ESS Ch 1.pdf

# FOUNDATIONS OF ENVIRONMENTAL SYSTEMS AND SOCIETIES ## 1.1 Environmental Value Systems ### Significant ideas: * Historical events, among other influences, affect the development of environmental values systems and environmental movements. * There is a wide spectrum of environmental value systems...

# FOUNDATIONS OF ENVIRONMENTAL SYSTEMS AND SOCIETIES ## 1.1 Environmental Value Systems ### Significant ideas: * Historical events, among other influences, affect the development of environmental values systems and environmental movements. * There is a wide spectrum of environmental value systems each with their own premises and implications. ### Applications and skills: * Discuss the view that the environment can have its own intrinsic value. * Evaluate the implications of two contrasting environmental value systems in the context of given environmental issues. * Justify the implications using evidence and examples to make the justification clear. ### Knowledge and understanding: * Significant historical influences on the development of the environmental movement have come from literature, the media, major environmental disasters, international agreements and technological developments. * An environmental value system (EVS) is a worldview or paradigm that shapes the way an individual, or group of people, perceives and evaluates environmental issues, influenced by cultural, religious, economic and socio-political contexts. * An EVS might be considered as a 'system' in the sense that it may be influenced by education, experience, culture and media (inputs) and involves a set of inter-related premises, values and arguments that can generate consistent decisions and evaluations (outputs). * There is a spectrum of EVSs from ecocentric through anthropocentric to technocentric value systems. * An ecocentric viewpoint integrates social, spiritual and environmental dimensions into a holistic ideal. It puts ecology and nature as central to humanity and emphasizes a less materialistic approach to life with greater self-sufficiency of societies. An ecocentric viewpoint prioritizes biorights, emphasizes the importance of education and encourages self-restraint in human behaviour. * An anthropocentric viewpoint argues that humans must sustainably manage the global system. This might be through the use of taxes, environmental regulation and legislation. Debate would be encouraged to reach a consensual, pragmatic approach to solving environmental problems. * A technocentric viewpoint argues that technological developments can provide solutions to environmental problems. This is a consequence of a largely optimistic view of the role humans can play in improving the lot of humanity. Scientific research is encouraged in order to form policies and understand how systems can be controlled, manipulated or exchanged to solve resource depletion. A pro-growth agenda is deemed necessary for society's improvement. * There are extremes at either end of this spectrum (eg deep ecologists - ecocentric - to cornucopian technocentric), but in practice EVSs vary greatly with culture and time and rarely fit simply or perfectly into any classification. * Different EVSs ascribe different intrinsic values to components of the biosphere. ## 1.2 Systems and models ### Significant ideas: * A systems approach can help in the study of complex environmental issues. * The use of models of systems simplifies interactions but may provide a more holistic view than reducing issues to single processes. ### Applications and skills: * Construct a system diagram or a model from a given set of information. * Evaluate the use of models as a tool in a given situation, eg for climate change predictions. ### Knowledge and understanding: * A systems approach is a way of visualizing a complex set of interactions which may be ecological or societal. * These interactions produce the emergent properties of the system. * The concept of a system can be applied to a range of scales. * A system is comprised of storages and flows. * The flows provide inputs and outputs of energy and matter. * The flows are processes and may be either transfers (a change in location) or transformations (a change in the chemical nature, a change in state or a change in energy). * In system diagrams, storages are usually represented as rectangular boxes, and flows as arrows with the arrow indicating the direction of the flow. The size of the box and the arrow may represent the size/magnitude of the storage or flow. * An open system exchanges both energy and matter across its boundary while a closed system only exchanges energy across its boundary. * An isolated system is a hypothetical concept in which neither energy nor matter is exchanged across the boundary. * Ecosystems are open systems. Closed systems only exist experimentally although the global geochemical cycles approximate to closed systems. * A model is a simplified version of reality and can be used to understand how a system works and predict how it will respond to change. * A model inevitably involves some approximation and loss of accuracy. ## 1.3 Energy and Equilibria ### Significant Ideas: * The laws of thermodynamics govern the flow of energy in a system and the ability to do work. * Systems can exist in alternative stable states or as equilibria between which there are tipping points. * Destabilizing positive feedback mechanisms will drive systems toward these tipping points, whereas stabilizing negative