Invasion of Gleditsia triacanthos in Lithraea ternifolia Montane Forests of Central Argentina

Gleditsia triacanthos and the native dominant Lithraea ternifolia in montane forests of central Argentina, considering life history and demographic traits of both the alien and the native species and different site conditions for population growth (good and bad sites). Matrix models are applied to project the consequences of differences in vital rates for population growth. Analyzing these models helps identify which life cycle transitions contributed most to population growth. Obtained population growth rates are considered to assess predicted rates of spread using the reaction-diffusion (R-D) model. G. triacanthos presents many of the life history traits that confer plants high potential for invasiveness: fast growth, clonal and sexual reproduction, short juvenile period, high seed production, and high seed germinability. These traits would ensure G. triacanthos invasive success and the displacement of the slow-growing, relatively less fecund native L. ternifolia. However, since disturbance and environmental heterogeneity complicate the invasibility pattern of G. triacanthos in these montane forests, the outcome of the invasion process is not straightforward as could be if only life history traits were considered. Great variation in demographic parameters was observed between populations of each species at good and bad sites. Though both good and bad sites signified increasing or at least stable populations for G. triacanthos, for L. ternifolia bad sites represented local extinction. Analyzing the results of matrices models helps design the optimal management for the conservation of L. ternifolia populations while preventing the invasion by G. triacanthos. The predicted asymptotic rate of spread for G. triacanthos at the good site was fourfold greater than the predicted one for L. ternifolia, although the difference was much smaller considering the bad site. The usefulness of the R-D model to study this invasion system is discussed.     

The biodiversity crisis and the future of evolution

A large proportion of existing species — possibly half, conceivably even more — may be lost within the foreseeable future. But this may not prove to be the most consequential outcome of the current biodiversity crisis. More significant could be the disruption and degradation of several basic processes of evolution. It appears likely that for mass extinction episodes (MEEs) in the geological past, the recovery period usually lasted at least five million years. Because of certain unique features of the present MEE — notably the near elimination of biomes such as tropical forests, wetlands and coral reefs, which have served as powerhouses of evolution in the past — the bounce-back phase could extend several times longer than five million years. Among distinctive features of future evolution could be; in the short term, homogenization of biotas, a proliferation of opportunistic species, an outburst of speciation among particular taxa, and a pest-and-weed ecology; and, in the long term, a decline of biodisparity, the elimination of megavertebrates, an end to speciation among large vertebrates, and multiple constraints on origination, innovation and adaptive radiation. These disruptive phenomena would rank among the most prominent departures in the entire course of evolution. Full knowledge and understanding of what may characterize future evolution remains largely a black hole of research. As a consequence, conservation policies fail to reflect a further problem of the biodiversity prospect, perhaps exceeding the better recognized problem of the mass extinction of species.Professor Norman Myers is an Editorial Board member and regular contributor toThe Environmentalist. He is an Honorary Visiting Fellow at Green College, Oxford. This paper is a greatly expanded version of a preliminary probing in a popular magazine a decade ago (Myers, 1985). It has been prompted by a major international conference organized by the US National Academy of Sciences, scheduled for late 1996.     

A priority-ranking strategy for threatened species?

