7 cites in January-February 2001

Huston MA. Local processes and regional patterns: appropriate scales for understanding variation in the diversity of plants and animals. Oikos 1999;86(3):393-401.

 

7

7 cites in September-October 2002

Oberdorster G. Pulmonary effects of inhaled ultrafine particles. International Archives of Occupational and Environmental Health 2001;74(1):1-8.

 

5

6 cites in September-October 2001

Glasgow HB, Burkholder JM. Water quality trends and management implications from a five-year study of a eutrophic estuary. Ecological Applications 2000;10(4):1024-1046.

 

3

5 cites in April-May 2004

Hulse DW, et al. Envisioning alternatives: using citizen guidance to map future land and water use. Ecological Applications 2004;14(2):325-341.

 

3

4 cites in April-May 2004

Baker JP, et al. Alternative futures for the Willamette River Basin, Oregon. Ecological Applications 2004;14(2):313-324.

Environment/ Ecology

3

4 cites in April-May 2004

Schumaker NH, et al. Projecting wildlife responses to alternative future landscapes in Oregon’s Willamette Basin. Ecological Applications 2004;14(2):381-400.

 

3

4 cites in April-May 2004

Berger PA, Bolte JP. Evaluating the impact of policy options on agricultural landscapes: an alternative-futures approach. Ecological Applications 2004;14(2):342-354.

 

3

4 cites in April-May 2004

Dole D, Niemi E. Future water allocation and in-stream values in the Willamette River Basin: a basin-wide analysis. Ecological Applications 2004;14(2):355-367.

 

3

4 cites in April-May 2003

Breitburg DL, et al. The pattern and influence of low dissolved oxygen in the Patuxent River, a seasonally hypoxic estuary. Estuaries 2003;26(2A):280-297.

 

3

4 cites in September-October 2003

Leibowitz SG, Vining KC. Temporal connectivity in a prairie pothole complex. Wetlands 2003;23(1):13-25.

 

3

4 cites in April-May 2002

Wiens JA. Riverine landscapes: taking landscape ecology into the water. Freshwater Biology 2002;47(4):501-515.

 

3

4 cites in April-May 2002

Detwiler PM, et al. The benthic invertebrates of the Salton Sea: distribution and seasonal dynamics. Hydrobiologia 2002;473(1-3):139-160.

 

3

3 cites in April-May 2004

Van Sickle J, et al. Projecting the biological condition of streams under alternative scenarios of human land use. Ecological Applications 2004;14(2):368-380.

 

3

3 cites in April-May 2002

Rogerson A, Hauer G. Naked amoebae (Protozoa) of the Salton Sea, California. Hydrobiologia 2002;473(1-3):161-177.

Environment/ Ecology

3

3 cites in March-April 1999

Karr JR. Defining and measuring river health. Freshwater Biology 1999;41(2):221-234.

Engineering

6

6 cites in June-July 2002

Douglas EM, et al. Trends in floods and low flows in the United States: impact of spatial correlation. Journal of Hydrology 2000;240(1-2):90-105.

 

4

5 cites in October-November 2002

Thomas-Smith TE, Blough NV. Photoproduction of hydrated electron from constituents of natural waters. Environmental Science & Technology 2001;35(13):2721-2726.

 

4

5 cites in November-December 1997

Mason RP, et al. Uptake, toxicity, and trophic transfer of mercury in a coastal diatom. Environmental Science & Technology 1996;30(6):1835-1845.

 

2

3 cites in September-October 2004

Karr JR, Yoder CO. Biological assessment and criteria improve total maximum daily load decision making. Journal of Environmental Engineering-ASCE 2004;130(6):594-604.

Plant & Animal Science

3

10 cites in October-November 2001

Glasgow HB, et al. A second species of ichthyotoxic Pfiesteria (Dinamoebales, Dinophyceae). Phycologia 2001;40(3):234-245.

 

3

4 cites in July-August 2000

Zak DR, et al. Elevated atmospheric CO 2, fine roots and the response of soil microorganisms: a review and hypothesis. New Phytologist 2000;147(1):201-222.

Mathematics

3

3 cites in September 2005

Drake JM. Allee effects and the risk of biological invasion. Risk Analysis 2004;24(4):795-802.

Multidisciplinary

11

31 cites in September-October 2001

Stoddard JL, et al. Regional trends in aquatic recovery from acidification in North America and Europe. Nature 1999;401(6753):575-578.

Multidisciplinary

5

5 cites in September-October 2004

Kolar CS, Lodge DM. Ecological predictions and risk assessment for alien fishes in North America. Science 2002;298(5596):1233-1236.

Author Self-Citation

Self-citations are journal article references to articles from that same author (i.e., the first author). Because higher author self-citation rates can inflate the number of citations, the author self-citation rate was calculated for the ecosystems papers. Of the 13,317 total cites, 834 are author self-cites—a 6.26% author self-citation rate. Garfield and Sher2 found that authors working in research-based disciplines tend to cite themselves on the average of 20% of the time. MacRoberts and MacRoberts3 claim that approximately 10% to 30% of all the citations listed fall into the category of author self-citation. Therefore, the 6.26% self-cite rate for the ecosystems papers is well below the range for author self-citation.

1 Thomson's Web of Science provides access to current and retrospective multidisciplinary information from approximately 8,500 of the most prestigious, high impact research journals in the world. Web of Science also provides cited reference searching.

2 Garfield E, Sher IH. New factors in the evaluation of scientific literature through citation indexing. American Documentation 1963;18(July):195-201.

3 MacRoberts MH, MacRoberts BR. Problems of citation analysis: a critical review. Journal of the American Society of Information Science 1989;40(5):342-349.

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