feedback mechanisms will resist such changes. ### Applications and skills: * Explain the implications of the laws of thermodynamics to ecological systems. * Discuss resilience in a variety of systems. * Evaluate the possible consequences of tipping points. ### Knowledge and Understanding: * The first law of thermodynamics is the principle of conservation of energy, which states that energy in an isolated system can be transformed but cannot be created or destroyed. * The principle of conservation of energy can be modelled by the energy transformations along food chains and energy production systems. * The second law of thermodynamics states that the entropy of a system increases over time. * Entropy is a measure of the amount of disorder in a system. An increase in entropy arising from energy transformations reduces the energy available to do work. * The second law of thermodynamics explains the inefficiency and decrease in available energy along a food chain and energy generation systems. * As an open system, an ecosystem, will normally exist in a stable equilibrium, either a steady-state or one developing over time (eg succession), and maintained by stabilizing negative feedback loops. * Negative feedback loops (stabilizing) occur when the output of a process inhibits or reverses the operation of the same process in such a way to reduce change - it counteracts deviation. * Positive feedback loops (destabilizing) will tend to amplify changes and drive the system toward a tipping point where a new equilibrium is adopted. * The resilience of a system, ecological or social, refers to its tendency to avoid such tipping points and maintain stability. * Diversity and the size of storages within systems can contribute to their resilience and affect the speed of response to change (time lags). * Humans can affect the resilience of systems through reducing these storages and diversity. * The delays involved in feedback loops make it difficult to predict tipping points and add to the complexity of modelling systems. ## 1.4 Sustainability ### Significant Ideas: * All systems can be viewed through the lens of sustainability. * Sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs. * Environmental indicators and ecological footprints can be used to assess sustainability. * Environmental Impact Assessments (EIAs) play an important role in sustainable development. ### Applications and skills: * Explain the relationship between natural capital, natural income and sustainability. * Discuss the value of ecosystem services to a society. * Discuss how environmental indicators can be used to evaluate the progress of a project to increase sustainability, eg Millennium Ecosystem Assessment. * Evaluate the use of EIAs. * Explain the relationship between ecological footprint (EF) and sustainability. ### Knowledge and understanding: * Sustainability is the use and management of resources that allows full natural replacement of the resources exploited and full recovery of the ecosystems affected by their extraction and use. * Natural capital is a term used for natural resources that can produce a sustainable natural income of goods or services. * Natural income is the yield obtained from natural resources * Ecosystems may provide life-supporting services such as water replenishment, flood and erosion protection, and goods such as timber, fisheries and agricultural crops. * Factors such as biodiversity, pollution, population or climate may be used quantitatively as environmental indicators of sustainability. These factors can be applied on a range of scales from local to global. The Millennium Ecosystem Assessment gave a scientific appraisal of the condition and trends in the world's ecosystems and the services they provide using environmental indicators, as well as the scientific basis for action to conserve and use them sustainably. * Environmental Impact Assessments (EIAs) incorporate baseline studies before a development project is undertaken. They assess the environmental, social and economic impacts of the project, predicting and evaluating possible impacts and suggesting mitigation strategies for the project. They are usually followed by an audit and continued monitoring. Each country or region has different guidance on the use of EIAs. * EIAs provide decision makers with information in order to consider the environmental impact of a project. There is not necessarily a requirement to implement an ElA's proposals and many socio-economic factors may influence the decisions made. * Criticisms of ElAs include the lack of a standard practice or training for practitioners, the lack of a clear definition of system boundaries and the lack of inclusion of indirect impacts. * An ecological footprint (EF) is the area of land and water required to sustainably provide all resources at the rate at which they are being consumed by a given population. Where the EF is greater than the area available to the population, this is an indication of unsustainability. ## 1.5 Humans and Pollution ### Significant ideas: - Pollution is a highly diverse phenomenon of human disturbance in ecosystems. - Management strategies can be applied at different levels. ### Applications and skills: - Construct systems diagrams to show the impact of pollutants. - Evaluate the effectiveness of each of the three different levels of intervention, with reference to figure 1.5.6. - Evaluate the use of DDT. ### Knowledge and Understanding: - Pollution is the addition