Large Wood Pieces Research Articles

Drivers of Low Instream Large Wood Retention and Imprints of Wood Mobility in Mountain Nonperennial Streams of a Mediterranean Semiarid Environment

AbstractThe majority of research on instream large wood (LW) focuses on perennial streams in temperate zones, and much less is known about wood distribution and its driving factors in other environments, such as semiarid bioclimatic regions. In this study, we sought to predict LW retention by assessing reach‐scale variables to infer the influence of external factors on the presence of LW in 37 independent reaches of ephemeral and intermittent streams draining a mountain range in a Mediterranean semiarid environment (Lefka Ori Mountains, Crete, Greece). In addition, we focused on LW pieces that had been mobilized by fluvial transport to find links between wood mobility and the external reach‐scale characteristics of this environment. Markedly low average LW frequency (6.5 LW/100 m) and volume (9.06 m3/ha) were observed in the studied reaches in comparison with streams draining other bioclimatic regions. Only one complex general linear model was found to predict LW volume (including valley confinement and basal area of coniferous trees), and five explanatory variables (elevation as a proxy of annual precipitation, valley type, valley confinement index, basal area of coniferous trees, and basal area of all trees) were significant in separated models predicting LW volume. Only two variables (valley floor width and the basal area of broadleaf trees) were significant in separated models for prediction of LW frequency. The mobilized LW in the studied streams tends to be stored as individual, dispersed pieces rather than in jams, likely due to overall low LW abundance which effectively prevents clustering of wood.

Controls on log step occurrence in steep headwater streams draining Carpathian managed forests

Instream wood in steep headwater streams impacts channel morphology and sediment fluxes via the development of log steps and related sediment storage. I investigated detailed characteristics of 73 log steps in managed temperate Carpathian forests and assessed channel- and wood-based thresholds for log step development. The limited recruitment of wood from managed forests was apparent in the low frequency of log steps (an average of 1.3 steps per 100 m channel length) in bedload-dominated channels when compared to temperate and boreal old-growth forests, and an even lower number of log steps was observed in streams recently affected by debris flows or hyperconcentrated flows. The upstream threshold of log step occurrence can be assigned to those locations in stream longitudinal profiles, where transport capacity during ordinary high flows exceeds the critical value for the initiation of bedload movement. Downstream thresholds are controlled by stream transport capacity and wood dimensions, which correspond to the limited recruitment of large wood pieces in managed forests. All log steps were found in contributing basin areas smaller than 1 km2, and the majority of log steps (93.1%) originated in channels less than two metres in width. The development of a log step at a particular channel width or basin area was controlled by the wood length, but the resultant step parameters (step height and width, length of upstream sedimentary wedge and volume of stored sediments) were better correlated with wood diameter. The parameters of horizontal and vertical wood orientation had less importance in the development of a log step or its dimensions. Wood pieces shorter than 4 m in length accounted for 72.2% of the step-forming pieces, and the maximal diameter was less than 0.1 m for 20.5% of the pieces. These findings show the significance of relatively small wood pieces in log step development and sediment routing in steep headwater streams; the average sediment storage generated by a log step was 0.51 m3. The support of log step development and their preservation in headwater streams draining managed forests represents an alternative low-cost approach for sediment management at the basin scale.

Alternative Carrier Solvents for Pigments Extracted from Spalting Fungi.

The use of both naturally occurring and synthetic pigmented wood has been prevalent in woodcraft for centuries. Modern manifestations generally involve either woodworkers’ aniline dyes, or pigments derived from a special class of fungi known as spalting fungi. While fungal pigments are more renewable than anilines and pose less of an environmental risk, the carrier required for these pigments—dichloromethane (DCM)—is both problematic for humans and tends to only deposit the pigments on the surface of wood instead of evenly within the material. Internal coloration of wood is key to adoption of a pigmenting system by woodworkers. To address this issue, five solvents that had moderate solubility with the pigments extracted from Chlorociboria aeruginosa and Scytalidium cuboideum were identified, in the hopes that a reduction in solubility would result in a greater amount of the pigment deposited inside the wood. Of the tested solvents, acetonitrile was found to produce the highest internal color in ash, Douglas-fir, madrone, mountain hemlock, Port-Orford cedar, Pacific silver fir, red alder and sugar maple. While these carrier solvents are not ideal for extracting the pigments from the fungi, acetonitrile in particular does appear to allow for more pigment to be deposited within wood. The use of acetonitrile over DCM offers new opportunities for possible industrial spalting applications, in which larger pieces of wood could be uniformly pigmented and sold to the end user in larger quantities than are currently available with spalted wood.

