Sound decision making in environmental research and management requires an understanding of causal relationships between stressors and ecological responses. However, demonstrating cause–effect relationships in natural systems is challenging because of difficulties with natural variability, performing experiments, lack of replication, and the presence of confounding influences. Thus, even the best-designed study may not establish causality. We describe a method that uses evidence available in the extensive published ecological literature to assess support for cause–effect hypotheses in environmental investigations. Our method, called Eco Evidence, is a form of causal criteria analysis—a technique developed by epidemiologists in the 1960s—who faced similar difficulties in attributing causation. The Eco Evidence method is an 8-step process in which the user conducts a systematic review of the evidence for one or more cause–effect hypotheses to assess the level of support for an overall question. In contrast to causal criteria analyses in epidemiology, users of Eco Evidence use a subset of criteria most relevant to environmental investigations and weight each piece of evidence according to its study design. Stronger studies contribute more to the assessment of causality, but weaker evidence is not discarded. This feature is important because environmental evidence is often scarce. The outputs of the analysis are a guide to the strength of evidence for or against the cause–effect hypotheses. They strengthen confidence in the conclusions drawn from that evidence, but cannot ever prove causality. They also indicate situations where knowledge gaps signify insufficient evidence to reach a conclusion. The method is supported by the freely available Eco Evidence software package, which produces a standard report, maximizing the transparency and repeatability of any assessment. Environmental science has lagged behind other disciplines in systematic assessment of evidence to improve research and management. Using the Eco Evidence method, environmental scientists can better use the extensive published literature to guide evidence-based decisions and undertake transparent assessments of ecological cause and effect.

We investigated the successional development of a benthic macrofaunal community in Kalmar Dämme, a man-made wetland in southeastern Sweden, over a 13-y period after construction (1997–2009). We assessed primary succession by monitoring changes in species composition, biological traits, and community structure. Predictable successional changes occurred, and the structure of the community was complex at the advanced phase. Three successional phases were observed, each with typifying species. At the advanced phase, dominant biological traits shifted to favor animals with longer life-cycle durations, aerial dispersal strategies, and certain feeding types (i.e., filter-feeders, fine sediment collectors, predators, and parasites). We selected the Coleoptera assemblage to represent the macroinvertebrate community in an evaluation of the extent to which man-made wetlands in different age classes (<3 y and ≥10 y) were similar to natural wetlands (>50 y). No significant differences in Coleoptera assemblages were found between natural wetlands and man-made wetlands ≥10 y. However, man-made wetlands ≥10 y had significantly higher coleopteran species richness than natural and man-made wetlands <3 y because of the convergence of pioneering species persisting from early successional stages with representative specialized taxa from natural wetlands. Our results suggest that 10 y may be sufficient time for the macrofaunal communities of man-made wetlands to resemble those of natural wetlands.

Habitat stability is an important driver of ecological community composition and development. River epilithic biofilms are particularly unstable habitats for the establishment of benthic communities because they are regularly disturbed by floods. Our aim was to determine the influence of habitat instability on meiobenthic organisms. We hypothesized that hydrologic variables are the most important predictors of meiofauna distribution. We monitored epilithic communities (meiofauna and microalgae) with a high sampling frequency during 2 sampling periods with contrasting hydrodynamic patterns in a temperate river (the Garonne, France). Nematodes and rotifers dominated meiofaunal assemblages. The critical flow velocity threshold for their maintenance in the biofilm was ∼30 cm/s, a result suggesting that meiofauna can resist higher flow velocity within the biofilm than within sediments. Nematode distribution was primarily influenced by the duration of undisturbed periods, whereas rotifer distribution was also correlated with the thickness of the biofilm. During the periods after floods, rotifers were faster colonizers than nematodes. Collectively, our results show that flow regime was an essential driver for biofilm community development.

