The physical environment
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This document discusses physical geography and environmental systems. It notes that physical geography research has progressed from detailed observations in small areas to modeling at global scales. It provides examples of interactions within the global physical environment, such as how changes in one region can impact climate in other regions. The document also discusses how viewing the biosphere as a system of nested environmental systems has helped scientists understand ecosystem structure and function.
![Note to readers:
This chapter, taken from The Physical Environment: A New Zealand Perspective, edited by Andrew
Sturman and Rachel Spronken‐Smith, South Melbourne, Vic. ; Auckland [N.Z.] : Oxford University
Press, 2001, has been reproduced with the kind permission of Oxford University Press (OUP). OUP
maintain copyright over the typography used in this publication.
Authors retain copyright in respect to their contributions to this volume.
Rights statement: http://library.canterbury.ac.nz/ir/rights.shtml](https://image.slidesharecdn.com/thephysicalenvironment-120703220242-phpapp01/85/The-physical-environment-1-320.jpg)
![420 Interactions and Applications
of which the Milky Way is but one of an enormous number. And the fifth was the first
direct account of the Earth as seen by astronauts orbiting far above the surface.
Over more than a century the belief in a fertile world created by a caring deity for
humans to transform and occupy (Glacken 1967; White 1967) slowly gave way to the
sober realisation that people may not be the centre of, let alone the reason for, cre-
ation. The old theological certainties began to crumble and Homo sapiens had to come
to terms with living on a very small rock orbiting a star near the edge of a fairly large
galaxy. We may now be better able to accept those things, but their psychological
impact on previous generations was profound. For the physical geographer, the fifth of
those discoveries holds particular importance because it supports the proposa ls of
theorists in the Earth sciences.
An important term, the 'biosphere', was coined by an Austrian geologist, Eduard
Suess, in the 1870s for the thin band in which life is concentrated on Earth. In 1926
the Russian scientist and philosopher Vladimir Vernadsky wrote a major text on the
'biosphere', which he saw as the site of transformers of solar radiation into diverse
forms of energy. In the 1960s the American physicist H.]. Morowitz described the
biosphere as an int.ermediate system: a functional ensemble substantially closed to the
import and export of matter but open to flows of energy. He proposed that the flow of
energy through a system of living things acts to organise it (Morowitz 1968).
Biologists, geologists, and physical geographers have long recognised the close
reciprocal relations between living things and the physical world . According to Love-
lock (1995), one of the earliest was the Scottish geologist James Hutton, who, in a lec-
ture to the Royal Society of Edinburgh in 1785, compared the movement of water
from oceans to land and back again with the circulation of blood. In 1935 the British
ecologist A.C. Tansley coined the term 'ecosystem' to cover such relations and their
spatial expression. With developments in communications theory in the mid twenti-
eth century came the notions of information and cybernetics, and the rise of systems
analysis, the latter offering an effective way to analyse interactions between living
things and their environments. More recently, complexity theory has proven helpful
in understanding the structure and function of ecosystems (Nicolis & Prigogine 1989;
Ruthen 1993).
Environmental systems
For more than two centuries, scientific inquiry has progressed by rigorous application
of the positivist paradigm, with strong theory permitting generation of novel research
hypotheses that can be evaluated with information from controlled experiments. Bod-
ies of knowledge grew and understanding of the world increased. The particular con-
tribution of two centuries of research in the life and environmental sciences has been
the identification of links, flows, and interactions in a complex milieu where it can be
difficult to isolate one organism from either its environment or other living things.
