Novel or emergent ecosystems emerge when human activities, land use, and anthropogenic climate change push ecological assemblages to morph outside of historical configurations, creating systems with no precedent in the ecological record. Novel ecosystems exist in urban, suburban, rural, and even wilderness areas that have been altered in structure and function by human agency, but a self-sustaining ecosystem is allowed to establish itself in the absence of ongoing human management. Novel vegetation associations growing along abandoned stone walls that once marked agricultural field boundaries and contaminated, esthetically unpleasant urban rivers undergoing ecologically-damaging "clean up" projects are examples of sites where research into novel ecosystem ecology is developing.
Definition Human society has transformed the planet to such an extent that, despite not being accepted as an official epoch on the geologic time scale, the Anthropocene has emerged as a useful term to describe the period of time over which humans have become a planetary force of change. While the term can also be used to describe naturally-occurring ecosystems characterized by new compositions or abundances of species that differ from historic and geologic baselines, the majority of scholars use the term to describe ecosystems with biotic and abiotic elements that are fundamentally and persistently changed by anthropogenic stressors.
Origin and development of the term The term "novel ecosystem" was first used in 2006 to describe 1.) recent or future anthropogenic changes characterized by new species combinations that have the potential to change ecosystem function and 2.) ecosystems resulting from either deliberate or inadvertent human actions that do not require maintenance to persist. These novel ecosystems result from biotic response to human-induced abiotic conditions and/or new biotic elements, including land degradation, soil enrichment, invasive species introduction, or the abandonment of human-created systems, such as unused agricultural or pastoral land. Clearly defining novel ecosystems is a much more difficult task than defining naturally-occurring ecosystems, given both the complexity of all of the human and ecological factors at play and the fact that their existence is inherently defined by disruption and change. Novelty is also defined by different parameters based on the scientific field in question. Climate scientists define novelty by departure from the long-term norm for temperatures or precipitation, while paleoecologists define novelty as any ecosystem shift observable in the geologic record. The term novelty is often employed without a clear working definition or may be used interchangeably with other words as a shorthand for change. The most commonly cited defining features of novel ecosystems are:
That the ecosystem components (abiotic, biotic, and social) have been altered beyond a certain threshold, which is subjectively defined by location, not broadly. The alteration was caused by human actions, whether direct or indirect. The ecosystem is self-sustaining or continues to develop novel properties after the anthropogenic disruption occurred. One analysis of novel ecosystem spread indicated that, unless rapid climate change mitigation tactics were taken, the coverage of novel ecosystems could include more than 50% of Earth's land surface by the year 2100, and 80% by the year 2300. However, another analysis argued against a "rough-and-ready discrete definition," as different areas exist on a continuum of novelty; defining novel ecosystems by human influence, which is omnipresent through land use, land management policies, and climate change, could result in a threshold so strict that no systems on earth could currently be considered 0% novel. Yet another analysis developed a quantifiable framework to define novel ecosystems in opposition to historical baselines (pre-human, early human, pre-industrial, recent-historical, and modern), developing applications and trajectories for each. Regardless of the discourse around a clearly-delineated definition, many researches agree that the emphasis should be placed on the trajectories of ongoing change, rather than on identifying the specific past moment of change.
Examples of novel ecoystems One poignant example of a novel ecosystem is the Orfordness lighthouse, which was decommissioned in 2013 due to erosion and sea encroachment causing instability and dismantled in 2020. The lighthouse was built on Orford Ness, a shingle spit on the Suffolk coast of Great Britain. It makes up part of a designated National Nature Reserve due to it containing 20% of the European biomass of vegetated shingle habitat, which is extremely fragile and scarce. Orford Ness has a long history of human-landscape interaction, with local people building tidal walls and using the salt marsh for grazing as early as the 12th century. During the first and second World Wars, it was used as a top-secret military test site, including for use in the development of radar, and it continued its history of experimentation in the mid-20th century with environmental atomic bomb tests, and the fragile ecosystem is littered with undetonated explosives. Other examples of agreed-upon novel ecosystems include:
Urban woodlands subject to weed control exhibit less diverse sub-canopy communities, which leads to a decline in bird populations Grasslands dominated by non-native plants and with altered fire regimes Algal dominated coral reefs caused by pollution, ocean acidification, and climate warming Areas where tropical forests have been replaced by agriculture with no erosion control, causing artificial wetlands River deltas inundated by sea level rise A decommissioned quarry that has been colonized by ruderal species An artificial island created by ships unloading their ballast Non-native mussels invading bodies of water, reducing the biomass of primary producers and clogging dams Non-native, sometimes invasive plants serving as an important habitat site for endangered or threatened species suffering from habitat loss
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