Novel ecosystems are ecosystems that arise composed of new combinations of species.

Human interventions often create novel ecosystems, either deliberately, for our benefit, or unintentionally. Thus, both climate change drivers themselves and human responses or adaptations to climate change can create novel ecosystems.

Novel ecosystems can still provide important ecosystem services such as clean water, soil stabilization, habitat and aesthetic value, making them an important adaptation strategy in some contexts. Novel ecosystems can, however, challenge our traditional understanding of what is a weed, as what is considered a weed in other contexts may be a valued contributor to a beneficial novel ecosystem. A plant is classified as a weed in a novel ecosystem based on the values ascribed to its impact on ecosystem function and resilience.