Large wood potential, piece characteristics, and flood effects in Swiss mountain streams

We present results of two studies on the (1) potential wood load in steep headwater streams and (2) properties of large wood (LW) transported in mountain rivers during the large August 2005 flood event in Switzerland. Ten headwater reaches of 1000 m length were surveyed in different regions of Switzerland. The potential wood load was estimated for in-channel deadwood, and possible driving factors were explored. Correlations were found with dead wood volume on hillslopes and mean channel width. We established size distributions of LW pieces and identified probable recruitment processes. Four reaches were resurveyed after an exceptionally severe flood in August 2005, showing limited LW transport in channels but considerable wood input by mass wasting processes. In addition, characteristics of deposits of LW along mountain rivers affected by the 2005 flood were investigated. Diameter and length distribution of transported and deposited pieces were comparable to those of LW from steep headwater streams, yet with considerably fewer long pieces in the deposits of mountain rivers. Most LW pieces were fresh wood, indicating that the portion of in-channel deadwood transported during the 2005 flood was limited. Findings of the study contribute to a better understanding of LW dynamics in Alpine mountain streams.

Characteristics of large wood in a headwater channel after an extraordinary event: The roles of transport agents and check dams

High-magnitude hydrogeomorphic events in steep streams (e.g., debris flows and debris floods) are capable of transporting considerable quantities of bed material, including large wood, although wood pieces that are longer than the channel width are often perceived as relatively stable elements in narrow headwater channels. We investigated present large wood distribution along 1.7 km of a steep headwater channel (the Klepáčský Stream; Eastern Sudetes; NE Czech Republic) surrounded by managed forests and engineered by twelve check dams (presently at various stages of destruction). The total wood volume was measured at 123.0 m3, including wood deposited on adjacent terraces by a high-magnitude hydrogeomorphic event in 2010 representing a ca. 20–30 year recurrence interval. Approximately a half of the total wood volume (58%) was stored in large jams (≥10 large wood pieces) that originated during that event. We observed reach controls (based on transport agents and valley morphology) and local controls (represented by individual check dams) of LW depositional patterns. The uppermost debris flow-affected reach produced high volumes of mobilised wood, including many pieces that were two-to-three times longer than the local active channel width; significantly shorter and thinner pieces were found within large jams in downstream reaches void of debris-flow processes. We also documented that this high-magnitude event was responsible for the notable out-of-channel storage of large wood, which decreases the volume of wood that might be transported by a future event. In addition, 30.5 m3 of large wood, that is ~one-quarter of the total volume measured along the stream, was deposited in relation to twelve damaged check dams despite their lowered trapping efficiency.

Longitudinal distribution and parameters of large wood in a Mediterranean ephemeral stream

Although large wood (LW) has been intensively studied in forested basins of humid temperate climates, data on LW patterns in different fluvial environments are rather scarce. Therefore, we investigated the dimensions, characteristics, longitudinal distribution, and dynamics of LW along a 4.05-km-long reach of an ephemeral channel typical of European Mediterranean mountainous landscape (Sfakiano Gorge, Crete, Greece). We analysed a total of 795 LW pieces, and the mean observed abundance of LW was generally lower (14.3 m3/ha of active valley floor or 19.6 LW pieces/100 m of stream length) than is usually documented for more humid environments. The number of LW pieces was primarily controlled by trees growing on the valley floor. These living trees acted as important LW supply agents (by tree throws or the supply of individual branches with sufficient LW dimensions) and flow obstructions during large flood events, causing storage of transported LW pieces in jams. However, the downstream transport of LW is probably episodic, and large jams are likely formed only during major floods; after >15 years, we still observed significant imprints of the last major flood event on the present distribution of LW. The geomorphic function of LW in the studied stream can only be perceived to be a spatially limited stabilising element for sediments, which was documented by a few accumulations of coarse clastic material by LW steps and jams.

