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Novel Ecosystems: Intervening in the New Ecological World Order, First Edition. Edited by Richard J. Hobbs, Eric S. Higgs, and Carol M. Hall.© 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.

Chapter 6

Defining Novel EcosystemsRichard J. Hobbs1, Eric S. Higgs2 and Carol M. Hall2 (on behalf of, and with input from, participants of

the Pender Island Workshop)1Ecosystem Restoration and Intervention Ecology (ERIE) Research Group, School of Plant Biology,

University of Western Australia, Australia2School of Environmental Studies, University of Victoria, Canada

What characterizes a novel ecosystem? Can a novel ecosystem be defined in a way that is both useful and general? These questions created heated debate both at the workshop and during the book-writing process. As workshop leaders, we deliberately steered discussion away from trying to come up with an agreed definition during the workshop in May 2011. Definitions inevita-bly provoke strong opinions and attachments to par-ticular wordings and emphases. Yet, how it is possible to discuss a topic effectively if you do not first define what you are talking about? Without clear definitions,

terms and concepts may become relatively useless either because there is no clarity around their use or because they can become ‘panchrestons’ or ‘plastic words’, or terms may be used so broadly and in so many contexts that they become vague and ambigu-ous (Poerksen 1995; Lindenmayer and Fischer 2007). Confused sets of ideas, multiple and normative mean-ings and academic discussions couched in highly abstract language can result. On the other hand, Reiners and Lockwood (2009) argue that ambiguity can spawn ‘creative pluralism’ and attempts to enforce

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 pre-vailed historically, having a tendency to self-organize and manifest novel qualities without intensive human

management. Novel ecosystems are distinguished from hybrid ecosystems by practical limitations (a combina-tion of ecological, environmental and social thresholds) on the recovery of historical qualities.

A WORKING DEFINITION THAT HAS ENDURED MANY CONVERSATIONS AND REFLECTIONS IS AS FOLLOWS

Defining novel ecosystems 59

character in the same way as physics lives with the dual notion of light as both a wave and a particle.

Figure 6.1 presents a simplified view of the defini-tion by illustrating the relationship between historical, hybrid and novel ecosystems, based on the degree of change from historical conditions and reversibility of that change. These ideas are expanded upon and pursued in more detail in subsequent chapters (see Chapter 18).

Why is it important to sort this out? Identifying an ecosystem as novel signals that management is restricted to goals associated with novelty, and that recourse to hybrid or historical ecosystems is no longer practical. In doing so, we leave behind traditional goals that underpin conservation and restoration, notably connection to historically rooted ideals. These goals embed deeply held values that inform and explain

rigid definitions compromise the utility of a concept. Sometimes ecologists get hung up on definitions when they should be asking if an idea, however used, has proven or may prove useful in practice or alternatively limits understanding.

As with many emerging concepts, it is perhaps easier to indicate what novel ecosystems are not: (1) a system that would have occupied that space in the past (i.e. part of a historical range of variability); (2) managed intensively for specific production or built over; or (3) managed with the purpose of reproducing the histori-cal ecosystem (i.e. classic restoration).

The earlier definitions of what is and what is not a novel ecosystem were viewed and agreed on by many, but not all, of the participants. This definition captures the essence of what we consider to be important factors characterizing novel ecosystems. We recognize also, however, that the term is in the public domain and being used in multiple ways already; any attempt to corral this process is likely to have at best limited success. However, the definition is ultimately our attempt at a working characterization.

Along the way towards this definition, various aspects of novel ecosystems were hotly debated. For instance, is novelty a continuum or are there clear breakpoints where it is clear that one system is novel and another is not? Several participants strongly sug-gested that novelty occurred along a continuum, while others posited that being able to classify systems as novel or not novel had clear management utility that was lacking in a continuum approach. Central to this discussion was the question of whether clear thresh-olds exist in the state space illustrated by Figure 3.2, as put forward by Hobbs et al. (2009). The idea of thresh-old dynamics has proven very useful in considering ecosystem management choices and techniques (e.g. Hobbs & Harris 2001; Suding & Hobbs 2009); includ-ing thresholds in considerations of novel ecosystems therefore seemed appropriate. This line of thought was carried through the book into chapters dealing with management interventions (e.g. Chapters 3, 4, 5, 18 and 24). Nevertheless, valid concerns remain about the actual ability to observe, measure and diagnose ecological thresholds and hence to make decisions effectively using the schemes outlined in Chapters 3, 18 and 24. This issue is not restricted to discussions on novel ecosystems, but is a live topic of urgent debate and research in applied ecology in general (Andersen et al. 2008; Samhouri et al. 2010; Bestelmeyer et al. 2011). Perhaps novel ecosystems can display a dual