Summary The rate of extinction has accelerated to the point where we are probably losing one species per day right now, and we could well lose one million of Earth's 5–10 million species by the year 2000, and a good many more within the early decades of the next century. Plainly we cannot assist all species that face extinction within the foreseeable future. Conservationists have limited resources at their disposal, in the way of finance, scientific skills, and the like. Even were these resources to be increased several times over, we could not hope to save more than a proportion of all species that appear doomed to disappear: the processes of habitat disruption are too strongly underway to be halted in short order. But when we allocate funds to safeguard one species, we automatically deny those funds to other species. Already we support only a small fraction of all species under threat, and we may soon find ourselves in a situation where we can assist only a very marginal number of species facing extinction. Thus a key question arises: how are we to allocate our scarce resources in the most efficient way to safeguard species? Indeed we may now have reached a stage where there is merit in determining which species are most deserving of a place on the planet. Agonizing as it will be to make choices along these lines, conservation strategy should be as systematically selective as possible. This means that we should design analytic methodologies to enable us to assign our conservation resources to achieve maximum return in terms of numbers of species protected. In essence, a triage strategy. An expanded approach along these lines postulates a quantum advance in our planning of responses to the growing threatened-species problem: while the techniques of the past have certainly helped the situation, we cannot confront the much greater challenges of the future with an attitude of the same as before, only more so—the future will not be a simple extrapolation of the past, but will represent a qualitatively larger set of problems, which require an appropriately scaled-up response in our save-species campaigns.Dr Norman Myers is an expert in the study of endangered species and ecosystems. He is an international consultant in Environment and Development. This paper is based in part on findings of a project that he conducted for the World Wildlife Fund—US, to which grateful acknowledgment is made. The responsibility for all conclusions and recommendations remains, of course, with the author.     

Island biogeographical theory: Can it be used to predict lotic recovery rates?

Classic island biogeographic theory predicts that equilibrium will be reached when immigration and extinction rates are equal. These rates are modified by number of species in source area, number of intermediate islands, distance to recipient island, and size of intermediate islands. This general model has been variously modified and proposed to be a stochastic process with minimal competitive interaction or heavily deterministic. Predictive models of recovery (regardless of the end point chosen) have been based on the appropriateness of the MacArthur-Wilson models. Because disturbance frequency, severity, and intensity vary in their effect on community dynamics, we propose that disturbance levels should first be defined before evaluating the applicability of island biogeographical theory. Thus, we suggest a classification system of four disturbance levels based on recovery patterns by primary and secondary succession and faunal organization by primary (invasion of vacant areas) and secondary (remnant of previous community remains) processes. Level 1A disturbances completely destroy communities with no upstream or downstream sources of colonizers, while some component of near surface interstitial or hyporheic flora and fauna survive level 1B disturbances. Recovery has been reported to take from five years to longer than 25 years, when most invading colonists do not have an aerial form. Level 2 disturbances destroy the communities but leave upstream and downstream colonization sources (level 2A) and, sometimes, a hyporheic pool of colonizers (level 2B). Recovery studies have indicated primary succession and faunal structuring patterns (2A) with recovery times of 90–400 days or secondary succession and faunal structuring patterns (2B) with recovery times of 40–250 days. Level 3 disturbances result in reduction in species abundance and diversity along a stream reach; level 4 disturbances result in reduction of abundance and diversity in discrete patches. Both disturbance types lead to secondary succession and secondary faunal organization. Recovery rates can be quite rapid, varying from less than 10 days to 100 or more days. We suggest that island biogeographical models seem appropriate to recovery by secondary processes after level 3 and 4 disturbances, where competition may be an important organizing factor, while models of numerical abundance and resource tracking are probably of better use where community development is by primary succession (levels 1 and 2). Development of predictive recovery models requires research that addresses a number of fundamental questions. These include the role of hydrologic patterns on colonization dynamics, the role of nonaerial colonizers in recovery from level 1 disturbances, and assessment of the impact of changes in the order of invasion by colonizers of varying energetic efficiencies. Finally, we must be able to assemble these data and determine whether information that guides community organization at one level of disturbance can provide insights into colonization dynamics at other levels.     