That does not mean the positivist mode of scientific inquiry is inapplicable to ecosys-
tems. Rather, it suggests that another mode of invest igation may be needed if we are to
understand the development, features, and prospects of the biosphere.](https://image.slidesharecdn.com/thephysicalenvironment-120703220242-phpapp01/85/The-physical-environment-7-320.jpg)
The physical environment
- 2. The Physical Environment A New Zealand Perspective Edited by Andrew Sturman and Rachel Spronken-Sm ith OXFORD UNIVERSITY PRESS
- 3. OXFORD UNIVERSITY PRESS 253 Normanby Road, South Melbourne, Victoria, Australia 3205 Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide in Oxford New York Athens Auckland Bangkok Bogota Buenos Aires Cape Town Chennai Dar es Salaam Delhi Florence Hong Kong Istanbul Karachi Kolkata Kuala Lumpur Madrid Melbourne Mexico City Mumbai Nairobi Paris Port Moresby Sao Paulo Shanghai Singapore Taipei Tokyo Toronto Warsaw with associated companies in Berlin Ibadan OXFORD is a registered trade mark of Oxford University Press in the UK and in certain other countries © Andrew Sturman and Rachel Spronken-Smith 2001 Authors retain copyright in respect of their contributions to this volume First published 2001 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means , without the prior permission in writing of Oxford University Press. Within New Zealand, exceptions are allowed in respect of any fair dealing for the purpose of research or private study, or criticism or review, as permitted under the Copyright Act 1994, or in the case of repro graphic reproduction in accordance with the terms of the licences issued by Copyright Licensing Limited. Enquiries concerning reproduction ou tside these term s and in other countries should be sent to the Rights Department, Oxford University Press, at the address above . ISBN 0 19 558395 7 Edited by Richard King Indexed by Russell Brooks Cover and text designed by Derrick I Stone Design Typeset by Derrick I Stone Design Printed through Bookpac Production Services, Singapore
- 4. Formal research in phys ical geography began with programmes of detai led observation in small areas. Over time the results were co llated and generalised to ever- larger sca les, culminating in such sem inal work as Dav is's model of landform development, Kop- pen's class ification of climate, and Schimper's vegetation map of the world. By the 1940s and 1950s, increas ing d issatisfaction with what had been produced saw a return to research in small areas, and a greater focus on natural processes and th eir environ- mental effects. By the early 1980s, physical geograp he rs h ad aga in become interested in scaling up the results of research in small areas to mode l what happens at the conti- nen tal and global scales. Growing recognition of the global nature of society's envi- ronmental problems, readily ava ilable sate lli te imagery, and powerful computers facilitated this shift in emphasis. Much of what fo llows in this chapter draws on new thinking about global envi- ronments, as a basis fo r d iscussing the implicat ions for New Zealand. Even though there is broad agreement on th e princ iples, many of the pred ictions are h ighly specu- lative. The geographer's search fo r understa nding abo ut inte ractions within the physical environment has scarcely begun. Models and predictions By late 1968, construction work on Egypt's Aswan High Dam was largely complete. At that time the da m was widely considered a triumph of engineering and a tribute to international cooperation . Since then many environmental bills have been submitted and the costs could prove significant. With completion of the first dam across the Nile several decades earlier, flows of fresh water, solutes, and sedimen t fro m the Ethiop ian highlands, down the ri ver, across th e delta, and into the eastern Mediterranean were impeded. O nce that dam was raised, the enlarged h old ing area covered a vast expanse of lowlands extending into Sudan . W ith furth er reduction in the volu me of fresh water entering the eastern Mediterranean , particularly d uring the normal flood sea- son, the sea became more sa lty. Recen t satellite images indicate warm saline waters flowing through the Straits of Gibraltar and out into the North Atlantic. An Ameri- can oceanographer has specu lated that if this outflow should deflect part of the Gulf
