Process-based Restoration Research Articles

Carbon stock quantification in a floodplain restoration chronosequence along a Mediterranean-montane riparian corridor

Uncertainty in the global carbon (C) budget has been reduced for most stocks, though it remains incomplete by not considering aquatic and transitional zone carbon stocks. A key issue preventing such complete accounting is a lack of available C data within these aquatic and aquatic-terrestrial transitional ecosystems. Concurrently, quantifiable results produced by restoration practices that explicitly target C stock accumulation and sequestration remain inconsistent or undocumented. To support a more complete carbon budget and identify impacts on C stock accumulation from restoration treatment actions, we investigated C stock values in a Mediterranean-montane riparian floodplain system in California, USA. We quantified the C stock in aboveground biomass, large wood, and litter in addition to the C and total nitrogen in the upper soil profile (5 cm) across 23 unique restoration treatments and remnant old-growth forests. Treatments span 40 years of restoration actions along seven river kilometers of the Cosumnes River, and include process-based (limited intervention), assisted (horticultural planting and other intensive restoration activities), hybrid (a combination of process and assisted actions), and remnant (old-growth forests that were not created with restoration actions) sites. Total C values measured up to 1100 Mg ha−1 and averaged 129 Mg ha−1 with biomass contributing the most to individual plot measurements. From 2012 to 2020, biomass C stock measurements showed an average 32 Mg ha−1 increase across all treatments, though treatment specific values varied. While remnant forest plots held the highest average C values across all stocks (336 Mg ha−1), C values of different stocks varied across treatment type. Process-based restoration treatments held more average biomass C (120 Mg ha−1) than hybrid (23 Mg ha−1) or assisted restoration treatments (50 Mg ha−1), while assisted restoration treatments held more average total C in soil and litter (58 Mg ha−1) than hybrid (35 Mg ha−1) and process-based restoration treatments (37 Mg ha−1). Regardless of treatment type, time was a significant factor for all C stock values. These findings support a more inclusive global carbon budget and provide valuable insight into restoration treatment actions that support C stock accumulation.

Evaluation of mangrove restoration effectiveness using remote sensing indices - a case study in Guangxi Shankou Mangrove National Natural Reserve, China

As one of the most productive marine ecosystems in the coastal wetlands, mangrove forests have been severely threatened by intensive human activities. Many countries and regions have carried out mangrove restoration projects. The evaluation of mangrove restoration effectiveness is of great significance for scientific decision-making for restoration engineering and wetland management. In this study, we presented a remote-sensing-based Mangrove Restoration Effectiveness Index (MREI) to evaluate mangrove restoration effectiveness. We took the Guangxi Shankou Mangrove National Natural Reserve (GSMNNR) in China, a UNESCO Biosphere Reserve, as our study area, where four phases of afforestation were implemented during 1990-2022. The MREI was developed based on Landsat-series images by considering the change in mangrove area and the Normalized Difference Vegetation Index (NDVI) from the start year to the end year of each afforestation phase (evaluation period). We further evaluated the Persistence of Restoration Effectiveness (PRE) based on the MREI change trajectory during the whole evaluation period, and the Process-based Restoration Effectiveness Index (PREI) was developed to evaluate the restoration effectiveness at village scale. The results showed that MREI can effectively represent the trajectory of mangrove restoration and showed consistent pattern with high-spatial-resolution imagery. From 1990 to 2022, the mangrove forest area increased from 235.26 ha in 1990 to 873.27 ha in 2022, and 84.59% of the mangrove forest was converted from tidal flats in the reserve. The average value of MREI in the five evaluation phases were 0.48, 0.24, 0.29, 0.17, and 0.72, respectively. The dynamic change of MREI showed that 5.24% of the zones had poor PRE, 44.17% of the zones had excellent PRE. From the perspective of spatial distribution, the Zones with PREI values ranging from high to low were follows: Zone A, E, J, G, C, H, I (D), F, B. Overall, the high value zones of PREI were mainly distributed in the central of the Dandou Sea and the northern part of the Yingluo Bay. The low value zones were distributed in the northwest of the Dandou Sea. We expect the MREI and PREI have great potential to be applied to other regions to evaluate mangrove restoration effectiveness.

