Biodiversity And Climate Change Dominate Environmental Research

Sidebars Most-Cited Papers By Subject In Ecology/Environmental Sciences From 1981-94 Highly Cited Papers on Global Climate Change Published Since 1993 Ranked by total citations through 1995) Editor's Note: Ever since the 1992 Earth Summit conference in Rio de Janeiro, Brazil, the scientific community has sharpened its focus on biodiversity and global climate change and how it relates to all manner of disciplines, including biomedicine and public health. In this article from the September/October 1996 issue of Science Watch, Peter D. Moore, the newsletter's ecology correspondent, examines the shift in research emphasis-from ecosystem-based studies to work on biodiversity and climate-over the last 15 years in the field of environmental sciences. The Science Watch article (7[5]:1, 1996), which analyzes the rankings, is reprinted here with the permission of the newsletter and the Philadelphia-based Institute for Scientific Information (ISI), its publisher. For more information on the citation databases and information discussed in this article, contact Christopher King, editor of Science Watch, ISI, 3501 Market St., Philadelphia, Pa. 19104; (800) 523-1850, Ext. 1341. Fax: (215) 387-1266. E-mail: cking@isinet.com. It is evident to all researchers in the field that the foci of research in the ecological and environmental sciences have changed considerably over the past 15 years. This is often reflected in the key words that one feels obliged to include in a grant-proposal title in order to ensure an up-to-date image. Back in the 1980s we were trying to find a way of including words like "ecosystem" or "energetic" in the title, whereas we now try to find an excuse for the use of "biodiversity." But it is difficult to extract objective information concerning changing tastes and trends over the years. One approach is the use of citation indices, which reflect not simply how many papers were published within particular fields, but also the impact of those papers on the course of science since their publication. The citation index can thus provide a means of locating the shifting hot spots of research activity within ecology over the years. The table above provides an analysis of citation data going back to 1981, breaking the field of ecology and environmental sciences into a series of somewhat subjective categories. The selection of these categories is essentially personal, and many papers were difficult to allocate within this restricted set of headings, but occasional inappropriate allocation is unlikely to affect the reasonably clear outcome of the analysis. As in all such exercises, allowance must be made for the effects of age of publication on the likelihood of citation. Only the highly cited papers are included in the analysis, with the number of citations required for inclusion increasing with age. Using percentages is the only appropriate means of producing comparable sets of data for the years under review, but there is the disadvantage that a change in one component of the sum will influence the proportions of all other components. From 1981-94 (expressed in percentages) Subject 1981 1986 1990 19931994 Pollution 23 34 31 26 19 Acid Rain 7 5 8 0 0 Ozone/UV 1 0 1 7 10 Nutrient Cycling/Hydrology 8 11 5 0 2 Production Ecology 10 6 6 0 1 Grazing/Herbivory 11 9 9 0 2 Population Ecology 18 12 10 9 12 Community Ecology 14 8 8 2 2 Evolutionary Ecology 8 7 6 4 2 Carbon Cycle/Greenhouse 1 2 9 26 9 Ocean-Atmosphere/Circulation 0 1 1 11 6 Conservation/Biodiversity 1 2 6 15 12 Agricultural Ecology 1 2 0 2 11 Minumum # of Citations per year 50 50 24 24 11 Total Number of Papers 248 131 77 54 83 Source: ISI's Science Indicators Database, 1981-95. Despite these caveats regarding analysis and expression, the data set clearly indicates that great changes have indeed occurred during the 1980s and are continuing in the 1990s. Some areas of research, such as pollution studies (including toxicology) and population ecology (including behavioral ecology), seem to be maintaining the interest they inspired in the early 1980s, while others, including acid rain and other acidification research, have declined. The "ecosystem"-type topics, including community ecology, production and energy-flow studies, and watershed studies of hydrology and nutrient budgets, have almost vanished from the highly cited list, apart from those areas concerned with agro-ecology, forestry, and the response of agricultural organisms to projected climate changes. Evolutionary ecology also appears to have declined, but this may be because papers in this area are becoming increasingly molecular in emphasis and may have found their way into a different range of journals. The examination of animal-plant interactions-like those investigated in grazing and herbivory studies that received much attention and citation in the 1980s-seems also to have stepped out of the limelight in the 1990s. What is clearly on the rise is any topic related to global environmental change. Of the pollution-related subjects, the one that is attracting increasing attention is stratospheric ozone depletion and the dangers of ultraviolet (UV) penetration. The actual mechanisms of climate change dominate the citations, including the greenhouse effect and putative carbon sinks, together with oceanic-atmospheric circulation patterns. Also on the increase are citations to studies related to the factors controlling species diversity in ecosystems and the means by which biodiversity can be conserved. Initial impressions seem to be confirmed: Ecological energetics is out, while climate and conservation are in. This shift in ecological research reflects the current public concern with global changes, especially climatic ones, and particularly with the possible impacts on world vegetation and the associated risk of feedback effects. It is possible to focus upon this area by examining the most highly cited papers