Novel ecosystems: the new normal?

What is a novel ecosystem?

The definition of novel, sometimes also called ‘emerging’, ecosystems has evolved over the last two decades, but there are a number of characteristics that are helpful in identifying them. Novel ecosystems:

• Comprise new species assemblages
• Have a suite of interactions and processes consistent with a self-organized, functioning ecosystem
• Are difficult to ‘restore’ to a previous condition due to considerable/significant biotic and/or abiotic alterations

A useful definition emerged from a workshop on Pender Island, Canada, in 2013:

“A novel ecosystem is a system of abiotic, biotic and social components (and their interactions) that, by virtue of human influence, differ from those that prevailed historically, having a tendency to self-organize, and manifest novel qualities without intensive human management.” (Hobbs, Higgs and Hall, 2013).

A key aspect of novel ecosystems is that they can include species living outside of their historical native ranges; either by anthropogenic introduction, whether intended or not, or through ‘natural’ range expansion, driven by e.g. climate change. Examples of terrestrial and marine novel ecosystems have only been increasing, whether they are formerly cultivated land seemingly ‘stuck’ in a state dominated by non-natives and an altered fire regime, algal-dominated coral reefs in polluted, warming seas, or woodlands with changed sub-canopy communities, with concomitant changes in interactions (Kuijper et al. 2024).

Novel ecosystems may provide new habitat for endangered plants and animals

Such examples would often be considered ‘bad’ from a restoration or conservation viewpoint. However, in some instances, novel ecosystems may provide benefits such as habitat for endangered plants and animals that are threatened by habitat loss elsewhere, or a valuable connection to nature for humans in peri-urban environments. If novel ecosystems can play that role, it will need to be reconciled with traditional conceptions of restoration and conservation (Clement et al. 2023), and relatively rigid strictures of conservation regulations: for instance, in a UK context, what constitutes Favourable Conservation Status if based on assemblage classifications from the 1970s to 1990s?

When did the concept of a novel ecosystem emerge?

Evidence that ecosystems had been changing permanently as a result of human activity, through drivers including land transformation and climate change, began to emerge in the latter part of the 20th century. The first mention of ‘novel ecosystems’ in peer-reviewed literature came from Chapin and Starfield’s 1997 modelling work on Arctic Alaska, and this term started to be used widely, alongside ‘emerging ecosystems’, in the early 2000s.

In 2006 Richard Hobbs and colleagues explored the accumulating evidence for novel ecosystems as a system response to anthropogenic environmental change, and the implications of this for how ecosystems might be managed and for contemporary approaches to conservation. At the same time, people working in restoration ecology began to consider the implications of climate change for their activities. In an area traditionally wedded to either reproducing ‘historical’ systems, or aiming for targets of ‘native ecosystems’, issues are readily apparent.

A rapidly changing environment can mean historical precedents are unhelpful

A rapidly changing environment may mean historical precedents are unhelpful. Attempts to ‘force’ stable novel systems ‘back’ to a historical state by traditional restoration and conservation approaches might result in systems collapse. In 2009, Hobbs et al. published an opinion piece in TREE which suggested that, provided novel ecosystems had the characteristics listed above, they could be considered legitimate targets for management, as they are likely to be persistent and resilient under changing conditions which brought them about.

Since then, the concept has attracted a lot of scientific interest. A recent Web of Science search indicates over 600 publications to date with novel ecosystem in the title, abstract or text, with numbers increasing by about 60 papers per year; covering subjects as wide as the impact of wolves recolonising novel ecosystems to attitudes of experts accepting novel ecosystems as a valid approach with the caveat of close monitoring and evidence gathering. Indeed, the importance of ecological novelty was emphasized as one of five priority themes for ecological research in a recent British Ecological Society strategy document (Malhi et al. 2023).

Controversies

The scientific debate around the novel ecosystem concept includes a range of criticisms, from there being insufficient evidence to support the argument through to it could give industry and government an excuse to ‘trash’ nature – this latter argument also being deployed two decades earlier when ecological restoration was gaining traction. However, despite these criticisms, the evidence for novel ecosystems appearing continues to mount, and it doesn’t appear that novel ecosystems are being used to excuse degradation.

There’s an urgent need to understand how novel ecosystems emerge and function

Another issue was whether managers would be able to identify when and where novel ecosystems have arisen. Recently, the use of the term has highlighted the widespread likelihood of novel ecosystems (by one estimate, 50% and 80% of the terrestrial surface by 2100 and 2300 respectively [Ordonez et al. 2024]) due to new climatic conditions outpacing migration capacities and/or existing climate relationships becoming disaggregated. This emphasizes the urgent need to understand novel ecosystem emergence and functioning and the implications for conservation and restoration.

