It’s a tough job these days being an environmentalist proponent of sustainability. Bad news and warnings of impending doom at every turn. One might be forgiven for craving a bit of sunshine every once in a while.
One of the especially troubling themes that has risen to dominance in recent years as a result of reports from the Millennium Ecosystem Assessment, the IPCC on climate change, and so on, is the idea that the world’s ecosystems are undergoing a fundamental and potentially irreversible shift into alternate states from which we may not be able to return. There is a good deal of evidence in support of this idea. And the question of how and whether ecosystems can recover form the wounds we inflict on them is a critical one because humanity is rapidly running out of wild nature to exploit. Thus, fixing degraded systems is now central to a sustainable future. Can we pull it off? Conventional wisdom’s answer is rather pessimistic.
So I was quite intrigued, and heartened, to read a new paper in the open-access journal PLoS ONE by by Holly Jones and Oswald Schmitz that set out to test this idea with quantitative data. They scoured the scientific literature for studies that had examined how fast ecosystems recover from disturbances. They found 240 studies — spanning land, sea, and freshwater and including a wide range of habitats – that met their criteria.
The results were surprising: across a broad range of ecosystem and perturbation types, they found that most ecosystems appear capable of rebounding surprisingly quickly—within a few decades—if treated properly (see the figure). The last point being the trick, of course. Forests rebounded most slowly, and agriculture and multiple stressors had the longest lasting effects. But, overall, most ecosystems were able to recover to something like their pre-disturbance state within a decade or two.
The analysis offers an unexpected ray of hope that damaged ecosystems may be much more resilient on average than previously expected.
Now, the glass might alternatively be seen as half-empty given that roughly half the systems and variables examined had not recovered by the end of their respective studies. In many cases this is probably because they had not been monitored long enough. Intriguingly, only 5% of the ecosystems showed evidence of shifting into an alternate stable state, suggesting that this phenomenon may rarely explain non-recovery despite the high-profile attention such regime shifts (as they are called in the technical literature) have received in recent years.
There are, of course, the usual questions about how representative are the published data found through an electronic literature search, and also the more specific spectre of “shifting baselines” affecting the results, that is, in trying to determine what the actual “natural” or equilibrium state of an ecosystem is in the absence of disturbances.
To me, perhaps the most sobering issue, which was not considered by this study, is that ability to measure recovery is only possible once the perturbation has been relaxed. Yet many of the pressures humans are now imposing, such as climate heating and agriculture, are long-term, sustained perturbations that are unlikely to be relaxed in the foreseeable future. The analysis also found that recovery is slower from multiple stressors, which is increasingly the situation facing most ecosystems.
Despit these caveats, this new analysis provides a first quantitative benchmark against which future refinements can be evaluated. Equally importantly, in my view, these data provide a valuable psychological jolt to an increasingly entrenched sense of resignation and hopelessness about the state of wild nature. While there is no arguing with the magnitude of impacts humans have had on ecosystems, this paper offers at least a hint that nature is more forgiving and resourceful than many have assumed.
[Original source (open access): Jones,H.P. and O. J. Schmitz. 2009. Rapid Recovery of Damaged Ecosystems. PLoS ONE 4(5): e5653. doi:10.1371/journal.pone.0005653]