published since 1993 in this field. The hot papers listed in the table below range from reports of global modeling exercises to physiological studies on particular ecosystems or groups of species. Most influential, as assessed by this means, has been the model of J.M. Melillo and colleagues (paper No. 1), which estimates global patterns of terrestrial net primary production (NPP) and nitrogen cycling in the soil under current climatic conditions and under a postulated doubled atmospheric level of CO2. These researchers show that approximately half the current global NPP occurs in the tropics. They also conclude that tropical and dry temperate ecosystems are most responsive to raised CO2 levels simply because the limitation to production in moist temperate, and more northerly, ecosystems may be nitrogen availability. But they also predict that raised temperatures in a greenhouse world will increase the availability of nitrogen in such situations, so raised CO2 levels coupled with global warming will increase NPP at all latitudes. One of the most attractive features of increasing productivity is that it could act as a global sink for atmospheric carbon, thus accumulating this environmentally troublesome element in terrestrial biomass. This is the subject explored by R.K. Dixon and colleagues (paper No. 4), who have published data indicating that low-latitude forest clearance is acting as a source of atmospheric carbon to the extent of 1.6 Gt (gigatonne = 1,015 grams) per year, whereas the expansion of forest in the higher latitudes is sequestering carbon at a rate of 0.7 per year. (Ranked by total citations through 1995) Rank PaperCitations Through 1995 Citations Through Sept. 1996 1 J.M. Melillo et al., "Global climate change and terrestrial net primary production," Nature, 363:234-40, 1993 [Marine Biological Laboratory, Woods Hole, Mass.; University of New Hampshire, Durham] 61 99 2 D. Skole, C. Tucker, "Tropical deforestation and habitat fragmentation in the Amazon: Satellite data from 1978 to 1988," Science, 260:1905-10, 1993 [University of New Hampshire, Durham; National Aeronautics and Space Administration Goddard Space Flight Center, Greenbelt, Md.] 59 87 3 H. Poorter, "Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration," Vegetation, 104 /105:77-97, 1993 [University of Groningen, Netherlands] 49 78 4 R.K. Dixon et al., "Carbon pools and flux of global forest ecosystems," Science, 263:185-90, 1994 [Environmental Protection Agency, Corvallis, Ore.; University of Illinois, Urbana-Champaign; Woods Hole Research Center, Woods Hole, Mass.; Trexler and Associates, Oak Grove, Ore.; Wisniewski and Associates, Falls Church, Va.] 43 72 5 H.W. Polley et al., "Increase in C3 plant water-use efficiency and biomass over glacial to present CO2 concentrations," Nature, 361:61-4, 1993 [Agricultural Research Service, Temple, Texas; Harvard University] 31 37 6 J.S. Coleman, K.D.M. McConnaughay, F.A. Bazzaz, "Elevated CO2 and plant nitrogen use: Is reduced tissue nitrogen concentration size-dependent?" Oecologia, 93:195-200, 1993 [Syracuse University; Harvard University] 27 37 C.E. Owensby, "Biomass production in a tallgrass prairie ecosystem exposed to ambient and elevated CO2," Ecological Applications, 3:644-53, 1993 [Kansas State University] 27 38 8 A.P.S. Adamsen, G.M. King, "Methane consumption in temperate and subarctic forest soils: Rates, vertical zonation, and responses to water and nitrogen," Applied Environmental Microbiology, 59:485-90, 1993 [Aarhus University, Denmark; University of Maine] 26 40 9 S. Diaz et al., "Evidence of a feedback mechanism limiting plant response to elevated carbon dioxide," Nature, 364:616-7, 1993 [University of Sheffield, United Kingdom; National University of Cordoba, Argentina; University of East London, U.K.] 24 37 10 S. Naeem et al., "Declining biodiversity can alter the performance of ecosystems," Nature, 368:734-7, 1994 [Imperial College at Silwood Park, Ascot, U.K.] 22 51 Source: ISI's Science Indicators Database, 1993-95 Low-latitude forest clearance is also examined by D. Skole and C. Tucker (paper No. 2), who conclude that deforestation may not be as fast as some estimates have indicated and that the impact on the global carbon cycle may also be less than expected. In paper No. 8, A.P.S. Adamsen and G.M. King examine the relationship between forest soils and methane, another powerful greenhouse gas. In contrast to global monitoring and modeling, some of the papers feature small-scale experiments-for example, studies of elevated CO2 levels on a range of plant and crop species (as in papers 3, 5, 6, and 9). Also emerging as an important technique in ecology is the manipulation of miniature ecosystems, or microcosms-as in paper No. 10, which examines the effects of decreased biodiversity on all trophic levels of the systems, not just the vegetation. The authors conclude that artificial reduction of the species diversity of their microcosms has a negative impact on ecosystem productivity, hence its capacity to act as a carbon sink. If we accept that the most diverse ecosystems on Earth, the tropical rain forests, are being fragmented in such a manner that their biodiversity is in decline (as suggested by the authors of paper No. 2) then the productive potential of this biome could be further reduced as a result-assuming, of course, that one can extrapolate from microcosms to macrocosms. Ecology seems now to be poised at a bifurcation of the ways, with global monitoring on the one hand and microcosm manipulation on the other. Peter D. Moore is a reader in ecology and chairman of human and environmental sciences at King's College in London.

Sidebars
Most-Cited Papers By Subject In Ecology/Environmental Sciences From 1981-94
Highly Cited Papers on Global Climate Change Published Since 1993 Ranked by total citations through 1995)

Biodiversity And Climate Change Dominate Environmental Research

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