Construction of an adaptive river-based recreational network for urban river restoration: A case study of Rencheng District, Jining City, China

Recreation-oriented urban river ecological restoration can help restore damaged ecosystems and improve human well-being. This study selects the urban river network of Rencheng District, Jining City, China as a case to map and construct a river-based recreational network (RRN) in an urban river restoration context. Morphological spatial pattern analysis, connectivity evaluation methods, and an overlay method of ArcGIS are applied to identify river network connectivity and ecological sources, which are used to map RRN. The research findings show that except rivers in the Liangshan-Jining Canal, other rivers have medium, poor, or extremely poor ecological connectivity. The ecological sources are mainly distributed in the vicinity of Nanyang lake and Taibai lake. The distribution of river connectivity is largely correlated with the regional physical geography pattern (e.g., geological structure and topological position of water patches), as well as historical human activities (e.g., canalization). Furthermore, the continuous subsidence of coal mining subsidence areas, urban expansion and rural construction, environmental damage and pollution, natural changes (e.g., climate change) are the risk sources of river network connectivity. To restore the ecological and social connectivity of urban river network, an adaptive RRN is proposed according to the current environmental status and the factors affecting the river connectivity. Specifically, form-based and process-based restoration measures can be adopted in urban built-up areas and rural areas, respectively. The findings provide a holistic solution for the restoration and recreational use of urban river network at a regional scale, thereby promoting the coordination of urban ecosystems and sociocultural systems.

Rehabilitating Valley Floors to a Stage 0 Condition: A Synthesis of Opening Outcomes

Degraded floodplains and valley floors are restored with the goal of enhancing habitat for native fish and aquatic-riparian biota and the protection or improvement of water quality. Recent years have seen a shift toward “process-based restoration” that is intended to reestablish compromised ecogeomorphic processes resulting from site- or watershed-scale degradation. One form of process-based restoration has developed in the Pacific Northwest, United States, that is intended to reconnect rivers to their floodplains by slowing down flows of sediment, water, and nutrients to encourage lateral and vertical connectivity at base flows, facilitating development of dynamic, self-forming, and self-sustaining river-wetland corridors. Synergies between applied practices and the theoretical work of Cluer and Thorne in 2014 have led this form of restoration to be referred to regionally as restoration to a Stage 0 condition. This approach to rehabilitation is valley scale, rendering traditional monitoring strategies that target single-thread channels inadequate to capture pre- and post-project site conditions, thus motivating the development of novel monitoring approaches. We present a specific definition of this new type of rehabilitation that was developed in collaborative workshops with practitioners of the approach. Further, we present an initial synthesis of results from monitoring activities that provide a foundation for understanding the effects of this approach of river rehabilitation on substrate composition, depth to groundwater, water temperature, macroinvertebrate richness and abundance, secondary macroinvertebrate production, vegetation conditions, wood loading and configuration, water inundation, flow velocity, modeled juvenile salmonid habitat, and aquatic biodiversity.

Design Criteria for Process-Based Restoration of Fluvial Systems

Abstract Process-based restoration of fluvial systems removes human constraints on nature to promote ecological recovery. By freeing natural processes, a resilient ecosystem may be restored with minimal corrective intervention. However, there is a lack of meaningful design criteria to allow designers to evaluate whether a project is likely to achieve process-based restoration objectives. We describe four design criteria to evaluate a project's potential: the expansion of fluvial process space and connectivity lost because of human alterations, the use of intrinsic natural energy to do the work of restoration, the use of native materials that do not overstabilize project elements, and the explicit incorporation of time and adaptive management into project design to place sites on recovery trajectories as opposed to attempts to “restore” sites via a single intervention. Applications include stream and infrastructure design and low-carbon construction. An example is presented in California's Sierra Nevada foothills.

