Restoration and repair of Earth's damaged ecosystems

Abstract

Given that few ecosystems on the Earth have been unaffected by humans, restoring them holds great promise for stemming the biodiversity crisis and ensuring ecosystem services are provided to humanity. Nonetheless, few studies have documented the recovery of ecosystems globally or the rates at which ecosystems recover. Even fewer have addressed the added benefit of actively restoring ecosystems versus allowing them to recover without human intervention following the cessation of a disturbance. Our meta-analysis of 400 studies worldwide that document recovery from large-scale disturbances, such as oil spills, agriculture and logging, suggests that though ecosystems are progressing towards recovery following disturbances, they rarely recover completely. This result reinforces conservation of intact ecosystems as a key strategy for protecting biodiversity. Recovery rates slowed down with time since the disturbance ended, suggesting that the final stages of recovery are the most challenging to achieve. Active restoration did not result in faster or more complete recovery than simply ending the disturbances ecosystems face. Our results on the added benefit of restoration must be interpreted cautiously, because few studies directly compared different restoration actions in the same location after the same disturbance. The lack of consistent value added of active restoration following disturbance suggests that passive recovery should be considered as a first option; if recovery is slow, then active restoration actions should be better tailored to overcome specific obstacles to recovery and achieve restoration goals. We call for a more strategic investment of limited restoration resources into innovative collaborative efforts between scientists, local communities and practitioners to develop restoration techniques that are ecologically, economically and socially viable.

Keywords: disturbance; recovery; resilience; restoration.

Figure 1.

Conceptual figure of two different ecosystem recovery trajectories following the end of a disturbance, according to ecological restoration theory. In trajectory A, the ecosystem fully recovers to the pre-disturbance or undisturbed reference state. Trajectory B would exhibit a lower recovery rate, as is evidenced by its shallower slope following restoration, and would exhibit a negative response ratio (recovery completeness) as it did not reach the pre-disturbance or undisturbed control level. There were two ways to end the disturbance and initiate the recovery process in our analysis: either end the disturbance or restore hydrology. Examples of active restoration are detailed in the electronic supplementary material, table S1. We emphasize that this figure conveys conceptual information and that actual recovery trajectories may take on nonlinearities not depicted here. (Online version in colour.)

Figure 2.

Recovery completeness ± 95% confidence intervals of variables categorized by (a) disturbance and (b) ecosystem type. Blue lines indicate response variables undergoing passive recovery, whereas red lines depict actively restored variables. Complete recovery is achieved when error bars overlap zero, which is represented by the dashed lines in the panels. Grey bars in the middle of each category are predicted values ± 95% confidence intervals for each independent variable without including recovery type in the models. Data are ordered by the grey bars closest to complete recovery (top) down to the furthest from recovery (bottom). Numbers next to each line are the number of response variables used to model that category and the number of studies from which those response variables were calculated in parentheses. Note that in some cases the same citation could fall in two different categories.

Figure 3.

Recovery rate (percentage improvement per year) ± 95% confidence intervals of variables categorized by (a) disturbance and (b) ecosystem type. Data are ordered by the grey bars with the fastest recovery rate (top) down to slowest recovery rate (bottom). See legend of figure 2 for interpretation of numbers next to lines.