- 5. Interactions and Applications Stream into Davis Strait between Canada and Greenland, then development of sea ice in that area could be inhibited, leading to increased surface water temperatures, greater evaporation, more snow, and an enhanced albedo. That could, he suggests, trigger a cooling phase. Ice sheets in North America, Greenland, and Eurasia grow during cool periods before collapsing into the northern oceans. Those surges and the subsequent collapses ('Heintich events') affect the volume of less saline water entering the North Atlantic southwest of Iceland. In that region, dense hypersaline waters apparently plunge deep below the sea surface to initiate the so-called 'global conveyor belt' that is thought to flow about 3 km below the sea surface down the Atlantic basin, into the South Indian Ocean, and from there southeast of Australia and into the tropical Pacific (as dis- cussed in Chapter 12). Branches of that current are said to reach the surface in the Southern and Indian Oceans, with the balance rising in the northern Pacific (Broecker 1995). The influx oflarge volumes of relatively fresh water to the southwest of Iceland could, it is proposed, inhibit development of the global conveyor belt. The global conveyor belt may ameliorate regional climates, particularly those of Western Europe (Rahmstorff 1997). A recent model suggests that if the current should cease, then mean winter temperatures in Western Europe could fall by 11 DC over a decade. Several other possibilities have been mooted, notably that global warming might trigger a cooling phase in Western Europe, that climatic recovery would be slow, and that the consequential macro-climatic effects need not be uniformly experi- enced or even synchronous across the globe (Karl et al. 1997). A further proposal is that periodic strengthening of Southern Ocean currents coulq force cool water across the equator to feed the Gulf Stream, allowing warm trop- ical waters to penetrate farther north and lead to enhanced precipitation and conse- quent growth of ice sheets in high latitudes. Despite the differences, both models point to links between environmental events in one part of the globe and climatic conditions in another. Research in the environmental sciences is now providing support for many global model predictions. For example, analyses of midge larvae preserved in a Scottish bog and on the bed of a Norwegian lake over the past 14000 years point to alternation of cool- and warm-water assemblages, with speedy transition from warm to cool- notably during the Younger Dryas, a millennium of possibly worldwide colder condi- tions that ended about 11 000 years ago--followed by slow recovery from cool to warm (Pearce 1997). Each species of midge in the two areas lives within a narrow tempera- ture range, allowing specification of summer temperatures at the time the material was deposited to within a few degrees Celsius. Recent analyses of ice cores from the Green- land and Antarctic ice caps are now pointing to asynchronous climate change in the Northern and Southern Hemispheres (Alley & Bender 1998). People everywhere are having to come to terms with rapid environmental change. The 1980s and 1990s have seen serious outbreaks of disease, usually of rapid onset, considerable virulence, and great impact, but also occasionally showing speedy cessation. Among the possible causes currently under investigation are the spread of humans into formerly isolated ecosystems, and subsequent contact there with animals and their disease loads, with some of the viruses able to survive and multiply outside
- 6. Interactions Within the Physical Environment 4I9 their normal hosts (Le Guenno 1995). What is less speculative is the predicted expan- sion of such insect-borne diseases as malaria because of global warming. At present, 60 million km 2 of the Earth's land surface have appropriate environmental conditions for malarial mosquitoes to flourish-an annual average temperature in excess of 20°C and atmospheric humidity greater than 55%. A model produced by the British Meteoro- logical Office suggests that malarial mosquitoes can be expected to extend their geo- graphical range by 17-25 million km 2 as global warming proceeds. Those examples support what the American environmentalist Paul Ehrlich argued in the 1960s: that a high order of connectivity exists between geographically separated places, with the consequences of environmental change in one part of the Earth system being experienced elsewhere. Table 22.1 contains other examples. Table 22.1 The geographical reach of an environmental event. Event Apparent consequences Plume of radioactive Iodi ne 129 Material carried by the Norwegian Current into the discharged from the Sellafield nuclear Barents Sea, where some of the discharge followed reprocessi ng plant in Cumbria, UK. the east coast of Greenland, thence north into Baffin Bay, with another segment moving along the northern coast of Siberia and into the western Arctic. Completion of the dam across Reduction in amount of dissolved silicates entering the the Danube at Iron Gates in 1972. Black Sea has led to decline in biomass of diatoms and increase in algal blooms, including species toxic to other marine life. Widespread use of fire to This is reported to reduce transpiration and increase control vegetation. albedo, with