Multiple drivers of global environmental change are fundamentally altering essential basal resources, such as detritus. Metabolic processes in most aquatic ecosystems are supported by terrestrial detritus, which contributes to the production of organisms and the energetic stability of ecosystems. We suggest that conservation and management approaches to ecosystems along river networks must incorporate the organic-matter resources that support them. Understanding changes in the dynamics of detrital organic matter is particularly important because the quantity of this resource is decreasing and its qualities are being altered as a result of effects of current global changes. We summarize these effects in lotic ecosystems from reach- to network-scales and suggest future research questions aimed at adding quantitative rigor to our understanding of the interactions between dynamics of organic matter and ecological outcomes. This approach is a necessary next step to address large-scale changes in stream and river ecosystems that derive from fundamental alterations in detrital resources, which propagate through the foodweb base to higher-order consumers and emergent ecosystem properties.

Invertebrate energy density (ED) values are traditionally measured using bomb calorimetry. However, many researchers rely on a few published literature sources to obtain ED values because of time and sampling constraints on measuring ED with bomb calorimetry. Literature values often do not account for spatial or temporal variability associated with invertebrate ED. Thus, these values can be unreliable for use in models and other ecological applications. We evaluated the generality of the relationship between invertebrate ED and proportion of dry-to-wet mass (pDM). We then developed and tested a regression model to predict ED from pDM based on a taxonomically, spatially, and temporally diverse sample of invertebrates representing 28 orders in aquatic (freshwater, estuarine, and marine) and terrestrial (temperate and arid) habitats from 4 continents and 2 oceans. Samples included invertebrates collected in all seasons over the last 19 y. Evaluation of these data revealed a significant relationship between ED and pDM (r²  =  0.96, p < 0.0001), where ED (as J/g wet mass) was estimated from pDM as ED  =  22,960pDM − 174.2. Model evaluation showed that nearly all (98.8%) of the variability between observed and predicted values for invertebrate ED could be attributed to residual error in the model. Regression of observed on predicted values revealed that the 97.5% joint confidence region included the intercept of 0 (−103.0 ± 707.9) and slope of 1 (1.01 ± 0.12). Use of this model requires that only dry and wet mass measurements be obtained, resulting in significant time, sample size, and cost savings compared to traditional bomb calorimetry approaches. This model should prove useful for a wide range of ecological studies because it is unaffected by taxonomic, seasonal, or spatial variability.

We evaluated macroinvertebrate-based metrics from Hester–Dendy samplers (HDs) that were either new or previously deployed (HS status) and were processed with either picking or scraping methods. The metrics assessed included the total number of individuals, the number of intolerant individuals, the total number of families, and the number of Ephemeroptera, Plecoptera, Trichoptera (EPT) individuals. No significant differences in mean number of individuals, intolerant individuals, and total families were detected between processing techniques or HD status (all p > 0.05). Mean number of EPT individuals did not differ between processing methods (p > 0.05), but previously deployed HDs yielded significantly more EPT individuals than new HDs (p  =  0.001). The EPT data are of particular interest because these organisms are important components of indices of biotic integrity and are used to assess water-quality status. Previously deployed and new HDs should not be used in the same study because colonization by EPT organisms differs between them.

Understanding species' temperature tolerances in the context of concurrent environmental stressors is critical because thermal regimes of freshwater ecosystems are changing. We evaluated the critical thermal maximum (CTM) of 3 freshwater mussel species (Alasmidonta varicosa, Elliptio complanata, and Strophitus undulatus) acclimated to 2 temperatures (15 and 25°C) and exposed to 2 aeration treatments (aerated vs unaerated) during CTM testing. Responses varied by species, but mussels acclimated to 25°C generally had a higher CTM than mussels acclimated to 15°C. For E. complanata, the effects of acclimation temperature and aeration were interactive, such that CTM was highest at 15°C but only under aerated conditions. Our results indicate that recent thermal history affects thermal tolerance, combinations of environmental stressors may influence thermal tolerance, and such responses vary among species.

