What is Passive Restoration and Its Potential Role in Ecological Restoration?

One of the terms and ideas that has long interested me is passive restoration. Passive restoration may seem disqualifying as ecological restoration defined as actions taken by humans to assist ecosystem recovery. Moreover, if any type of unassisted ecological recovery (on any time scale including indeterminately long) or unassisted establishment of any type of functioning ecosystem is considered ecological restoration, then restoration may be indistinguishable from numerous ecological processes such as simply maturation of ecosystems absent human intervention. However, a deeper assessment suggests that restorationists are interpreting passive restoration in different ways. Furthermore, passive restoration invokes thoughtful questions as to the degree and type of interventions required for ecological restoration and how natural recovery unassisted by humans can inform or be part of a continuum of restoration approaches.

In the simplest dichotomy, some authors frame ecological restoration as either passive or active (Krishman and Osuri 2023). Passive restoration can refer to strategies without any human intervention or with minimal intervention, such as fencing an area to encourage natural recovery or removing a source of degradation (e.g., removing pollutants in a stream before it flows into a wetland, then allowing the wetland to recover naturally). In the case of minimal intervention, a management action is being taken, but the passive refers to recovery (if it occurs) being driven by ecological processes absent further human assistance. By contrast, active restoration may be considered to entail removing a source of degradation only as a first step, followed by direct human interventions to further assist recovery such as through introducing biotic propagules or manipulating habitats. Beyond a passive/active dichotomy, some restorationists frame ecological restoration as a continuum from intensive, highly manipulative approaches to minimal or no direct human intervention (Chazdon et al. 2024). The latter case of no direct human intervention could be included in active restoration projects as controls for comparison with more active approaches and to potentially provide resources (e.g., seeds of early colonizers) that could be used in phased, active restoration approaches. However, leaving areas in a disturbed state using a passive approach may not always be feasible, with such cases including unabated generation of pollutants or source areas for spread of non-native species (Zahawi et al. 2014).

To provide further context for how papers specifically in Ecological Restoration are framing passive restoration, I non-exhaustively reviewed examples. Two examples assessed the potential for soil seed banks to facilitate what the authors regarded as passive recovery of native species following treatment of non-native plants along the Rio Grande River, Texas (Rubio et al. 2014) and in urban forests in Portland, Oregon (Clements and Bierzychudek 2017). In a different context, Wigginton and Meyerson (2018) considered a reduction in frequency of mowing along roadsides to constitute passive restoration in Rhode Island. In South Africa, Mabunda and Ruwanza (2023) viewed abandonment of former agricultural fields as passive restoration and discussed how legacy microtopographic features (furrows and ridges) from cultivation and utilization of the old fields by zebras (Equus quagga) may influence recovery toward uncultivated reference habitats. Also in South Africa, Van Zitters et al. (2025) considered non-native plant removal followed by unassisted natural recovery to represent passive restoration and compared this with active restoration including both removing non-native plants and reintroducing natives. In the current issue of Ecological Restoration, Neiswenter (2026) discusses ways that small mammals could assist ecosystem recovery via their activities such as digging to increase soil heterogeneity, dispersing seeds, and reestablishing flooding (e.g., beaver [Castor canadensis]) by incorporating animals in a continuum of passive to more active restoration approaches. These examples showcase a variety of contexts where restorationists publishing in Ecological Restoration have described passive approaches in restoration. The examples also raise questions such as how different restorationists view removing a non-native species or encroaching native species as an action by itself to constitute passive or active restoration, or another management action altogether (e.g., non-native species management) that could be independent from, part of, or fully constitute ecological restoration.

In reflecting upon how I have considered passive, active, and continuums of approaches in my own papers, some examples may be illustrative but not prescriptive. I have usually considered treating non-native plants in isolation (i.e., not at restoration sites and not combined with other treatments) to be non-native plant management (rather than passive restoration, as restoration may not be a goal) and have typically published this work in journals such as Invasive Plant Science and Management rather than in restoration journals. However, arguments can also be made that treating non-native species is ecological restoration, an example being non-native plants that altered soils and caused ecosystem degradation. I have regarded testing candidate treatments for non-native plants specifically at restoration sites or when connected with other interventions, such as establishing native plants to compete with non-natives, to constitute active restoration or part of actively maintaining quality of restored habitats (e.g., Abella et al. 2012). I have considered removing or reducing native species encroaching into open habitats as active rather than passive restoration based on the idea that the treatments used (e.g., prescribed fires) are often intended to also reinstate ecological processes and have a goal of restoring open habitat conditions (e.g., Abella et al. 2025). My viewpoints on these distinctions would be flexible based on context. For instance, using the logic in the Wigginton and Meyerson (2018) study mentioned earlier of stopping mowing to enable native community recovery, it is possible that in some (though not all) cases, simply stopping the suppression of fires could facilitate recovery of open habitats through what could be viewed as passive restoration. On the other hand, whether this should be considered fire management rather than active or passive restoration may be debated. In another example, I have not considered recovery of plant communities via soil seed banks in the absence of human intervention to be restoration (though potentially important for informing restoration), while I have considered human-implemented treatments intended to stimulate germination of seed banks for assisting habitat recovery to be active restoration (e.g., Abella 2022). Additionally, studies of soil seed banks at restoration sites can offer guidance on the potential resilience and sustainability of plant populations and food resources for wildlife.

In a final example out of many others possible, I have not considered unassisted ecological recovery (or lack thereof) as restoration, but I have made this a focus of our research program and view understanding natural recovery as a fundamental component of restoration programs. For example, our long-term studies of vegetation changes after Mojave Desert wildfires suggest that many sites may have transitioned to alternative states incapable of recovering on their own or that may require 500+ years for recovery assuming future conditions are conducive to recovery (Abella et al. 2021). Studies of ecological change absent human interventions can provide foundations for justifying whether restoration is required and facilitating treatment development, such as identifying limitations to recovery that restoration must overcome.

How might these considerations relate to submissions to Ecological Restoration? Since its inception in 1981, the journal has published papers across the spectrum of less to more intensive interventions, as well as work on natural recovery when connected with restoration. As a forum for communicating ideas and perspectives in restoration and representing restoration occurring in a variety of habitats and contexts, the journal continues to be open to work spanning the intervention continuum. We offer encouragement for manuscripts to explain the restoration context and terminology used, such as what passive restoration may mean in a study and how it connects with developing or implementing restoration practices. The journal is also open to other perspectives, such as dropping active/passive terminology and exploring alternatives like autogenic or autonomous to refer to unassisted recovery. This may avoid potential confusion with passive restoration not entailing the human interventions many restorationists view as requisite for ecological restoration. When making statistical comparisons between sites receiving restoration treatments and those passively allowed to recover, it can also be important to accommodate or avoid selection bias (e.g., if a site assigned active restoration is more degraded to start with compared with a less degraded site thus perceived more amenable to unassisted recovery) or to frame the comparisons as condition assessments with varying starting conditions. Ultimately, determining where and when restoration is most needed or effective continues to be a vital research area to prioritize limited resources for restoration. Assessments of unassisted recovery, whether termed passive restoration or other names, can contribute to this endeavor.

Zebra (Equus spp.). George J. Hagar. 1916. The Standard American Encyclopedia, Volume 12. New York, NY: The University Society, Inc. The Florida Center for Instructional Technology, fcit.usf.edu.