consequent changes to regional climate. Volcanic eruptions in low latitudes. They have been implicated with increased storminess in Scotland, and decreased temperatures elsewhere. Science, knowledge, and the environment As the methods of sc ientific inquiry were refined and applied , so knowledge of the human environment grew, with the following five discoveries having an especially profound impact on Western thought. The first was the re-affirmation by Nicolaus Copernicus in the sixteenth century that the Earth is not the centre of the universe: the fixed point around which the Sun and planets rotate. The second was the proposi- tion of the Swiss geologist Horace Benedict de Saussure in the early nineteenth cen- tury that the Earth is much older than the approximately 5000 years that a literal reading of the Old Testament had suggested to theologians. During the second half of the nineteenth century Charles Darwin's theory of biotic evolution caused a major upheaval in European thinking about living things and their environments. On the basis of information from many domains of scientific inquiry, Darwin argued that the entities termed 'species' by taxonomists are not immutable, that the genotype is con- tinuously tested by environmental forces, and that life in all its diversity had evolved over many millions of years. The fourth was the discovery by astronomers during the first half of the twentieth century of galaxies dispersed through the vastness of space,
- 7. 420 Interactions and Applications of which the Milky Way is but one of an enormous number. And the fifth was the first direct account of the Earth as seen by astronauts orbiting far above the surface. Over more than a century the belief in a fertile world created by a caring deity for humans to transform and occupy (Glacken 1967; White 1967) slowly gave way to the sober realisation that people may not be the centre of, let alone the reason for, cre- ation. The old theological certainties began to crumble and Homo sapiens had to come to terms with living on a very small rock orbiting a star near the edge of a fairly large galaxy. We may now be better able to accept those things, but their psychological impact on previous generations was profound. For the physical geographer, the fifth of those discoveries holds particular importance because it supports the proposa ls of theorists in the Earth sciences. An important term, the 'biosphere', was coined by an Austrian geologist, Eduard Suess, in the 1870s for the thin band in which life is concentrated on Earth. In 1926 the Russian scientist and philosopher Vladimir Vernadsky wrote a major text on the 'biosphere', which he saw as the site of transformers of solar radiation into diverse forms of energy. In the 1960s the American physicist H.]. Morowitz described the biosphere as an int.ermediate system: a functional ensemble substantially closed to the import and export of matter but open to flows of energy. He proposed that the flow of energy through a system of living things acts to organise it (Morowitz 1968). Biologists, geologists, and physical geographers have long recognised the close reciprocal relations between living things and the physical world . According to Love- lock (1995), one of the earliest was the Scottish geologist James Hutton, who, in a lec- ture to the Royal Society of Edinburgh in 1785, compared the movement of water from oceans to land and back again with the circulation of blood. In 1935 the British ecologist A.C. Tansley coined the term 'ecosystem' to cover such relations and their spatial expression. With developments in communications theory in the mid twenti- eth century came the notions of information and cybernetics, and the rise of systems analysis, the latter offering an effective way to analyse interactions between living things and their environments. More recently, complexity theory has proven helpful in understanding the structure and function of ecosystems (Nicolis & Prigogine 1989; Ruthen 1993). Environmental systems For more than two centuries, scientific inquiry has progressed by rigorous application of the positivist paradigm, with strong theory permitting generation of novel research hypotheses that can be evaluated with information from controlled experiments. Bod- ies of knowledge grew and understanding of the world increased. The particular con- tribution of two centuries of research in the life and environmental sciences has been the identification of links, flows, and interactions in a complex milieu where it can be difficult to isolate one organism from either its environment or other living things. That does not mean the positivist mode of scientific inquiry is inapplicable to ecosys- tems. Rather, it suggests that another mode of invest igation may be needed if we are to understand the development, features, and prospects of the biosphere.
