Topic:Open and closed Systems
Context
This topic forms part of the systems and complexity area of study. People who are competent in the topic can apply their knowledge of artificial and natural ecosystems, hierarchies of environmental systems, and the difference between closed systems and open systems to understand and conduct experiments into optimum system operations.
Competencies
Expected competencies after study of this topic are:
- being able to describe the difference between a closed, open, and isolated systems
- understanding the five environmental systems in ecological systems theory (microsystems, mesosystems, exosystem, macrosystem, and chronosystems) and how to describe a real-world systems environment using these concepts
- being able to describe ecological scales and control levels (microcosms, mesocosms and macrocosms)
- being able to describe an experiment using a microcosm or mesocosm that can usefully test a hypothesis about proposed systems changes
Summary
Systems can be described as operating in one of three primary modes:
- Open systems exchange matter and energy with its surroundings. Most systems are open, including ecosystems.
- Closed systems exchange energy but not matter. Closed systems are extremely rare in nature. No natural closed systems exist on Earth but the planet itself can be thought of as an “almost” closed system.
- An isolated system exchanges neither matter nor energy.
Systems are almost always open, nested and overlapping. Several frameworks have been proposed to examine and generate hypotheses of behaviours arising from the bi-directional influences across these levels of systems. For example:
- Bronfenbrenner Ecological systems theory (later the bioecological model) examines individuals' relationships within communities and the wider society using a set of nested systems
- Panarchy provides a model for systems evolution over time by describing a nesting of systems whereby smaller, faster levels invent and experiment while the larger levels stabilise and conserve accumulated memory
Key concepts
Most systems are open, including ecosystems. In forest ecosystems plants fix energy from light entering the system during photosynthesis. Nitrogen is fixed by soil bacteria. Herbivores that live within the forest canopy may graze in adjacent ecosystems such as a grassland, but when they return they enrich the soil with feces. After a forest fire top soil may be removed by wind and rain. Mineral nutrients are dissolved out of the soil and transported in ground water to streams and rivers ... Closed systems are extremely rare in nature. No natural closed systems exist on Earth but the planet itself can be thought of as an “almost” closed system.—Nigel Gardner, Types of System
The panarchy framework connects adaptive cycles in a nested hierarchy. There are potentially multiple connections between phases of the adaptive cycle at one level and phases at another level. Two significant connections are labeled 'revolt' and 'remember'. The smaller, faster, nested levels invent, experiment and test, while the larger, slower levels stabilize and conserve accumulated memory of system dynamics. In this way, the slower and larger levels set the conditions within which faster and smaller ones function ... the dynamic of each level which is organized in the four phase cycle of birth, growth and maturation, death and renewal. That cycle is the engine that periodically generates the variability and novelty upon which experimentation depends ... The adaptive cycle explicitly introduces mutations and rearrangements as a periodic process within each hierarchical level in a way that partially isolates the resulting experiments, reducing the risk to the integrity of the whole structure.—Resilience Alliance, Panarchy