Invertebrate and Microbial Response to Hyporheic Restoration of an Urban Stream

All cities face complex challenges managing urban stormwater while also protecting urban water bodies. Green stormwater infrastructure and process-based restoration offer alternative strategies that prioritize watershed connectivity. We report on a new urban floodplain restoration technique being tested in the City of Seattle, USA: an engineered hyporheic zone. The hyporheic zone has long been an overlooked component in floodplain restoration. Yet this subsurface area offers enormous potential for stormwater amelioration and is a critical component of healthy streams. From 2014 to 2017, we measured hyporheic temperature, nutrients, and microbial and invertebrate communities at three paired stream reaches with and without hyporheic restoration. At two of the three pairs, water temperature was significantly lower at the restored reach, while dissolved organic carbon and microbial metabolism were higher. Hyporheic invertebrate density and taxa richness were significantly higher across all three restored reaches. These are some of the first quantified responses of hyporheic biological communities to restoration. Our results complement earlier reports of enhanced hydrologic and chemical functioning of the engineered hyporheic zone. Together, this research demonstrates that incorporation of hyporheic design elements in floodplain restoration can enhance temperature moderation, habitat diversity, contaminant filtration, and the biological health of urban streams.

Great Expectations: Deconstructing the Process Pathways Underlying Beaver-Related Restoration

ABSTRACTBeaver-related restoration is a process-based strategy that seeks to address wide-ranging ecological objectives by reestablishing dam building in degraded stream systems. Although the beaver-related restoration has broad appeal, especially in water-limited systems, its effectiveness is not yet well documented. In this article, we present a process-expectation framework that links beaver-related restoration tactics to commonly expected outcomes by identifying the set of process pathways that must occur to achieve those expected outcomes. We explore the contingency implicit within this framework using social and biophysical data from project and research sites. This analysis reveals that outcomes are often predicated on complex process pathways over which humans have limited control. Consequently, expectations often shift through the course of projects, suggesting that a more useful paradigm for evaluating process-based restoration would be to identify relevant processes and to rigorously document how projects do or do not proceed along expected process pathways using both quantitative and qualitative data.

Restoring Dynamic Fluvial Processes in Urban Rivers: Learning from the Aire and Isar Rivers

In process-based restoration, the objective is not to create a complex river form directly; instead, interventions are intended to “prompt” the natural processes to restore such forms. The improvements in ecological conditions are actually made over time by flowing water during floods (using the stream’s energy), and by the growth of riparian vegetation (using incoming solar energy). On the Aire River in Geneva, ecological function was restored to a formerly canalized river by providing the river with an <i>espace de liberté</i>. A grid of channels cut into the valley bottom allowed the river to freely flood, erode its bed and banks, and deposit bars, creating complex surfaces on which riparian vegetation established to support the food web of the riverine ecosystem. The diamond-shaped bits of land left between these channels (“lozenges”) gradually erode and evolve as the river migrates, creating complex channel forms. The Isar River in Munich restoration involved adding coarse sediment load, creating erodible bed and banks in place of formerly rigid boundaries, expanding process space for river migration, erosion, and deposition, and increased human access to the river over 8 km. Since restoration, natural transport of sediment has resulted in deposition of gravel bars, whose forms evolve during floods, supporting diverse habitats. The Isar and Aire Rivers provide compelling examples of processbased restoration meeting 4 criteria for process-based restoration: space, energy, materials, and time. They demonstrate the possibilities of urban river restoration to achieve both ecological and social goals through restoration of fluvial process.

Ecosystem restoration is risky … but we can change that

The forthcoming UN Decade of Ecosystem Restoration brings the challenge of massively increasing restoration efforts to halt and reverse environmental degradation. This challenge must move beyond a focus on the size and number of projects to a focus on how those projects are designed and implemented. Approaches based on restoring the fundamental ecological processes that lead to self-sustaining ecosystems are essential.

