Thresholds, novel ecosystems, and the sanctity of history

Brandon Bestelmeyer's picture

How is an ecosystem supposed to be? The answers determine how millions of dollars are spent and how ecosystems are transformed, with effects lasting centuries. Conflict over this question used to be between industry and environmentalists. Now ecologists are doing battle with one another too.


The standard for ecosystem management is historical or “reference” condition. Ecologists argue about how long ago we should look to, what historical ecosystems looked like, and what processes shaped them, but history captures much of what we value in nature. History set the evolutionary stage for the Earth’s biological diversity, unspoiled by human domination (but perhaps aided by human activities, such as fire use). Historical soil forming processes produced the deep, dark soils of the Great Plains (although humans produced them in the Amazon). Ecologists bicker about the details, but history is at the core of every land management framework—land potential, wilderness, ecosystem health, historical range of variation, and resilience. When we allow ecosystems to deviate from historical conditions, we risk losing the diversity of life and our precious soil. In fact, we don’t even know what we are losing, because we know so little about the machinery of evolution and ecosystem function. So historical conditions must be preserved and restored at even great cost. History is, in a word, sacred.


Proponents of “novel ecosystems”, then, are heretics. These scientists propose that preservation or restoration of historical conditions is sometimes impractical (1). The core of their argument is that ecosystems can cross ecological thresholds beyond which recovery to historical conditions is limited. Some ecosystems can cross thresholds and be restored with effort. Woody plants can be removed, allowing grass to recover and the fire cycle to be restored (2). There is another kind of threshold, however. When soil is stripped away by erosion after careless grazing or earthmovers seeking minerals; when a suite of invasive plants pervade a landscape, then historical conditions cannot be entirely recreated (3-5). Add to that climate change, which will prevent recovery of historical species, and we have difficult decisions to make (6).


The problem is that we often choose to ignore the difficult cases. We abandon ecosystems because they are “irreversibly degraded”. Even if we believe they are not a total loss, they are placed at the bottom category of triage—treatment is indefinitely delayed. “Novel ecosystems” proponents offer us another option (1). They suggest that we consider accepting these cases for what they are and managing them for whatever ecosystem services can be supported by the new ecosystem. Although the ecosystem differs from its historical state, it can have value as a wild ecosystem. We adapt. Or is the word—surrender (7)?


Some conservation and invasive species biologists are attacking the concept of novel ecosystem on two grounds (8). First is that there are no ecological thresholds that would ultimately prevent restoration to historical conditions with enough effort. Second, a focus on ecosystem services is a challenge to the inherent value of biodiversity and complexity of undomesticated historical ecosystems (9). “For those who care about global extinctions or about preserving historical ecosystems, [novel ecosystems] are bad news”(10).


This critique denies fundamental realities about ecosystem change and management. While it is true that not all ecosystems that have been characterized as “crossing a threshold” are unrestorable, there is clear evidence that highly persistent or irreversible transitions have occurred in certain cases, often involving invasive species and soil degradation. In contrast to the assertion that “no proof of ecological thresholds that would prevent restoration has ever been demonstrated” (8), I would take the opposite position that there is no evidence that restoration to the historical reference can occur even with intensive efforts in such cases (3, 5, 11). I would also assert that limited restoration potential puts an even greater premium on preserving historical ecosystems. We acknowledge that restoration cannot fully mitigate additional losses of intact ecosystems (11).


The critique also takes an unnecessarily polar view of biodiversity vs. human well-being and fails to acknowledge land use. Within wildland and low intensity land uses such as rangeland, historical conditions will continue to be prized whether or not novel systems are considered. This is because options for most ecosystem services, including wildness and soil fertility, are maximized in historical ecosystems. A critical problem, however, is the loss of wildlands and rangelands to more intensive cropland and urban land uses. Conversion of rangelands to cropland is accelerating in several parts of the world, including novel ecosystems such as some retired croplands in the US (Conservation Reserve Program lands) or degraded forests in Argentina (12, 13). Further, energy development may be increasingly focused on “degraded” ecosystems (14). A decision to manage land as a novel ecosystem is a decision to retain wildland or rangeland land uses for the benefit of biodiversity conservation.


It might reconcile the debate to consider novel ecosystems not as a type of ecosystem but as a land use. It means that that we will value and maintain an area as wildland in spite of its limitations. We manage it to maintain biodiversity, ecosystem complexity, and low intensity uses as well as it can. To condemn such areas as degraded, to wait in vain for restoration to occur, is to invite conversion to other land uses. Conservation biologists should not let the perfect, or the sacred, become the enemy of conservation.



