What are (eco)systems?
System (noun): A regularly interacting or interdependent group of items acting according to a set of rules to form a unified whole. - Merriam Webster
A system is any set of ordered, interrelated components that are connected by flows of energy and matter. A forest, a lake, a river, a storm - these are all examples of systems.
Satellite images of the ten costliest Atlantic hurricane systems as of January 2025: Katrina (2005), Harvey (2017), Helene (2024), Ian (2022), Maria (2017), Milton (2024), Irma (2017), Ida (2021), Sandy (2012), and Ike (2008)
Equilibrium state
Systems exist in an equilibrium state - the changing (dynamic) or relatively non-changing (steady-state) conditions of a system.
- Steady-state Equilibrium: When a system is in balance over time, neither growing or contracting but existing in full operation. Steady-state systems may have small oscillations around an average level or condition, but the average value will remain steady over time.
- Dynamic Equilibrium: When a system exhibits wide fluctuations around an average value, and the average value demonstrates a trend (e.g. growth or decrease) over time.
All systems will change over time, but at different rates. Thus, some systems are seemingly in a steady state (at least according to our limited perception of time as humans), but are actually moving towards a new state of equilibrium. For example, geologic systems are constantly changing: rocks are constantly becoming new kinds of rocks through processes like weathering and erosion. However, these changes take place over thousands and millions of years, so seem relatively unchanging to us.
Open and Closed Systems
There are two main types of system: Open and Closed.
In an open system, boundaries are open between parts of the system and other systems. This allows for the exchange of energy and matter between them. For example a forest ecosystem may interact with river systems, weather systems, the atmosphere, and so on.
A closed system is completely self-contained, and does not exchange energy or matter across any boundaries. There are very few examples of fully closed systems on Earth. However, Earth itself is essentially a closed system in terms of matter and resources. We don't exchange physical matter with other systems - it all stays on Earth, so we are stuck with what we have!
However, Earth is an open system in terms of energy. Earth receives solar energy from the sun (a process known as insolation), and dissipates energy in the form of heat.
The sun provides over 99% of the total energy used on Earth. Sunlight is used to grow plants and is thus the basis for our entire food system. Solar energy drives most climate patterns, winds, and currents. Even fossil fuels were created from the metamorphosis of woody plants over billions of years, which originally used solar energy to grow.
Ecosystems
Ecosystems are self-sustaining associations of living plants and animals and their non-living physical environment. Internally, ecosystems are highly complex webs of interconnected biotic (living) and abiotic (non-living) variables which function independently yet in concert with one another.
Ecosystems vary wildly in terms of size. They range from the micro-scale (e.g. a drop of water) to small scale (e.g. a city park, back yard, pond) to mid-scale (e.g. a beach, mountaintop, meadow) to large scale (e.g. a forest, desert, river system).
Ecosystems are open systems in terms of both energy and matter, with their boundaries functioning more as transition zones than hard borders. Of the abiotic or non-living components within ecosystems, none are more important than solar energy. Nearly all ecosystems on Earth depend, one way or another, on energy from the sun to function. The next section will describe the process by which ecosystems convert solar energy into biomass.