| Rank | Institution | Papers | Citations | Citations per paper |
| 1 | Stanford University, California | 1,020 | 21,318 | 20.90 |
| 2 | University of California, Santa Barbara, California | 823 | 16,099 | 19.56 |
| 3 | Princeton University, New Jersey | 555 | 10,832 | 19.55 |
| 4 | Smithsonian Institution, Washington DC | 939 | 17,964 | 19.13 |
| 5 | University of California, Santa Cruz, California | 583 | 10,965 | 18.81 |
| 6 | University of Edinburgh, Edinburgh | 663 | 12,411 | 18.72 |
| 7 | University of Sheffield, Sheffield | 789 | 14,357 | 18.20 |
| 8 | University of Oxford, Oxford | 699, | 12,655 | 18.10 |
| 9 | University of Alaska, Fairbanks and other campuses, Alaska | 657 | 11,706 | 17.82 |
| 10 | Max Planck Society, Various locations, Germany | 1,008 | 17,861 | 17.72 |
| 11 | Michigan State University, Michigan, Michigan | 1,124 | 19,481 | 17.33 |
| 12 | Duke University, North Carolina | 1,136 | 19,560 | 17.22 |
| 13 | Umeå University, Umeå, Sweden | 641 | 10,979 | 17.13 |
| 14 | Imperial College London, London | 986 | 16,790 | 17.03 |
| 15 | Harvard University, Massachusetts | 1,134 | 19,172 | 16.91 |
| 16 | University of Minnesota, Minnesota | 1,488 | 24,620 | 16.55 |
| 17 | University of Maryland, Maryland | 1,157 | 18,605 | 16.08 |
| 18 | Arizona State University, Arizona | 687 | 10,8 | 15.76 |
| 19 | University of Wisconsin, Wisconsin | 1,801 | 28,372 | 15.75 |
| 20 | Swiss Fed Inst Environmental Science, Duebendorf, Switzerland | 697 | 10,974 | 15.74 |
The data above were extracted from Thomson Scientific’s Essential Science Indicators database. This database, currently covering the period January 1998 to February 2008, surveys only journal articles (original research reports and review articles) indexed by Thomson Scientific. Articles are assigned to a category based on the journals in which they were published and Thomson Scientific’s journal-to-category field definition scheme. Both articles tabulated and citation counts to those articles are for the period indicated. Naturally, institutions publishing large numbers of papers have a greater likelihood of collecting more citations than scientists publishing fewer papers. This ranking is by citations per paper (impact) among those institutions that have collected 10,000 or more citations in environment and ecology journals. For papers with multiple institutional addresses each institution receives full, not fractional, citation credit. Essential Science Indicators lists institutions ranked in the top 1 per cent for a field over a given period, based on total citations. For the current version, 461 institutions are listed in the field of environment and ecology, meaning that a total of 46,100 institutions were reviewed to obtain these results. Of the 461, 61 institutions collected 10,000 or more citations in environment and ecology. US institutions take the top five places in this ranking, and a total of 13 in this list of the top 20 by citations per paper. UK institutions rank 6th, 7th, 8th and 14th. Germany, Sweden and Switzerland are represented by one institution each.
For more information on Thomson Scientific’s Essential Science Indicators, see http://scientific.thomson.com/products/esi. For more information on Thomson Scientific, see http://scientific.thomson.com.