Midge larvae (Pseudochironomus richardsoni Malloch) in the South Fork Eel River, California, weave retreats in mats of Cladophora glomerata (L.) Kütz. and graze on its algal epiphytes. Densities of these midges and their effects on Cladophora vary over time (seasonally, over the course of succession, and interannually) and space (down the drainage network). New Cladophora growth is green, turns yellow with early colonization by a monolayer of Cocconeis, and rusty-red as it becomes heavily epiphytized by a multistory layer of Epithemia spp. (Rhopalodiaceae), diatoms that contain N-fixing endosymbiotic cyanobacteria. To determine how midges influence epiphyte assemblage structure, we incubated Cladophora in early (green [G]), mid (yellow [Y]), and late (rusty-red [R]) stages of succession with and without midges and assessed changes in epiphyte density and composition. Midge effects on epiphyte composition and density (as measured by % cover on Cladophora filaments) varied with stage of succession and proximity to the ends of midge retreats. Local increases in retreat-associated cyanobacteria occurred in Y and R stages. Percent cover of Cocconeis increased on Y filaments >2 cm from midge retreats (ambient) indicating indirect midge effects (e.g., fertilization). Midges were less effective grazers on adnate Cocconeis cells than on loosely attached Epithemia and often ingested Cladophora in the process of grazing or retreat building, especially in G and Y stages. In contrast, midges that grazed on R Cladophora primarily consumed diatoms in the Rhopalodiaceae. Midge survival and retreat quality were lower in G than in Y or R stages, where retreats were longer and denser. Shifts in epiphyte composition and % cover caused by midge–algae interactions at small scales (µm–m) could affect ecologically significant processes, such as N-fixation and foodweb interactions at larger reach and watershed scales.

Streams affected by acid mine drainage (AMD) are highly stressed ecosystems and occur worldwide. These streams typically have low pH, high concentrations of dissolved metals, and substrata coated with metal hydroxide precipitates. This combination of chemical and physical stressors creates a challenging environment for aquatic biota. We provide a synthesis of the effects of AMD on stream food webs to provide a holistic perspective of these highly stressed ecosystems. First, we reviewed the effects of AMD on the structure and function of algal, microbial, invertebrate, and fish communities. Then, we used this published information to propose generalized food webs and identify areas for future research. In general, AMD-affected streams have depauperate communities that are dominated by a few tolerant species, and ecosystem processes (e.g., decomposition) are often impaired. Biota respond differently to the individual stressors (e.g., pH compared to precipitates), which may complicate remediation efforts that focus primarily on neutralizing acidity and removing metals from mine discharges. Food webs in these streams are substantially altered because basal resources are less productive or inaccessible, microbial processing of organic matter is slow, many grazers and shredders are absent, and fish are replaced by invertebrates as top predators. Structurally, declines in species diversity and the loss of fish shorten and simplify food webs by decreasing the number of interactions among species. Functionally, most energy pathways are weakened by disrupted trophic links, and this problem should to be a key target of restoration efforts. We think research that focuses on species interactions in a foodweb context is needed to provide a better understanding of community organization and functioning in these highly stressed ecosystems.

We used dual-isotope mixing models (δ¹³C/δ¹⁵N and δ²H/δ¹⁵N) in a Bayesian framework to partition allochthonous and autochthonous energy sources for salmonids in 2 headwater streams in the Kenai Lowlands, Alaska (USA). Our 1^st objective was to estimate the production base for juvenile coho salmon (Oncorhynchus kisutch) and Dolly Varden (Salvelinus malma). We hypothesized that consumers would be reliant on both autochthonous (filamentous algae and periphyton) and allochthonous sources, but that autochthonous sources would dominate because of the open canopy and lower-quality litter inputs provided by the riparian wetland vegetation, primarily bluejoint grass (Calamagrostis canadensis). Our 2^nd objective was to evaluate the utility of stable H isotopes for tracing energy pathways in a northern-latitude ecosystem. We hypothesized that δ²H-based models would provide more precise estimates of source partitioning than δ¹³C-based models because of greater source separation. Allochthonous source contributions consistently exceeded autochthonous sources for all fish species and size classes at both study sites. However, diet shifted during ontogeny, and larger Dolly Varden relied more on autochthonous sources than did smaller individuals of both species. Last, we found good correspondence and similar levels of precision between the δ¹³C- and δ²H-based models despite greater source separation by δ²H. Our results highlight the importance of allochthonous sources in headwater streams, and we suggest that litter inputs from grasses may be an under-appreciated subsidy to salmon production. Stable H isotopes can be an effective foodweb tracer in northern-latitude streams, but source partitioning results were not sufficiently different from stable C isotope models for us to recommend unequivocally using them to replace or enhance δ¹³C in similar studies.

