Rewilding watersheds: using nature’s algorithms to fix our broken rivers

Abstract

Rewilding is an ecological restoration concept that promotes the natural recovery of ecosystems, through (initial) active or passive removal of human influence. To support the application of rewilding approaches in rivers and their watersheds, we propose a framework to assess 'rewilding potential' based on measurement of basic river ecosystem functions (e.g. restoring flood and nutrient pulses), including examples of specific indicators for these processes. This includes a discussion of the challenges in implementing rewilding projects, such as lack of spatio-temporal data coverage for certain ecosystem functions or tackling ongoing problems once active management is removed. We aim to stimulate new thinking on the restoration of wild rivers, and also provide an annotated bibliography of rewilding studies to support this.

Catchment‐scale distribution, abundance, habitat use, and movements of European eel (Anguilla anguilla L.) in a small UK river: Implications for conservation management

“…For lotic habitat, suitable refuges in which elvers can settle and mature may be particularly limiting. Thus, where lacking, bankside tree growth that provides living root systems and a supply of woody material to the channel, should be promoted through rewilding techniques (Rideout et al, 2021). Such measures are also likely to confer wider biodiversity benefits (Thompson et al, 2018).…”

The role of rewilding in mitigating hydrological extremes: State of the evidence

“…Hydrological response to different levels of agricultural intensity (e.g., Berdeni et al, 2021; Bond et al, 2021; Cerdà et al, 2021) and the hydrological functioning and restoration of rivers and wetlands (e.g., Clilverd et al, 2013; Dixon et al, 2016; Quin & Destouni, 2018) were also relatively common in our retained papers, and the hydrological outcomes of more recent and innovative approaches to river restoration such as “stage zero” (Cluer & Thorne, 2014) are likely to represent future contributions to the evidence base. Removal of flow regulation structures was beyond the scope of our systematic review searches but may represent an important precursor to rewilding actions in many freshwater systems (Rideout et al, 2021). NFM measures were fewer and supplied by 10 papers.…”

“…For example, wilder terrestrial landscapes characterized by removal of or reductions in land management (e.g., Tree, 2018), natural vegetation regeneration (Cerdà et al, 2019), and, sometimes, species reintroductions (large grazing and browsing herbivores; Vermeulen & Nature, 2015, beaver;Brazier et al, 2021, and potentially apex predators such as wolves and lynx; Beschta & Ripple, 2015;Mysterud & Ostbye, 2004) can be expected to drive changes in infiltration rates, soil water storage, overland flow, interception, and evapotranspiration (Harvey & Henshaw, 2023). Wilder river systems, achieved through reduced management, terrestrial landcover change, and/or river restoration approaches (e.g., Cluer & Thorne, 2014), sometimes in conjunction with removal of flow regulation structures (Rideout et al, 2021) can also be expected to increase instream and floodplain roughness (Thomas & Nisbet, 2006), alter floodplain inundation and storage (Addy & Wilkinson, 2019) and conveyance of water through the river network (Harvey & Henshaw, 2023). This generates potential for flood attenuation and low flow alleviation effects, but a full understanding of the nature and magnitude of these effects, and any benefits and/or risks, is lacking.…”

How Wide, How Much? A Framework for Quantifying Economic and Ecological Trade-Offs of Altering Riparian Width on Agricultural Land

“…RBZs can mitigate the impact of localised and downstream flooding by reducing surface runoff and providing space for water retention (Kurki-Fox et al, 2022). The variability of river morphology and hydrological regimes, in addition to the provision of woody debris in-stream and standing deadwood from within the riparian zone itself, leads to the provision of many in-stream habitat niches for aquatic biota (Rideout et al, 2021), with freshwater ecoregions accounting for over thirty percent of vertebrate species despite their limited spatial extent (Tickner et al, 2020).…”