Ecological processes and sustainability

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Ecological processes and sustainabilityT. R.E. Southwood a ba Department of Environmental Sciences and Policy , Central European University ,Budapest, Hungaryb Department of Zoology , Oxford University , UKPublished online: 02 Jun 2009.

To cite this article: T. R.E. Southwood (1995) Ecological processes and sustainability, International Journal of SustainableDevelopment & World Ecology, 2:4, 229-239, DOI: 10.1080/13504509509469904

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Int.J. Sustain. Dm. World Ewl. 2 (1 995) 229-239

Ecological processes and sustainability

T.RE. Southwood

Department of Environmental Sciences and Policy, Central European University, Budapest, Hungary and Department of Zoology, Oxford University, UK

Key words: impact, sustainability, population dynamics, extinction, ecosystem processes, pollution, biogeochemical cycles, development

SUMMARY Ecology has developed from its position as an obscure science to being at the interface of science and public policy. The impact of mankind can be described in ecological terms relating to population size, energy use and non-renewability. Sustainable development needs to be addressed on the basis of knowledge of ecological processes which maintain the environment in a state of change; the processes need to be conserved, not maintained in any particular state. Recent advances in the understanding of ecological processes are reviewed to highlight the potential contribution of this knowledge to the development of a sustainable policy. At the level of the population the significance of considering the extinction risks in the framework of spatio-temporal dynamics is now established indicating opportunities for planning land use more precisely to sustain biodiversity. Whilst the maintenance of habitats is generally the key to the persistence of biodiversity, they must be viewed as everchanging mosaics within which cycles of succession, best described by Markovian sets of probabilities, are occurring continually. The extent to which these probabilities are distorted will determine whether the ecosystem returns to the same system or moves to a novel one. At the global level, biogeochemical cycles have a certain flexibility in relation to fluxes and stocks, hence pollution must be defined by relating the flow rate of the substance to this flexibility, which often permits the accommodation of anthropogenic perturbations. Non-sustainable processes can be defined in ecological terms, thus providing functional definitions of a sustainable policy and of sustainable development.

INTRODUCTION

Over the last halfcentury has moved

science with major practical implications and a

has come about through the recognition that mankind is now Powerful enough to influence large-scale ecological processes.

The t ~ ~ m ‘ecology’ was originally coined by Ernst Haeckel in 1869 - the study of the ‘house’ of the organism. I t is ra ther more than a continuation of the natural history observations

of pioneers such as Carl Linne, Gilbert White and Henri Fabre, in that the concept of the house demanded a holism; the house should be seen as

last century and in the early part of this the

Schrimper, Clements, Gleason, Braun-Blanquet, Gause, Tansley, Raunkiaer, Grinnell, Elton, Hutchinson and others described the basic patterns in the house: biocoenoses, foodchains, the pyramid of numbers, the niche and so on.

Whilst it would be entirely wrong to imply that humankind has had little impact on the biosphere

from being an Obscure branch Of to a a whole: a functioning system. At the end of the

potent political force (Southwood, 1981) 9 This present one the founders of ecology - Mobius,

This paper is based on the Opening Plenary Lecture given by the author to EURECO ’95, the 7th European Ecological Congress held in Budapest, 20-25 August, 1995 Correspondence: Prof. Sir Richard Southwood, Department of Zoology, South Parks Rd., Oxford OX1 3PS, UK

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Ecological pocesses and sustainability Southwood

until recently (Ehrlich and Ehrlich, 1972; Diamond, 1986, p. 266), it was in the 1940s that human technological prowess increased dramatically. The awesome power of the nuclear bomb brought humankind’s destructive potential vividly into focus. Mercifully, it is other technological developments that have hitherto had the more significant impact on the environment - on the global house. New, biologically active chemicals such as DDT and all manner of herbicides and antibiotics have become widely distributed. Fossil fuel has been exploited on a much greater scale than ever before; a few bulldozers can replace thousands of men and hundreds of horses, bringing instant local change.