1.         Hobbs RJ, Higgs E, & Harris JA (2009) Novel ecosystems: implications for conservation and restoration. Trends Ecol. Evol. 24(11):599-605.

2.         Twidwell D, Fuhlendorf SD, Taylor CA, & Rogers WE (2013) Refining thresholds in coupled fire-vegetation models to improve management of encroaching woody plants in grasslands. J Appl Ecol 50(3):603-613.

3.         Peters DPC, et al. (2006) Disentangling complex landscapes: New insights into arid and semiarid system dynamics. Bioscience 56(6):491-501.

4.         Chambers J, et al. (2014) Resilience to stress and disturbance, and resistance to Bromus tectorum L. invasion in cold desert shrublands of western North America. Ecosystems 17(2):360-375.

5.         Herrick JE, Havstad KM, & Rango A (2006) Remediation research in the Jornada Basin: Past and future. . Structure and function of a Chihuahuan Desert ecosystem: The Jornada Basin LTER., eds Havstad KM, Schlesinger WH, & Huenneke LF (Oxford University Press, New York, NY), pp 278–304.

6.         Bradley BA & Wilcove DS (2009) When invasive plants disappear: Transformative restoration possibilities in the western United States resulting from climate change. Restor Ecol 17(5):715-721.

7.         Perring M, Audet P, & Lamb D (2014) Novel ecosystems in ecological restoration and rehabilitation: Innovative planning or lowering the bar? Ecological Processes 3(1):8.

8.         Murcia C, et al. (in press). A critique of the ‘novel ecosystem’ concept. Trends Ecol. Evol.

9.         Doak DF, Bakker VJ, Goldstein BE, & Hale B. (2014) What is the future of conservation? Trends Ecol. Evol. 29(2):77-81.

10.       Marris E (2009) Ragamuffin earth. Nature 460(7254):450-453.

11.       Coffman JM, Bestelmeyer BT, Kelly JF, Wright TF, & Schooley RL (2014) Restoration practices have positive effects on breeding bird species of concern in the Chihuahuan Desert. Restor Ecol 22(3):336-344.

12.       Wright CK & Wimberly MC (2013) Recent land use change in the Western Corn Belt threatens grasslands and wetlands. P Natl Acad Sci USA 110(10):4134-4139.

13.       Zak MR, Cabido M, Caceres D, & Diaz S (2008) What drives accelerated land cover change in central Argentina? Synergistic consequences of climatic, socioeconomic, and technological factors. Environ Manage 42(2):181-189.

14.       Stoms DM, Dashiell SL, & Davis FW (2013) Siting solar energy development to minimize biological impacts. Renewable Energy 57(0):289-298.



Great post Brandon. It brings up some interesting questions regarding ecosystem function and structure, land use, and the suit of ecosystem services that native vs. novel ecosystems provide. Many of these questions however, lie at an intersection between the social sciences and the biologial sciences. I believe land use provides a potential reconciliation approach but only if we take an interdisciplinary approach that includes the economic and social sciences.
This said, I completely agree that too much focus is placed on the past. Meanwhile we are facing unprescedented changes in climate that make managing for the past unrealistic. Additionally, what we call a native ecosystem or a historical reference in many cases is based on incomplete information and ignores evolutionary processes (Toledo et al. 2011. Restoration Ecology 19(5): 564-568).  

Brandon Bestelmeyer's picture

Thanks David. I would bet that many conservation biologists might have trouble with social science approaches in this regard. It could be viewed at a way to subordinate the idea of the inherent value of biodiversity and the value of land potential for future generations (that are not yet able to offer their opinions).  And i do think history is  an important guide to management. I guess the question is when, given an ecosystem and the options, you shift from managing it with respect to the inherent value of historical condition and start thinking about  what people in the here and now want for the ecosystem.  The Belnap et al paper in the Rangeland Ecology and Management 2012 special issue gets at this.

Brandon Bestelmeyer's picture

Or is history and universal values a guide for managing novel ecosystems as well?