Short-Term Stream and Riparian Responses to Beaver Dam Analogs on a Low-Gradient Channel Lacking Woody Riparian Vegetation

As ecosystem engineers, beavers (Castor canadensis) influence biogeomorphology and riparian vegetation. Streams with historic beaver removal and grazing often become incised, thereby altering stream and riparian processes. Anthropogenic structures that mimic beaver dams called beaver dam analogs (BDAs) may reverse incision by reintroducing historic processes. To understand BDAs as a process-based restoration tool, monitoring is needed across a range of watershed and stream conditions, but monitoring lags behind implementation. We constructed five BDAs in Central Oregon, on a low-gradient stream to test whether it may transport sufficient sediment to favor streambed aggradation behind BDAs. The stream also lacks woody riparian vegetation, and we examined how water temperatures and restoration plantings respond to BDAs where woody riparian vegetation is absent. We monitored structure integrity, aggradation, water temperature, groundwater, and vegetation for 1–2 yr after structures were installed. BDAs retained flows equally whether they were constructed from on-site juniper or off-site willow. During high flows, three structures failed and were rebuilt using improved design. After one year, aggradation of sediment above the two structures that survived flooding was negligible at one structure and high (33.7 m3) at the other. Groundwater levels rose 18–30 cm up to 135 m upstream of BDAs and 12 m into the floodplain. We found no evidence that BDAs raised stream temperatures. Within six months, willow cuttings planted near BDAs exhibited 1.3 times more growth than those on unimpounded locations. Overall, BDAs promoted a restoration trajectory on a low-gradient stream lacking woody riparian vegetation.

Socio-environmental implications of process-based restoration strategies in large rivers: should we remove novel ecosystems along the Rhône (France)?

River restoration efforts require interdisciplinary approaches involving fluvial geomorphology, hydraulic engineering, ecology, sedimentology, chemistry, social geography, and sociology. We investigated the functioning of artificial structures called “Casiers Girardon” (groyne fields) in the Rhône River. We assessed potential benefits and risks linked to removing the Rhône groyne fields in a restoration context, with particular focus on the potential for increased bank erosion. Hydraulic, morphological, chemical, ecological, and social issues resulting from dismantlement were studied for terrestrialized and aquatic Casiers Girardon. Only 10% of Casiers Girardon have maintained their aquatic features, whereas most of the Casiers are terrestrialized. Our results help to confirm the effectiveness of restoration actions; however, they also indicate uncertainties and additional knowledge needs, especially in regard to potential incompatibilities between Casier restoration and conservation. Then, an interdisciplinary conceptual model was developed to identify interventions to be considered in Casiers Girardon, according to their terrestrialization rate and physiochemical characteristics (connectivity, amount of gravel vs. fine sediment, contamination level). This model synthetizes scientific results and expert judgment and provides management recommendations based on ecological and sociological expectations about the restoration of Casiers Girardon. The model highlights high heterogeneity in functioning and ecological potential between terrestrialized and aquatic Casiers. Dismantling of terrestrialized Casiers has strong potential to provide multiple benefits, whereas aquatic Casiers could be maintained as valuable backwaters. The managing guidelines for the Casiers Girardon of the Rhône River should be adapted according to local conditions, as well as expected benefits and needs, and conducted in co-ordination with all actors involved in and affected by the restoration.

Integrating Limiting-Factors Analysis with Process-Based Restoration to Improve Recovery of Endangered Salmonids in the Pacific Northwest, USA

Two approaches to ecological restoration planning, limiting-factors analysis and process-based restoration, are employed in efforts to recover endangered salmonid species throughout the Pacific Northwest of North America. Limiting-factors analysis seeks to identify physical limitations to fish production that may be addressed by habitat restoration; it is known as the “Field of Dreams” hypothesis (i.e., if you build it, they will come). Process-based restoration, in contrast, assumes that protection and/or restoration of watershed-scale processes will best achieve self-sustaining habitat features that support salmon populations. Two case studies from the Columbia River basin (northwestern USA) display current efforts to integrate these two restoration approaches to improve salmonid populations. Although these examples both identify site-specific habitat features to construct, they also recognize the importance of supporting key watershed processes to achieve restoration goals. The challenge in advancing the practice of restoration planning is not in simply acknowledging the conceptual benefits of process-based restoration while maintaining a traditional focus on enumerating site-specific conditions and identifying habitat-construction projects, but rather in following process-based guidance during recovery planning and, ultimately, through implementation of on-the-ground actions. We encourage a realignment of the restoration community to truly embrace a process-based, multi-scalar view of the riverine landscape.

