Stability, Resilience and Complexity, Ecosystem management in the Anthropocene.

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1 Resilience of Ecological Systems Chris J Kettle Lecture 1: Stability, Resilience and Complexity, Ecosystem management in the Anthropocene. We are living in a period of rapid and enormous global change. At no other time in the Earth s history has a single species had so much impact on the earth. Scientists refer to the geological time period as the anthropocene (see Box 1). Population growth and technological advances have enabled us to impact broadly and deeply across all the earths natural processes. For example, the emissions of hazardous and toxic chemicals (CFC s), Green House Gases (GHG s), global-scale deforestation and land use change, over fishing, urbanisation and mass migration and global travel. All of these factors exert enormous pressure on the Earth system. Box 1: In the last three centuries human population growth has increased 10 fold to 6 billion. With on average one cow per family the global Cattle stock is estimated at 1.4 billion. Urbanisation has increased 13 fold in the last 100 years alone, more than 50% of accessible fresh water is used for humans consumption,between 25% and 35% of primary production from the oceans is removed by fisheries. Landcover under crops has doubled in the last 100 years corresponding to more than 20% global decline in forests. More nitrogen is fixed artifically for fertilizer production than naturally but terrestrial ecosystems. See ref 7 and other papers by P J Crutzen form more information. The past century has largely focused on technological advances to maximise yields, profits and productivity, with relatively little consideration of the environmental consequences. This has led to collapse in many natural ecosystems, examples include, fisheries, soil erosion and water shortages due to deforestation, desertification and eutrophication of lakes. Despite these system collapses, the Earth system persists. As ecologists and environmental scientists, our challenge is to inform better management systems, which meet human needs while minimising the negative consequences to the earth systems through optimisation rather than maximization. Technological advances have contributed to rapid global degradation but can also provide many opportunities for understanding and resolve environmental problems and complexities. For the early part of the 20 th Century the dogma in natural resource management was largely one of ecological equalibria, where the objective was to manage in states. Managers and ecologists believed that ecological systems have a tendency to return to a steady stable state through selfregulatory processes or homeostasis. There is now an increasing body of evidence that this earlier view of complex ecological systems does not hold - in fact many ecosystems appear to have thresholds which lead them to flip from one configuration to an alternative state. Thresholds One outcome of the complex interactions of fast and slow variables is that systems may suddenly, and unpredictably, undergo dramatic changes. It seems that there are thresholds in many systems that separate (in time and space) two or more different system states. Once we cross these

2 thresholds, dramatic changes in the economic, ecological or social systems unfold, and these may lead to huge ecological degradation, economic loss, or social conflicts. Examples include the collapse of fisheries, the sudden transformation of grasslands to deserts, the transformation of coral reef systems to algae-dominated communities 3, and the outbreak of pests in forests and agriculture following years of pesticide applications or fire suppression. Under such circumstances traditional management agencies and processes become paralyzed they are unable to respond effectively to these new conditions because all models, concepts, and knowledge is based on a single ecosystem state, which may vary, but which does not undergo wholesale change to another totally different state. As traditional agencies fail to cope with the changes, the public lose trust in their ability to manage, and in the governments ability to implement effective policies. The Pathology of Resource Management The lack of flexibility of management implementing institutions has been called the pathology of resource management 4. This implies an overemphasis on the control of natural systems and process by humans so-called command and control, here the focus was on the prevention of disturbances and the maintenance of equilibrium (constant) states. This type of management may initially be very successful in delivering increased productivity by reducing detrimental impacts, but eventually it may lead to environmental systems that are increasingly vulnerable to large scale changes because the normal checks and balances that are imposed by natural disturbances are not occurring. Thus, the inherent variability and uncertainty in natural systems is replaced with human control, but this, over time, leads to slow changes in ecological, social and economic components, and ultimately to dramatic changes as certain thresholds are crossed. Additionally, management agencies become increasingly less flexible and adaptable to natural changes because their whole philosophy is aimed at avoiding or preventing natural variability. Economic sectors also become increasingly dependent on management practice that aims to deliver a constant supply of product, when in fact this can only be achieved through the control of the natural variability expressed by ecosystems. When a collapse does occur, these economic systems are therefore much more vulnerable. 1. Briske DD, Washington-Allen RA, Johnson CR, Lockwood JA, Lockwood DR, et al. (2010) Catastrophic Thresholds: A Synthesis of Concepts, Perspectives, and Applications. Ecology and Society Interesting general reading on these topics include Something New Under the Sun: An Environmental History of the Twentieth-Century World by John Robert McNeill and Paul Kennedy, and The World Is Flat: A Brief History of the Twenty-first Century by Thomas L. Friedman 3 For coral reefs, see Mumby, P.J. et al. (2006) Fishing, trophic cascades, and the process of grazing on coral reefs. Science 311, An excellent paper that introduced this concept is that of Holling, C.S. and Meffe, G.K. (1996) Command and control and the pathology of natural resource management. Conservation Biology, 10:

3 What makes ecosystems stable? If we wish to avoid collapses, or at least incorporate sudden ecosystem changes into current management practice, then we need to understand both why shifts in ecosystem states occur, and what maintains ecosystem stability. Ecosystems have a certain amount of resilience to change. In other words, if an ecosystem is disturbed (by human action or as a result of natural events) it is usually able to recover after a period of time to its original (or near original) state. This robustness is derived from the fact that ecosystems are the products of processes that operate at a variety of scales. A disturbance may occur at one scale and temporarily impact the processes operating at that scale, but other processes operating at other spatial and temporal scales will serve to bring the system back to the steady state. Thus an extremely dry summer may impact the vegetation of a grassland community, perhaps even causing changes in the structure of a community, but the large scale and long-term processes of seed dispersal and soil hydrology remain largely unaffected allowing for re-colonisation and maintenance of soil moisture. A second reason is that natural ecosystems have functional diversity: when conditions change, some species will suffer, but others will benefit, the overall result at the landscape or ecosystem scale being no large change in biomass, productivity or system processes. Functional diversity is effectively a natural insurance against perturbation. Biodiversity is thought to be a primary determinant of functional diversity, and hence biodiversity underlies the ability of an ecosystem to recover from disturbance. Consequently, ecologists argue that loss of biodiversity degrades the stability of ecosystems which could lead to dramatic changes in ecosystem states. The spatial heterogeneity or patchiness of a landscape also offers protection from disturbances, partly because a patchy landscape limits the extent over which a disturbance is expressed, but also because following disturbance, patches that are little affected by the disturbance act as source populations for recolonisation. Myths of Nature There are a number of different ways in which ecosystems have been perceived. Such viewpoints have been called myths of nature, that is partial truths that describe some aspects of the way nature behaves. These perspectives are illustrated in Figure 1. In these images, the ball indicates the state of the environment, and the surface on which it sits represents the forces acting on the ecosystem should the environment be perturbed. Pushing the ball in any direction represents a disturbance or management intervention. In the first diagram, Nature Flat indicates that there are no natural forces that affect the direction in which an ecosystem moves, and therefore humans can manipulate nature in any direction they want. In this scenario nature is amenable to human control and largely predictable we simply manage the environment as we wish. Issues of resource use and development are considered to be entirely within human control, and movement of the ecosystem in one direction can be, with appropriate

4 management intervention, reversed. This is the promethean viewpoint: humans can overcome any environmental problem. Figure 1. Four myths of nature. Nature Balanced refers to nature existing at some equilibrium condition: there is always a tendency to return to the original state following disturbance. You push the ball a little and it will return to the equilibrium state represented by the bottom of the depression. This is the viewpoint that is associated with traditional resource management systems prevalent in forestry and fisheries. Harvesting of trees or fish is expected to be followed naturally by a gradual recovery of the harvested population to the carrying capacity. The carrying capacity is the equilibrium point to which populations are expected to return to. The equivalent concept at the community level is the climax vegetation type. This scenario forms the basis of much modeling work that underpins management agency policies, and includes at its core the concepts of the logistic model of growth. Nature Anarchic is equivalent to viewpoints that emphasise the fragility of nature. A small perturbation will cause the ecosystem to change dramatically with no possibility or recovery. This perspective is held by many environmentalists who refer to the fragility of, for example, rainforests, coral reefs, species rich grasslands etc. All of these views are partly correct, but each on its own is an incomplete description of reality.