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.

Air protection programmes in Poland in the context of the low emission

The protection of the air against pollutants from individual boiler plants is a big challenge in Poland. It results mainly from the preference for coal, the national energy carrier, the use of old low-efficiency boilers and the location of Poland in a temperate climate where the heating period lasts at least 5 months. This article presents a wide range of activities aimed at the reduction of the environmental impact of the emissions of pollutants from individual heat sources—the so-called low emission. The article presents the extent of the national legislation resulting from the European Union regulations. It discusses the assumptions of the air protection programmes (APPs) and the low emission reduction programmes (LERPs). The assumptions mentioned above are analysed as part of a life cycle assessment (LCA) analysis and a multi-criterion analysis. An important result of these analyses (in the Polish conditions) is the conclusion that a boiler fired with large pieces of wood is an optimal solution from the economic and ecological points of view. The article proposes systemic, organisational and legislative solutions whose implementation could contribute to raising the effectiveness of the protection of the atmosphere.

Temporal variations of large wood abundance and mobility in the Blanco River affected by the Chaitén volcanic eruption, southern Chile

The aim of this study is to analyze the temporal variation in abundance and transport of in-channel wood along a river affected by a volcanic eruption, considering the mobility and retention rates in detail. The 2008 eruption of Chaitén Volcano (Southern Chile) severely affected the Blanco River basin, causing changes in channel morphology and large wood (LW) dynamics along the fluvial corridor of the river, a fourth-order stream on the southern slope of the volcano. Temporal dynamics of LW were investigated, from January 2015 until March 2016, in three 80m-long study reaches of the active channel in the lower course of the river. Every wood element (≥1m in length and ≥0.1m in diameter) within the active channel of each reach was georeferenced, measured, tagged, and characterized. Wood mobility rate, defined as the number of tagged wood pieces repositioned or not found within each study reach to total tagged LW in the same reach; and retention rate, defined as the number of tagged LW pieces found within each study reach to total tagged wood pieces in the same reach, were calculated considering two periods, one in summer and one in autumn-winter. A regional flood frequency analysis estimated flood magnitude, defining a recurrence interval of ~1year for summer floods, and 10–25years for autumn-winter floods. Results highlighted how, eight years after the eruption, the types of LW are still influenced by the impacts of pyroclastic density currents on riparian vegetation. The characteristics and abundance of monitored LW are typical of a river system with frequent wood transport. The mobility rate ranges between 42 and 94% during the summer and autumn-winter period, respectively; while the wood volume decreases during the summer and increases in autumn-winter. Large wood mobility was also found to vary according to the predominant morphological settings, with lower values in narrower channels compared to wider wetted areas. In this context the greatest abundance of LW was detected after the higher floods, corresponding to an input of LW up to 285.35m3·ha−1. Along the Blanco River ordinary floods deliver LW mainly through fluvial transport, and bank erosion during higher floods appears as an additional and important wood recruitment process. The bank erosion processes, with up to 5200m2 of eroded area, confirmed the widening tendency occurring in river systems following volcanic disturbances. As there are dead riparian trees along the easily erodible banks, it is reasonable to suppose that the Blanco River will continue to widen for a long period, recruiting and transporting downstream huge volumes of LW. In this context these analyses appear of fundamental importance to better manage the river system, also for decreasing hazards to the downstream village of Chaitén.