Thus it was in the 1950s that many persons began to recognize that the house was showing ‘cracks’; its structure was being altered in a profound manner. Widespread anxiety among biologists and naturalists was crystallized by Rachel Carson in her book Silent Spring published in 1962. A decade later the issues were in the public’s eye worldwide. Meadows et al. (1972) highlighted the global nature of the problem in their Limits to Growth, and in 1974 the United Nations held the first conference on the environment in Stockholm. There followed a series of international reports and conferences, the most recent being the Brundtland Commissions’s Our Common Future and the 1992 conference in Rio de Janeiro. These decades have also seen the growth of political parties focused on environmental issues. Initially, several adopted the name ‘Ecology’ but, to the relief of many professional scientists, this was soon replaced by the label ‘Green’.

Whilst in the 1950s and 1960s the role of the ecologist was largely to warn, once political concern had been aroused ecology was turned to provide a rational and intellectually rigorous framework on which policy could be based. Battling with considerable complexity on one hand (Ludwig et al., 1993) and limited funding on the other, ecologists often disappointed decision-makers by the uncertain terms in which they framed their advice. It was necessary for them to move away from particular cases, where they were secure in their detailed knowledge, and consider the global scale.

THE IMPACT OF HUMANKIND ON A GLOBAL, SCALE Ehrlich and Holdren (1971; 1972) were the first to consider holistically and quantitatively the per capita impact of humanity on the environment. The relationship they developed is often expressed as:

I = P.A.T

where P = population, A = affluence and T = technology. Many people resisted the concept that the improvement in the standard of living (affluence) and the continuation of technical progress were necessarily always destructive to the environment. This formulation seemed inimical to further development, the goal of most countries, especially those in the Third World. Following the distinction that Ehrlich and Holdren made between renewable and non- renewable resources, I expressed the relationship (Southwood, 1972; 1992) as:

I = P.E.N

or more formally as:

I = P . 4 t P.Eii.N

where E is the use of energy per capita and N is the proportion that is ‘non-renewing’ (i.e. the use of non-renewable resources, non-reversible land degradation, or pollution that is non- reversible). The importance of the distinction between the two components is being increasingly recognized. Ei is the energy of our food gained by practices that are sustainable, generation after generation, and the energy obtained from renewable resources. This term also applies for other animals; it represents an impact, but a sustainable one, on the environment. Eii is the energy derived from non-renewable resources and/or generated or used in a way that causes pollution that is, in the long-term, degrading the environment and other natural resources beyond the point of recovery. Thus, this term represents non-sustainable activity and is the converse of the concept of sustainability.

SUSTAINABLILITY The last decade or so has seen a widespread recognition that: ‘Yes, there is an environmental

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Ewbgicul pT0cesse.i and sustainability Southwood

crisis’, but that ‘No, we cannot give up technical progress; to do so is socially and politically impossible’.

The Brundtland Commission and the Rio conference both focused on the concept of sustainability. This concept has been variously applied to growth and development. As many writers have pointed out, ‘sustainable growth’, a continuous increase in the matterenergy used by mankind is, in the long-term, impossible: the biosphere is finite (Daly, 1991). Vitousek et a1 (1986) calculated that, 10 years ago, 40% of the net primary production of the world’s terrestrial ecosystems were used by mankind. Although cultivation practices, (which normally involve an input of fossil energy) may increase productivity slightly, an upper limit is fured by photosynthetic efficiency, land surface and solar energy.

Sustainable development has been defined as ‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs’ (Brundtland, 198’7). As Meyer and Helfman (1993) emphasize, intergenerational equity is the backbone of the concept, and although the ‘generational environmental debt’ can be defined (Azar and Holmberg, 1995), we cannot know what future generations will regard as their needs, nor the abilities (the technical fixes) they will have; however, ‘as trustees it behoves us, when in doubt, to err on the side of caution and be provident’ (Southwood, 1970). Put simply, we must not change the world in ways that, on present knowledge, mean that the next generation cannot live as we do.