of a substance or an agent to an environment by human activity, at a rate greater than that at which it can be rendered harmless by the environment, and which has an appreciable effect on the organisms in the environment. - Pollutants may be in the form of organic/ inorganic substances, light, sound or heat energy, or biological agents/invasive species, and derive from a wide range of human activities including the combustion of fossil fuels. - Pollution may be non-point or point source, persistent or biodegradable, acute or chronic. - Pollutants may be primary (active on emission) or secondary (arising from primary pollutants undergoing physical or chemical change). - Dichlorodiphenyltrichloroethane (DDT) exemplifies a conflict between the utility of a 'pollutant' and its effect on the environment. ## 1.6 Pollution from Humans - Pollutants are released by human activities and may be: - matter (gases, liquids or solids) which is organic (contains carbon atoms) or inorganic - energy (sound, light, heat) - living organisms (invasive species or biological agents). ## 1.7 Point Source and Non-Point Source Pollutants - **Non-point source (NPS) pollution**: - Is the release of pollutants from numerous, widely dispersed origins, for example gases from the exhaust systems of vehicles, chemicals spread on fields. - May have many sources and it may be virtually impossible to detect exactly where it is coming from. - Rainwater can collect nitrates and phosphates which are spread as fertilizer as it infiltrates the ground or as runoff on the surface. It may travel many kilometres before draining into a lake or river and increasing the concentration of nitrates and phosphates so much that eutrophication occurs. It would not be possible to say which farmer spread the excess fertilizer. - Air pollution can be blown hundreds of kilometres and chemicals released from open chimneys mix with those from others. - So one solution is to set limits for all farmers and all industries to reduce emissions and then monitor what they actually do. - **Point source (PS) pollution**: - Is the release of pollutants from a single, clearly identifiable site, for example a factory chimney or the waste disposal pipe of a sewage works into a river. - Is easier to see who is polluting - a factory or house. - Is usually easier to manage as it can be found more easily. ## 1.8 Persistent Organic Pollutants (POPs) and Biodegradable Pollutants - **POPs**: - Were often manufactured as pesticides in the past. - Are resistant to breaking down and remain active in the environment for a long time. - Bioaccumulate in animal and human tissues and biomagnify in food chains. - Can cause significant harm. - Examples of these are DDT, dieldrin, chlordane and aldrin. - Other POPs are polyvinyl chloride (PVC), polychlorinated biphenyls (PCBs) and some solvents. - They have similar properties: - high molecular weight - not very soluble in water - highly soluble in fats and lipids - which means they can pass through cell membranes - halogenated molecules, often with chlorine. - **Biodegradable pollutants**: - Do not persist in the environment and break down quickly. - May be broken down by decomposer organisms or physical processes, eg light or heat. - Examples are soap, domestic sewage, degradable plastic bags made of starch. - One common herbicide is glyphosate which farmers use to kill weeds. It is degraded and broken down by soil organisms. ## 1.9 Acute and Chronic Pollution - **Acute pollution**: - Is when large amounts of a pollutant are released, causing a lot of harm. - An example of this was when the chemical aluminium sulphate was accidently tipped into the wrong place in a water treatment works in Cornwall in the UK in 1988 and many people drank water which poisoned them. - Another example was in the Bhopal Disaster of 1984 in India (1.1). - **Chronic pollution**: - Results from the long-term release of a pollutant but in small amounts. - It is serious because: - often it goes undetected for a long time - it is usually more difficult to clean it up - it often spreads widely. - Air pollution is often chronic causing non-specific respiratory diseases, for example asthma, bronchitis, emphysema. Beijing's poor air quality is an example of chronic air pollution. ## 1.10 Detection and Monitoring of Pollution - Pollution can be measured directly or indirectly. - **Direct measurements** record the amount of a pollutant in water, the air or soil. - Direct measurements of air pollution include measuring: - the acidity of rainwater - amount of a gas, for example carbon dioxide, carbon monoxide, nitrogen oxides in the atmosphere - amount of particles emitted by a diesel engine - amount of lead in the atmosphere. - Direct measurements of water or soil pollution include testing for: - nitrates and phosphates - amount of organic matter or bacteria - heavy metal concentrations. - **Indirect measurements** record changes in an abiotic or biotic factor which are the result of the pollutants. - Indirect measurements of pollution include: - measuring abiotic factors that change as a result of the pollutant (eg oxygen content of water) - recording the presence or absence of indicator species - species that are only found if the conditions are either polluted (eg rat-tailed maggot in water) or unpolluted (eg leafy lichens on trees). ## 1.11 Pollution Management Strategies - Pollution can be managed in three main ways: - by changing the human activity which produces