Brazil's Balbina Dam: Environment versus the legacy of the Pharaohs in Amazonia

The Balbina Dam in Brazil's state of Amazonas floods 2360 km² of tropical forest to generate an average of only 112.2 MW of electricity. The flat topography and small size of the drainage basin make output small. Vegetation has been left to decompose in the reservoir, resulting in acidic, anoxic water that will corrode the turbines. The shallow reservoir contains 1500 islands and innumerable stagnant bays where the water's residence time will be even longer than the average time of over one year. Balbina was built to supply electricity to Manaus, a city that has grown so much while the dam was under construction that other alternatives are already needed. Government subsidies explain the explosive growth, including Brazil's unified tariff for electricity. Alternative power sources for Manaus include transmission from more distant dams or from recently discovered oil and natural gas deposits. Among Balbina's impacts are loss of potential use of the forest and displacement of about one third of the surviving members of a much-persecuted Amerindian tribe: the Waimiri-Atroari. The dam was closed on 1 October 1987 and the first of five generators began operation in February 1989. The example of Balbina points to important ways that the decision-making process could be improved in Brazil and in the international funding agencies that have directly and indirectly contributed to the project. Environmental impact analyses must be completed prior to decisions on overall project implementation and must be free of influence from project proponents. The current environmental impact assessment system in Brazil, as in many other countries, has an undesirable influence on science policy, in addition to failing to address the underlying causes of environmentally destructive development processes and inability to halt irreversible projects like Balbina.     

Can intensive management increase carbon storage in forests?

A possible response to increasing atmospheric CO₂ concentration is to attempt to increase the amount of carbon stored in terrestrial vegetation. One approach to increasing the size of the terrestrial carbon sink is to increase the growth of forests by utilizing intensive forest management practices. This article uses data from the literature and from forest growth and yield models to analyze the impact of three management practices on carbon storage: thinning, fertilization, and control of competing vegetation. Using Douglas-fir (Pseudotsuga menziesii) and loblolly pine (Pinus taeda) as example species, results from experiments with computer simulation models suggest that, for these two species, thinning generally does not increase carbon storage and may actually cause a decrease. The exception is thinning of very dense young stands. Fertilization generally increases carbon storage, although the response can be quite variable. The largest gains in carbon storage are likely to come from fertilizing lower-quality sites and from fertilizing thinned or less dense stands. Forests usually show increased growth in response to fertilization over a wide range of ages. Simulation of the growth of loblolly pine indicates that controlling competing vegetation at an early age helps to maximize stand growth and carbon storage. The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract number 68-C8-0006 to NSI Technology Inc. It has been subjected to the agency’s peer and administrative review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

Assessment of frequent cutting as a plant-community management technique in power-line corridors

Repeated cutting of vegetation at or near ground level in power-line corridors is a common practice for inhibiting tree growth and regeneration. However, few data exist on long-term community responses. In this study, we sampled 20 northern Kentucky power-line corridors and compared their seedling and sapling communities to the edges and interiors of adjacent undisturbed forests. Mean seedling and sapling density in corridors was roughly twice that of adjacent undisturbed forest interiors, suggesting that repeated cutting is not a viable method of inhibiting tree regeneration. Corridor communities were dominated byRobinia pseudoacacia (black locust) andFraxinus americana (white ash), but ordinations indicated strong similaritties among communities in corridors and adjacent forests. Many of the tree species found in adjacent forests, with the exception of a few shade-tolerant species, had highest seedling and sapling densities in corridors. Stump or root sprouting by many species appears to regenerate forests quickly after cutting. However, disturbed soil and detritus accumulations caused by management crews and their equipment may also create a large variety of microsites for seedling establishment. Because repeated cutting selects for dominance by species with highest sprout growth rates, it should not be used as the sole management technique. It may instead be used to alter the vigor, stature, and stored reserves of trees so that herbicides or other methods of tree control can be used more efficiently.     

On the value of endangered and other species

This paper describes two frameworks—utilitarian and Kantian—society uses to make decisions concerning environmental management and, in particular, species protection. The utilitarian framework emphasizes the consequences of choices for prior preferences. A perfectly competitive market, on this model, correctly values environmental resources. The Kantian approach identifies rules appropriate to recognized situations given the identity of the decision maker. It relies on democratic political processes and institutions to provide the means by which citizens determine the identity of their community—its moral character and aspirations—and match appropriate rules to recognized situations. This paper argues that markets do not fail in any general way in measuring the economic value of plants and animals. Market prices, in general, correctly represent the marginal or exchange value of species. If society legislates against extinction, this must be understood as an exercise in Kantian decision making in view of the moral value of species, not as an attempt to correct a market failure or to promote social welfare or utility.     

