By Jeff Balland
The recent concept of novel ecosystems has aroused many debates. Novel ecosystems can be defined as new systems where new species combinations and functions that have never interacted historically, occur irreversibly and sustainably (Morse et al. 2014), due to anthropogenic activities, species introduction and climate change (Hobbs et al. 2006; Hobbs et al. 2009). The stage between an ecosystem and a novel ecosystem is called “hybrid ecosystem”, and can be defined by a changing system where a return to previous conditions is still possible before it reaches a tipping point (see Hobbs et al. 2013). Almost 12 years after its introduction (see also Chapin & Starfield 2005), two sides are opposed, whether restoration ecologists should integrate the concept of novel ecosystems into practice or not. I attempt to expose and criticize both of them to see what should be retained about this issue.
Embracing the concept
The proponents of this approach argue that it is more relevant to adapt to climate change, and help ecosystems to keep their functions and services when their communities are unbalanced by changing conditions. As most of existing ecosystems are concerned by changes, “novel ecosystems constitute the new normal” (Marris 2010).
As climate change affects species ranges, migrations and invasions (Parmesan 2006) and because non-indigenous species introduction is one of the biggest causes of native communities changes (natives can be excluded by losing competition) (Clavero & Garcia-Berthou 2005), promoting novel ecosystem management is to say tolerating invasive species (Rodriguez 2006). Indeed, invasive species removal has a real cost for governances. For instance, the removal costs to USA more than 22 billion dollars per year for all invasive species (Pimentel et al. 2005). Is Invasive Non-Native Species (INNS) removal compulsory? Many studies showed that sometimes, removing those species could have unexpected negative impacts on native species and ecosystems so that recovery of native species after their removal is not allowed (see Zavaleta et al. 2001; Ewel & Putz 2004): some INNS have even been described as keystone and engineer species (species playing a crucial role in the ecosystem) (Rodriguez 2006; Sousa & Gutiérrez 2009). For example, an invasive tree in Puerto Rico allows some native plants to settle where there were not able before (Lugo 2004). Considering this, exotic species should not be neglected just because they are non-native (Davis et al. 2011).
By the way, the new concept of assisted migration (translocation of species threatened by climate change into more suitable locations), emerging as a solution to face environmental changes, will permit the creation of novel ecosystems in the areas where species are voluntary introduced (Minteer & Collins, 2010).
Finally, the novel ecosystems approach may allow improving quality of ecosystem services in exploited ecosystems such as plantation forestry or agriculture. In their study, Smaill et al.(2014) showed that the Coast Redwood Sequoia sempervirens matched all the considerations of New-Zealand foresters and could deliver better ecosystem services than the actual most exploited species (Pinus radiata). By the way, the Coastal Redwood is already naturalized in some part of the country (Figure 1).
Yet, many scientists strongly disagree with the novel ecosystems concept. In their critique, Murcia et al.(2014) pointed several oversights of such an approach. First, assuming novel ecosystems are “the new normal” is denying successful stories of restoration and ignoring that many ecosystems are well-preserved. Secondly, it is argued that species responses to climate change are unpredictable on a local or regional scale (the usual restoration scales). Furthermore the thresholds of irreversibility in species combination, namely the tipping points determining whether a hybrid ecosystem may recover to the ancestral one or evolve toward a novel ecosystem, are still difficult if not impossible to identify (Aronson et al. 2014). According to the detractors, such a concept could provide a “license to disturb” for resource exploitation companies, and may reduce the investment in research and restoration projects because they may become unnecessary, as transformation of ecosystems may be accepted. At last, introducing or managing new species combinations, often including INNS, is not worth taking the risk and the precautionary principle should be applied to avoid any aggravation of ecosystems perturbations.
Integration in management
According to Hobbs et al.(2014), novel ecosystem approach in conservation can also be an alternative to classical restoration. In this paper, the authors made a framework on how decisions about ecosystem management should be taken (Figure 2), struggling between different limitations the managers could have in regards of management goals.
However, according to the authors, this framework is theoretic and crucially need further implementation. By the way, decision-making processes may be influenced by the degree of sympathy managers have towards novel ecosystems.
