What is a System
A system is a set of interacting or interdependent components organised to create a functional whole.
Environmental Systems and Societies is built on the idea that the natural and human worlds cannot be understood by examining one piece in isolation. A forest is not just trees, a lake is not just water, and a city is not just buildings. Each is a collection of components that depend on one another, connected by flows of energy and matter that keep the whole functioning.
Every system shares four basic structural features:
- Components: the parts of the system, living or non-living (biotic or abiotic).
- Storages: places where energy or matter accumulates for a period of time, such as biomass, soil, or ocean water.
- Flows: processes that move or transform energy and matter between storages.
- Inputs and outputs: flows crossing the system boundary, entering or leaving the system.
A system also has a boundary, which defines what belongs to the system and what lies outside it. Boundaries can be physical (the shoreline of a lake) or conceptual (the limits of the carbon cycle we choose to model).
Environmental systems are dynamic: they change continuously in response to both internal interactions and external pressures. Stability, where it exists, is actively maintained, not simply a default condition.
The Systems Approach
A systems approach is a holistic way of visualising a complex set of interactions, applicable to ecological or societal situations.
The systems approach asks us to focus on relationships rather than parts. Instead of isolating one variable, it maps how components connect, how changes ripple through feedback loops, and how the whole behaves as a result.
This contrasts with a reductionist approach, which breaks a system into its smallest parts and studies each separately. Reductionism is powerful for understanding specific mechanisms, such as the biochemistry of photosynthesis, but it cannot explain what happens when all the parts interact simultaneously.
The systems approach is particularly valuable in ESS because environmental problems rarely have a single cause or a single effect. Deforestation, for example, simultaneously affects carbon storage, local rainfall, soil stability, and biodiversity. A reductionist analysis of just one of those threads would miss the others entirely.
In a forest ecosystem, the systems approach tracks all of the following together:
- Inputs: solar radiation, rainfall, CO₂
- Storages: plant biomass, soil organic matter, groundwater
- Flows: photosynthesis, respiration, decomposition, transpiration
- Outputs: oxygen, heat, runoff
Only by considering all of these at once can we understand how the forest responds to, say, a prolonged drought.
The systems approach is described as holistic because it treats the whole as the unit of analysis. Properties that appear only when parts interact, called emergent properties, are invisible to reductionist study but central to how environmental systems actually work.