The concept of development must be placed in an economic and social framework, as well as an ecological one, but this involves significant changes from the conventional economic perspective: lengthening the time-scale, ensuring that environmental costs are not externalized and recognizing that natural resources are limited (Costanza, 1991). It can also lead, as Conway and Barbier (1990) comment, to providing an umbrella for virtually everything that is perceived as ‘good’. Whilst this has encouraged its political acceptability, for sustainability to be a meaningful guide to policy, it must be firmly based on humankind’s usage of matterenergy.

Whilst the stream of matterenergy utilized by humanity cannot increase indefinitely, we have

considerable freedom as to how it is allocated; it is variation in this allocation that constitutes sustainable development (Daly, 1991).

The challenge to ecological knowledge is therefore:

To assess the effects of further growth in any particular environment on the ecological processes that maintain the natural resources of that environment;

To determine the extent that re-allocations (i.e. development) will perturb the ecological processes affected; and

To advise on developments that would lessen the impact of humankind’s existing activities on ecological processes, and so enhance the conservation of natural resources.

it may be said that we are concerned with both conservation and repair. The two are not alternatives, but facets of the same process. The objective may be to maintain a certain level of species’ richness in a habitat or to keep the level of free mineral oil below a certain level (conserving a limit on pollution), but in each case the desired level will be fured by the ecological processes in the environment. It is these that must be conserved - not a particular state. Within their domain of stability, natural ecological processes are mostly self-repairing.

PROCESS AND CHANGE, STABILITY AND CHAOS

The only constant feature of Nature is change. The concept of conservation in the sense of stasis is unreal; the birth and death processes that are characteristic of Life ensure changes in the matter-energy distribution in any location. Furthermore, organisms - especially microbes - in a functional partnership with various chemical reactions are key players in the cycles through which the elements pass; the biosphere as a whole functions in some ways like a organism having feedback mechanisms that tend to maintain homeostasis - this view is encapsulated in the Gaia hypothesis (Lovelock, 1988). Through millions of years, such cyclic processes have operated and undoubtedly will continue to function, in some form, as long as the planet with

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its mantle of gas exists. Over 1000 million years ago anaerobic processes dominated until the early photobionts overwhelmed the system with their ‘pollution’, namely oxygen. The potential variability is great (Webb and Bartlein, 1992), but humankind is not concerned simply with sustaining the biosphere, not even just sustaining the biosphere in a state in which human life can exist, but with the much narrower bands of variation: those in which modern societies exist and flourish. These conditions are described by the mean values of various physical and biological parameters over the very recent past (100-200 years). One must note that we are selective in our requirements; whilst most of us would want the mean population levels of wild birds of 200 years ago, there would be a different response if we were considering rats or the smallpox virus. We assume that future generations will hold a similar view to ourselves on ‘progress’, but moves to reintroduce the wolf to several parts of Europe would amaze our 16th/17th century ancestors.

What laws underlie the dynamics of change? What governs the risk of extinction? Following May’s (1971) seminal work, considerable progress has been made in the understanding of the fundamental dynamics of ecological processes; this may best be followed by reference to populations. All plant and animal populations fluctuate: this fluctuation can be governed by deterministic predator-prey relationships, but, as May (1976, 1986) showed, under certain conditions the outcomes may be chaotic. Small populations will also exhibit variation simply because of their smallness; May (1971) termed this ‘demographic stochasticity’. Populations may also be perturbed by external factors, of which anthropogenic factors are particularly relevant in the present context. If any of these fluctuations take the population outside its domain of stability it will become extinct. Key variables in determining the risk of extinction are the magnitudes of the intrinsic rate of increase and of its variance, due either to demographic or environmental factors. Natural populations have an upper boundary determined by the carrying capacity. With demographic stochasticity, the larger the carrying- capacity population, and the larger the intrinsic rate of increase, the less likely is extinction or, put another way, the greater the persistence-time of the population (MacArthur and Wilson, 1967;