Reintroduced large wood modifies fine sediment transport and storage in a lowland river channel

AbstractThis paper explores changes in suspended sediment transport and fine sediment storage at the reach and patch scale associated with the reintroduction of partial large wood (LW) jams in an artificially over‐widened lowland river. The field site incorporates two adjacent reaches: a downstream section where LW jams were reintroduced in 2010 and a reach immediately upstream where no LW was introduced. LW pieces were organized into ‘partial’ jams incorporating several ‘key pieces’ which were later colonized by substantial stands of aquatic and wetland plants. Reach‐scale suspended sediment transport was investigated using arrays of time‐integrated suspended sediment samplers. Patch‐scale suspended sediment transport was explored experimentally using turbidity sensors to track the magnitude and velocity of artificially generated sediment plumes. Fine sediment storage was quantified at both reach and patch scales by repeat surveys of fine sediment depth. The results show that partial LW jams influence fine sediment dynamics at both the patch and reach scale. At the patch‐scale, introduction of LW led to a reduction in the concentration and increase in the time lag of released sediment plumes within the LW, indicating increased diffusion of plumes. This contrasted with higher concentrations and lower time lags in areas adjacent to the LW; indicating more effective advection processes. This led to increased fine sediment storage within the LW compared with areas adjacent to the LW. At the reach‐scale there was a greater increase in fine sediment storage through time within the restored reach relative to the unrestored reach, although the changes in sediment transport responsible for this were not evident from time‐integrated suspended sediment data. The results of the study have been used to develop a conceptual model which may inform restoration design. Copyright © 2017 John Wiley & Sons, Ltd.

Unlimited fuel wood during the middle Mesolithic (9650–8300 cal. yr BP) in northern Sweden: Fuel typology and pine-dominated vegetation inferred from charcoal identification and tree-ring morphology

A fuel wood analysis based on the ‘Principle of Least Effort’ helps to decipher the ecological limitations imposed on prehistoric hunter-gatherers. This study is based on botanical identification of wood charcoal from ‘Swedish middle Mesolithic’ archaeological sites dating from between ca. 9650 and 8300 cal. yr BP in northern Sweden, a period when the land was freshly released from ice cover. Charcoal fragments were analysed based on their anatomical and morphological features and anomalies. Tree-ring thickness gives an indication of the growing conditions experienced by woody plants, the tree-ring curvature provides an indication of the diameter of the pieces of wood used for fuel and the percentage of fragments with spiral thickening indicates the importance of compression or tension wood, which is related to branches or trunks stressed by snow burden or wind. Among the main woody species, the assemblages are dominated by Pinus sylvestris with some Salicaceae trees ( Populus, Salix). Large wood pieces including branches were used as fuel. Several taxa were rarely recorded ( Betula, Sorbus, Ericaceae) or not observed ( Juniperus, Hippophae, Alnus) although their presences were expected based on other local palaeobotanical records. Because (1) charcoal of Pinus sylvestris abounds despite not being a good fuel wood and (2) certain consumable or combustible taxa are scarce ( Betula) or are only present at certain sites (Salicaceae), it appears that Mesolithic hunters were not selective when choosing wood for fuel, although wood was not a limiting factor for the first settlers in northern Sweden. Pine tree-ring width range is within the modern range for the same species, indicating growing conditions similar to those experienced today. The results suggest the occurrence of woodland, probably in the lowlands. During the early-Holocene, trees rapidly covered the land after the ice-sheet melted, facilitating the life of Mesolithic hunters following reindeer herds.

The Effects of Replacing Native Forest on the Quantity and Impacts of In‐Channel Pieces of Large Wood in Chilean Streams

AbstractDead trees in rivers can significantly affect their morphological and ecological properties by increasing flow resistance, affecting sediment transport, and storing organic matter. Logs are usually recruited from banks or along the entire upstream basin. Although it is generally acknowledged that forested headwater streams feature higher volumes of in‐channel pieces of large wood, the influence of forest type and forest management of the potential recruitment zone on the volumes and effects of wood have been less explored, especially in relation to the effects of replacing native forests with pine plantations. This paper presents a comparison of volumes of wood, and characteristics and effects on streams draining paired basins with comparable slopes, areas, and hydrologic regimes, but different in terms of land use. The five selected pairs of basins are located in the Coastal and Andean mountain Ranges in central Chile, in order to compare native forest and pine plantation basins. The results show that logs tend to be shorter and with larger diameters in streams draining native forest basins. Because of their smaller dimensions, logs and jams tend to be more mobile and oriented parallel to the flow. Volumes of in‐channel wood in native forest basins are only slightly larger than in pine plantation basins, and no differences have been identified in terms of morphological effects on channel geometry. Also, fish type and biomass were comparable among pairs. Evidence highlights the importance of the width of riparian buffers in mitigating the effects of land use change, especially the substitution of native forest with plantations. Copyright © 2016 John Wiley & Sons, Ltd.

