Ecological Resilience Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Natural system sare dynamic, complex, and interdependent. Ecological resilience describes the amount of change such a system can undergo and still remain within the same state. This definition is also referred to as engineering resilience, since it concentrates on stability at a presumed point of equilibrium, resistance to a disturbance, and the speed of return to equilibrium.

As applied to ecosystems, or to integrated systems of people and the natural environment, ecological resilience therefore has three defining characteristics: the amount of change a system can undergo and still retain the same controls on function and structure, the degree to which a system is capable of self-organization, and the ability to build and increase the capacity for learning.

The key concepts to explain ecological resilience are nonlinearity, adaptive cycles, panarchy, adaptability, and transformability. Nonlinearity can be illustrated by a ball in a basin. The state of this twodimensional system is the ball. Its dynamics cause it to move to the bottom of the basin. The system can change regimes either by the state changing, or through changes in the shape of the basin.

Ecological systems are never static, and they tend to move through four recurring phases, known as adaptive cycles, the second key concept. Generally, the pattern of change is a sequence from a rapid growth phase (exploitation) through a conservation phase in which resources are increasingly unavailable, followed by a release phase that quickly moves into a phase of reorganization, and then into another growth phase. For example, a tropical rain forest may be afforested, established, destroyed by a fire, then regrow again. Multiple possible transitions among the four phases are possible and the pattern may not reflect a cycle. The growth and conservation phases together constitute a relatively long developmental period with fairly predictable, constrained dynamics; the release and reorganization phases constitute a rapid, chaotic period during which capitals (natural, human, social, built, and financial) tend to be lost and novelty can succeed.

The third element is panarchy. Adaptive cycles never occur only on one scale, but all systems exist and function at multiple scales of space, time, and social organization, and the interactions across scales are fundamentally important in determining the dynamics of the system at any particular focal scale. This interacting set of hierarchically structured scales has been termed a panarchy.

Fourth, adapatability is the capacity of systems to alternate regimes (sometimes called adaptive capacity). It involves either or both of the following two abilities: The ability to determine the trajectory of the system state (the position within its current basin of attraction), and the ability to alter the shape of the basins, that is, move the positions of thresholds or make the system more or less resistant to perturbation. The abilities to affect both of these are determined by a combination of attributes of both the social domain and the ecosystem.

The fifth and final key concept of ecological resilience is transformability. In cases where a system is already in an undesirable regime and efforts to get it back into a desirable regime are no longer possible (or worse, make the undesirable basin larger), one option for resolving the predicament is transformation to a different kind of system-new variables, new ways of making a living, different scales-a different panarchy.

Although all natural systems are inherently resilient, since they can withstand shocks and rebuild themselves when necessary, resilience can be reduced if disturbances become greater than they can handle. And even in the absence of disturbances, gradually changing conditions, such as nutrient loading, climate, or habitat fragmentation can surpass threshold levels, triggering an abrupt system response. When resilience is lost or significantly decreased, a system is at high risk of shifting into a qualitatively different state. The new state of the system may be undesirable, as in the case of productive freshwater lakes that become eutrophic, turbid, and depleted of their biodiversity.

As an example, coral reefs are spectacular marine ecosystems known for their diversity of eye-pleasing fish and corals. In the Caribbean, overfishing and increased nutrient loading from land water runoff is believed to be responsible for declines in herbivorous fish populations which allowed the sea urchin Diadema antillarum to dominate the coral reefs. In 1981, a hurricane severely damaged the coral reefs. The sea urchin continued to graze on the algae, which allowed the coral to recolonize the reefs. In subsequent years, the urchin was hit hard by a pathogen and, as a consequence, was no longer in a position to control the algae. Fleshy brown algae came to dominate the reefs. The adult algae that now cover the reefs are largely unpalatable to the remaining herbivores, which serves to keep the reefs in this state of algal dominance.

Restoring a system to its previous state can be complex, expensive, and sometimes impossible. The key to resilience is diversity. Biodiversity plays a crucial role by providing functional redundancy. For example, in a grassland ecosystem, several different species will commonly perform nitrogen fixation, but each species may respond differently to climatic events, thus ensuring that even though some species may be lost, the process of nitrogen fixation within the grassland ecosystem will continue.

Bibliography:

Carpenter et al., “From Metaphor to Measurement. Resilience from What to What?” Ecosystems (v.4, 2001);
H. Gunderson, “Ecological Resilience-In Theory and Application,” Annual Review of Ecology and Systematics (v.31, 2000);
H. Gunderson and C.S. Holling, eds., Panarchy. Understanding Transformations in Human and Natural Systems (Island Press, 2002);
S. Holling, “Resilience and Stability of Ecological Systems,” Annual Review of Ecological Systems (v.4, 1973);
S. Holling, “The Resilience of Terrestrial Ecosystems. Local Surprise and Global Change,” in Sustainable Development of the Biosphere (Cambridge University Press, 1986);
S. Scheffer et al., “Catastrophic Shifts in Ecosystems,” Nature (v.413, 2001).