Caughley, 1994; May et al., 1995). It has been believed that catastrophic environmental events were more likely to lead to extinction than ‘normal’ environmental stochasticity, but environmental catastrophes are in fact simply the more spectacular environmental changes. As Lande (1993) has shown, persistence in time depends simply on the magnitude of the variance in the rate of increase as influenced by environmental events, whether viewed as catastrophes or not, in relation to the intrinsic rate of increase, scaled against the population size at carrying capacity. It has long been recognized that the stability of a species in a region would be increased if there were movements between individual populations, such that the risk was spread (Nicholson and Bailey, 1935; Andrewartha and Birch, 1954; den Boer, 1968). These ideas underlie the modern concept of the metapopulation (Hanski 1991; Hanski and Gilpin, 1991; Hassell et aL, 1991; Nee and May, 1992; Hastings and Harrison, 1994; Moilanen and Hanski, 1995; Paradis, 1995). Theoretical work on spatio-temporal dynamics has shown how spatial heterogeneity may not always be a reflection of environmental heterogeneity, but results from the intrinsic dynamics of the populations (Bascompte and Sole, 1995). The dynamical behaviour, and hence the stability, of populations is strongly influenced by the nature of the dispersal movements of the organisms and by the extent and scale of the fragmentation of the landscape.

Several of the emergent principles from this work on metapopulations underpin certain conclusions from field observations. One begins to understand why species loss is more frequently due to habitat destruction than to the mortality of individuals; why species’ richness is high in nonequilibrium (transient) communities; and why populations in large, relatively homogeneous areas may exhibit regular population cycling, while those in more variable habitats do not.

As the mechanisms become better understood, so it will become possible to make contributions to land-use planning based on a theoretical understanding of species persistence, and not simply on experience. This greater precision will surely provide opportunities for reallocation, in Daly’s (1991) sense, i.e. for sustainable development. One can draw the parallel with


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structural engineering; when the construction of a building had to be based on experience, far more materials were used than were necessary. In modern parlance, they were ‘overdesigned’. Even so, these medieval buildings sometimes fell down because the resources - the building materials - were not distributed appropriately.

This current work on the dynamic processes in populations and metapopulations has shown that the reductionist approach has limits; ecological processes need to be viewed on larger spatial scales: the global scale and the ecosystem.

ECOSYSTEM PROCESSES AND BIODIVERSITY The distribution of organisms of different species in a habitat changes with time. This process has long been recognized and termed ‘succession’. Originally seen as a unidirectional replacement on a bare land surface of pioneer species by others until the climax was achieved, it is now recognized as a cyclic process with varying spatial and temporal scales. It is best described as a Markovian process; each event - i.e. the replacement of one species by another - has a certain probability (Horn, 1975; Tanner et al., 1994). In most ecosystems, the individuals of the dominant space-holders (plants, corals, etc.) , have a finite life at the end of which they release their space and the Markovian cycle starts again (though in a probabilistic sequence, not a deterministic one). Thus, neither forests nor coral reefs are uniform and static ecosystems which (according to the objectives of a sustainable conservation policy) can be preserved unchanged. Rather, they are mosaics in which the distributions of the space- holding species, and all the other flora and fauna associated with them, are continually changing. This is another glimpse at the metapopulation concept (Hanski and Gilpin, 1991; Hassell et aL, 1991). Combining the insights gained from these developments in theoretical ecology, we are beginning to understand the complexity of the dynamic and uncertain processes that ‘hold’ a species in its ecosystem. It is not surprising the conservationists have concluded empirically that the maintenance of biodiversity is best achieved on a habitat basis, rather than on a species one (Franklin, 1993).