According to theory, the rate and stoichiometry of microbial mineralization depend, in part, on nutrient availability. For microbes associated with leaves in streams, nutrients are available from both the water column and the leaf. Therefore, microbial nutrient cycling may change with nutrient availability and during leaf decomposition. We explored spatial and temporal patterns of mineralization by heterotrophic microbes by placing packs of red maple leaves at sites in 5 Appalachian streams spanning a range of N and P availability. We collected packs 4 times from each site. Leaf disks from these packs were incubated in microcosms, and uptake rates and steady-state concentrations of NH₄ and soluble reactive P (SRP) were used to calculate mineralization rates. N uptake peaked between 50 and 60 d, whereas P uptake peaked ∼10 d later. Clear patterns were found for fungal biomass-specific uptake or mineralization fluxes of either nutrient over time or space, but the microbes grown in the site with the lowest nutrient availability had the highest fungal biomass-specific cycling. The ability of microbes to access nutrients from their substrate may prevent dissolved nutrient availability from being a strong driver of microbial nutrient cycling.

Development of radio frequency identification (RFID) technology and passive integrated transponder (PIT) tags has substantially increased the ability of researchers and managers to monitor populations of aquatic organisms. However, use of transportable RFID antenna systems (i.e., backpack-mounted) is currently limited to wadeable aquatic environments (<1.4 m water depth). We describe the design, construction, and evaluation of a boat-mounted RFID antenna to detect individually PIT-tagged benthic aquatic organisms (mussels). We evaluated the effects of tag orientation on detection distances in water with a 32-mm half-duplex PIT tag. Detection distances up to 50 cm from the antenna coils were obtained, but detection distance was dependent on tag orientation. We also evaluated detection distance of PIT tags beneath the sediment to simulate detection of burrowing mussels with 23- and 32-mm tags. In sand substrate, the maximum detection distance varied from 3.5 cm and 4.5 cm (vertical tag orientation) to 24.7 cm and 39.4 cm (45° tag orientation) for the 23- and 32-mm PIT tags, respectively. Our results suggest a 1.4-m total detection width for tagged mussels on the substrate surface by the boat-mounted antenna system regardless of tag orientation. However, burrowed mussels may require multiple passes to increase detection that would be influenced by depth, tag orientation, and tag size. Construction of the boat-mounted antenna was relatively low in cost (<500 USD) and had several advantages (less labor and time intensive, increased safety) over traditional mussel sampling techniques (diving, snorkeling) in nonwadeable habitats.

Many physicochemical factors potentially impair stream ecosystems in urbanizing basins, but few studies have evaluated their relative importance simultaneously, especially in different environmental settings. We used data collected in 25 to 30 streams along a gradient of urbanization in each of 6 metropolitan areas (MAs) to evaluate the relative importance of 11 physicochemical factors on the condition of algal, macroinvertebrate, and fish assemblages. For each assemblage, biological condition was quantified using 2 separate metrics, nonmetric multidimensional scaling ordination site scores and the ratio of observed/expected taxa, both derived in previous studies. Separate linear regression models with 1 or 2 factors as predictors were developed for each MA and assemblage metric. Model parsimony was evaluated based on Akaike's Information Criterion for small sample size (AICc) and Akaike weights, and variable importance was estimated by summing the Akaike weights across models containing each stressor variable. Few of the factors were strongly correlated (Pearson |r| > 0.7) within MAs. Physicochemical factors explained 17 to 81% of variance in biological condition. Most (92 of 118) of the most plausible models contained 2 predictors, and generally more variance could be explained by the additive effects of 2 factors than by any single factor alone. None of the factors evaluated was universally important for all MAs or biological assemblages. The relative importance of factors varied for different measures of biological condition, biological assemblages, and MA. Our results suggest that the suite of physicochemical factors affecting urban stream ecosystems varies across broad geographic areas, along gradients of urban intensity, and among basins within single MAs.