Short-term Impacts of Prescribed Burning on the Spider Community (Order: Araneae) in a Small Ohio Grassland

Prescribed burning is a management tool that is widely accepted for prairie management and restoration, yet little is known how burning may impact the spider community. Although it is generally thought that prescribed burning may alter the spider community composition and structure, few studies have examined these shifts in a controlled manner with both a burned grassland and a nearby unburned companion grassland. On October 25, 2014 we conducted a prescribed burn of a grassland at the Gwynne Conservation Area, London, Ohio. Spiders were sampled using pitfall traps for four weeks pre-burn and six weeks post-burn in both the treatment grassland and adjacent unburned grassland. A total of 298 spiders were collected from sixteen families, over 60% of which were in the family Lycosidae. Overall, we found the prescribed burn did not significantly alter the abundance or diversity of spiders collected, and interestingly it appears the community composition of the unburned grassland changed more over the sample period than the burned grassland. Anecdotal observations also suggest that some spiders are capable of surviving the fire in situ. As we continue to study these communities, we will develop a better understanding of role that prescribed burning plays in regulating the structure and composition of the spider communities. Such information is important to develop process-based restoration and management practices in grassland ecosystems.

Application of science-based restoration planning to a desert river system.

Persistence of many desert river species is threatened by a suite of impacts linked to water infrastructure projects that provide human water security where water is scarce. Many desert rivers have undergone regime shifts from spatially and temporally dynamic ecosystems to more stable systems dominated by homogenous physical habitat. Restoration of desert river systems could aid in biodiversity conservation, but poses formidable challenges due to multiple threats and the infeasibility of recovery to pre-development conditions. The challenges faced in restoring desert rivers can be addressed by incorporating scientific recommendations into restoration planning efforts at multiple stages, as demonstrated here through an example restoration project. In particular, use of a watershed-scale planning process can identify data gaps and irreversible constraints, which aid in developing achievable restoration goals and objectives. Site-prioritization focuses limited the resources for restoration on areas with the greatest potential to improve populations of target organisms. Investment in research to understand causes of degradation, coupled with adoption of a guiding vision is critical for identifying feasible restoration actions that can enhance river processes. Setting monitoring as a project goal, developing hypotheses for expected outcomes, and implementing restoration as an experimental design will facilitate adaptive management and learning from project implementation. Involvement of scientists and managers during all planning stages is critical for developing process-based restoration actions and an implementation plan to maximize learning. The planning process developed here provides a roadmap for use of scientific recommendations in future efforts to recover dynamic processes in imperiled riverine ecosystems.

Historical geomorphic analysis (1932–2011) of a by-passed river reach in process-based restoration perspectives: The Old Rhine downstream of the Kembs diversion dam (France, Germany)

The Old Rhine downstream of the Kembs diversion dam is one of the largest by-passed river reaches in the world (50km). It offers a unique opportunity to study the morphological effects of by-passing and address physical and ecological restoration approaches in regulated rivers. We conduct a space-time analysis of channel adjustment over a period of 80years (1932 to 2011). We examine planform changes (from aerial photographs), erosional and depositional patterns (from vertical profiles), sediment sizes within the active channel and the new established floodplain, and we date riparian vegetation encroachment. Results show that the Old Rhine exhibited rapid response to the completion of the by-passing scheme in the 1950s, with a 26% narrowing in median active channel width between 1956 and 2008, from vegetation encroachment on dewatered channel margins (mostly groyne fields). The narrowing was accompanied by overbank fine sediment deposition (~1.5cmy−1 aggradation since 1950) as well as slight bed degradation (~0.7cmy−1 since 1950). We found no downstream propagation of active channel narrowing over time, nor propagation of bed degradation. The channel was already significantly adjusted prior to the diversion scheme, following the nineteenth century river straightening and groyne construction. By-passing (dewatering) mainly provided new pioneer habitat for synchronous vegetation establishment and promoted channel stability by decreasing sediment transport owing to peak flow reduction. The morphological budget calculated over the past 20years estimated a downstream output for coarse sediments at 16,000m3y−1, with 80% originating from bed degradation and 20% from bank erosion, without significant inputs from upstream. The present-day morphodynamics remain sensitive to changes because of dynamic bed armouring (<2.1). This retrospective analysis permits us to discuss management strategies for altered rivers. Recommended activities are gravel reintroduction with particle-sizes finer than the armoured river bed to enhance sediment transport and promote form dynamism under current flood magnitudes. This should be coupled with river widening to allow for complex depositional patterns that benefit ecological habitats. These actions should not be implemented without prior analysis of local sediment transfer processes based on in situ experiments and modelling.