The novel ecosystem concept is a new way of looking at the environment. Integrating it in management practices may allow to use what were threats (for example invasive species) as advantages (ecosystem functioning). It may help to preserve species that are jeopardized by climate change though assisted migration, and ecosystem services of exploited lands may be enhanced by selecting species in regards of their ecological functions. In my opinion, the concept is not ignoring successful stories of restoration, nor it will provide “licence to disturb”, because novel ecosystems are not worth studying to replace conservation but to provide alternative management. However, I agree some new approaches such as assisted migration are uncertain because of unpredictable species responses (to climate change, to new community compositions, etc.). Likewise, the difficulty of identifying the tipping points in hybrid ecosystem is an obstacle to management decisions. But it is definitely worth putting energy in further investigations, because of all the knowledge about ecosystem functioning the discovery of these thresholds would bring. The concept crucially needs implementation even if the principle of precaution regarding the risks should be considered. That is why I strongly believe the concept should be embraced only as an ultimate alternative, when neither sufficient protection (reserves, protection status for species, conservation programs…) nor classical restoration can be done. In that way, the novel ecosystem approach will only provide good overcomes and exciting discoveries.
Aronson, J., Murcia, C., Kattan, G.H., Moreno-Mateos, D., Dixon, K., Simberloff, D., 2014. The road to confusion is paved with novel ecosystem labels: a reply to Hobbs et al. Trends in Ecology & Evolution 29, 646–647. doi:10.1016/j.tree.2014.09.011
Murcia, C., Aronson, J., Kattan, G.H., Moreno-Mateos, D., Dixon, K., Simberloff ,D., 2014. A critique of the “novel ecosystem” concept. Trends Ecol Evol 29, 548–553. doi:10.1016/j.tree.2014.07.006
Chapin, F.S., Starfield, A.M., 1997. TIME LAGS AND NOVEL ECOSYSTEMS IN RESPONSE TO TRANSIENT CLIMATIC CHANGE IN ARCTIC ALASKA. Climatic Change 35, 449–461. doi:10.1023/A:1005337705025
Clavero, M., García-Berthou, E., 2005. Invasive species are a leading cause of animal extinctions. Trends in Ecology & Evolution 20, 110. doi:10.1016/j.tree.2005.01.003
Davis, M.A., Chew, M.K., Hobbs, R.J., Lugo, A.E., Ewel, J.J., Vermeij, G.J., Brown, J.H., Rosenzweig, M.L., Gardener, M.R., Carroll, S.P., Thompson, K., Pickett, S.T.A., Stromberg, J.C., Tredici, P.D., Suding, K.N., Ehrenfeld, J.G., Philip Grime, J., Mascaro, J., Briggs, J.C., 2011. Don’t judge species on their origins. Nature 474, 153–154. doi:10.1038/474153a
Ewel, J.J., Putz, F.E., 2004. A place for alien species in ecosystem restoration. Frontiers in Ecology and the Environment 2, 354–360. doi:10.1890/1540-9295(2004)002[0354:APFASI]2.0.CO;2
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., Zobel, M., 2006. Novel ecosystems: theoretical and management aspects of the new ecological world order. Global Ecology and Biogeography 15, 1–7. doi:10.1111/j.1466-822X.2006.00212.x
Hobbs, R.J., Higgs, E., Hall, C.M., Bridgewater, P., Chapin, F.S., Ellis, E.C., Ewel, J.J., Hallett, L.M., Harris, J., Hulvey, K.B., Jackson, S.T., Kennedy, P.L., Kueffer, C., Lach, L., Lantz, T.C., Lugo, A.E., Mascaro, J., Murphy, S.D., Nelson, C.R., Perring, M.P., Richardson, D.M., Seastedt, T.R., Standish, R.J., Starzomski, B.M., Suding, K.N., Tognetti, P.M., Yakob, L., Yung, L., 2014. Managing the whole landscape: historical, hybrid, and novel ecosystems. Frontiers in Ecology and the Environment 12, 557–564. doi:10.1890/130300
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Hobbs, R.J., Higgs, E.S., Harris, J.A., 2014. Novel ecosystems: concept or inconvenient reality? A response to Murcia et al. Trends in Ecology & Evolution 29, 645–646. doi:10.1016/j.tree.2014.09.006
Lugo, A.E., 2004. The outcome of alien tree invasions in Puerto Rico. Frontiers in Ecology and the Environment 2, 265–273. doi:10.1890/1540-9295(2004)002[0265:TOOATI]2.0.CO;2
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Morse, N.B., Pellissier, P.A., Cianciola, E.N., Brereton, R.L., Sullivan, M.M., Shonka, N.K., Wheeler, T.B., McDowell, W.H., 2014. Novel ecosystems in the Anthropocene: a revision of the novel ecosystem concept for pragmatic applications. Ecology & Society 19, 85–94. doi:10.5751/ES-06192-190212
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“The pathway of degradation differs from that of recovery.” – Suding and Hobbs, 2009.