Genus-specific and total secondary production of a nonbiting midge assemblage (Chironomidae) were estimated along a hyporheic gradient (surface to 40–50-cm depth) in 2 contrasting stream types and 3 habitat types in north-central Alabama to assess the extent of the variation within a river basin. Total production (surface hyporheic) was much higher in a gravel–cobble habitat (68 g m⁻² y⁻¹) of a Valley and Ridge stream than in either the sandy habitat (8 g m⁻² y⁻¹) or mud–silt habitat (12 g m⁻² y⁻¹) of a Coastal Plain stream. A strong seasonal pattern of high production in spring was apparent in the Valley and Ridge stream and differed from the more uniform seasonal production of the Coastal Plain stream. In the Valley and Ridge stream, 37% of production (25 g m⁻² y⁻¹) occurred in the hyporheic zone (below 10-cm depth). In the sandy habitat of the Coastal Plain stream, 42% of production (3.2 g m⁻² y⁻¹) occurred at depths below 10 cm. In both streams, the dominant hyporheic taxa were generally the same as the dominant taxa in the surface (0–10 cm) zone. In contrast, only ∼5% of total chironomid secondary production was found below 10-cm depth in the mud–silt habitat of the Coastal Plain stream (0.6 g m⁻² y⁻¹). These data suggest that the contribution of chironomids to stream ecological processes can be substantially underestimated without considering the hyporheic distributions of their production in certain habitats. Production may be a direct reflection of other functional variables, such as respiration, nutrient turnover, and decomposition. Furthermore, these deeper sediments may serve as an important refuge from natural or human disturbance at the benthic surface.

Stream indicators used to make assessments of biological condition are influenced by many possible sources of variability. To examine this issue, we used multiple-year and multiple-reach diatom, fish, and invertebrate data collected from 20 least-disturbed and 46 developed stream segments between 1993 and 2004 as part of the US Geological Survey National Water Quality Assessment Program. We used a variance-component model to summarize the relative and absolute magnitude of 4 variance components (among-site, among-year, site × year interaction, and residual) in indicator values (observed/expected ratio [O/E] and regional multimetric indices [MMI]) among assemblages and between basin types (least-disturbed and developed). We used multiple-reach samples to evaluate discordance in site assessments of biological condition caused by sampling variability. Overall, patterns in variance partitioning were similar among assemblages and basin types with one exception. Among-site variance dominated the relative contribution to the total variance (64–80% of total variance), residual variance (sampling variance) accounted for more variability (8–26%) than interaction variance (5–12%), and among-year variance was always negligible (0–0.2%). The exception to this general pattern was for invertebrates at least-disturbed sites where variability in O/E indicators was partitioned between among-site and residual (sampling) variance (among-site  =  36%, residual  =  64%). This pattern was not observed for fish and diatom indicators (O/E and regional MMI). We suspect that unexplained sampling variability is what largely remained after the invertebrate indicators (O/E predictive models) had accounted for environmental differences among least-disturbed sites. The influence of sampling variability on discordance of within-site assessments was assemblage or basin-type specific. Discordance among assessments was nearly 2× greater in developed basins (29–31%) than in least-disturbed sites (15–16%) for invertebrates and diatoms, whereas discordance among assessments based on fish did not differ between basin types (least-disturbed  =  16%, developed  =  17%). Assessments made using invertebrate and diatom indicators from a single reach disagreed with other samples collected within the same stream segment nearly ⅓ of the time in developed basins, compared to ⅙ for all other cases.