Process-based Principles for Restoring River Ecosystems

Process-based restoration aims to reestablish normative rates and magnitudes of physical, chemical, and biological processes that sustain river and floodplain ecosystems. Ecosystem conditions at any site are governed by hierarchical regional, watershed, and reach-scale processes controlling hydrologic and sediment regimes; floodplain and aquatic habitat dynamics; and riparian and aquatic biota. We outline and illustrate four process-based principles that ensure river restoration will be guided toward sustainable actions: (1) restoration actions should address the root causes of degradation, (2) actions must be consistent with the physical and biological potential of the site, (3) actions should be at a scale commensurate with environmental problems, and (4) actions should have clearly articulated expected outcomes for ecosystem dynamics. Applying these principles will help avoid common pitfalls in river restoration, such as creating habitat types that are outside of a site’s natural potential, attempting to build static habitats in dynamic environments, or constructing habitat features that are ultimately overwhelmed by unconsidered system drivers.

Inside the &amp;#8220;Black Box&amp;#8221; of River Restoration: Using Catchment History to Identify Disturbance and Response Mechanisms to Set Targets for Process-Based Restoration

Mika, S., J. Hoyle, G. Kyle, T. Howell, B. Wolfenden, D. Ryder, D. Keating, A. Boulton, G. Brierley, A. P. Brooks, K. Fryirs, M. Leishman, M. Sanders, A. Arthington, R. Creese, M. Dahm, C. Miller, B. Pusey, and A. Spink. 2010. Inside the “black box” of river restoration: using catchment history to identify disturbance and response mechanisms to set targets for process-based restoration. Ecology and Society 15(4): 8. [online] URL: http://www.ecologyandsociety.org/vol15/iss4/art8/ https://doi.org/10.5751/ES-03451-150408

A Review of Stream Restoration Techniques and a Hierarchical Strategy for Prioritizing Restoration in Pacific Northwest Watersheds

Millions of dollars are spent annually on watershed restoration and stream habitat improvement in the U.S. Pacific Northwest in an effort to increase fish populations. It is generally accepted that watershed restoration should focus on restoring natural processes that create and maintain habitat rather than manipulating instream habitats. However, most process-based restoration is site-specific, that is, conducted on a short stream reach. To synthesize site-specific techniques into a process-based watershed restoration strategy, we reviewed the effectiveness of various restoration techniques at improving fish habitat and developed a hierarchical strategy for prioritizing them. The hierarchical strategy we present is based on three elements: (1) principles of watershed processes, (2) protecting existing high-quality habitats, and (3) current knowledge of the effectiveness of specific techniques. Initially, efforts should focus on protecting areas with intact processes and high-quality habitat. Following a watershed assessment, we recommend that restoration focus on reconnecting isolated high-quality fish habitats, such as instream or off-channel habitats made inaccessible by culverts or other artificial obstructions. Once the connectivity of habitats within a basin has been restored, efforts should focus on restoring hydrologic, geologic (sediment delivery and routing), and riparian processes through road decommissioning and maintenance, exclusion of livestock, and restoration of riparian areas. Instream habitat enhancement (e.g., additions of wood, boulders, or nutrients) should be employed after restoring natural processes or where short-term improvements in habitat are needed (e.g., habitat for endangered species). Finally, existing research and monitoring is inadequate for all the techniques we reviewed, and additional, comprehensive physical and biological evaluations of most watershed restoration methods are needed.

Response of bay scallops to spawner transplants:a test of recruitment limitation

Response of bay scallops to spawner transplants:a test of recruitment limitation