The fall of a forest tree continues the Markovian cycle, and for much of the time in many ecosystems such events produce small-grain successional change. However, various natural events may greatly increase the spatial scale of change - events such as fires, floods, avalanches and hurricanes. These events have been viewed, described and usually treated as catastrophes, but the existence of certain ecosystems, with their associated biodiversity, is dependent on such events. Fire- dependent ecosystems are particularly characteristic of regions with a Mediterranean climate, and their plant species, adapted to a fire regime, are sometimes called pyrophytes. In such habitats, the vegetational and faunal composition, together with the carbon and nutrient balances, can be predicted on the basis of the number of years since the last fire (e.g. Hilbert and Larigauderie, 1990; San Jose and Farinas, 1991; Morrison et al., 1995). These ecosystems are normally resilient; the same system will return after the fire (e.g. Carreira et aL, 1992). However, the probabilities in the Markovian chain can be altered by the intensity of the fire; this is largely dependent on the amount of biomass, which is itself dependent on the interval since the last fire. Hence, fire-protection measures that lengthen abnormally the interfire interval may alter the Markovian probabilities so that the cycle of succession is diverted and the original ecosystem may never return. Similar processes follow biomass destruction by storm (e.g. Labbe, 1994) or flood (e.g. Roberts, 1993).

Besides influencing the frequency of these events, humankind may bring about large-scale changes directly, an example being the clear felling of forests. Natural regeneration processes may not restore the previous ecosystem; it is not an evolved situation. The manner in which the operation is carried out - for example, the extent to which the soil is disturbed (Mou et al., 1993) - can have a major effect on the composition and nature of the vegetation that develops. When human-managed ecosystems are eventually abandoned, they will not necessarily return to their original condition (Bacilieri et aL, 1994).

Set against the growth in human population, and our ability (and believed need) to modify increasingly large areas of natural habitat, the objective of maintaining biodiversity may seem particularly difficult. However, as the examples


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given above show, ecosystem composition is determined by complex processes, and our increasing knowledge of these processes should enable us to achieve compatibility in combining the twin objectives of utilizing resources and maintaining biodiversity. But it is how something is done that often determines the extent to which it is sustainable. This may be illustrated by analogy with the problem of marching an army regiment across a fragile bridge. Clearly, the soldiers have to break step, and the officer in charge has to give up the satisfaction of seeing all the troops march in synchrony: this is a cost. However, the principal aim is achieved - the bridge is crossed. Furthermore (in theory at least) there are no hidden external costs placed on future users of the bridge; they are not left a damaged bridge.

As already indicated, the exact way in which a piece of land is managed will have a profound effect, not only on its flora (as described above) but also on its fauna. For example, a single recent issue (November 1994: vol. 31, no. 4) of the Journal of Apiblid Ecologv contained five papers reporting studies on the impact of forest or farmland management methods on vertebrate populations. It was reported that in tropical rainforests selective logging led to increased numbers of some primates and, minimal impact on the other species (Plumptre and Reynolds, 1994) ; herbicide spraying in boreal forests had no discernible effect on snowshoe hare populations (Sullivan, 1994), while ungulate numbers in the Bialowieza Forest in Poland were reduced where conifers had been planted Uednejewska et aL, 1994). Two studies (Green et al., 1994; Parish et aL, 1994) on hedgerow birds in Britain show the complexity of the relationship and the potentially adverse effects of modern mechanized techniques for hedgerow management; however, illustrating my analogy with the army on the bridge, Parish et aL (1994) recommend five management options that will benefit bird populations at very little cost to the farmer (and possibly some benefit from an increased biological control of pests).

