This meta-analysis of 400 studies compared passive and active ecosystem repair outcomes in terms of the speed and completeness of recovery, and found little difference between the two approaches.
Active restoration did not result in faster or more complete recovery than simply ending the disturbances ecosystems face [Jones 2018: 1].
Passive recovery simply means ending the anthropogenic disturbance that was causing the degradation, while active restoration here includes anything from fertilizer application to recontouring/dredging to planting a desired species mix.
The authors speculate that the lack of different outcomes between the two approaches could be due to restoration managers correctly choosing to actively restore the ecosystems that “are not recovering on their own and require active restoration to improve recovery outcomes relative to passively recovering systems” [Jones 2018: 6]. Also, the actively managed sites in the study had, on average, less time to recover than the passively managed sites. Finally, the authors suggest there may be right and wrong ways to actively restore ecosystems, and “recommend that restoration strategies be tailored more closely to overcome the specific barriers to recovery in individual sites” [Jones 2018: 6].
Assuming active and passive restoration achieve comparable outcomes in many cases, then passive restoration deserves serious consideration, given limited resources available for the vast amount of ecosystem repair required in the world today.
Letting ecosystems repair themselves in many cases may be the most effective restoration strategy – a counterintuitive yet critical finding that could help society allocate restoration funds more efficiently in the future [Jones 2018: 6].
The study also consistently found that across systems, ecosystems didn’t fully recover, at least not within the timeframe of the studies.
Our results expand those findings to a broader range of ecosystems and geographies, and, together with previous work, suggest the majority of ecosystems have not yet recovered fully following disturbance and may not in the future. Thus, restoration should not be considered a substitute for conservation, which is a key strategy to ensure sustained support of biodiversity and delivery of ecosystem services in the future [Jones 2018: 4].
Jones, Holly P., et al., 2018, Restoration and repair of Earth’s damaged ecosystems, Proceedings Royal Society B 285, https://royalsocietypublishing.org/doi/suppl/10.1098/rspb.2017.2577.