The biodiversity challenge: Expanded hot-spots analysis

Summary This paper aims to throw light on the mass extinction that is overtaking Earth's species. Using an analytic methodology developed for an earlier partial assessment, it focuses on a series of hot-spot areas, these being areas that (a) feature exceptional concentrations of species with high levels of endemism, and (b) face exceptional threats of destruction. The paper identifies another eight such areas, four of them in tropical forests and four in Mediterranean-type zones. The analysis reveals that the four tropical-forest areas contain at least 2,835 endemic plant species in 18,700 km², or 1.1 percent of Earth's plant species in 0.013 percent of Earth's land surface; and that the four Mediterranean-type areas contain 12,720 endemic plan: species in 435,700 km², or 5.1 percent of Earth's plant species in 0.3 percent of the Earth's land surface. Taken together, these eight hot-spot areas contain 15,555 endemic plant species in 454,400 km², or 6.2 percent of Earth's plant species in 0.3 percent of Earth's land surface. This is to be compared with the earlier hot-spots analysis of 10 tropical-forest areas, with 34,400 endemic plant species in 292,000 km², or 13.8 percent of Earth's plant species in 0.2 percent of Earth's land surface.Taking all 18 hot-spot areas together, we find they support 49,955 endemic plant species, or 20 percent of Earth's plant species, in 746,400 km², or 0.5 percent of Earth's land surface. This means that one fifth of Earth's plant species are confined to half of one percent of the Earth's land surface — and they occur in habitats that are mostly threatened with imminent destruction.By concentrating on these hot-spot areas where needs are greatest and where the pay-off from safeguard measures would be greatest, conservationists can engage in a more systematised response to the challenge of large scale impending extinctions.Dr Norman Myers is a consultant in environment and development, a member of this journal's Advisory Board, and a regular contributor to the journal. He is a Senior Fellow of World Wildlife Fund — US. This paper enlarges on an important theme developed by Dr Myers in a contribution which appeared inThe Environmentalist,8(3), 187–208. The research for this paper has been supported by the MacArthur Foundation, Chicago, USA.     

Fluorosis - a case study from the Sambher Salt Lake region in Jaipur, Rajasthan, India

Assistant Professor in Human Ecology, in the Indira Gandhi Centre for Human Ecology, Environment and Population Studies at the University of Rajasthan. Although fluorine is an essential element for human growth and development, its intake in excessive amounts beyond the permissible limits can be very harmful. Dental and skeletal fluorosis are some of the common afflictions of fluorine poisoning and it can even have crippling effects in aged individuals. With the rise in industrialization fluoride contamination is increasing in the human environment as it is a basic component of the ground water. Certain regions of India, particularly the arid zones of Rajasthan, have serious fluoride problems and it has become a serious health hazard in several villages of Rajasthan.     

The Effect of Oil Spraying on Eggs of Double-Crested Cormorants

Spraying eggs with oil has been used as a method of decreasing the reproductive success of super abundant avian species. Double-crested Cormorant (Phalacrocorax auritus) abundances have created a potential disturbance to some endangered species of birds, sport fishing communities and aquaculture facilities. The hatching success of oil sprayed Double-crested Cormorant eggs was investigated. Oil spraying was done during the first, second, or third week of the eggs incubation to determine the most effective time during the incubation period for a one-time treatment. The oil spraying technique was 95–98% effective at preventing hatching. Hatching success was independent of the week of incubation that an egg was sprayed with oil. The maximum number of eggs on the colony occurred four weeks after the first egg was laid. This would be the most efficient week to spray the colony to decrease hatching success.     

