Energiflöde

Energiflöde, or energy flow, is the passage of energy through an ecosystem or other system from its source to various sinks. It emphasizes the rate at which energy enters, moves through, and leaves the system, rather than the amount of energy stored at a given moment.

In most ecosystems, the ultimate energy source is solar radiation captured by photosynthetic organisms (producers). These organisms convert light into chemical energy, creating gross primary production (GPP). A portion is used for respiration, leaving net primary production (NPP) that becomes available to herbivores and higher trophic levels as energy. At each transfer between trophic levels, energy is lost mainly as heat due to metabolic processes, leading to energy pyramids and a typical transfer efficiency that is relatively low, often around 5–20% per step.

Energy flow is usually quantified as energy per unit area per time, such as kilojoules per square meter per year (kJ/m²/yr) or kilocalories per square meter per year. Ecologists construct energy budgets for ecosystems by accounting for inputs (production), outputs (respiration and maintenance), and changes in biomass. Decomposers also participate by processing detritus, but the overall flow remains from production to consumers to decomposers, with energy increasingly dissipated as heat.

The concept helps researchers understand ecosystem productivity, trophic structure, and sustainability, and is applied across terrestrial, aquatic, and microbial systems. It complements studies of matter cycles by focusing on the rate and pathways of energy transformation rather than energy storage.