it - by regulating or preventing the release of the pollutant or - by working to clean up or restore damaged ecosystems. - The pollution management model in Figure 1.5.6 lists the actions available in each category of management and will be referred to throughout the book when specific pollutants are considered. ## 1.12 DDT and Malarial Mosquitoes - In 1970, the WHO (World Health Organization) banned the use of DDT, a persistent organochlorine insecticide. - It is still used in some countries in the tropics but in small quantities for spraying inside houses to kill the malarial mosquito, Anopheles, which is the vector for malarial parasites. - The question is whether banning DDT did more harm than good. - It is believed that malaria kills 2.7 million people a year, mostly children under the age of five, and infects 300-500 million a year. - It is also thought that DDT prevented millions of deaths due to malaria. - So why the ban? In her book, Silent Spring, Rachel Carson discusses the effect of DDT on birds of prey in thinning their eggshells and reducing their population numbers. But some say that evidence was slight for bird egg shell thinning and DDT is an effective insecticide against the malarial mosquito. - The manufacture and use of DDT was banned in the US in 1972, on the advice of the US Environmental Protection Agency. - The use of DDT has since been banned in most other MEDCs, but it is not banned for public health use in most areas of the world where malaria is endemic. - DDT was recently exempted from a proposed worldwide ban on organophosphate chemicals. - DDT for malarial control involves spraying the walls and backs of furniture, so as to kill and repel adult mosquitoes that may carry the malarial parasite. - Although other chemicals could be used, DDT is cheap and persistent and good at the job. - Outside DDT is not used because of its persistence and toxicity. - Also, its persistence means that mosquitoes become resistant (the ones that survive, breed and develop a population of resistant mosquitoes). - Malaria incidence is increasing, partly due to resistance, partly to changes in land use and migration of people to areas where malaria is endemic. - In treating the cause, DDT use is just one tool along with other chemicals, mosquito nets and removal of stagnant water where mosquitoes breed. - There is hyperbole, bias and misinformation in the debate on DDT but malaria probably does not receive enough funding for research as it is mostly a disease of the poor. ## 1.13 Ecological Footprints - EF is a model used to estimate the demands that human populations place on the environment. - The measure takes into account the area required to provide all the resources needed by the population, and the assimilation of all wastes. - Where the EF is greater than the area available to the population, this is an indication of unsustainability. - EFs may vary significantly from country to country and person to person and include aspects such as lifestyle choices (EVS), productivity of food production systems, land use and industry. ## 1.14 The Millennium Ecosystem Assessment - The Millennium Ecosystem Assessment (MEA), funded by the UN and started in 2001, is a research programme that focuses on how ecosystems have changed over the last decades and predicts changes that will happen. - In 2005, it released the results of its first four-year study of the Earth's natural resources. It was not happy reading. ## 1.15 Environmental Impact Assessments - An environmental impact assessment or EIA is a report prepared before a development project to change the use of land, for example to plant a forest or convert fields to a golf course. - An EIA weighs up the relative advantages or disadvantages of the development. - It is therefore necessary to establish how the abiotic environment and biotic community would change if a development scheme went ahead. - An EIA will try to quantify changes to microclimate, biodiversity, scenic and amenity value resulting from the proposed development. These measurements represent the production of a baseline study. - EIAs look at what the environment is like now and forecast what may happen if the development occurs. - Both negative and positive impacts are considered as well as other options to the proposed development. - While often EIAs have to deal with questions about the effect on the natural environment they can also consider the likely effects on human populations. - This is especially true where a development might have an effect on human health or have an economic effect for a community. ## 1.16 The Importance of EIAs - EIAs are often, though not always, part of the planning process that governments set out in law when large developments are considered. - They provide a documented way of examining environmental impacts that can be used as evidence in the decision-making process of any new development. - The developments that need EIAs differ from country to country, but certain types of developments tend to be included in the EIA process in most parts of the world. These include: - major new road networks - airport and port developments - building power stations - building dams and reservoirs - quarrying - large-scale housing projects. ## 1.17 Where Did EIAs Come From? - In 1969, the US Government passed the National Environmental Policy Act (NEPA). - NEPA made it a priority for federal agencies to consider the natural environment in any land use planning. - This