Species in complex ecosystems, such as streams, are influenced by multiple top-down and bottom-up control factors. Food-resource and competition/predation mechanisms are among the most influential factors controlling population ecology. Balancing the effects of bottom-up control by food resources and top-down control by competition/predation can trigger compensatory responses leading to changes in species ecology within the limit of their plasticity. These effects have been well studied in simple controlled conditions, but predicting their outcome is difficult for natural populations in genuine ecosystems because of the heterogeneity of environmental conditions and the complexity of biotic interactions. We investigated the ecological response in terms of feeding habits and population parameters of the stream-dwelling predator, Siphonoperla torrentium, to modifications of its prey abundance and of competition/predation mechanisms induced by a gradient of acidification. We conducted a 1-y survey in a set of 3 streams showing very similar abiotic conditions except for their acidification status. Despite significantly lower potential prey availability and higher potential intraspecific competition in the most acidic stream compared to neutral streams, the proportion of prey in the diet of S. torrentium did not differ across streams. However, S. torrentium was less aggregated, and had higher secondary production, longer larval development, and smaller adult size in the most acidic stream than in the less acidic streams, results suggesting compensatory mechanisms. Our study design did not permit us to differentiate the importance of the biotic factors involved, but the study contributes to our understanding of the importance of conjugated biotic effects on population ecology.

Limestone-based (karstic) freshwater wetlands of the Everglades, Belize, Mexico, and Jamaica are distinctive in having a high biomass of CaCO₃-rich periphyton mats. Diatoms are common components of these mats and show predictable responses to environmental variation, making them good candidates for assessing nutrient enrichment in these naturally ultraoligotrophic wetlands. However, aside from in the Everglades of southern Florida, very little research has been done to document the diatoms and their environmental preferences in karstic Caribbean wetlands, which are increasingly threatened by eutrophication. We identified diatoms in periphyton mats collected during wet and dry periods from the Everglades and similar freshwater karstic wetlands in Belize, Mexico, and Jamaica. We compared diatom assemblage composition and diversity among locations and periods, and the effect of the limiting nutrient, P, on species composition among locations. We used periphyton-mat total P (TP) as a metric of availability. A total of 176 diatom species in 45 genera were recorded from the 4 locations. Twenty-three of these species, including 9 that are considered indicative of Everglades diatom flora, were found in all 4 locations. In Everglades and Caribbean sites, we identified assemblages and indicator species associated with low and high periphyton-mat TP and calculated TP optima and tolerances for each indicator species. TP optima and tolerances of indicator species differed between the Everglades and the Caribbean, but weighted averaging models predicted periphyton-mat TP concentrations from diatom assemblages at Everglades (R²  =  0.56) and Caribbean (R²  =  0.85) locations. These results show that diatoms can be effective indicators of water quality in karstic wetlands of the Caribbean, but application of regionally generated transfer functions to distant sites provides less reliable estimates than locally developed functions.

Emulation of natural disturbance (END) is an emerging paradigm for modern, ecosystem-based forest management in North America. On the premise that periodic disturbance is an integral part of natural, determinative processes on forest landscapes, managing forests by emulating natural disturbance is thought to produce landscape patterns that resemble those arising from natural disturbances and that are known to maintain critical processes and habitat for conserving biodiversity. Applying END principles to forest watersheds has implications for the protection of aquatic ecosystems because END can include intentional logging disturbance near water to emulate natural riparian disturbance. Literature shows that logging in watersheds, and especially in riparian areas, can lead to negative abiotic and biotic effects in aquatic ecosystems. However, an integration of the current understanding of land–water linkages in forest watersheds with general disturbance ecology would suggest that periodic watershed and riparian disturbances may be natural renewal processes that are required for long-term sustainability of aquatic ecosystems. Previous syntheses of END in forestry failed to consider the implications for aquatic ecosystems, and most forest-management guidelines default to the protection of water resources by systematic riparian (shoreline) buffers. This paper introduces the concepts of END and provides a theoretical basis for using intentional riparian forest disturbance to sustain aquatic habitat complexity and ecosystem integrity.