Field history and dissipation of atrazine and metolachlor in Colorado

Farmers in eastern Colorado have commented that atrazine does not provide the length of weed control that they expected in fields that have received multiple applications of the herbicide. Multiple laboratory studies suggest that atrazine dissipates more rapidly in soils with a history of atrazine use compared with soils that had not been treated with the herbicide and this could be related to the above observation. Field and laboratory studies were conducted to determine the rate of dissipation of atrazine and metolachlor in fields in Colorado. The published half-lives of atrazine and metolachlor are 60 and 56 d, respectively. In the field studies, the half-lives of atrazine and metolachlor in the top 15 cm of the soil ranged between 3.5 and 7.2 d and 17.9 and 18.8 d, respectively. In laboratory studies, the half-life of atrazine varied from 1.4 to 19.8 d with the shortest half-life occurring in soils which had been treated with atrazine for at least 5 yr. The longest half-life was in a soil that had never received atrazine. The half-life of metolachlor in these same soils varied from 10.6 to 28.2 d. There was no apparent relationship between the half-life of metolachlor and the half-life of atrazine in the laboratory studies. These results confirm farmers' observation of the shorter residual activity of atrazine in Colorado fields receiving atrazine over multiple years.     

A pest is a pest is a pest? The dilemma of neotropical leaf-cutting ants: Keystone taxa of natural ecosystems

Leaf-cutting ants of the generaAcromyrmex andAtta are considered the principal polyphagous pests of the Neotropics Although some members of these genera are of economic importance, have a broad geographic distribution, and are extremely good colonizers, others are endemic and closely interact with native ecosystems. Control is generally practiced against any colony, irrespective of its taxonomic status. Indiscriminate control coupled with habitat destruction threatens endemic species with extinction, and, through habitat simplification, favors other pest species. As nests ofAtta are large, having several square meters of nest surface, the endemic taxa can be easily used as environmental indicators for natural ecosystems Likewise, the pest species can be used to detect environmental disturbance As these ants are keystone species and easily identified by nonspecialists, efforts should be made to integrate these into viable conservation programs     

Sensitivity of Indices of Biotic Integrity to Simulated Fish Assemblage Changes

Multimetric indices of biotic integrity (IBIs) are commonly used to assess condition of stream fish assemblages, but their ability to monitor trends within streams over time is largely unknown. We assessed the trend detection ability of two IBI formulations (one with traditional scoring and metrics, and one with nontraditional scoring and region-specific metrics) and of similarity and diversity indices using simulations that progressively altered the fish assemblages of 39 streams in the United States mid-Atlantic Highlands region. We also assessed responses to simulated 50% variability in fish abundances, as a measure of background noise. Fish assemblage indices responded little to changes that affected all species proportionally despite substantial changes in total fish number. Assemblage indices responded better to scenarios that differentially affected fish species, either according to life history traits or by increasing dominance of already common species, but even these changes took some time to detect relative to background variability levels. Ordinations of stream fish assemblage data suggested that differences among sites were maintained even after substantial alterations of fish composition within sites. IBIs are designed to detect broad assemblage differences among sites while downplaying abundance changes and variability increases that were the first indications of within-site changes, and they appear more suited to detecting large departures from natural fish assemblages than for monitoring gradual changes such as those our simulations produced. Inferences about causes of assemblage changes should be made with caution because of correlations among species traits and interdependence among IBI component metrics. Site trend assessments should be made based on all available data rather than just by summary indices.     

Evaluation of large-scale CO2 storage on fresh-water sections of aquifers: An example from the Texas Gulf Coast Basin

Large-scale injections of CO₂ into subsurface saline aquifers have been proposed to remediate climate change related to buildup of green house gases in the atmosphere. The pressure buildup caused by such injections may impact a volume of the basin significantly larger than the CO₂ plume itself. In areas with hydrological settings similar to the Gulf Coast Basin, the perturbation of the flow-field in deep parts of the basin could result in brines or brackish water being pushed up-dip into unconfined sections of the same formations or into the capture zone of fresh-water wells. The premise of the current study is that the details of multiple-phase flow processes necessary to model the near field evolution of the CO₂ plume are not necessary to describe the impact of the pressure anomaly on up-dip aquifers. This paper quantitatively explores conditions under which shallow groundwater would be impacted by up-dip displacement of brines, utilizing an existing carefully calibrated flow model. Modeling an injection of water, arguably equivalent to 50 million tons of CO₂/year for 50 years resulted in an average water-table rise of 1 m, with minor increase in stream baseflow and larger increase in ground water evapotranspiration, but no significant change in salinity.     