Brandon, it won't surprise you that I agree with David: We won't be able to address land degradation and thresholds without applying both the natural and social sciences to the problem. Also I suspect you're right that many conservation bioogists will have difficulty with social scientist approaches, although that's a bit ironic since conservation biology is an inherently social-ecological discipline. (Mascie et al. 2003. Conservation Biology 17:649-650). A related, more value-centered argument has been raised by a conservation biologist colleague with whom I recently completed a non-native species study in Hawaii, where nearly every environment below 1000m is dominated by one kind of exotic or another. Whenever I've suggested we can frame the problem as a novel ecosystems issue, I was met with resistance because "That means we're saying invasive species are 'good.'"  If one has dedicated one's life to protecting native ecosystems or battling non-natives, I suppose it's an existential leap to acknowledge there might be a more feasible path.

Since I do not, unfortunately, have time to think this through thoroughly, here's my gut response on a few points in reference to southern New Mexico:
1) Regarding the sanctity of history:
a) I don't think this saint has yet been canonized. I don't believe that we are, or ever have been, serious about restoring public rangelands to a reference state, regardless of how often that goes in the headline when land management is being sold to ecologists, environmentalists, or when NEPA documents are written. Instead, we have made some half-hearted, pro forma attempts. For instance, if we use herbicide to kill shrubs and "restore grassland" while maintaining livestock grazing--given that livestock grazing is the primary driver converting grassland to shrubland and that the same land management action is being sold to ranchers as "more cattle forage"... how seriously can we take the attempt? Our intent is ambiguous and we already know (or should know, by now) that livestock grazing is incompatible with the reference state--i.e., that this attempt to have our cake and eat it too is not realistic. I think it is premature to talk about the sanctity of history or say that "historical conditions will continue to be prized". We're still hemming and hawing about whether we want to try.
b) The saint is also somewhat anonymous. The reference state is largely a guess--we simply do not have reliable records of what was here 200 years ago. The sparse records we have are extremely limited--e.g., we may know that an area was black grama grassland. However, that is not a plant community nor an ecological state. That is one abundant species. I still do not know what black grama grassland is. What is the plant community--not just one species!--that we're talking about? Is there even a plant community, or is black grama simply abundant under some conditions independently of the other plants that are present? In what conditions does black grama persist or expand? How about all the others? So far as I can tell, these are all unanswered questions. If we're interested in restoring black grama grassland, this should be deeply troubling. Supposing we know black grama grassland used to occur at a given site (even this often sends us into speculation)... what, exactly, does that mean? If we try to restore it, do we even know what the goal is? Pile that onto the above, and failure is not necessarily meaningful. I'm not sure that we have either a well-defined goal or a serious attempt to reach it.
2) Regarding novel ecosystems:
There are a couple of different categories here that I think we should distinguish. For instance, if a site was black grama grassland historically and is now creosote shrubland, then creosote shrubland is a novel plant community at this site. However, the plant community that results from our attempt to restore black grama grassland will, in all likelihood, also be novel (e.g., bush muhly / fluffgrass grassland). To my mind... if creosote shrubland has been stable at the site for many decades, and especially if it has persisted or reestablished despite our attempts to shove the vegetation in one direction or another, we might reasonably call it the "new normal", the climax community under current conditions. In that context, I am inclined to agree with the "heretics". The danger of embracing novel plant communities, then, is that it does not distinguish between management that is aimed at minimizing disturbance and allowing the present climax community to flourish (leaving the creosote shrubland unmolested) and management that is aimed at creating disturbance and destroying the present climax community in favor of an alternate plant community that is more valuable to a vanishingly small minority of humans (herbicide treatments to remove creosote and enhance livestock forage). A "novel ecosystem" could be either a diverse community of native plants or a cattle-nuked expanse of tumbleweed. Novelty encompasses too much for us to embrace or reject it. I would hate for "novel ecosystem" to be the new buzzword for what amounts to a war on native plants in favor of livestock forage. This feeds back into the "sanctity of history"--if we are in fact choosing between land management strategies that both result in novel plant communities, it's not clear that "restoration" is a meaningful term that can be taken seriously as a management goal.
Gist of all the above being: We don't know what we're doing. We don't know why we're doing it. Perhaps this a problem.