Restoration ecologists have long worked to restore native habitats to their “natural state” by eradicating non-native species. Such conservation efforts need the community’s support to succeed. To obtain this support, a clear message was crafted: non-native species (including invasives) are harmful and must be eradicated. But this assertion is no longer entirely true. We now know that some non-natives are actually beneficial and should be preserved…or even introduced. Most habitats are now “novel” and will never again be “natural.” To ensure the community’s continued support for ongoing and future restoration efforts, the message must be changed. Realistic goals and practices must be conveyed convincingly to the public. Economic and cultural values should also be considered. Scientific credibility and community support are at stake.
Changing the Perspective
Global human movement of species has resulted in a breakdown of biogeographic barriers. Combined with climate change, the consequence has been novel ecosystems and species combinations (Hobbs 2006 & Meyerson 2007). Conservationists have declared war on these non-natives. The battle cry has remained unchanged: native habitats should be restored to their natural state by eradicating non-native species. This message has been forcefully and repeatedly conveyed to the public. And to some extent the message-bearers have a point. Some non-native species have had devastating effects: causing extinctions of native species, altering and destroying native habitat, and threatening animal and human health by spreading disease. Non-native species are recognised as a great threat to biodiversity. They also threaten our global environmental and economic welfare. The estimated economic impact of non-natives, including control costs, is $1.4 trillion annually, which is almost 5 percent of the global GDP (Pimentel 2001).
But it is equally clear that some non-native species are beneficial, both directly and indirectly, to native species and ecosystems. Conciliation biology, a subgroup of invasion biology, recognises just this. It promotes the concept that short- and long-term conservation management should include these interactions (Caroll 2011).
Restoration ecologists already know this, and more adaptive management plans now call for the preservation and/or introduction of non-natives. Yet, the conservation community continues to deliver a contrary message to public. Let’s take a look at some essential restoration practices that are currently in use.
Take for Example…
Taxon substitutes are non-natives that support restoration efforts by filling ecological niches left by extinct or fragmented populations. One example is the non-native Aldabra giant tortoise (Aldabrachelys gigantea) which was introduced to the surrounding islands of Mauritius. These animals were intended to replace extinct native large-bodied vertebrates that served as generalists and seed dispersers. The tortoises’ introduction has succeeded in maintaining ecosystem heterogeneity and native biodiversity. As a result, the giant tortoise is being considered for other similarly degraded insular ecosystems around the world (Griffiths & Harris 2010, Hansen 2010).
The introduced African honeybee (Apis mellifera scutellata) had an unexpected positive effect on Dinizia excelsa (canopy tree) in Amazonian pastures (Figure 2). Due to human-induced habitat loss and fragmentation, D. excelsa was expected to experience a decline in population resulting from the disruption in mutualism by native pollinators. Instead, the honeybee replaced the native pollinators, enabling the D. excelsa to not only thrive in fragmented areas but to have a higher vigour and genetic diversity than the same trees in a contiguous forest (Dick 2001). Once considered a pest, this non-native has become an invaluable part of the management strategy, ensuring the preservation of this native habitat and species.
And lest we forget about biocontrol…
Biocontrol is another restoration practice which introduces non-native species to control other non-natives. A prime example of biocontrol is the introduction of the non-native Tanzania Eurytoma erythrinae to control a non-native gall wasp (Quadrastichus erythrinae). The wasp was introduced to Hawaii and soon attacked a native Erythrina species, leading to massive population declines (Rayna 2013). The biocontrol successfully suppressed some of the wasp infestation, allowing the Erythrina population to partially recover. This non-native biocontrol agent should be preserved. It has become part of its adopted environment and will protect the native Erythrina from extinction.
Changing the Message
Introducing and/or preserving non-natives are essential to restoring and protecting native habitats. But how can conservationists reconcile these practices with the repeated message that all non-natives should be eradicated? They can’t. And worse, they will likely have trouble promoting these new practices to a public made sceptical by the conflicting messages. The public may even lose confidence in the scientific community, seeing the changing message as an admission of faulty science. (“Hey Alexander, did you hear that the world really isn’t flat after all?!”) And if they were wrong before, perhaps they are wrong now. The public may oppose these new practices or simply throw their hands up in resignation, not knowing what to believe.