Impact of climatic and soil conditions on environmental fate of atrazine used under plantation forestry in Australia

We studied the leaching and dissipation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-s-triazine) and its two principal metabolites (desethylatrazine and desisopropylatrazine) for more than two years through soil profiles at five forestry sites across Australia (representing subtropical, temperate and Mediterranean climatic conditions with rainfall ranging from 780 to 1536 mm yr^?1). Following atrazine applications at local label rates, soil cores were collected at regular intervals (up to depths of 90–150 cm), and the residues of the three compounds in soil were analysed in composite samples using liquid chromatography. Bromide was applied simultaneously with atrazine to follow the movement of the soil water. While bromide ion rapidly leached through the entire profile, in most cases the bulk of atrazine, desethylatrazine and desisopropylatrazine remained in the top 45 cm of the soil profile. However, a small fraction of residue moved deeper into the soil profile and at a subtropical site (Toolara) trace levels (ng L^?1) of atrazine and one of its metabolites (DEA) were detected in perched groundwater located at a depth of 1.8 m. Data on the total residues of atrazine in soil profiles from all sites except the Tasmanian site fitted a first-order decay model. The half-life of atrazine in surface soils at the subtropical sites (Toolara and Imbil) ranged from 11 to 21 days. Four separate applications of atrazine at Toolara resulted in a narrow range of half-lives (16 ± 3.6 days), confirming relatively rapid dissipation of atrazine under subtropical conditions (Queensland). In contrast, a prominent biphasic pattern of initial rapid loss followed by very slow phase of degradation of atrazine was observed under the colder temperate climate of Highclere (Tasmania). The data showed that while its 50% (DT₅₀) loss occurred relatively rapidly (36 days), more than 10% of herbicide residue was still detectable in the profile even a year after application (DT₉₀ = 375 days). The rate of dissipation of atrazine at warm subtropical Queensland sites (Imbil and Toolara) was 2–3 times faster than sites located in colder climate of Tasmania. The marked contrast in DT₅₀ values between subtropical and temperate sites suggest that climatic conditions (soil temperature) is one of the key factors affecting atrazine dissipation. At the Tasmanian site, the combination of leaching of the herbicide in subsoil and slower microbial activity at cooler temperatures would have caused a longer persistence of atrazine.     

Vulnerability of Rehabilitated Agricultural Production Systems to Invasion by Nontarget Plant Species

Vast areas of arable land have been retired from crop production and “rehabilitated” to improved system states through landowner incentive programs in the United States (e.g., Conservation and Wetland Reserve Programs), as well as Europe (i.e., Agri-Environment Schemes). Our review of studies conducted on invasion of rehabilitated agricultural production systems by nontarget species elucidates several factors that may increase the vulnerability of these systems to invasion. These systems often exist in highly fragmented and agriculturally dominated landscapes, where propagule sources of target species for colonization may be limited, and are established under conditions where legacies of past disturbance persist and prevent target species from persisting. Furthermore, rehabilitation approaches often do not include or successfully attain all target species or historical ecological processes (e.g., hydrology, grazing, and/or fire cycles) key to resisting invasion. Uncertainty surrounds ways in which nontarget species may compromise long term goals of improving biodiversity and ecosystem services through rehabilitation efforts on former agricultural production lands. This review demonstrates that more studies are needed on the extent and ecological impacts of nontarget species as related to the goals of rehabilitation efforts to secure current and future environmental benefits arising from this widespread conservation practice.     