Brandon Bestelmeyer's picture

Regarding black grama, I think in many places we have better evidence of state change than you suggest (we have great photos from the Summerford fan piedmont in what is now creosotebush shrubland), but I'll grant your point that the reference is obscure in many other places. But your second point more or less obviates the first. Even if we knew there was departure from reference, if the system is so completely reorganized around a different set of species, will restoration attempts do more harm than good ( this is the essence of the novel ecosystems argument). Here is where detailed evaluations of ecosystem responses are needed and, as Mark Brunson suggests, rigorous evaluation of how society views those responses. For example, we have designed a survey based on Restore NM to gauge what different interest groups think about the ecosystem responses to herbicides , including ranchers, sportsman, agency employees, and members of environment organizations (such as Audubon and Native Plant Society). We could use those responses to guide additional measurements. Will we be able to create consensus through quantification? I expect not, but at least we'd be talking about facts rather than speculation about facts.
Interestingly, even though Restore NM does not recreate black grama grasslands, or may alter native shrublands,  John Coffman's thesis (referenced in the post) showed that some regionally declining birds have greater occupancy in treated areas. One way or another, facts are going to be mixed and make people uncomfortable. 

Suppose we have the following set of information: site A is within ecological site M and has changed from plant community X to plant community Y. Now suppose we do the following: 1) define plant community X as the reference state for ecological site M; 2) determine that site B is also in ecological site M and currently has plant community Y; 3) infer that site B must have previously had plant community X and has since undergone a transition to plant community Y. I think we have now arrived at a guess, albeit an educated one. We are, essentially, assuming that areas within a given ecological site are uniform in their historical plant communities. Given that areas within a given ecological site can have varying plant communities at present, that our description of current plant communities is still pretty rudimentary even in well-studied areas (i.e., limited to a small number of relatively abundant perennials and generally omitting 90+% of the plants!), and that our observations of their historical plant communities are extremely limited (both taxonomically and spatially), this requires a fairly large leap of faith. I should mention that I absolutely appreciate the importance of work on ecological sites. I think they provide the best conceptual framework and set of information about the ecology of our area that exists and do have substantial predictive power. However, I also think that the issue of attempting to understand both current and historical plant communities is -extremely- complicated and that we are just barely getting started. In my opinion, we are dealing with a field orders of magnitude more complicated than quantum mechanics with much less funding and personnel. We should keep that in mind and take it very seriously!
Regarding my "second point more or less obviat[ing] the first"--probably I should have been clearer about where I am making my own guesses and on what they are based! Given our present knowledge and what is presently possible (both technically and politically), I think it is reasonable to interpret a plant community that has been stable for several decades and has resisted our attempts to change it as the current climax community. However, that is -contingent upon- our current knowledge and willingness to pursue restoration. Those, of course, will probably change. That we are not willing to engage in serious attempts at restoration of historical plant communities is a precondition of my statements about current climax communites. If ecological conditions change, of course so do the climax communities.
And who is this John Coffman guy, anyways? :-)

Basically, what I'm trying to get at in my second paragraph above is that we should accept the results of our land management practices -unless- we are willing to change those practices in a way that we can reasonably expect to produce different results--i.e., unless we are willing to engage in a serious attempt at restoration.

Brandon Bestelmeyer's picture

Thanks for the comments, this is precisely what I hoped this blog could do. 

Thanks for this well written post on an important concept.  This goes a long way to improving communication within the ranks of ecologists, including those on the lower rungs (such as myself) who attempt to apply ecology.  I didn't know I was a proponent of 'novel ecosystems', but now I suppose that I am.
Whenever I try to present or discuss a state & transition model for an ecological site, I make a point of conveying that the abscence of an arrow (a transition or community pathway) is just as meaningful as the presence of an arrow.  Typically, ecological sites I work with have no arrow pointing back towards the reference state.  Commonly, a S&T model will depict a downward cascade of increasingly 'degraded' states with no arrows pointing back towards a previous state. 
This often leaves a user dissatisfied and with a feeling of hopelessness.  I try to convey these points:  1)  just because the S&T model does not depict a return to a previous state, does not mean it is impossible.  It only means that we have never observed it. 2) Arrows returning to previous states are not excluded because they are considered 'infeasible' or too expensive.  It means that we have never observed it under any circumstance.  3) If you choose to try and return to a previous state in an S&T model where there is no arrow, then that action is in the realm of research, and not a management action.  If you want to make a management decision based on the best avalible information, then rely on the S&T model's direction, bleak as it may be. 4) If you attempt to return to a previous state in an S&T model where there is no arrow and are successful, then we can update the S&T model.
If this outlook makes me a proponent of novel ecosystems, so be it.  I thought I was just keeping it real.