Two issues remain around the novel ecosystem concept that have pertinence for conservation and restoration policy and practice:

• Restoration targets

Restoration and conservation generally focus on habitats or ecosystems as seen in the guidelines that have proliferated during the UN Decade on Ecosystem Restoration. For example, the Society of Ecological Restoration has ‘Standards and Guidelines’ for ecological restoration based on ‘native indigenous ecosystems’. Although widely adopted this remains a contentious approach, considering the difficulties associated with adopting rigid standards, which do not recognize the dynamic nature of ecosystems under normal conditions. Not taking account of environmental change could lock sites into being conserved or restored around a set of species that could lead to system collapse.

• Non-native species

It has long been recognized that a large majority of non-native species cause no observable harm. However, some cause massive problems, as highlighted by the recent IPBES Invasive Alien Species Assessment. We are still poor at predicting which non-natives will become invasive, and this uncertainty will increase in a changing climate. This raises issues concerning the extent to which novel ecosystems could become ‘bridgeheads’ for future invasive non-native species as well as how ecosystem functioning will be affected where non-natives have few predators, pathogens and/or herbivores.

What’s next in studying novel ecosystems?

As the evidence for functioning, and self-sustaining novel ecosystems continues to accumulate there is a hard question to be answered – if we can’t compare a novel ecosystem’s ecological, conservation and/or restoration value by similarities to existing or historical examples, what can we measure? Increasingly work is looking at the scale of the whole system rather than focussing on species identity – are systems properties being exhibited, such as resilience to perturbation. Indeed, is the resilience in the system unhelpful or helpful for conservation and restoration goals? The following questions are a priority amongst those which need to be asked:

• How do we identify novel ecosystems – and does it even matter if novelty is going to be the new normal?
• How and when does something become a novel ecosystem?
• Should we deliberately produce novel ecosystems as part of conservation and restoration programmes, or must they exclusively be accidental consequences of anthropogenic drivers?
• How does conservation/restoration guidance need to evolve to take account of the reality of novelty?

This is an exciting area for research, and its philosophical roots can be equally applied to any system which needs to be managed. Importantly, understanding these systems and acting on the evidence gained is pressing in our rapidly changing environment.

Case studies

Várzeas – novel wetlands in Brazil

Throughout Brazil

Giselda Durigan, Instituto de Pesquisas Ambientais do Estado de São Paulo

Várzeas cover huge portions of land across the whole of Brazil. They occur in areas with heavy rain, and where tropical forests have been replaced by agriculture without erosion control.

How are these ecosystems novel? The soil is waterlogged, often deep, often fertilized. Biodiversity is low for plants and poorly known for animals. Usually dominated by Typha, together with some native and exotic grasses and forbs adapted to waterlogged conditions. Cecropia trees are the most common, with some other species surviving in the forest buffer around the waterlogged soils. Functioning: the massive herbaceous vegetation is stable, evapotranspiration is very high, the systems works as a filter benefitting water quality downstream.

Until recently, there was a Federal Program (Pró-várzeas) to foster drainage and cultivation of these areas (rice was the most common crop). Currently, cultivation is no longer allowed, but the law is not clear.

Most people see them as ‘degraded areas’ and sometimes we see farmers being ‘obliged to restore’ these areas, by planting trees that never survive.

A floodplain forest in the Jean Lafitte National Historic Park & Preserve

Louisiana’s Mississippi River Delta region, USA

Loretta Battaglia, Texas A&M University-Corpus Christi

This ecosystem is a semi-permanent/permanent floodplain forest in the backswamp of Bayou des Familles. It is experiencing rapid subsidence and so, rapid relative sea level rise, leading to increasing hydroperiod. The forest canopy is dominated by Taxodium distichum and Fraxinus profunda. The understory is dominated by Eichhornia crassipes and Salvinia minima, two floating invasive aquatic species that are native to South America.

Lehmann lovegrass in the the Chihuahuan Desert

Near Las Cruces, New Mexico, USA

Brandon T. Bestelmeyer, New Mexico State University

Lehmann lovegrass (Eragostis lehmanniana), an exotic species in the USA from South Africa, that established in an area formerly dominated by native desert grassland in the Chihuahuan Desert of New Mexico, USA. Lehmann lovegrass invaded this site after the native grasses had declined due to historical overgrazing episodes and soil loss. Native grasses have difficulty reestablishing, but Lehmann lovegrass seems to establish readily, conferring some of the ecosystem services provided by native grasses (excellent soil stabilisation, but low quality forage). Given that eradication is impractical due to the lovegrass’s abundant seedbanks, and because restoration of native grasses is similarly impractical, managers often accept Lehmann lovegrass grassland as a novel ecosystem and consider its potential benefits.

A decommissioned quarry

Puslinch, Ontario, Canada

Stephen Murphy, University of Waterloo

This is a novel ecosystem from a local decommissioned quarry that was left to undergo succession before there were regulations about quarry closures.  It is a mixture of species that are forming a mosaic of dry and wet alvars – which do not exist as a natural system in the species mixture seen here and should not be in the area because there aren’t many alvars locally (most of the quarried rock is well below soil surfaces). A red flower Aquilegia canadensis does colonize exposed rock but is not common in the area and is not considered as a local species. This was not a cultivar, so it is not a garden escape (it can disperse on wind or far ranging animals).