Trade-Based Carbon Sequestration Accounting

This article describes and illustrates an accounting method to assess and compare early carbon sequestration investments and trades on the basis of the number of standardized CO₂ emission offset credits they will provide. The gold standard for such credits is assumed to be a relatively riskless credit based on a CO₂ emission reduction that provides offsets against CO₂ emissions on a one-for-one basis. The number of credits associated with carbon sequestration needs to account for time, risk, durability, permanence, additionality, and other factors that future trade regulators will most certainly use to assign official credits to sequestration projects. The method that is presented here uses established principles of natural resource accounting and conventional rules of asset valuation to score projects. A review of 20 early voluntary United States based CO₂ offset trades that involve carbon sequestration reveals that the assumptions that buyers, sellers, brokers, and traders are using to characterize the economic potential of their investments and trades vary enormously. The article develops a universal carbon sequestration credit scoring equation and uses two of these trades to illustrate the sensitivity of trade outcomes to various assumptions about how future trade auditors are likely to score carbon sequestration projects in terms of their equivalency with CO₂ emission reductions. The article emphasizes the importance of using a standard credit scoring method that accounts for time and risk to assess and compare even unofficial prototype carbon sequestration trades. The scoring method illustrated in this article is a tool that can protect the integrity of carbon sequestration credit trading and can assist buyers and sellers in evaluating the real economic potential of prospective trades. Published online     

Agricultural area impacts within a natural area: Cades cove,a case history

Agricultural management in Cades Cove, an historic district in Great Smoky Mountains National Park, has affected natural resources both within the district and in the adjoining natural areas. Aquatic impacts of haying and cattle grazing included increases in water temperatures, turbidity, nutrient loading, and bacterial counts and decreases in benthic macroinvertebrate density and fish biomass. Wildlife populations, including groundhogs, wild turkeys, and white-tailed deer, have increased in the open fields and around the periphery of the historic district. Intensive deer foraging has removed deciduous seedlings and saplings from woodlots, lowering species diversity and favoring coniferous reproduction. Cades Cove has limestone habitats unique in the park, and both deer browse and cattle grazing may have disturbed populations of rare plant species. Effects on water quality are detectable at a campground 15 stream km from the agricultural area, and the effects of deer foraging extend about 1 km beyond the open fields.Since historic landscape preservation is presently a goal of the park, managing for open vistas in Cades Cove will require some sort of continuing disturbance. Conversion of cattle pastures to hayfields would reduce aquatic impacts but the deer herd might increase as a result of reduced competition for forage. Retarding old field succession would increase populations of native plant species dependent on sunlight, but would require government-funded mowing. Other options are discussed. Completely eliminating the effects of the historic district on adjoining areas may be impossible, at least under present economic constraints.     

The evolution of sustainability

Six separate but related strains of thought have emerged prominently since 1950 in discussions of such phenomena as the interrelationships among rates of population growth, resource use, and pressure on the environment. They are the ecological/carrying capacity root, the resources/environment root, the biosphere root, the critique of technology root, the no growth/slow growth root, and the ecodevelopment root.Each of these strains of thought was fully developed before the word sustainable itself was used. Many of the roots are based on fundamentally opposing assessments of the future of mankind. Many of the roots, such as the ecology/carrying capacity root, are based on physical concepts, and they exclude normative values. Others, such as the ecodevelopment root, include such values as equity, broad participation in governance, and decentralized government.When the word sustainability was first used in 1972 in the context of man's future, in a British book,Blueprint for Survival, normative concepts were prominent. This continued to be the case when the word was first used in 1974 in the United States to justify a no growth economy.Sustainability was first used in a United Nations document in 1978. Normative concepts, encapsulated in the term ecodevelopment, were prominent in the United Nations publications.After about 1978, the term sustainability began to be used not only in technological articles and reports but also in policy documents culminating in the use of the term in the report of the summit meeting of the Group of Seven in 1989.The roots of the term sustainability are so deeply embedded in fundamentally different concepts, each of which has valid claims to validity, that a search for a single definition seems futile. The existence of multiple meaning is tolerable if each analyst describes clearly what he means by sustainability.