Yes, the message must change, but it must be done in a thoughtful way, considering ongoing and future management practices including non-natives. In other words, we have to learn from our mistakes.
In the excitement of a dawning movement and the rush to convince the public, scientists sometimes put little thought into crafting the message. For example, environmentalists used to warn against “global warming”. Scientists subsequently changed the message to the broader term, “climate change” after determining that other environmental changes posed more significant impacts on humans than increasing surface temperatures. The changing message fuelled scepticism about the legitimacy of the underlying science, eroding public support.
In the conservation context, non-native species were once referred to as “alien” species. That term, which conjured up visions of space invaders, was subsequently discouraged. Similarly, “invasive” species suggests an unwelcome visitor. “Non-native” connotes a species that doesn’t belong. These terms implicitly suggest that the subject species is harmful and intrusive. The negative connotation of these terms supports the message that non-native (alien, invasive, etc.) species should be eradicated. Predictably, this will make it even harder to garner public support when the message is changed to call for the preservation and/or introduction of “non-native” or “invasive” species.
Perhaps then it is time to retire the terms, “native” and “non-native.” In “Who’s Invading What,” the author suggests that the non-native/native dichotomy may eventually give way to “dominant”/“non-dominant” species. The spread of a dominant species may promote a decline in species diversity (Larson 2007). Whether the dominant species is “native” or “non-native” would seem to be of little importance (Houlahan and Findlay 2004; White 2006; Meiners 2007). More important is the reduction in ecological functioning and the diminished landscape diversity.
The New Message
So, the message should change. But what should it become? Perhaps something like this: Although there are legitimate reasons to eradicate some non-natives, restoring a native habitat to its natural state should not top the list. Restoring a habitat to its natural state is a largely unattainable goal – a financial “luxury” affordable by only a handful of communities. For the rest, restoration efforts should be designed to restore merely some of the habitat’s original functional attributes. This could be watershed preservation, providing habitat for natives, and economic recovery or return (Ewel and Putz 2004). The use of non-natives can play an integral part in these efforts. But even partial restoration efforts are not inexpensive (Mitsch and Gosselink 2000). Non-natives are often the most cost-effective option (D’Antonio and Meyerson 2002). Reducing the restoration price tag may engender social acceptance.
The new message should inform the public about the unavoidable development of “novel” ecosystems which are normal responses to environmental changes and disturbances. Alterations in climate change and land use affect species distributions and the environment. These alterations modify the composition and/or function of ecosystems. If you think about it, all ecosystems were novel at some point in time (Root 2006 and Harris 2006).
The new message should also consider the cultural uses and socio-economic value of non-native species. Restoration ecologists should be mindful of the cultural and political sensitivities of local communities. The success or failure of any particular restoration project can easily turn on social acceptance or rejection. The public’s support may be a prerequisite to obtaining the funds, labor, and regulatory approval necessary to complete the project. Resources should be carefully allocated to conservation efforts that yield more desirable results.
The new message should be broad enough to encompass ongoing as well as future practices. New research, co-evolutionary responses, and environmental resilience should be considered.
Now is the Time
It is time to modify efforts to restore native habitats to their “natural” state. Long-term adaptive management plans must include appropriate non-natives to promote the efficient use of resources. Most habitats are now novel and dependent on non-native species. There will continue to be a subgroup of non-native species that cause environmental, economic, and social damage. However, other non-natives will adapt and contribute to evolving ecosystems (Schlaepfer 2011). Messaging is key to obtaining critical public support. Evolving science and conservation practices may require future changes to the messaging. Today’s message must be flexible enough to accommodate these future changes. Scientific credibility and community support depend on a coherent message. We must always look forward while working to preserve the past.
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Paul G. Roman is currently enroled in the Masters of Conservation Biology programme. This unique programme is offered jointly by Victoria University of Wellington, located in New Zealand’s capital city, and The University of New South Wales in Sydney, Australia. Mr. Roman graduated with a Bachelor of Science in Biology from the University of Hawaii in 2010. After graduation, he worked in conservation in Hawaii for 3 years as a field technician for both the Ko’olau Mountains Watershed Partnership and the Wai’anae Mountains Watershed Partnership.