gave the natural environment the same status as economic priorities. - Within 20 years of NEPA becoming law in the US, many other countries also included EIAs as part of their planning policy. - In the US, environmental assessments (EA) are carried out to determine if an EIA (called EIS - environmental impact statement) needs to be undertaken and filed with the federal agencies. ## 1.18 What Does an EIA Need in it? - There is no set way of conducting an EIA, but various countries have minimum expectations of what should be included in an EIA. - It is possible to break an assessment down into three main tasks: - Identifying impacts (scoping). - Predicting the scale of potential impacts. - Limiting the effect of impacts to acceptable limits (mitigation). ## 1.19 Weaknesses of ElAs - Different countries have different standards for EIAs which makes it hard to compare them. - Also, it is hard to determine where the boundary of the investigation should be. - How large an area, how many variables, how much does the EIA cost? - It is also very difficult to consider all indirect impacts of a development so some may be missed. ## 1.20 The Ecology of Systems - Systems can be thought of as one of three types: open, closed and isolated. - An open system exchanges matter and energy with its surroundings (see figure 1.2.3). - A closed system exchanges energy but not matter with its environment. - A isolated system exchanges neither matter nor energy. ## 1.21 The Tragedy of the Commons - The result of the 'tragedy of the commons', when many individuals act in their own self-interest to harvest a resource but destroy the long-term future of that resource so there is none for anyone. - It may be obvious that this will happen, but each individual benefits from taking the resource in the short term so they continue to do so. - For example, hunting an endangered species may result in its extinction but if your family are starving and it is the only source of food, you will probably hunt it to eat it. ## 1.22 The Prisoner's Dilemma - A big question about us is whether we are, by nature, loving or aggressive, noble or selfish, nice or nasty. - Do we not steal or cheat because we may be found out or because we know it is wrong. - Is it our default position to be kind and helpful to each other or to be top even if, or particularly if, it hurts someone else? - Scientists, sociologists, philosophers, politicians and all thinking people want to know about our innate nature and why we react as we do. - There is a type of game that you can play as an example of Game Theory and it is called the Prisoner's Dilemma. - Two people A and B are suspected of a crime and arrested. There is not enough evidence to convict them unless they confess. - The police separate them and offer each one the same deal. - If one admits that they both did the crime and betrays the other, that one goes free and the other goes to prison for 10 years. - If both stay silent, they both go to prison for a year. - If both confess, they both go to prison for 5 years. - What should they do? - The best scenario for one is to confess and the other stays silent. But they don't know what the other will do. - What has this to do with pollution? Quite a lot. ## 1.23 Implications of the Second Law for Environmental Systems - We experience the second law in our everyday lives. - All living creatures die and in doing so: - entropy or disorder tends to increase - the creatures move from order to disorder - but organisms manage to 'survive' against the odds, that is against the second law of thermodynamics - living creatures manage to maintain their order and defy entropy to stay alive by continuous input of energy by continuously getting chemical energy from organic compounds via respiration - energy is even required at rest - if they do not respire they die. - This is the same as the example of the room; the only way to keep the room tidy is to continuously clean it, that is to expend energy. - In any process, some of the useful energy turns into heat. - Low-entropy (high-quality) energy degrades into high-entropy (low-quality) heat. - So the entropy of the living system stays low, whilst the entropy of the environment is increasing. - Photosynthesis and respiration are good examples: - Low-entropy solar energy turns into higher-entropy chemical energy. - Chemical energy turns into even higher-entropy mechanical energy and is ’lost’ as heat (low-quality, high-entropy). - This increases the entropy of the environment, in which heat dissipates. - As a consequence, no process can be 100% efficient. ## 1.24 The Complexity and Stability of Systems - Most ecosystems are very complex. - There are many feedback links, flows and storages. - It is likely that a high level of complexity makes for a more stable system which can withstand stress and change better than a simple one can, as another pathway can take over if one is removed. - Imagine a road system where one road is blocked by a broken-down truck; vehicles can find an alternative route on other roads. - If a community has a number of predators and one is wiped out by disease, the others will increase as there is more prey for them to eat and prey numbers will not increase. - If on the other hand systems are simple they may lack stability. - Tundra ecosystems are fairly simple and thus populations in them may fluctuate widely, eg lemming population numbers. - Monocultures (farming systems in which there is only one major