Novel ecosystems are ecosystems that as a result of human influences have changed to the extent that the biotic elements (living things such as animals, plants or bacteria) and abiotic elements (non-living things such as water, rocks and air) are almost entirely different from what they have been in a historical state of the ecosystem. Novel ecosystems are defined relative to a past state of the ecosystem and the role humans have had in changing it. While this means that what does and does not count as a novel ecosystem is context dependent and subject to interpretation, the concept is generally used to refer to ecosystems that have experienced substantial human-induced changes in recent history (say the past two centuries). Examples of ecosystems that are often considered as ‘novel’ are deforested primary forests and areas that have a very different species composition due to the introduction and spread of non-native species resulting from human activity such as intercontinental trade.