- 8. Interactions Within the Physical Environment Taking their lead from approaches developed by communication scientists and information theorists, environmentalists began to view the biosphere as a suite of nested systems (as discussed in Chapter O. At the largest scale is the thin layer-a mixture of rock, water, and air, and a source of energy-in which living things conduct their affairs. From there it was possible to scale down to, for example, a small pond of fresh water surrounded by bare rock. The fundamental notions of modern ecosystem theory were worked out by a young American ecologist, Raymond Lindeman (1942), applied with notable effect by Howard Odum to aquatic systems the following decade (Odum 1956), and by many other scientists since then. To the physical geographer, an environmental system has extent, boundaries, resources of matter and energy, a characteristic suite of living things, a past, a present, and a future. It is useful to distinguish between the various types of natural system. There are those about which we have the following information: they can be located and their boundaries mapped, it is known what materials enter and leave, and there is some appreciation of what each such system looks like. They are termed black box systems. A grey box system is one for which all the previously listed qualities are known, but about which there is fair knowledge of the constituents as well as how they interact. Finally, when we are able to describe all internal flows of matter and energy, and to specify the functional interactions between the components, we have an account of a white box system. The latter is a goal of scientific inquiry, but one no environmental scientist is ever likely to attain. Systems analysis treats the constituents of a system, how they are linked and operate, in much the same way as an electrical engineer deals with the parts on a printed circuit board. Early advocates of systems analysis employed an array of terms, many borrowed from electronics, and produced 'wiring diagrams' for such entities as cells and body organs, trees, peasant holdings, Paris during the Franco-Pruss ian War, national energy balances, and ecosystems. The text of Chorley and Kennedy (1971) remains a useful account of this approach in physical geography, yet several of those who first applied systems theory to ecosystems occasionally missed their nested nature and ignored their 'leaky' boundaries, instead treating them as stable compo- nents of a manifestly dynamic world. It is important not to confuse representation with reality. Systems thinking is a helpful guide to our world, but it is not the world itself. Perhaps the most contentious of recent proposals is the 'Gaia' theory of James Lovelock, an approach to research in the Earth sciences rooted in the notion that liv- ing things and their environments are interactive (Lewin 1996; Lovelock 1986, 1995). It was designed to help astrophysicists detect life elsewhere in the universe, but may also permit the diagnosis and prevention of environmental 'maladies' on Earth. To Lovelock, a living thing and its environment are two elements of a closely coupled system. There is considerable debate about this theory because it harks back to the 'superorganism' view of nature (where the ensemble exhibits a collective response over and above that of each constituent species) that was an alternative to the indi- vidualistic notions of evolutionary thinking. In effect, the system is perceived to manifest a form of 'intelligence'.
- 9. Interactions and Applications Physical geography is about environmental systems in time and across space. Dur- ing its exploration phase, geography proved successful in describing the new lands and accounting for their products, but it took the publication in 1859 of Charles Darwin's Origin of Species for geographers to appreciate the time and spatial dimensions of the human environment. The world might be geographically differentiated, but the map- ping units do not remain stable. Darwin showed biological and earth scientists that change is one of the few cer- tainties. He viewed change in living things in terms of a steady progression, with evo- lution leading to the gradual accumulation of new and environmentally tested traits. Since then there has been vigorous debate about the nature of such change: is it smooth and relatively steady, or is it episodic with short bursts of intense change fol- lowed by long periods of comparative stasis? Systems analysis helped explain the buffered quality of many species ensembles-stability achieved by negative feed- back-and the notion of equilibrium permeated the life and environmental sciences to an even greater depth. Close experience of the natural world, on the other hand, often pointed to something quite different: change concentrated into periods of short duration, followed by relatively short intervals marked by little variation. The term 'punctuated equilibrium' was coined by evolutionary scientists to describe that sort of change, and it has considerable implications for the physical geographer. Inquiry also showed how the functioning of a natural system could be rendered unstable by positive feedback. Negative feedback may be evident in the shrubby vegetation of semi-arid areas where soil water is limiting. In such places it is not unusual to find mature shrubs with virtually constant spacing. Although those plants may flower annually and set viable seeds, seedlings are seldom seen, and this, along with the persistent spatial pattern of adult plants, is often ascribed to intense competition for soil water. In effect, a form of negative feedback is in operation. An example of positive feedback comes from models of global warming. As described in Chapter 8, further increases in the concentration of atmospheric carbon dioxide might be expected to enhance the greenhouse effect and result in generally warmer, more stratified oceans with slower circulation. Because carbon dioxide is less soluble in warm than cool water, one might expect less of that gas to go into solution: the current rate is about two billion tonnes per annum. A 50% reduction in that amount could greatly enhance the greenhouse effect and lead to surface water temper- atures rising by about 5°C. As a result, the pace of global warming might accelerate. Consider an ecosystem under somewhat marginal environmental conditions for a few of its constituent species. Let some of them be fire-tolerant, and the majority, which initially dominate the ensemble, be much less so. In the event of a widespread fire, the former will be more likely to survive than the latter, and with every new fire the mix can be expected to shift a little further towards one dominated by fire-tolerant species. Once that happens the system will be dependent on fire to maintain its struc- ture and composition-the very qualities that allow a species to survive occasional burning may, with each successive fire, make further outbreaks of fire more likely. That situation involves positive feedback leading to a new ensemble with negative feedback sustaining it.
