An ecosystem that substantially resembles — in terms of species composition, structure, and ecological function — one that is or would be found in a given area in the absence of major human impacts. This includes human-managed ecosystems where much of the natural species composition, structure, and ecological function are present.

• Natural ecosystems include:
  1. Largely ‘pristine’ natural ecosystems that have not been subject to major human impacts in recent history.
  2. Regenerated natural ecosystems that were subject to major impacts in the past (for instance by agriculture, livestock raising, tree plantations, or intensive logging), but where the main causes of impact have ceased or greatly diminished and the ecosystem has attained species composition, structure, and ecological function similar to prior or other contemporary natural ecosystems.
  3. Managed natural ecosystems (including many ecosystems that could be referred to as ‘semi-natural’) where much of the ecosystem’s composition, structure, and ecological function are present; this includes managed natural forests as well as native grasslands or rangelands that are, or have historically been, grazed by livestock.
  4. Natural ecosystems that have been partially degraded by anthropogenic or natural causes (eg, harvesting, fire, climate change, invasive species, or others), but where the land has not been converted to another use and where much of the ecosystem’s composition, structure, and ecological function remain present or are expected to regenerate naturally or by management for ecological restoration.