In traditional engineering design, one seeks to maintain the independence of functional requirements. Functional requirements are the specific functions that the design feature is to provide. The engineer selects specific physical elements (design features) to meet each functional requirement. In the final design, each functional requirement has one solution and does not rely on other design features; that is, modification of any one design parameter affects only one functional requirement. There is no interaction or coupling of design features to multiple functional requirements. This is exemplified by the concept of modularity in software design where individual modules can be swapped in and out of programs without affecting program stability or performance.
Engineering designs seek tight tolerances and rigid, stable systems that do not change. Nothing is left to nature; everything is preplanned. In the event of system or component failure, identical back-up systems or components may be built to provide redundancy. The traditional engineering approach of maintaining independence between subsystems ignores the interrelationships and complexity of ecosystems.
Nature does not build things the way humans do. There is no external plan, design engineer, or architect that creates steps to achieve an envisioned final product. It is the flow of energy and material through an open system that allows for self-organization. Ecosystems are complexly coupled, that is, everything is connected to everything else. Ecosystem structure and function can be maintained through many different pathways that can operate under varying conditions, that is, wide tolerances. For example, accumulation of biomass can be accomplished by a wide array of plant and animal species. The actual species that live in a given ecosystem are adapted to the abiotic and biotic environment of the system. The loss of one species, either through succession or extinction, does not destroy the ecosystem. Other species continue the flow of energy and the cycling of nutrients and materials. In other words, there is redundancy of function but not necessarily of structure.
One measure of self-organization is the amount of information that is required to predict the final outcome. Higher levels of self-organization require large amounts of information to predict the final composition. To predict what an office building will look like when finished requires the blueprint and some drawings; to predict which organisms will provide structure and function to an ecosystem at any given time is almost impossible except in general terms. Self-organization also gives ecosystems properties of robustness, persistence, the ability to self-repair, and flexibility in the face of changing environmental conditions. Because of the interactions among system components, biotic and abiotic, changes in one component can ripple through the system and change many other components.
Self-organization is visible as an ecosystem goes through successional stages. It derives from the overarching actions of natural selection and evolution through which organisms have adapted to certain physical, chemical, and biological environments over time. For example, bare rock exposed by glacial retreat will pass through a series of plant and animal communities composed of different combinations of species over time as it develops into a forest. The general progress of this succession is understood, but predicting the exact composition of each step and the duration of each step is not. The exact composition is an emergent property of the interaction between the biotic and abiotic components of the ecosystem.
This ability of self-organization is taken advantage of by ecological engineers. Ecological engineering designs work with nature and allow nature to do some of the 'engineering'; that is, rather than fully proscribing only one satisfactory end result, the ecological engineered design recognizes that more than one final state may meet the functional requirements of the design. Engineering designs that ignore the self-organization properties of ecosystems require continued inputs of human-based energy and dollars (to buy materials and energy) to keep the system in the designed state (the desired, predicted outcome). Allowing nature to finalize the outcome of the design uses solar energy to organize the system and ensures some flexibility in the face of changing conditions.
Ecological engineers can take advantage of ecosystem self-organization in various ways. For example, a wetland or streambank restoration project may plant a variety of species that are water tolerant. But rather than insisting that the original mix is the best and inputting labor and energy to maintain the original composition of species, the system is allowed to mature without interference, resulting in a set of species that is most suited to the conditions at a given site. The species most able to survive and reproduce in that particular environment will spread and grow. In a stream restoration effort, material necessary to create lost habitat complexity and diversity, such as large organic debris or sediment, can be provided to the system and then be distributed by natural stream forces to distribute rather than anchoring it in place. By incorporating natural process into ecological engineering designs, ecological engineers reduce the use of nonrenewable energy and nonrecyclable material input and allow the self-organization capacity of the ecosystem to determine what is most suitable in a given location using natural goods and services.
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