- 10. Interactions Within the Physical Environment 423 Environmental change How we think about change has implications for how we think about our subject. Ecosystems have changed and will continue to do so. Some change is spontaneous- vegetation succession, discussed in Chapter 20, provides an example-but some is cat- astrophic. Consider a river in flood . Several days of steady rain in its catchment will increase the river's discharge rate. It will then rise, perhaps occupying the entire bed until its course is unable to accommodate all the water flowing down it. Then the river will break its banks and quickly flood any low- lying land nearby. That is an example of catastrophic change, and is the subject of a body of theory developed by the French topologist Rene Thorn. Catastrophe theory is about non-linear change, or when a small increase in one factor leads to sudden and major change in system state: the proverbial straw that breaks the camel's back. Flood and wind damage, the adverse effect of high or low air temperature on plant growth, and fire kindled by lightning are a few of many possible examples. Their origin and impact have led to new ways of thinking about the environment and how it changes. Change is one of geography's most important notions. A common precept is that change leads to improvement through the steady accretion of desirable qualities. Environmental change is se ldom linear, may not be progressive, and is seldom advan- tageous to all living things in an area. The New Zealand geomorphologist Maxwe ll Gage (1970) applied those ideas to landform development and described situations where landforms are built or destroyed during floods, and where the processes of envi- ronmental change might best be described as chaotic. The fossi l record provides clear evidence that climates have changed abruptly in the past, with sudden onset of cold cond itions even during interglacial periods. What is noteworthy is that the past 10 000 years have been unusually equable. In the absence of evidence to the contrary, it is probably best to think of environmental ch ange as a shift from one system state to another, free of any pre-suppositions about the direction of such change. Of great importance, however, is what humans do about change: manage it or respond pas- sively to it; attempt to lessen its impact or foster its effects. Change is driven by internal or external forces. For example, as plants age and weathering proceeds, standing crop and vegetation structure may alte~ without major shifts in species compos ition. Alternatively, a fire kindled far away may sweep across the landscape; a long-dormant volcano may erupt and thick ash layers may be deposited to great distances; a tropical storm that develops far out to sea may bring heavy rain and acce lerated eros ion to a hill catchment; or an introduced plant disease like manuka blight may become establ ished in an area and start killing its hosts: all will affect ecosystem structure, function, and compos ition. Several key ideas are involved. The oldest, and in many respects the most con- tentious, is equi librium. Equilibrium thinking is a deep river flowing through the nat- ural, Earth, and life sciences. It is fundamental to classical physics and central to much of chemistry. According to the equilibrium argument, system state will progressively shift until resource demands match resource production. The climax community of the succession model is analogous to the chem ist's equ ilibrium mixture, as is the old- age landscape of the American geomorphologist W.M. Davis. In the latter instance,
- 11. Interactions and Applications however, it was soon recognised that few places on the Earth's surface have experi- enced sufficiently long periods of environmenta~ stability for a true equilibrium state to develop. In response, geomorphologists factored in episodes of environmental change. The proposed 'climatic accidents' that the New Zealand geomorphologist Charles Cotton grafted on to W.M. Davis's model of landform evolution exemplify responses by geomorphologists to its weaknesses. A half-century of investigation into environmental change over the past two mil- lion years tells us that few parts of the globe have experienced stable, highly pre- dictable environmental conditions. Any that did are likely to be in the deep oceans. Where system response is of the order of years or shorter, the notion of equilibrium remains a helpful concept in physical geography. However, if the system response is longer than centuries, the application of the notion of equilibrium should be used judiciously. An important geological concept, and one that is also used by physical geogra- phers, is the principle of uniformitarianism (i.e. present environmental processes are the best guide to the origins of analogous past events), but in many respects the key quality of the human environment is its unpredictability. Of even greater interest these days are the notions of sensitivity, switching, and lag. The first indicates how rapidly the system responds to external forces. The second concerns rapid shifts in sys- tem state and what causes them, while the third is about the delay between a perturb- ing event and system response. There are several ways to view the lag effect, but drawing the analogy with a fly- wheel in an engine may be the most helpful. A