Frequency of large in-channel wood in eastern Oklahoma ecoregions and its association with channel morphology

Regional climate, geology, vegetation, and land use influence hydrogeomorphic processes, which influence stream channel form and the recruitment and transport of wood in streams. We studied relationships between channel morphology and frequencies of large in-channel wood in three upland ecoregions of eastern Oklahoma where streams contain high fish diversity and valuable sport fisheries. We surveyed 138 streams for wood within the Boston Mountains (n=30), Ozark Highlands (n=30), and Ouachita Mountain (n=78) ecoregions. Our study investigated whether (1) the frequency of large wood differed among ecoregions; (2) channel morphology influenced the distribution of large wood within and among ecoregions; and (3) a relationship existed between the frequency and size of trees in the riparian zone and the frequency of large wood within and among ecoregions. The frequency of single large wood pieces did not differ among ecoregions or vary with drainage area. However, the presence of one or more wood accumulation (2 to 4 pieces) increased with drainage area and increased at a higher rate in the Boston Mountains and Ozark Highlands than in the Ouachita Mountains. The frequency of single wood pieces decreased in narrower channels with larger substrates but increased in larger stream channels overall. No association existed between riparian tree density and in-channel wood in study reaches. We discuss these results in the context of wood recruitment and transport, and highlight key questions that remain regarding wood in eastern Oklahoma streams.

Palaeontology of the upper Turonian paralic deposits of the Sainte-Mondane Formation, Aquitaine Basin, France

The upper Turonian lignite deposits of Sainte-Mondane, Dordogne (Aquitaine Basin, SW France), consist of clays bearing translucent, orange to red, amber micrograins. The amber exhibits different types of microbial inclusions. The clays contain several conifers including the genera Brachyphyllum, Frenelopsis and Glenrosa, and a few leaf fragments of eudicot angiosperms. Among the plant meso-fossils the occurrence of Costatheca, Spermatites and abundant, diverse megaspores, including species of Ariadnaesporites, Bacutriletes, Echitriletes, Erlansonisporites, Maexisporites, Minerisporites and Verrutriletes, is noteworthy. Pollen grains of the Normapolles group are important components of the palynomorph assemblage. The clays were deposited in a calm, estuarine or lagoonal, muddy environment. The overlying lignitic sands contain large fossil wood pieces of the conifer Agathoxylon, small solitary corals, fragmentary oysters and pectinids, echinoid spines, a few teeth of marine selachians and bony fishes, but no amber is present. These sands were deposited in a high-energy coastal marine environment.

Use of remote imagery to analyse changes in morphology and longitudinal large wood distribution in the blanco river after the 2008 chaitén volcanic eruption, southern chile

The 2008 haitén volcanic eruption generated significant changes in the channel morphology and large wood () abundance along the fluvial corridor of the lanco iver, southern hile. Comparisons of remote sensing images from the pre‐eruption (year 2005) and post‐eruption (years 2009 and 2012) conditions showed that in a 10.2 km long study segment the lanco iver widened 3.5 times from 2005 to 2009, and that the maximum enlargement was nine times the original width. Changes in channel width were lower between the years 2012 and 2009. The sinuosity and braiding indexes also changed between 2005 and 2009. After the eruption the channel sinuosity was higher and specific river reaches developed a braided pattern, but by 2012 the channel was recovering pre‐eruption characteristics. Huge quantities of were introduced to the study segment; individual per km of channel length were 1.6 and 74.3 in 2005 and 2009, respectively, and more than 30 log jams km−1 were observed in the year 2009. Between 2009 and 2012 the quantity of was very similar. Statistically significant relationships were found between the number of log jams and channel sinuosity and between the number of pieces of large wood with sinuosity and channel width. Wood was highly dynamic between 2009 and 2012: 78% of individual pieces and 48% of log jams identified in the 2009 image had moved by 2012. Finally the supervised classification of imagery associated with ArcMap tools was tested to identify large wood.

The early impact of large wood introduction on the morphology and sediment characteristics of a lowland river

• Sediment properties are examined in five location types in a wood-restored channel. • Channels with restored large wood are morphologically more complex. • Sediment retained around restored large wood is finer and organic-rich. • Fine sediment retained around wood jams contains relatively more plant propagules. • Large wood is a potential self-restoration tool for degraded river channels. Habitat degradation in river ecosystems has considerably increased over the past decades, resulting in detrimental effects on aquatic and riparian communities. During the last two decades, the value of large wood as a resource for river restoration and recovery has been increasingly documented. However, post-project appraisal of the associations between restored large wood, morphological complexity and river ecology as a result of river restoration is extremely rare and thus scientific knowledge is essential. To investigate restored wood-induced morphological response and sediment complexity in an overwidened reach along a low gradient lowland river (River Bure, UK), two sub-reaches containing 12 jams initiated by wood emplacement in 2008 and 2010 and a sub-reach free of wood were studied. Wood surveys recording the dimensions and number of wood pieces in jams, geomorphological mapping of the reach illustrating the spatial distribution of features in and around the jams and in a section free of wood, and sediment sampling (analysed for particle size, organic content and plant propagule abundance) of five recurring patch types surrounding each jam (two wood-related patches and three representing the broader river environment) were performed. Wood jams partially spanned the river channel and contained large pieces of wood that created more open structures than naturally-formed wood jams. Where no wood was introduced, the channel remains wide and the gravel bed is buried by sand and finer sediment. In the restored reaches, fine sediment has accumulated in and around the wood jams and has been stabilised by vegetation colonisation, enhancing flow velocities in the narrowed channel sufficiently to mobilise fine sediment and expose the gravel bed. Sediment analysis reveals sediment fining with time since wood emplacement, largely achieved within the two wood-related patch types. Fine sediment retained around the wood shows a relatively higher plant propagule content than other patch types, suitable for sustaining plant succession as the vegetated side bars aggrade. Although channel narrowing and morphological adjustment has occurred surprisingly rapidly in this low energy, over-widened reach following wood introduction (2–4 years), sustaining the recovery in the longer term to suitably support flora and fauna communities depends on the continued delivery of wood by ensuring a natural supply of sufficiently large wood pieces from riparian trees both upstream and within the reach.

The influence of geomorphology on large wood dynamics in a low gradient headwater stream

AbstractUnderstanding large wood dynamics is critical for a range of disciplines including flood risk management, ecology and geomorphology. Despite the importance of wood in rivers, our understanding of the mobility of large wood remains limited. In this study individual pieces of large wood were tagged and surveyed over a 32 month period within a third and fourth order lowland forest river. Individual pieces of wood were found to be highly mobile, with 75% of pieces moving during the survey period, and a maximum transport distance of 5.6 km. Multivariate analyses of data from this study and two other published studies identified dimensionless wood length as the important factor in explaining likelihood of movement. A length threshold of 2.5 channel widths is identified for near functional immobility, with few pieces above this size moving. In addition, for this study, wood type, branching complexity, location and dimensionless wood diameter were found to be important in determining mobility only for sinuous reaches with readily inundated floodplains. Where logjams persist over multiple years they were shown to be reworked, with component pieces being transported away and replaced by newly trapped pieces. The findings of this study have implications for river management and restoration. The high mobility observed in this study demonstrates that only very large pieces of wood of length greater than 2.5 channel widths should be considered functionally immobile. For pieces of wood of length less than the channel width the possibility of high rates of mobility and long transport distances should be anticipated.

Tracking log displacement during floods in the Tagliamento River using RFID and GPS tracker devices

Large pieces of in-channel wood can exert an important role on the ecological and morphological properties of gravel-bed rivers. On the other side, when transported during flood events, large wood can become a source of risk for sensitive structures such as bridges. However, wood displacement and velocity in river systems are still poorly understood, especially in large gravel-bed rivers. This study focuses on log transport in a valley reach of Tagliamento River (Italy). Log displacement during flood events of different magnitudes recorded from June 2010 to October 2011 has been analysed thanks to the installation of 113 radio frequency identification (RFID) tags and 42 GPS tracker devices in logs of different dimensions. Recovery rates of logs equipped with RFID and GPS trackers were about 43% and 42%, respectively. The GPS devices allowed us to analyse in details the log displacement and transport overtime, indicating a higher log entrainment during rising limb of hydrographs. The threshold for the entrainment of logs from low bars is around 40% of bankfull water stage. No clear relationship was found between the peak of flood and log displacement length and velocity. However, log displacement length and velocity appear significantly correlated to the ratio between the peak of flow and the water stage exceeding the flow duration curve for 25% of time (i.e. the ratio hmax/h25 ratio). Log deposition was observed to occur at the peak flow, and logs transported during ordinary events are preferably deposited on low bars. This study reveals the potentials of GPS tracker devices to monitor the entrainment and movements of logs in large gravel-bed rivers during floods. These observations could be useful for better planning of river management practices and strategies involving the use of large wood pieces and could help for calibrating wood budgets at the reach scale.

Diversification of stream invertebrate communities by large wood

Summary To evaluate the effects of large wood (LW) on benthic habitats and macroinvertebrates in sand‐bed lowland rivers, we compared invertebrate communities recorded on four pieces of LW (12 samples in total) and around them (60 samples) with those in four control sites in the same river (four samples). Mean flow velocity was 32% lower in the channel areas surrounding the LW than in control sites, while median sediment grain size was 50% higher, and the organic matter content of the riverbed sediments was 287% higher. At the same time, habitat conditions showed threefold to 1000‐fold increases in variance for five key abiotic habitat descriptors in the surrounding channel extending at least 60 cm upstream and 160 cm downstream of the LW. Three habitat patches typically occurred around the LW pieces: scouring pools, sand bars and accumulations of organic matter. These patches were colonised by distinctive invertebrate communities (e.g. accumulations of organic matter and gravel hosted 15 and 2 indicator taxa, respectively) that overall harboured 110% more taxa and exhibited a 168% higher diversity than control sites. The LW itself contributed only a small fraction to these increases, exhibiting a 15% increase in taxa richness and a 21% increase in species diversity compared to the control sites. The diversification of benthic invertebrate communities colonising streambed sediments around LW could be directly linked to the much more heterogeneous habitat conditions recorded there. Thus, local additions of large wood within river restoration programmes have the potential to promote the establishment of diverse invertebrate communities in extended areas of a river channel.

Variability in Radiocarbon Dates in Middle Pleniglacial Wood from Kurtak (Central Siberia)

The chronology of long Upper Pleistocene loess sequences in Eurasia is based on combined pedostratigraphy and radiocarbon dating of high-quality charcoal. The accuracy of such a chronology depends on the reproducibility and precision of the 14C dates. However, certain dates may show discrepancies with regard to their chronostratigraphic context based on series of coherent dates. In order to evaluate the consistency and variation in the 14C dates obtained from small charcoal pieces, this question was tested on a set of spruce wood remains with well-preserved tree rings found in the Middle Pleniglacial loess-loam sequence of Kurtak (central Siberia). Tree-ring analysis of five fairly large wood pieces from three successive layers, dated to about 30.0, 30.8, and 32.2–32.5 ka BP previously, was done by continuous sampling of 90–150 rings on each wood piece. This enabled direct comparison of the succession of tree rings with the 14C dates. A total of 133 dates was obtained for the five wood pieces. The results show fluctuations in the 14C dates within a time range between 1000 and 2000 yr. Four possible causes for such variation will be discussed herein: (1) internal variability of the AMS dating method; (2) outliers; (3) variations in the 14C background; and (4) external factors such as past atmospheric 14C variations.