Figure 6.1 A simplified view of the definition that illustrates the relationship between historical, hybrid and novel ecosystems. Many people contributed to the development of this figure and the ideas supporting it, especially Jim Harris, Joe Mascaro, Steve Murphy and Cara Nelson.

Is target ecosystemaltered because of

anthropogenicforcing?

No

No

Yes

Yes

Historicalecosystem

Time and/orrestoration

Hybridecosystem

Novelecosystem

Are changesreversible?

Time withoutintervention

60 Novel ecosystems

shifts: approaches to identification. Trends in Ecology and Evolution, 24, 49–57.

Bestelmeyer, B.T., Goolsby, D.P. and Archer, S.R. (2011) Spatial perspectives in state-and-transition models: a missing link to land management? Journal of Applied Ecology, 48, 746–757.

Higgs, E.S. and Hobbs, R.J. (2010) Wild design: Principles to guide interventions in protected areas, in Beyond Naturalness: Rethinking Park and Wilderness Stewardship in an Era of Rapid Change (eds D. Cole and L. Yung), Island Press, Washington, DC, 234–251.

Hobbs, R.J. and Harris, J.A. (2001) Restoration ecology: Repairing the Earth’s ecosystems in the new millennium. Restoration Ecology 9, 239–246.

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

Lindenmayer, D.B. and Fischer, J. (2007) Tackling the habitat fragmentation panchreston. Trends in Ecology & Evolution, 22, 127–132.

Poerksen, U. (1995) Plastic Words: The Tyranny of a Modular Language. The Pennsylvania University Press, University Park, PA.

Reiners, W.A. and Lockwood, J.A. (2009) Philosophical Foundations for the Practices of Ecology. Cambridge University Press, Cambridge.

Samhouri, J.F., Levin, P.S. and Ainsworth, C.H. (2010) Identifying thresholds for ecosystem-based management. PLoS ONE, 5, e8907.

Suding, K.N. and Hobbs, R.J. (2009) Threshold models in res-toration and conservation: A developing framework. Trends in Ecology and Evolution, 24, 271–279.

Thompson, A. and Bendik-Keymer, J. (2012) Ethical Adaptation to Climate Change: Human Virtues of the Future. MIT Press, Cambridge, MA.

our actions (Higgs and Hobbs 2010; Thompson and Bendik-Keymer 2012).

Accepting new natures means that we need to rein-vent or at least rethink goals and how these are anchored. With the emergence of ecosystems services in a society already given over to consumerism, the demise of historical goals may suggest that anything goes. There are three strategies for dealing with this. First, a distinction between novel elements and novel ecosystems acknowledges there can be significant novel elements (invasive species, modified soil conditions) without the ecosystem passing a critical threshold that renders it practically impossible to return to hybrid or historical conditions. Hence, there are many ecosys-tems with novel elements that are in fact hybrid between historical and novel. Second, again invoking a physics metaphor, there is a gravitational pull in our discus-sions toward historical conditions. In acknowledging novel ecosystems, it is plain that this gravitational pull is sometimes very weak; it remains however, if only as a reminder that the past matters and has mattered. Third, the definition features social drivers of novelty alongside ecological and environmental drivers. While it may be practically impossible to reverse certain envi-ronmental drivers (e.g. N deposition) in some cases, it is more likely that social drivers can be addressed. Not that these are easy in the case of deeply embedded economic constraints, political intransigence or cul-tural values. Thresholds matter, but they should not be trotted out as an excuse to avoid resolute action.

REFERENCES

Andersen, T., Carstensen, J., Hernandez-Garcıa, E. and Duarte, C.M. (2008) Ecological thresholds and regime