A Welsh harbour

Porthmadog Harbour, Cardigan Bay, North West Wales

Michael P. Perring, UKCEH & University of Western Australia

Porthmadog became one of the main ports for the Welsh slate trade in the 19^th Century. When returning from overseas, ships needed to unload their ballast; initially, these mixed rocks (e.g. Scandinavian granites, sandstones, limestones) formed quaysides around the harbour. Once complete, an alternative unloading point was required. A sandbank to one side of the main channel was deemed suitable, and from these sandy origins and timber foundations, Cei Balast (Ballast Island) came into being.

Perhaps Cei Balast is the archetypal novel ecosystem: over the years it has become a self-sustaining, functional ‘Dense continuous scrub’ ecosystem of UK native plants (e.g. Prunus spinosa, Crataegus monogyna) and species from around the world (e.g. Matricaria disciodea, Oenothera agg.) on an abiotic stage that is entirely changed from the historical system.

Cei Balast may not raise conservation conundrums, but the wider Porthmadog environment does. In adjacent saltmarsh, a diminutive plant has taken up residence with only a few isolated Welsh populations – Welsh mudwort. Yet its common name and listing on Schedule 8 of the Wildlife and Countryside Act (1981) belies its non-native origins and likely introduction through ballast. Scientifically, mudwort is Limosella australis. What should become of this nationally scarce and rare plant that most likely arrived from eastern North America?

Eucalyptus and monarch butterfly roost sites

Big Sur and the California Coast, USA

Stuart Weiss, Creekside Science

More than a hundred groves of non-native eucalyptus, primarily Eucalyptus globulus, growing in the mild climate of the immediate California coast, have been adopted by monarch butterflies as overwintering roost sites, thereby greatly expanding the monarchs’ range beyond the few ancestral overwintering sites in groves of native Monterey pines. These eucalyptus groves now require careful forest management to maintain the sunny, wind-sheltered microclimate nooks that the monarchs seek. The understories are often dominated by poison oak (Toxicodendron diversiloba) but are capable of supporting many native shrubs if tended appropriately.

Find out more

This article was first published in The Niche, the British Ecological Society’s membership magazine. Subscribe by becoming a member today.

Read more about novel futures in our Future of Ecology report.

 

 

 

References

Sarah Clement, Rachel J. Standish, Patricia L. Kennedy, (2023) Expert preferences on options for biodiversity conservation under climate change. Global Environmental Change,  83, 102759, ISSN 0959-3780, https://doi.org/10.1016/j.gloenvcha.2023.102759.

Hobbs, R.J., Arico, S., Aronson, J., Baron, J.S., Bridgewater, P., Cramer, V.A., Epstein, P.R., Ewel, J.J., Klink, C.A., Lugo, A.E., Norton, D., Ojima, D., Richardson, D.M., Sanderson, E.W., Valladares, F., Vilà, M., Zamora, R. and Zobel, M. (2006), Novel ecosystems: theoretical and management aspects of the new ecological world order. Global Ecology and Biogeography, 15: 1-7. https://doi.org/10.1111/j.1466-822X.2006.00212.x

Hobbs, R.J., Higgs, E., & Hall, C.M. (2013) Defining Novel Ecosystems in Novel Ecosystems: Intervening in the New Ecological World Order, First Edition. Ch.6.  John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd

Hobbs, R.J., Higgs, E., Harris, J.A. (2009) Novel ecosystems: implications for conservation and restoration Trends in Ecology and Evolution 24(11) 599 – 605.

Kuijper, D. P. J., Diserens, T. A., Say-Sallaz, E., Kasper, K., Szafrańska, P. A., Szewczyk, M., Stępniak, K. M., & Churski, M. (2024). Wolves recolonize novel ecosystems leading to novel interactions. Journal of Applied Ecology, 61, 906–921. https://doi.org/10.1111/1365-2664.14602

Malhi Y., et al. (2023) The Future of Ecological Research in the UK. British Ecological Society, London, UK. www.britishecologicalsociety.org/FutureEcology

Ordonez, A., Riede, F., Normand, S. & Svenning, J.-C. (2024) Towards a novel biosphere in 2300: rapid and extensive global and biome-wide climatic novelty in the Anthropocene. Philosophical Transactions of the Royal Society B: Biological Sciences 379: 20230022 https://doi:10.1098/rstb.2023.0022

Authors

Jim Harris¹, James Bullock², Nathalie Pettorelli³, Michael Perring^2,4, Theresa Mercer¹

¹Cranfield University, ²UK Centre for Ecology and Hydrology, ³Zoological Society of London, ⁴University of Western Australia