5 More realistic is the Nature Resilient view, where there are some ecosystem states that are fragile, and some that are relatively stable with a local equilibrium, but there is also the possibility that the ecosystem can flip from one state to another (when the ball is pushed hard enough that it escapes the stability domain and falls into another). This view includes the concept of thresholds and alternative stable states, and therefore it implies that the resiliency of an ecosystem is limited. Equilibrium and Dynamic Ecosystem Perspectives If we ignore the Nature Flat and Nature Anarchic views as being overly simplistic, we are left with the traditional resource management perspective (Nature Balanced) and the more complex, dynamic, and unpredictable, Nature Resilient view. Nature balanced emphasizes the equilibrium of nature, while Nature resilient recognizes local equilibria, but emphasises the dynamic nature of ecosystem change. An equilibrium perspective focuses on the carrying capacity, and its central management idea is that of achieving a maximum sustained yield. The dynamic view focuses on stability domain boundaries, thresholds, and the possibility of switching to alternative states, and management therefore has to be adaptable. We now recognize that key features of ecosystems include: Periodic and unpredictable disturbance and change Considerable patchiness and several alternative recovery profiles Multiple equilibria representing different states Thresholds that are uncertain Given these features, we may question what we exactly mean by stability. What is Stability? Stability can be defined in terms of the resilience an ecosystem has in response to change. However, there are at least two ways of defining resilience. The first is the speed of recovery to the original state after a perturbation, and assumes an equilibrium state in the direction of which the recovery will proceed. This implies a predictable recovery profile (we can predict, for example, that following selective harvest of trees, a forest will return to its pre-harvest state in 30 years). Managers will try to determine the resiliency (rate of recovery following impact) of an ecosystem and manage resource use to ensure optimal recovery for maximum efficiency. This perspective falls within the traditional resource use management paradigms and has been called engineering resilience to reflect the desire of human control. The second definition of resilience is the amount of stress, or size of disturbance, that can be absorbed before the ecosystem switches to an alternative stable state. This view recognizes the possibility that a system might not recover to its original state and instead changes to something very different (for example the collapse and subsequent failure of fish stocks to recover). Concepts that are implied by this definition of resilience are ecosystem persistence, adaptiveness, variability and unpredictability, and the term Ecosystem resilience is often applied to reflect this complexity. Management recognizes multiple stable ecosystem states, and therefore proceeds with caution. The precautionary principle becomes important. Such management is appropriate when there is uncertainty about the dynamics of the ecosystem. Spruce-fir Forests and Insect Outbreaks An example (see Figure 2) will illustrate how ecosystems may have resilience but can also be subject to sudden and dramatic change. Spruce-fir forests in North America are subject to herbivory by insects, notably the spruce budworm. When the forest stand is young the structure is relatively open and there is little foliage. Consequently, birds that eat the budworm are able to control budworm populations and maintain them at low population densities. As the tree population slowly matures it becomes increasingly difficult for the birds to find their prey in the denser foliage. After several decades the formation of a dense mature forest stand and the corresponding loss of predator efficiency allow the budworm to be released from predator

6 pressure leading to a budworm outbreak. The rapid population expansion of the budworm is maintained for a few years owing to the extensive forest areas, but also causes widespread defoliation and forest death. Following a few years of decomposition and seedling establishment, the forest returns to the young stage where birds can once more control budworm populations. Here we see local equilibria (budworm populations maintained at low population densities throughout most of the life of the forest trees), and also thresholds (the point at which birds are no longer able to control budworm populations, not because of increasing budworms, but because of a reduction in bird foraging efficiency), collapses (widespread forest mortality), and alternative ecosystem states (low budworm populations and high budworm populations). Figure 2. The dynamics of the Spruce-fir forests of North America. It is very possible that similar dynamics operate within the Alpine spruce-fir forests in Switzerland. The Adaptive Cycle This example can be generalized into a conceptual model of system dynamics that has been termed the Adaptive Cycle 5 (Figure 3). This adaptive cycle, which incorporates the concepts of equilibria, but also thresholds, collapse, fast and slow variables and alternative states, can be equally applied to the dynamics of economic and social systems as well as ecological systems (see references on web site for more information on this).

7 Gunderson and Holling (2002) Panarchy. Island Press. Hysteresis An important element of alternative stable states is that once an ecosystem has switched from one state to another it may be very difficult, and very expensive, to return it to the original state. This is the concept of hysteresis 6, and is illustrated in Figure 4. +A clear lake (blue line) is maintained by vegetation that soaks up the additional nutrients derived from fertilizer runoff, with only a small increase in turbidity due to increasing phytoplankton. Once a critical turbidity is reached, however, the light reaching the ground vegetation is not sufficient to maintain them, and the vegetation dies. At this point turbidity increases dramatically, because without vegetation the phytoplankton-grazing fish have no refuge from predators and therefore also decline, allowing a rapid explosion in phytoplankton. We are now in the alternative state of a turbid lake that lacks vegetation (red line). To return to the original state nutrient input must be reduced to very low levels (far below the point which triggered the change from clear to turbid) because there are no longer any phytoplanktonfeeding fish to reduce plankton biomass (figure from Scheffer et al. 2001).

8 Complexity from Simplicity We now realize that ecosystems dynamics is exceedingly complex, but also that this complexity arises from the interaction of a few very simple interactions. The idea that complexity arises from very few critical variables and processes that operate over different scales in space and time is receiving considerable research interest 6-7. It also represents a challenge for the management of ecosystems over the long term. Implications for Management In conclusion, there are a number of issues that ecosystem managers should recognize: Ecosystem shifts cause large losses of economic and ecological resources Restoration may require extensive action (hysteresis) Gradual reduction in resilience is rarely noticed Management should focus on: maintaining resilience, and NOT preventing disturbance sustaining a large stability domain slowly-changing variables: land use, nutrient stocks and biodiversity. 6 See Scheffer et al. (2001) Catastrophic shifts in ecosystems. Nature 413: See, for example, Fragile Dominion (1999) by Simon Levin, or Deep Simplicity (2005) by John Gribbin, both very readable books. 7 Steffen W, Crutzen PJ, McNeill JR (2007) The Anthropocene: Are humans now overwhelming the great forces of nature. Ambio 36: