Large Wood Loads Research Articles

Large wood loads in channels and on floodplains after a 500-year flood using UAV imagery in Mark Twain National Forest, Ozark Highlands, Missouri

Anthropogenic climate change has increased the frequency of large floods in rivers draining the Ozark Highlands. This study assesses the effects of a > 500-yr flood in spring 2017 on riparian forests and large wood loads in the North Fork of the White River watershed, Missouri, for six stream reaches with drainage areas from 5 to 124 km2. Standing trees and large wood (LW) were assessed using unmanned aerial vehicle (UAV) imagery and calibrated by field surveys. Scaled flood magnitude (flood stage/bankfull depth) correlated with percent urban and agricultural land above each reach suggesting that land use may have contributed to forest damage. Canopy loss on the valley floor ranged from 7 to 63 % by reach and correlated with mean and cross-sectional stream power (p < 0.01). Standing tree density after the flood ranged from 50 to 243 trees/ha. The density of LW pieces ranged from 25 to 147 trees/ha. Most LW was aligned with stream flow, not in jams, and located on floodplains below riffles or bar heads, along channel bends, or in chutes. Wood loads on the valley floor increased downstream from 12 to 45 m3/ha. Channel loads were < 30 m3/ha while floodplain, terrace, and chute loads were > 30 m3/ha at drainage areas >50 km2. Channel LW loads increased with flood magnitude and in narrow valleys (p < 0.02), but not drainage area. Increased wood storage occurred on floodplains and terraces, but it is not clear if the stored wood will be available for downstream transport by future floods.

Large wood loads in an urban stream: The role of recruitment limitation versus transport dominance

AbstractLarge wood (LW) has important physical and ecological functions in streams. Riparian vegetation is extensively removed during urban expansion, and urban streams may experience enhanced fluvial transport of LW due to flashy hydrology. In this study, LW loads were assessed for three reaches on North Buffalo Creek, an urban stream located in Greensboro, North Carolina, United States. These three reaches have similar hydrology but different riparian vegetation densities. We measured the frequencies and sizes of both in‐channel LW and riparian vegetation across the three reaches. Our results showed that the recently reforested reach had greater LW volume (22.5 m3/km) compared to the unmanaged forested site (16 m3/km) and the site with low riparian vegetation density (4.78 m3/km). The difference in LW frequency among reaches was statistically significant (). However, the difference in the volume of individual pieces was not significantly different across reaches (, indicating that a similar size of wood is recruited across the three sites. Our findings also showed that there is a positive relationship between riparian vegetation frequency and in‐channel LW frequency, which are significantly related as a power function. Spatial lag models (integrating upstream riparian trees) did not show better results compared to a non‐lagged model, suggesting that storage and recruitment were predominantly local and that the LW distribution at our reaches is limited by recruitment rather than dominated by fluvial transport. Our findings suggested that a fully forested watershed is not needed to provide some of the benefits of wood to urban streams.

Large wood dynamics in a mountain river disturbed by a volcanic eruption

Volcanic eruptions can dramatically alter river basins and channel networks by delivering huge amounts of sediments into the channels and affecting the surrounding vegetated area. These disturbances modify the process chain of large wood (LW) recruitment, storage, and transport. We investigated the effects of the 2015 Calbuco volcanic eruption in southern Chile on the dynamics of LW along two reaches of the Blanco Este River, which drains the north-eastern flanks of the volcano. The two reaches, R1 and R2, were surveyed for almost four years, combining field and remote analyses to better comprehend LW dynamics. We framed our study around three research questions: i) what are the processes explaining the spatial and temporal variations of LW load into the active channel of the Blanco Este River? ii) can the longitudinal (dis)connectivity be considered a controlling factor rather than flood magnitude? iii) is it possible to infer a relationship between recruitment sources, and flood events, with LW load fluctuations? The abundance of individual LW pieces and wood jams (WJs) were always higher in the downstream reach (R2). LW source areas to R1 were limited to forested bank erosions, while in R2 LW was recruited from bank erosions with the addition of wood pieces entering in the main channel from a lateral affluent and from eroded old lahar deposits that re-connected this source to the active channel. WJs were highly unstable and there were not statistically significant relationships between LW fluctuations and water discharge. In the Blanco Este River, LW delivery and export can be classified as event-driven processes, but alternating periods with longitudinal (dis)connectivity led to events delivering wood into the channel which seemed to occur asynchronously with those exporting LW. Finally, LW load in R1 appeared to be in equilibrium, but this condition might change in the future since the area of upper forested streambanks is rapidly declining.

Large wood mobilization and morphological changes in an alpine river following the release of an ordinary experimental flood from an upstream dam

The work documents morphological changes and large wood (LW) mobilization in a river-reach located downstream of a dam along the Spöl River (Switzerland), following an 8 h experimental release of 1.2-year flood. The aim of the flood was to mimic a natural event able to wash out either or both the sediment and LW. Two field campaigns (before and after the event) were made to generate DEMs and to collect data concerning the river morphology and LW characteristics. The formers were used to produce a Dem Of Difference (DoD) while the latter to identify the LW load fluctuations. Statistical analyses were implemented taking advantage of a 2D flowing model software (HEC-RAS 5.0.7) in order to compute the dimensionless diameter (D* = Flow depth (m)/ LW diameter (m)) and to detect, along with analysis of resident and mobile groups of wood, a mobility threshold (D* = 2.77) by means of a binary regression model (60 % accuracy). The threshold was used to estimate different mobility rates according to different water discharge scenarios. Overall, the event produced slight widespread morphological changes all over the channel, with a modest sediment deposition (2341 m3). Although evidence of LW fluctuations was detected, the LW input and output were almost equal (3.6 m3 ha−1 and 3.9 m3 ha−1, respectively) generating a net difference of – 0.79 m3. The median of the mobile LW was considerably lower compared to that of the resident LW. The results obtained demonstrated that the original aim of the experimental flood, to transport out wood and sediment, was not achieved because the duration and magnitude of such type of flood was limited, inducing equilibrium in the LW load and generating only slight morphological changes.

Disturbance and valley confinement: Controls on floodplain large wood and organic matter jam deposition in the Colorado Front Range, USA

AbstractOrganic matter dynamics (entrainment, transport, deposition) can influence ecogeomorphic complexity in rivers. However, the depositional controls on downed large wood (LW) and coarse particulate organic matter (CPOM) on floodplains have rarely been assessed. We investigate the influence of different disturbance histories, as well as geomorphology and forest stand density, on the deposition of LW and CPOM accumulations, or jams, between two adjacent drainages (West Creek, North Fork Big Thompson) in the semi‐arid Colorado Front Range, USA. Both basins recently experienced an extreme flood, but West Creek experienced a larger flood peak as well as a recent upstream fire. We also analyse jam fabric (LW piece orientation) between floodplain and in‐channel jam types. We measured LW and CPOM jams on the North Fork to compute jam frequencies (jams ha−1) and loads (volume per area; m3 ha−1), and we compare these data to a previously published dataset from West Creek. Average floodplain LW jam frequencies (70.4 jams ha−1) and loads (678.6 m3 ha−1) on West Creek were significantly higher than on the North Fork (frequency: 14.8 jams ha−1; load: 94.3 m3 ha−1). Average floodplain CPOM jam frequencies (West Creek: 19.0 jams ha−1; North Fork: 15.1 jams ha−1) and loads (West Creek: 10.70 m3 ha−1; North Fork: 9.98 m3 ha−1) were not significantly different between basins. A larger flood peak, likely enhanced by a recent upstream fire and a more confined valley bottom, resulted in greater deposition of LW jams on West Creek compared to the North Fork. Geomorphic characteristics, such as valley confinement and slope, also influence jam frequencies and loads. Floodplain jam types oriented parallel to the stream were significantly different than other jam types. This work will inform river restoration efforts using wood and organic matter and provide insight on the transport and depositional processes influencing floodplain LW jam formation.

Impacts of an extreme flood on large wood recruitment and transport processes

ABSTRACT This research investigates impacts of an extreme flood on recruitment and transport of large wood (LW) in sub-basins of the North Fork River, Missouri. Data collection took place two months after a >500 year flood to characterize LW conditions before natural recovery processes could obscure impacts. We used sites from previous LW studies in the region as reference to help identify flood impacts. Results showed 1) LW load volumes were no different than reference sites, but individual LW pieces comprised a greater percentage of the total load, 2) a high proportion of pieces at flood-impacted sites contained root wads, 3) transport capacity of the flood-impacted sites was high compared to reference sites, and 4) LW recruitment increased exponentially with flood magnitude. These results suggest that extreme floods have a significant impact on the composition of the LW load, and that geomorphic impacts of such floods may result in enhanced transport capacities. Based on these findings, we present two possible post-flood LW response/recovery scenarios; one in which elevated transport capacity serves to speed system recovery to the pre-flood LW regime, and one in which the enhanced LW piece composition results in a new post-flood LW regime with an enhanced load.

Wildfire and the patterns of floodplain large wood on the Merced River, Yosemite National Park, California, USA

We quantified floodplain large wood load (m3 wood/ha) and spatial distribution on the Upper Merced River in Yosemite National Park, California, USA. The upstream portion of the study area includes a recently burned section of the Merced River corridor and the downstream portion contains floodplain with undisturbed forest, facilitating investigation of the effects of wildfire on floodplain large wood. We used measurements of wood load and spatial distribution to test hypotheses regarding floodplain wood dynamics in the channel versus the floodplain and in burned versus unburned portions of the study area. The median wood load on the Merced River floodplain, as measured along numerous transects, is 259 m3/ha overall, with non-significant differences between burned (median 196 m3/ha) and unburned (median 277 m3/ha) portions of the floodplain. We found that jams can occur across the entire width of the floodplain. Burned wood pieces are present throughout the study area in the channel but are largely absent from unburned portions of the floodplain, despite the occurrence of overbank flows since the wildfire. A greater proportion of large wood is within logjams in burned portions of the floodplain. We infer that wood recruited to the channel via bank erosion moves readily downstream within the channel, whereas wood moving from the channel onto the floodplain concentrates near the margin of the main channel or within secondary channels and depressions on the floodplain, leading to the formation of long, narrow logjams.

Logjams as a driver of transient storage in a mountain stream

AbstractWe use four stream segments along a wood‐rich, pool–riffle mountain stream in the Southern Rockies of Colorado, USA to examine how spatial variations in wood load and variations in discharge during and after the snowmelt peak flow influence the magnitude of surface and subsurface transient storage. Segments range in complexity from a single channel with no large wood to an anabranching channel with closely spaced, channel‐spanning logjams. Discharges at which transient storage was assessed range from base flow to snowmelt peak flow. To explore these relations, we used 10 geomorphic variables representing channel morphology and bed substrate, four wood‐related variables representing wood load and associated backwater storage, and two measures of skewness from instream and bulk electrical conductivity breakthrough curves during tracer tests. Instream curves reflect surface and subsurface transient storage, whereas bulk curves primarily represent subsurface transient storage. Higher values of skewness indicate greater retention, and we used the values here as a metric of increased transient storage. Although limited sample size restricts the power of our results, our findings suggest that stream segments with greater instream large wood loads have more and larger pools, greater storage of fine sediment and particulate organic matter, and higher values of skew from instream conductivity. The results also suggest that the presence of instream wood, rather than changes in channel morphology associated with wood, is the most important driver of transient storage. This implies that river management designed to foster transient storage should focus on retaining instream large wood. We did not find significant correlations between geomorphic or wood‐related variables and the skew estimated from bulk conductivity, which may reflect the relatively thin alluvium present in the field area and the prevalence of surface transient storage in this system.

Large wood load fluctuations in an Andean basin

AbstractThe importance of monitoring and analysing wood fluxes in mountain environments is widely recognized. However, there is a lack of information related to the long‐term fluctuations in wood load and associated to the changes in large wood (LW) characteristics. The main aims of the research were to analyse (i) changes in wood characteristics, (ii) fluctuations in wood load, and (iii) the relationship between wood load and sub‐reach settings, proposing an ad hoc roughness index (RI). Repeated field surveys to measure wood load and LW characteristics during a 13‐year period were conducted within a 2.2 km‐long reach of the Rio Toro (Chile), which flows through the Malleco Forest National Reserve that was affected by wildfires in 2002 and 2015. Two spatial scales (i.e. study reach and sub‐reach) were considered. Irrespective of the adopted scale wood load fluctuated considerably, in both number and volume, with significant changes in LW characteristics (i.e. mean diameter and length). Moreover, a clear tendency to the aggregation in wood jams (WJs) was observed within the entire study reach. Based on our results, we conclude that 17 years after the first wildfire wood recruitment has started in the upper parts of the basin. Moreover, Generalized Linear Mixed Models (GLMM) analyses were carried out to investigate the relationship between RI and both number and volume of LW. Both models are characterized by high adjusted R2 of 74.9% and 72.8% for volume and number, respectively. This demonstrated that the RI can characterize the reaches in terms of tendency to deposition and trapping of wood. These results are promising, particularly in improving the knowledge related to potential deposition areas that can control wood load fluctuations, also permitting its management to be improved. © 2020 John Wiley &amp; Sons, Ltd.

Large wood load and transport in a flood‐free period within an inter‐dam reach: a decade of monitoring the Dyje River, Czech Republic

AbstractThis study examined the large wood (LW) load and transport during the non‐flood period (2009–2018) following major floods that occurred in 2002 and 2006 within the inter‐dam reach of the Dyje River (Czech–Austrian border). The LW load was examined in 36 river corridor segments scattered within the reach in the 2009–2018 period. Two whole‐reach surveys (2011 and 2019) on LW frequency and distribution were conducted, and the export of LW to the downstream reservoir was analysed between June 2013 and December 2018.In the period of non‐flood discharges, the recruitment and depletion of LW were highly variable processes in space and time, leading to a considerable change in the total LW quantity. Whereas the total number of LW pieces decreased, the total LW volume increased because of the increasing dimensions of newly recruited pieces. The annual variability in the quantity of newly recruited pieces was better explained by the variation in the maximum annual discharges (y = 41.043ln(x) + 3.2737, R2 = 0.5352) than by the variability in the number of days with wind gusts &gt;17.2 m/s (y = 1.5004x + 82.096, R2 = 0.118). The land use change with the abandonment of human settlements after World War II and the progressive expansion of forest was the major historical factor driving the increased recruitment of LW to the river corridor.While the 2006 (&gt;100‐year RI) flood brought approximately 1,250 LW pieces to the reservoir, the 2013 (1.5‐year RI) flood delivered 45 pieces. The long‐term average monthly input of LW to the reservoir was 7.7 pieces. The exceptional low‐magnitude flood of 2013, which occurred at the beginning of the monitoring period, was shown to be a threshold above which the number of LW pieces that floated to the dam significantly increased. © 2020 John Wiley &amp; Sons, Ltd.

Evaluating floodplain organic carbon across a gradient of human alteration in the boreal zone

River corridors play an important role in the carbon cycle as sites of carbon transport, storage, and transformation. Floodplain soil organic carbon (OC) and dead, downed large wood (LW) are two of the largest OC stocks in rivers. Human modifications of river corridors, such as damming and floodplain land-use change, have likely modified floodplain OC storage and retention through removal of LW and potential reduction of OC concentrations in soils. However, the effect of human alterations on floodplain OC storage is poorly understood. We measured floodplain soil OC and downed LW loads on three rivers in northern Sweden that display a gradient in the degree of human alteration. The Muddus River is located in a national park and is unaltered. The Vindel River is free-flowing but has been modified via logging and other land-use changes within the floodplain. The Ume River is dammed along its length and has also experienced floodplain logging and land-use change. We used statistical models to determine which factors are associated with differences in mineral soil OC and LW among rivers with different degrees of human alteration. We find the highest mineral soil OC concentrations on the unaltered Muddus River (mean ± standard error (SE) = 3.70 ± 0.59%; median = 3.81%), with lower soil OC along the Vindel (mean ± SE = 1.44 ± 0.22%; median = 0.72%) and Ume (mean ± SE = 2.47 ± 0.44%; median = 1.12%) Rivers. The Muddus River also has the highest downed LW loads (mean ± SE = 22.25 ± 6.99 m3 ha−1) compared to the Vindel (mean ± SE = 3.10 ± 1.26 m3 ha−1) and Ume (mean ± SE = 7.26 ± 3.53 m3 ha−1) Rivers. Variations in soil OC and downed large wood loads indicate that damming may reduce floodplain OC in these boreal systems through reducing lateral channel-floodplain connectivity and longitudinal connectivity. Logging and other land-use changes likely reduce OC inputs to the floodplain surface through removal of organic matter and LW. Further research is needed to elucidate the impact of human modifications on floodplain OC across diverse regions and to inform river restoration efforts to enhance floodplain OC storage.

Response of In‐Stream Wood to Riparian Timber Harvesting: Field Observations and Long‐Term Projections

AbstractIn‐stream large wood (LW) is a prominent feature of forested aquatic ecosystems worldwide, yet many questions remain regarding the response of LW patterns to riparian timber harvesting. This paper proposes a conceptual model of wood storage response to harvesting and combines a unique 45 year record of LW with output from a wood budget model to examine changes in LW characteristics and long‐term impacts from riparian logging. The wood budget model is used to predict the timing of minimum storage and assess storage recovery time scales under three scenarios representing different spatial harvest patterns and harvest severity. The impact of harvesting is reflected in the field data: Reductions in wood volume and the loss of large logjams were apparent in channel areas adjacent to logged zones, but wood volume changed less where a riparian buffer was retained. Results from the budget model indicate that impacts from timber harvesting are projected to continue beyond 150 years while riparian forests recover. Minimum modeled LW loads are projected to be nearly 50% lower than preharvest conditions, and minimums occur 50 to 80 years postharvest, depending on the influence of LW transport and proximity to harvesting. In evaluating the conceptual model, harvesting configuration and severity are not found to greatly impact time to minimum storage and recovery, but do impact the magnitude of LW losses. Similar to other studies, these findings indicate that riparian harvesting has an impact beyond the century scale, with major implications for stream channel functionality and aquatic habitat.

Drivers of variability in large wood loads along the fluvial continuum of a Mediterranean intermittent river

AbstractAlthough in‐channel and floodplain large wood (LW) has been recognized as an important component of lotic ecosystems, there is still limited knowledge on the recruitment, mobility and retention of LW in rivers with an intermittent hydrological regime. In this study, we analysed the LW characteristics and related reach‐scale variables of 22 reaches in a Mediterranean intermittent river (Evrotas, Greece) in order to identify predictors of in‐channel and floodplain LW distribution. Our results indicated high downstream variation in LW volumes in the fluvial corridor (0.05–25.51 m3/ha for in‐channel LW and 0–30.88 m3/ha for floodplain LW). In‐channel and floodplain LW retention was primarily driven by the hydrological regime of the studied reaches (i.e. perennial or non‐perennial) with higher volumes of LW observed in perennial sections. The width of the riparian corridor was an important predictor of LW storage at the reach scale. Non‐perennial reaches had a disproportionally larger number of relatively small‐diameter living trees at the expense of mature trees with larger diameters typical for riparian stands functioning as LW recruitment areas in perennial reaches. The smaller dimensions of in‐channel LW in non‐perennial reaches, coupled with the dominance of loose LW pieces, implies frequent LW transport during ordinary flood events. Nevertheless, overall low LW retention in the fluvial corridor under non‐perennial flow regime predicts low volumes of mobilized LW. In contrast, the recruitment of relatively long and large‐diameter LW from mature riparian stands in perennial reaches, together with additional LW stabilization by banks, bed sediments, living trees or other LW pieces decreases the potential for further LW transport. © 2020 John Wiley &amp; Sons, Ltd.

Modelling headwater channel response and suspended sediment yield to in-channel large wood using the Caesar-Lisflood landscape evolution model

Forest management activities have the potential to significantly modify large wood loads in riparian areas, and thus the availability of material for recruitment into the stream channel, hence it is important that forest management practices take account of the role wood supplied from riparian areas play in the development of channel structure and sediment retention capacity. In this study the cellular landscape and river reach process model CAESAR LISFLOOD (C-L) was used to simulate the effect of in-channel obstructions created by large wood on the distribution of erosion and deposition within a small headwater channel and suspended sediment yield at the catchment outlet. The process model was parameterised and calibrated against an observed discharge and suspended sediment record. Following calibration, 12 discharge and large wood obstruction scenarios were carried out to model erosion and suspended sediment transport over a timber harvesting cycle. The inclusion of obstructions into the model runs to simulate in-channel LW pieces substantially reduced suspended sediment yields in all three discharge scenarios and increased sediment storage along the channel. The modelled location of channel bed degradation and aggradation generally coincided with the pattern of sediment storage along the channel bed demonstrating that C_L was predicting the pattern of erosion and deposition in the channel reasonably well. Modelled erosion rates were extremely low for the respective discharge and large wood model scenarios, with the highest rates ranging from 0.02 t ha−1 year−1 to 0.1 t ha−1 year−1 for the no large wood model over the 22-year period. These findings reinforce the importance of maintaining sufficient volume of standing wood in buffer strips alongside small headwater channels to ensure ongoing recruitment of large wood to the channel network in forests managed for timber production.

Long‐term large wood load fluctuations in two low‐order streams in Southern Chile

AbstractThe eco‐hydrogeomorphic significance of large wood (LW) and its potential for increasing downstream hazards during extreme floods have been widely recognized. We used LW data collected for a 10‐year period from the two low‐order streams of Pichún (Pi) and Vuelta de Zorra (VZ) in Southern Chile to (a) determine if the abundance and dimensions of individual LW pieces change with time, (b) quantify wood load fluctuations during the 10‐year period, and (c) assess the role of LW recruitment from the riparian forests to explain wood load fluctuations during the study period. Nine years after the first survey, the number of LW pieces in Pi and VZ diminished by 60 and 40%, respectively. Despite the reduction in these numbers, in Pi, the LW dimensions did not change significantly during the study. In VZ, the dimensions exhibited statistically significant differences, despite being within the same class. In both catchments, the LW load fluctuated during a 10‐year period, but the drivers of change differed. Although tree toppling was the recruitment mechanism responsible for LW in both stream cases, the high wood load measured in Pi at the beginning of the study suggested massive tree recruitments before the first survey, followed by wood exports which were higher than inputs in the subsequent 10‐year period. In VZ, LW load decreased during the first 9 years (mean annual rate of ~9.2 m3 year−1) and then increased by ~12.1 m3 year−1 in year 10. At VZ, the inputs consisted of single trees that were recruited from the riparian area and by upstream flotation, while exports occurred by downstream fluvial transport. Wood inputs and exports occurred asynchronously and led to LW load fluctuations at decadal and annual intervals. Land management and tree species thus exert a major influence on wood inventory and budget in streams. © 2020 John Wiley &amp; Sons, Ltd.

Wood process domains and wood loads on floodplains

AbstractDowned large wood on floodplains creates similar geomorphic and ecological effects as wood in the active channel, but has been the subject of fewer geomorphic studies. I propose floodplain large wood process domains that are distinguished based on recruitment source at the reach to river‐length scale. Wood recruited to the floodplain can be autochthonous (individual or mass recruitment from floodplain forest), fluvially transported, or transported from adjacent hillslopes via mass movements that come down the valley side slopes or down the main channel. Fluvially transported wood can be further distinguished as being deposited: within the channel and subsequently accreted to the floodplain; marginal to the channel; on the floodplain during overbank flow; or on tributary fans. The mechanism of wood recruitment to a floodplain influences the spatial distribution of the wood across the floodplain and the proportion of wood pieces within jams, which in turn influences geomorphic and ecological effects of the floodplain wood. Using published studies of floodplain wood load for unmanaged river corridors, I hypothesize that the climate‐controlled balance between forest primary productivity and decay rates of downed wood is the first‐order control on floodplain large wood loads. Disturbance regime and wood recruitment mechanism are second‐order controls on wood load and primary controls on the spatial distribution of large wood. Understanding of floodplain large wood can be applied to quantifying the effect of large wood on river corridors; river restoration; paleoenvironmental inferences; and estimation of organic carbon stock in river corridors. © 2019 John Wiley &amp; Sons, Ltd.

Distribution of Large Wood Within River Corridors in Relation to Flow Regime in the Semiarid Western US

AbstractThe cumulative volume and spatial distribution of large wood (LW) along river corridors (channels and floodplains) reflect interactions between rates and volumes of LW recruitment and channel transport capacity through time. Rivers of the semiarid interior western US can have relatively low‐magnitude disturbances associated with annual snowmelt or relatively high‐magnitude disturbances associated with episodic rainfall runoff, especially following wildfires. We use characteristics of LW from 25 river segments in four regions of New Mexico and Colorado to analyze wood loads and spatial patterns of wood distribution in relation to disturbance regime. High‐magnitude disturbances move LW onto floodplains and create longitudinally nonuniform LW distributions with aggregated (closer together than random) LW pieces and abundant LW jams in the floodplain. Sites with low‐magnitude disturbances have a greater proportion of LW in the channel and much of this wood is within segregated (farther apart than random) jams. These results imply that river management, which typically focuses on LW within channels, should focus on floodplain as well as in‐channel LW in rivers with high‐magnitude disturbances. The results also indicate that the proportions of LW loads in channels versus floodplains can differ significantly among rivers with different disturbance regimes that are otherwise similar in terms of forest type or drainage area. This is particularly relevant to mountainous regions with elevation‐related changes in flow and disturbance regime. River management that reintroduces LW to river corridors will be most effective if it incorporates the mobility and spatial distribution of LW.

Instream large wood loads across bioclimatic regions

Instream large wood in forested rivers creates diverse physical and ecological effects and is a vital component of river process and form. The majority of research on wood in rivers has been conducted within a limited geographic range, raising questions about the applicability of resulting insights. We analyze data from 438 river segments in old-growth or unmanaged forests and 250 river segments in lightly managed forests representing diverse environments. We evaluate whether drainage area, channel width, and channel slope influence instream wood load in unmanaged forests across bioclimatic regions. Here we show that, without accounting for variations across regions, these numeric variables do not correlate significantly with wood loads. When accounting for the influence of all available potential influences on wood load in unmanaged forest rivers, bioclimatic region, drainage area, and channel width are the dominant predictors of wood load, and the relationship between wood load and channel width differs between regions. Combining data across bioclimatic regions, unmanaged rivers have significantly greater wood loads than lightly managed forests. Splitting data by bioclimatic region, unmanaged rivers in the northern dry conifer and northern wet conifer regions have significantly greater wood loads than lightly managed forests, but wood loads in the northern wet deciduous region do not differ between unmanaged and lightly managed forests. Our findings suggest that (i) bioclimatic region is a critical factor in predicting and understanding wood dynamics in rivers, (ii) even historic or relatively light levels of timber harvest and wood removal can create persistent differences in wood loads, and (iii) substantial variation in wood load among river segments within a bioclimatic region suggests that riparian forest and river management should focus on processes that maintain wood loads capable of creating desired physical and ecological effects rather than specified volumes of wood.

Lack of maintenance is a major challenge for stream restoration projects

AbstractEnvironmental infrastructure and practices designed to restore and protect aquatic systems are now mainstream. Yet many of these projects are failing to produce the biophysical outcomes that they are designed for because of poor maintenance. The success of restoration projects is just as much a consequence of how they are maintained, as it is how the project was initially designed and implemented. Successful maintenance relies on understanding the ecological and biological recovery trajectories of aquatic systems. Some interventions will require ongoing maintenance indefinitely, whereas others will reach a self‐sustaining point where maintenance is no longer required. Different management arrangements are required to ensure the maintenance of different types of project. Those projects that involve high costs should be managed using more robust arrangements, such as legal regulation, compared to those projects that involve lower costs. This paper describes the maintenance required for common river restoration projects and outlines a classification of projects based on maintenance and recovery trajectories. It then considers the types of management arrangements required to ensure maintenance. Finally, these points are illustrated with 3 case studies of typical restoration actions (riparian stock exclusion, fish passage, and restoring large wood loads). Projects that require ongoing maintenance, particularly those that involve high costs, such as environmental flows, require strong management arrangements to ensure successful outcomes. Voluntary instruments are more appropriate for self‐sustaining interventions. Regardless of the chosen management arrangements, monitoring and independent assessment are essential for successful maintenance.

Floodplain downed wood volumes: a comparison across three biomes

AbstractDowned large wood (LW) in floodplains provides habitat and nutrients for diverse organisms, influences hydraulics and sedimentation during overbank flows, and affects channel form and lateral migration. Very few studies, however, have quantified LW volumes in floodplains that are unaltered by human disturbance. We compare LW volumes in relatively unaltered floodplains of semiarid boreal lowland, subtropical lowland, and semiarid temperate mountain rivers in the United States. Average volumes of downed LW are 42.3 m3 ha−1, 50.4 m3 ha−1, and 116.3 m3 ha−1 in the semiarid boreal, subtropical, and semiarid temperate sites, respectively. Observed patterns support the hypothesis that the largest downed LW volumes occur in the semiarid temperate mountain sites, which is likely linked to a combination of moderate‐to‐high net primary productivity, temperature‐limited decomposition rates, and resulting slow wood turnover time. Floodplain LW volumes differ among vegetation types within the semiarid boreal and semiarid temperate mountain regions, reflecting differences in species composition. Lateral channel migration and flooding influence vegetation communities in the semiarid boreal sites, which in turn influences floodplain LW loads. Other forms of disturbance such as fires, insect infestations, and blowdowns can increase LW volumes in the semiarid boreal and semiarid temperate mountain sites, where rates of wood decay are relatively slow compared with the subtropical lowland sites. Although sediment is the largest floodplain carbon reservoir, floodplain LW stores substantial amounts of organic carbon and can influence floodplain sediment storage. In our study sites, floodplain LW volumes are lower than those in adjacent channels, but are higher than those in upland (i.e. non‐floodplain) forests. Given the important ecological and physical effects of floodplain LW, efforts to add LW to river corridors as part of restoration activities, and the need to quantify carbon stocks within river corridors, we urge others to quantify floodplain and instream LW volumes in diverse environments. Copyright © 2016 John Wiley &amp; Sons, Ltd.