Brandon Bestelmeyer's picture

Thanks. I suspect that much of what we refer to as restoration in STMs is actually production of novel ecosystems (or, to add another term--"hybrid ecosystems" that are not entirely novel). I have been guilty of this in the STMs I produced in the past, before I really started measuring the states, but our recent STM revisions will incorporate the real products of restoration efforts. 

Seems to me ALL ecosystems are novel, in that they are continually (if not continuously) evolving in response to weather, fire, grazers, seed dispersal, etc. Long-lived common species like creosote or mesquite can provide a semblance of stability, but even these species are subject to rapid reduction by drought or flooding or burial. The arrival of new species  (not necessarily "exotic") can rapidly alter a vegetation community (witness the arrival of creosotebush to North America not so long ago).
Nostalgia for past ecosystem configurations is an irrational basis for land management. Nostalgia reflects a shallow misunderstanding of the dynamics of nature, and a lazy response to the ethical difficulties of prescribing what species OUGHT to be in a place. 

Brandon Bestelmeyer's picture

I agree with you at a fundamental science level (that nonequilibrium ultimately rules) and especially for longer time scales novelty loses its significance. But I consider the novel ecosystems idea an important operational construct for managing ecosystems given shorter-term changes that are clearly anthropogenic and that involve thresholds/regime shifts. To jump way ahead to the end of the debate about novel vs. historical ecosystems: should we try to manage ecosystems at all? 
One's answer could be "no" or "do what feels good". In fact, I recently read an FAO report on pastoralism that essentially says that because all rangelands are nonequilibrial, there is no degradation and therefore constructs such as carrying capacity of livestock to limit degradation are meaningless to the environment and only harms pastoralists. This quote is quite illustrative: "From this perspective, sustainable rangelands management cannot be obtained through separation from users (restricted use), because the rangelands themselves are a making of human-environment interaction. In this perspective, sustainable rangeland management can only be achieved by the users themselves."  The portion I bolded sounds alot like novel ecosystems. The question is, which humans and whose values are reflected in the "making of human-environment interaction"? (And to paint all pastoralists, even subsistence herders, with the same brush is wrong).
Alternatively, we could say "yes", goal-directed management is utilitarian or a moral imperative to preserve  productivity and biodiversity for future generations. Then is interest in history worthwhile? Is it of interest to preserve thick organic matter rich A horizons? In this case, the language of "trajectory without interference by humans" is used to accomodate nonequilibrium. Then maybe the question is, would the A horizons in the midwest be there and persist if we hadnt stripped off the vegetation and tilled it continuously? Would black grama still be the dominant grass around Las Cruces without early 20th century overgrazing? 
Novel ecosystems vs. degradation, as I see them, relate to values and management responses to powerful anthropogenic effects, against a background of continual change. Ive argued that we should start making those values (and contexts) explicit rather than burying them in general terms.
I'd really like for state-and-transition models to do that.

I guess this platform is kind of defunct at this point, which is too bad. You all should post more! In any case, this issue has been on my mind recently so I figured I'd make another comment here. So, Brandon, you write:

"Basically, what I'm trying to get at in my second paragraph above is that we should accept the results of our land management practices -unless- we are willing to change those practices in a way that we can reasonably expect to produce different results--i.e., unless we are willing to engage in a serious attempt at restoration."

I agree. My concern is that novel ecosystems can be a way of moving the bar rather than talking seriously and honestly about whether or not we are accomplishing restoration goals and whether or not we're putting the kind of effort into restoration that would be needed for success.

Basically I'm imagining a flowchart like this:

a) identify a reference state-like restoration goal --> b) take actions to accomplish goal --> did it work? c) yes; d) no

c --> congratulations, you restored the land!

d --> do you think it is realistic to achieve the restoration goal with a modified action? e) yes; f) no

e --> go back to "b"

f --> identify novel ecosystem as the new goal --> congratulations, you restored the land!

I think the more reasonable interpretation at "f" is that either restoration is not possible or we aren't willing to put in the work.

Clearly we do need to be realistic about what we can accomplish and what effort would be needed. If we can't reach the holy grail, we need to know that and we need to say that and we need to talk about what more achievable goals we can reach. But I don't want us to just redefine those lesser goals as the new "holy grail", like, if we get there it's all good, mission accomplished, and so forth.

A novel ecosystem is fundamentally a restoration failure. It may still be a reasonable and realistic management goal, but it's not restoration. It's settling. It's deciding not to do restoration. Quite often that's going to be the right decision, but we need to understand it for what it is.