crop) are also simple and thus vulnerable to the sudden spread of a pest or disease through a large area with devastating effect. - The spread of potato blight through Ireland in 1845-8 provides an example; potato was the major crop grown over large areas of the island, and the biological, economic and political consequences were severe. ## 1.25 Equilibrium - Equilibrium is the tendency of the system to return to an original state following disturbance; at equilibrium, a state of balance exists among the components of that system. - We can think of systems as being in dynamic (steady-state) or static equilibria as well as in stable or unstable equilibria. - We discuss each of these here. - Note that the term steady-state equilibrium is used instead of dynamic equilibrium in this book. - Open systems tend to exist in a state of balance or stable equilibrium. - Equilibrium avoids sudden changes in a system, though this does not mean that all systems are non-changing. - If change exists it tends to exist between limits. - A steady-state equilibrium is a characteristic of open systems where there are continuous inputs and outputs of energy and matter, but the system as a whole remains in a more-or-less constant state (eg a climax ecosystem). ## 1.26 Feedback Loops - Systems are continually affected by information from outside and inside the system. - Simple examples of this are: - If you start to feel cold you can either put on more clothes or turn the heating up. The sense of cold is the information, putting on clothes is the reaction. - If you feel hungry, you have a choice of reactions as a result of processing this ’information’: eat food, or do not eat and feel more hungry. - Natural systems act in exactly the same way. - Feedback loop mechanisms can either be: - **Positive**: - Change a system to a new state. - Destabilizing as they increase change. - **Negative**: - Return it to its original state. - Stabilizing as they reduce change. ## 1.27 Examples of Negative Feedback - Your body temperature starts to rise above 37 °C because you are walking in the tropical sun and the air temperature is 45 °C. The sensors in your skin detect that your surface temperature is rising so you start to sweat and go red as blood flow in the capillaries under your skin increases. Your body attempts to lose heat. - A thermostat in a central heating system is a device that can sense the temperature. It switches a heating system on when the temperature decreases to a predetermined level, and off when it rises to another warmer temperature. - So a room, a building, or a piece of industrial plant can be maintained within narrow limits of temperature. - Global temperature rises causing ice caps to melt. - More water in the atmosphere means more clouds, more solar radiation is reflected by the clouds so global temperatures fall. But compare this with figure 1.3.14 which interprets it differently. - Predator-prey interactions. - The Lotka-Volterra model (proposed in 1925 and 1926) is also known as the predator-prey model and shows the effect of changing numbers of prey on predator numbers. - When prey populations (eg mice) increase, there is more food for the predator (eg owl) so they eat more and breed more, resulting in more predators which eat more prey so the prey numbers decrease. - If there are fewer prey, there is less food and the predator numbers decrease. - The change in predator numbers lags behind the change in prey numbers. - The snowshoe hare and Canadian lynx is a well- documented example of this (see box, p36). - Some organisms have internal feedback systems, physiological changes occurring that prevent breeding when population densities are high, promoting breeding when they are low. - It is negative feedback loops such as these that maintain 'the balance of nature'. ## 1.28 Examples of Positive Feedback - You are lost on a high snowy mountain. When your body senses that it is cooling below 37 °C, various mechanisms such as shivering help to raise your body core temperature again. - But if these are insufficient to restore normal body temperature, your metabolic processes start to slow down, because the enzymes that control them do not work so well at lower temperatures. - As a result you become lethargic and sleepy and move around less and less, allowing your body to cool even further. - Unless you are rescued at this point, your body will reach a new equilibrium: you will die of hypothermia. - In some developing countries poverty causes illness and contributes to poor standards of education. - In the absence of knowledge of family planning methods and hygiene, this contributes to population growth and illness, adding further to the causes of poverty: 'a vicious circle of poverty'. - Global temperature rises causing ice caps to melt. Dark soil is exposed so more solar radiation is absorbed. This reduces the albedo (reflecting ability of a surface) of Earth so global temperature rises. - Compare this with figure 1.3.12 and you can see that the same change can result in positive or negative feedback. - This is one reason that predicting climate change is so difficult. ## 1.29 The Resilience of Systems - The resilience of a system measures how it responds to a disturbance. - The more resilient a system, the more disturbance it can deal with. - Resilience is the ability of a system to return to its initial state after a disturbance. - If it has low resilience, it will enter a new state - see figure 