form of inertia is evident in many ecosystems. For example, if a long-lived plant requires a particular insect species for pollination and production of seeds, the consequences of local extinction of that ani- mal (assuming nothing else in the area can serve its role) will not be evident until the oldest trees die without being replaced by individuals of the same species. For humans that has worrying implications: the full consequences of our actions in the environ- ment may not be evident for years, decades, or even centuries. Coupled with those three temporal notions are the spatial qualities of reach, rate, and magnitude. The former measures the extent of environmental perturbation, the second indicates the pace of change, and the latter gives the impact. For living things, the conjunction of these three is central to understanding what is meant by an envi- ronmental hazard. An informative view on hazards was provided by the social scientist Blaikie (1985), who argued that an environmental hazard is a natural event visited upon unprepared people. But that is only part of the story. Our environment changes spon- taneously, and erosion is the unceasing accompaniment to our lives. New Zealand experiences unusually high rates of erosion, with the annual average equivalent to a surface lowering in the order of several millimetres away from areas of human modifi- cation. Geomorphologists refer to this as the 'background rate' of erosion. During the period of exclusively Maori occupation, the annual rate of surface lowering in settled areas was probably a little larger, but since the 1840s the rate has increased greatly. New Zealand is not alone in this. The chief physical environmental legacies of 8000 years of human settlement in Greece, for example, are deforestation and catastrophic
- 12. Interactions Within the Physical Environment 425 soil erosion. What is distinctive about New Zealand is that tectonic uplift virtually balances the natural rate of sUlface lowering in many parts of the country (O'Loughlin & Owens 1987). For a physical geographer, the key is to understand what happens when people and their animals set to work. Then the reach, rate, and magnitude of a natural process are likely to increase and the risk of hazard will be enhanced. Among the most changeable of the Earth's environments are those of islands. Because many islands lie close to geophysical plate margins or are associated with crustal 'hot spots', they tend to be tectonically dynamic. They are also characterised by often steep environmental gradients and ecologically specialised plants and ani- mals. Many islands harbour unusual combinations of species, with whole families miss- ing and others represented by unusually large numbers of species. In part, that is the outcome of long periods of evolution in isolation, but it also reflects the forces of evo- lution acting on chance aggregates of immigrant species. Recent biogeographic and ecological research points to the role of a 'keystone' species. If it should disappear will the ecosystem change catastrophically? We need to inquire into the likely roles played by the now-extinct large ratite birds of New Zealand, the megafauna of Australia, or the dodo of Mauritius if we are ever to under; tand how our respective island ecosys- tems functioned before the arrival of humans altered the environmental rules. Summary This chapter has considered some key principles and models of interactions within the phys ical environment. After discuss ing environmental models and predictions, a tten- tion turned to the profound impact of five scientific discoveries on Western thought. The chapter continued by revisiting environmental systems (first introduced in Chap- ter 1) and then discussed recent thinking on environmental change. What we understand about physical interactions within the environment is a product of how we think about it, the questions we ask, and what we choose to do with the answers. As James Lovelock (1995) has argued, life will go on regardless of what humans do to the environment. But the ecosystems we feel most comfortable with might disappear, to be replaced by others we could find much less congenial. Despite the political, practical, and economic difficulties, the best way ahead is likely to be the on e where all people learn to use the resources of the Earth in a sustainable fashion. Particularly in island nations like New Zealand, we can be certain that many of the old ecosystems will give way to new, and that some plant and animal species will become extinct despite our best efforts to protect them. The challenge facing the physical geographer employed as an env ironmental manager is to ensure the persis- tence of as many functional assemblages of native species and their habitats as possible. Further reading Lovelock, J. 1995, The Ages of Gaia: A Biography of Ow' Living Earth, 2nd edn, Oxford University Press, Oxford. N ico lis, G. & Prigogine, 1. 1989, Exploring Complexity : An Introdu~ tio n , Freeman , San Francisco.
- 13. Interactions and Applications O'Loughlin, c.L. & Owens, I.E 1987, 'Our dynamic environment', pp.59-90 in South- ern Approaches: Geography in New Zealand, eds P.G. Holland & W.B. Johnston, New Zealand Geographical Society, Christchurch. Ruthen, R. 1993, 'Adapting to complexity', Scientific American, vol. 268, no. 1, pp. 130-40.