GLOBAL PROCESSES Consideration of global processes inevitably focuses on the basic biogeochemical cycles. All major cycles have fluxes (flows), stocks and sinks

(Figure 1). Once material has passed to the sink it passes out of the natural cycle. Human operations may take materials out of one stage, a stock or a sink, and add them to another. If the additions are sufficient to cause some apparent qualitative change in that stage or the consequent flux, then we may say that ‘pollution’ has occurred. It is important to note that it is not simply the alteration of the matter-energy system; the addition of material or energy does not automatically cause pollution. This description is only appropriate when the scale of the alteration is outside the natural variances, i.e. when the concentration/time parameters change to such an extent that other physical factors (e.g. aerial visibility) or biological systems change. In general, it is only on the basis of experience that an anthropogenic process may be said to produce substances in polluting concentrations. This is because the material may pass rapidly into a sink or may be insufficient to overload the natural cycle. The elasticity of these biogeochemical cycles has already permitted considerable proportions of many anthropogenic matter-energy streams to be ‘processed’ without causing pollution.

Our inability to identify, ab initio, a substance as a pollutant does not invalidate the application of the ‘precautionary principle’ (O’Riordan and Cameron, 1995), because a number of criteria may be used to evaluate the extent to which caution is justified. An activity is likely to be polluting if, firstly, the substance is removed from a sink (e.g. in the Earth’s crust) and released into the active segments of the cycle; secondly, the quantity released is significant in relation to the levels occurring naturally in the cycle; and thirdly, the substance is known to be biologically active (to be toxic) or to have a significant effect on other major components of the global matterenergy system.

The impact of anthropogenic carbon dioxide on the carbon cycle and on the radiation balance of the earth is certainly a major issue in the sustainability debate. In spite of much work, there is still uncertainty about the nature of the sinks that hitherto have removed annually about 4 billion tons of carbon released by humankind from fossil fuel. The major oceans probably account for about half the amount removed (Eglinton et aL, 1995), and the forests for the remainder (Ciais et al., 1995; Grace et aL, 1995).


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STOCKS FLUXES

Southwood

SINKS

_ - - - - - - - I

llution

natural - - - - - anthropogenic

Figure 1 activities

The general form of biogeochemical cycles and their relationship to potentially polluting anthropogenic

Forests are unlikely to prove to be a permanent sink; they should more correctly be referred to as holding a stock of carbon for a particular residence time. T h e increased primary production (encouraged, it is thought, by higher levels of atmospheric carbon dioxide, slightly higher temperatures and increased airborne nitrate) will eventually become part of the soil and litter layer from which the carbon will be lost by respiration. The magnitude of the mean time-lag (the residence time) between incorporation in the forest (the stock) and release during respiration, varies; currently 20% of the carbon respired in northern latitudes has a time-lag of up to 100 years (Ciais et aL, 1995). As the rate of respiration from the soil and litter is very temperature- dependent, increases in temperature could reduce the lag-times, releasing increased amounts of carbon dioxide which would be likely to have a positive feedback on temperature increases.

Gases other than carbon dioxide will also reflect back the radiation from the Earth - most of them having, on a molecular basis, a greater effect than carbon dioxide. The concentrations of such gases in the atmosphere have also increased (Vitousek, 1992). As indicated, the major cause of most of

these changes is the increasing use of fossil fuels for the rising per capita use of energy worldwide. Changes in land cover have made a subsidiary, though significant contribution (Vitousek, 1992). Nevertheless, if sustainability is to be achieved, then it is vital that we have a global picture of land cover and the changes in land use, and utilize models for forecasting that permit the incorporation of such data (e.g. the IMAGE system; Leemans and Zuidema, 1995). This requirement is particularly important because various changes in land use could be part of a sustainable development programme to mitigate the effects of the increased levels of carbon dioxide and other ‘greenhouse gases’.

Although there are many environmental problems arising from humankind’s activities, the climatic changes resulting from the increasing atmospheric concentrations of these gases pose the greatest threat to the whole concept of sustainability. Ecologists do not need convincing that the implications of the apparently modest change in average temperature on rainfall patterns, on naturalvegetation, and on agriculture will be profound (Breymeyer and Melillo, 1991; Parry and Duncan, 1995). Furthermore, there


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are a number of potential nonlinearities that could, in catastrophe-theory terms, switch the parameters that govern our climate; for example, raised temperatures could cause the release of methane from methane hydrate deposits in the permafrost and the seabed (Leggett, 1990) or accelerate of the rate of release of carbon dioxide from the currently augmented stock in forest soils and litter. Both these processes would have powerful feedback effects on themselves. Notwithstanding all these indications, many decision makers are very reluctant to apply the precautionary principle and, so long as doubt remains, efforts to reduce energy consumption by fiscal means seem politically impossible. This highlights the urgency with which the remaining uncertainities in our understanding of these processes should be addressed.