1.3.17. - Resilience is generally considered a good thing, whether in a society, individual or ecosystem as it maintains stability of the system. - In eucalypt forests of Australia, fire is seen as a major hazard. But eucalypts have evolved to survive forest fires. - Their oil is highly flammable and the trees produce a lot of litter which also burns easily. - But the trees regenerate quickly after a fire because they have buds within their trunks and plants that would have competed with them are destroyed. - The eucalypts are resilient. - But when the indigenous eucalypts are replaced by tree species that cannot withstand fire, it can be devastating. - In managed systems, such as agriculture, we want stability so we can predict that the amount of food we grow is about the same each year. - If this does not happen, there can be disastrous consequences, for example the Irish potato famine or the Sahel drought and famine. - But resilience is not always good, eg a pathogenic bacterium causing a fatal disease could be very resilient to antibiotics which means it will kill many people so, in this case, its resilience is not so good for us. ## 1.30 Factors Affecting Ecosystem Resilience - The more diverse and complex an ecosystem, the more resilient it tends to be as there are more interactions between different species. - The greater the species biodiversity of the ecosystem, the greater the likelihood that there is a species that can replace another if it dies out and so maintain the equilibrium. - The greater the genetic diversity within a species, the greater the resilience. A monoculture of wheat or rice can be wiped out by a disease if none of the plants have resistance which is more likely in a diverse gene pool. - Species that can shift their geographical ranges are more resilient. - The larger the ecosystem, the more resilience as animals can find each other more easily and there is less edge-effect. - The climate affects resilience - in the Arctic, regeneration of plants is very slow as the low temperatures slow down photosynthesis and so growth. - In the tropical rain forests, growth rates are fast as light, temperature and water are not limiting. - The faster the rate at which a species can reproduce means recovery is faster. So r-strategists (2.4) with a fast reproductive rate can recolonize the system better than slowly reproducing K-strategists. - Humans can remove or mitigate the threat to the system (eg remove a pollutant, reduce an invasive species) and this will result in faster recovery. ## 1.31 Tipping Points - Small changes occur in systems and may not make a huge difference. - But when these changes tip the equilibrium over a threshold, known as a tipping point, the system may transform into a very different one. - Then positive feedback loops drive the system to a new steady state. - An ecological tipping point is reached when an ecosystem experiences a shift to a new state in which there are significant changes to its biodiversity and the services it provides. - Characteristics of tipping points: - They involve positive feedback which makes the change self- perpetuating; eg deforestation reduces regional rainfall, which increases fire risk, which causes forest dieback. - There is a threshold beyond which a fast shift of ecological states occurs. - The threshold point cannot be precisely predicted. - The changes are long-lasting. - The changes are hard to reverse. - There is a significant time lag between the pressures driving the change and the appearance of impacts, creating great difficulties in ecological management. ## 1.32 Examples of Tipping Points - Lake eutrophication – if nutrients are added to a lake ecosystem, it may not change much until enough nutrients are added to shift the lake to a new state - then plants grow excessively, light is blocked by decomposing plant material, oxygen levels fall and animals die. - The lake becomes eutrophic and it takes a great effort to restore it to the previous state (4.4). - Extinction of a keystone species (eg elephants) from a savanna ecosystem can transform it to a new state which cannot be reversed. - Coral reef death - if ocean acidity levels rise enough, the reef coral dies and cannot regenerate. - Tipping points are well-known in local or regional ecosystems but there is debate about whether we are reaching a global tipping point. - Some people say that climate change caused by human activities will force the Earth to a new, much warmer state - as much as 8 °C warmer than today. - But evidence is that we see warming in one region and cooling in others, wetter in some and drier in others. - The global system is so complex and ecosystems respond differently, often independently of other ecosystems. - If there were to be global tipping points, there are major implications for decision-makers. - Some may think that below this point, not much would change while, once it is reached, all is lost as society could not respond fast enough. - That could lead to inaction or despair - the 'what's the point, there is nothing we can do now' point of view. - The best approach we can have may be the precautionary one where we don’t know what will happen exactly but can take steps to modify what we do in case. - Such risk management is the responsible route to take. ## 1.33 The Gaia Hypothesis - The 'Great Aerial Ocean' was Alfred Russel Wallace's description of the atmosphere. - 'You can cut the atmosphere with a knife' is a common saying. - If we could