A1.1.2 Continued…


Ecosystems consist of living components and non-living components.

Living components

“Biotic”, e.g.:

  • Plants
  • Animals
  • Microbes


Non-living components

“Abiotic”, e.g.:

  • Air
  • Water
  • Mineral soil
  • Nitrogen


Ecosystems are controlled both by external and internal factors.

External factors

External factors control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem.

  • Climate (including rainfall)
  • Topography
  • Time


Internal factors

Internal factors in ecosystems not only control ecosystem processes, but are also controlled by them (often in feedback loops)

  • Decomposition
  • Root competition
  • Shading
  • Disturbance
  • Succession
  • Types of species present


NatureServe and its natural heritage program members, with funding from The Nature Conservancy, have completed a working classification of terrestrial ecological systems in the coterminous United States, southern Alaska, and adjacent portions of Mexico and Canada. This report summarizes the nearly 600 ecological systems that currently are classified and described. We document applications of these ecological systems for conservation assessment, ecological inventory, mapping, land management, ecological monitoring, and species habitat modelling.

The report is available here:   US Ecological Systems