Riparian buffers provide improved protection for water quality and biota, and narrow, fixed-width buffers of native vegetation along streams have been used to mitigate the effects of forest harvest at least since the 1960s. The practice of leaving unmanaged strips of vegetation along water courses in agricultural lands had been used before the 1960s in southern Europe and in eastern North America, but the scientific basis for leaving riparian buffers on forested lands came from observations in the coastal temperate rainforests of western North America. Those observations often were applied to other forested landscapes without further considerations. Fixed-width buffers are administratively simple to implement and assess, and have come to be the norm for streamside protection from forestry. Most guidelines for streamside protection allow some local modification for site and watershed-scale considerations, but frequently, the option to deviate from fixed-width buffers is not exercised because of uncertainty about outcomes. Few experiments have been done to test the efficacy of buffers of a particular width or of site- or landscape-specific modifications.

Forest disturbance agents, such as wildfire and windthrow, often differ in magnitude and frequency between upland and riparian zones. Riparian forests may be subject to additional disturbance agents that do not affect uplands, including debris flows, floods, bank erosion, and avulsions. Forest harvesting, with or without a streamside buffer, is an additional riparian disturbance agent in managed landscapes. The effects of riparian harvesting on stream habitat and ecology are qualitatively similar to those of wildfire, with the important exception of recruitment of large in-stream wood. For most other disturbance agents, current knowledge is insufficient to assess the degree to which natural disturbance can be emulated via riparian forest harvesting. In particular, the effects of the spatial patterns and frequencies of disturbance on the trajectories and rates of postdisturbance recovery are poorly understood for many landscapes and are complicated by the potential for propagation of effects down the stream network. Broadly based, long-term research on riparian disturbance regimes is needed to provide the scientific basis required for designing strategies for sustainable streamside forest management.

The Crown Forest Sustainability Act stipulates that Ontario's public forests be managed to conserve biological diversity and long-term health by following an emulation of natural disturbance (END) paradigm. Upland forests have been managed following an evolving END approach since the mid-1990s, but operations have been largely excluded from riparian forests. The new Forest Management Guide for Conserving Biodiversity at the Stand and Site Scales attempted to integrate the protection of fish habitat and water quality with the desire to emulate natural disturbance patterns in riparian forests to create a diversity of habitats to support a broad range of riparian plants and animals. Where wildfire is the dominant agent of disturbance, it encourages thoughtfully planned and carefully implemented clearcutting within riparian forest. We provide some examples of how science-based knowledge was used to develop direction to achieve these objectives.

Designing management strategies based on the emulation of natural disturbance (END) to promote long-term sustainability of riparian forests and their adjacent aquatic ecosystems is an evolving process. Conceptually, the goal of END in riparian forest management is to mimic, to the extent possible, natural disturbance processes within the range of natural variability of the ecosystem while accounting for both temporal (frequency) and spatial (size) scales of the disturbance. The application of END in riparian forests has been evaluated in a limited but growing number of studies. From these studies, the idea has emerged that END could be used as a tool to enhance forest complexity and resilience capacity through carefully implemented management strategies. In practice, however, this tool presents a formidable challenge, constrained by scientific and social uncertainty. In this BRIDGES cluster we have critically examined: 1) the historical, scientific, and practical foundations of applying END in riparian forest management as an alternative to fixed-width buffers, and 2) the extent to which mimicking natural disturbance and renewal processes can protect aquatic ecosystems through conservation of riparian and aquatic biodiversity. In this synthesis paper, we identify some of the outstanding questions and uncertainties that constrain the integration of END into riparian forest management, provide some initial guiding principles for applying END in riparian areas, and offer recommendations for future research.