PROGNOSIS The objective of sustainable development is, in many ways, a daunting one. Some commentators (Ludwig et ah, 1993) believe that human short- sightedness and greed make its achievement unlikely. When one sees the resistance to taking effective steps, as opposed to making grandiloquent statements, to reduce the impact of ‘greenhouse gases’, one is inclined to agree. However, when I look back over the more than a quarter of a century during which I have been concerned with environmental issues, I see grounds for optimism. Environmental concerns are now addressed in almost every democratic political programme; a recent editorial in the journal Sciencecommenced ‘One of the defining social themes of the decade has been ecological awareness. Consequently, ecology now stands at the interface between science and public policy’ (Gallagher et al., 1995). It is, of course, necessary to replace the talking with action wherever possible, and ecologists have a major role to play; we need to ensure that our research programmes address the cardinal issues. An appropriate agenda has been developed by Lubchenco et aZ. (1991), whilst examples of the application of ecological knowledge are presented for a number of case studies in Orians et ah (1986). It is also essential that ecologists are willing to go further and help interpret their knowledge in the context of policy, taking

account of economic and social factors, as well as coping with uncertainty. Such a task is fraught with difficulties; as Carpenter (1994) has pointed out, ecologists are far more capable of detecting unsustainability than prescribing for sustainability. This, I suggest, provides the clue for functional definitions that are appropriate for ecological analysis and for the determination of policy. A non-sustainable process uses or modifies a natural resource in such a way that its availability in the future is permanently impaired, making present opportunities no longer attainable. A sustainable policy (as sought by governments) is one that reduces and eventually eliminates non-sustainable processes within the system to which the policy is applied. Consequently, sustainable developmat is development - defined for example, as an increase in gross disposable product per capita - that is achieved through a sustainable policy. Brady and Geets (1994) define it more widely, requiring an accounting framework that ‘indexes the reduction in the value of natural resources as social assets’ i.e. one that internalizes environmental costs. This certainly brings the concept within conventional economic thinking, but I believe that it permits ecologically non-sustainable processes. Any process defined as non-sustainable has, effectively, a ‘thou shalt not’ label. Few, if any, would dissent from the view that the hunting of Stellar’s sea cow (Hydrodamalis gigas) to extinction over the brief period 1742-1769 could not be viewed as sustainable development, yet had there been arguments at the time, one can imagine the case being made for the importance of such hunting to the development of the North Pacific fisheries and the annual cull being indexed within that economic framework. It is therefore necessary for ecologists to identify activities that will modify ecological processes in a non-sustainable manner. Specifically, these activities that belong to the ‘thou shalt not’ category are: activities that will lead to the extinction of a species, activities that will modify the climate in an irreversible manner beyond its normal limits, and activities that will use non-renewable resources in a manner that will clearly deprive future generations. In the case of the latter category, we must remember the richness of the Earth’s crust, in terms of mineral deposits; estimates of reserves are frequently more a reflection of humankind’s knowledge and current technical abilities than of absolute quantities.


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The chances of ecologists succeeding - of gaining the necessary knowledge and then influencing the policy makers - will be far greater if we work together and are familiar with and understand each other’s work. In this respect I also see grounds for optimism. When I had the opportunity, as President of the British Ecological

Society in 1976, to launch the series of European Ecological Congresses, ecological work in Europe resembled a much-fragmented habitat with little migration of knowledge. How different the situation today! The recent 1995 Congress marks another major step in the development of our subject in this continent.

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Ecological processes and sustainability