Large Woody Debris Volume Research Articles

The Evaluation of Color Spaces for Large Woody Debris Detection in Rivers Using XGBoost Algorithm

Large woody debris (LWD) strongly influences river systems, especially in forested and mountainous catchments. In Taiwan, LWD are mainly from typhoons and extreme torrential events. To effectively manage the LWD, it is necessary to conduct regular surveys on river systems. Simple, low cost, and accurate tools are therefore necessary. The proposed methodology applies image processing and machine learning (XGBoost classifier) to quantify LWD distribution, location, and volume in river channels. XGBoost algorithm was selected due to its scalability and faster execution speeds. Nishueibei River, located in Taitung County, was used as the area of investigation. Unmanned aerial vehicles (UAVs) were used to capture the terrain and LWD. Structure from Motion (SfM) was used to build high-resolution orthophotos and digital elevation models (DEM), after which machine learning and different color spaces were used to recognize LWD. Finally, the volume of LWD in the river was estimated. The findings show that RGB color space as LWD recognition factor suffers serious collinearity problems, and it is easy to lose some LWD information; thus, it is not suitable for LWD recognition. On the contrary, the combination of different factors in different color spaces enhances the results, and most of the factors are related to the YCbCr color space. The CbCr factor in the YCbCr color space was best for identifying LWD. LWD volume was then estimated from the identified LWD using manual, field, and automatic measurements. The results indicate that the manual measurement method was the best (R2 = 0.88) to identify field LWD volume. Moreover, automatic measurement (R2 = 0.72) can also obtain LWD volume to save time and workforce.

Ecological uniqueness of fish communities from streams in modified landscapes of Eastern Amazonia

Abstract Ecological uniqueness is one aspect of beta (β) diversity that shows the relative contribution of sites (local contribution to beta diversity – LCBD) and taxa (species contribution to beta diversity – SCBD) in the formation of a unique environment in terms of species composition, and may be directly related to habitat quality. Our objective was to evaluate the uniqueness of fish communities from streams in modified areas of the Amazon, and to investigate the main environmental predictors at local and landscape scale. We sampled 58 streams in the Capim river basin (Para, Brazil) located within areas of preserved forest, reduced-impact logging, conventional logging and pasture. We found greater β diversity and higher LCBD in the pasture areas, making this land use the largest contributor to β diversity in the study area. At local scale, this high contribution was primarily influenced by environmental heterogeneity, thalweg depth, percentage of land use and cover (all positively), and volume of large woody debris in the riverbed (negatively). This indicates that the β diversity of fish is highly affected by streams with greater thalweg depth, possibly due to the reduced amount of large woody structures entering streams within pasture areas. These streams also showed greater environmental heterogeneity due to the large variation in disturbance levels of this area, which renders their sites suitable for potential occupation by different species, making them high contributors (high LCBD) and also leading them to present high β diversity. On the other hand, areas with a higher percentage of forest at landscape scale (including preserved forest, reduced-impact logging and conventional logging) were the main contributors, while pasture areas had a higher percentage of exposed soil. We did not find any association between SCBD values and the habit of the species, as the taxa that contributed most to β diversity can be classified as having reduced niches (specialists) as well as broader niches (generalists). We conclude that modified areas may contribute substantially to β diversity because they have a distinct species combination, however different patterns can be observed at local and landscape scales.

Estimating large woody debris volume and distribution floated and accumulated in reservoir using aerial photographs

Large woody debris (LWD) could increase the risk of flooding in the event of heavy rainfall, and fast estimation of the accumulated LWD is crucial for river basin management. We develop a method to automatically detect LWD floating in reservoirs using airborne images, and estimated the total volume of LWD accumulated in a reservoir during a severe flood event in northern Kyushu, Japan, early July 2017. The LWD was successfully extracted from the images based on colour and brightness by using ImageJ. The total volume of the accumulated LWD estimated from images was similar to the LWD volume actually removed from the reservoir by the end of October. Most LWD pieces were concentrated in the upstream-side of the reservoir, and a longitudinal variation in density and length of LWD pieces was also evident.

Comparing Stream Restoration Project Effectiveness Using a Programmatic Evaluation of Salmonid Habitat and Fish Response

AbstractHundreds of millions of dollars have been spent on stream restoration projects to benefit salmonids and other aquatic species across the Pacific Northwest, though only a small percentage of these projects are monitored to evaluate effectiveness and far fewer are tracked for more than 1 or 2 years. The Washington State Salmon Recovery Board and the Oregon Watershed Enhancement Board have spent more than US$500 million on salmonid habitat restoration projects since 1999. We used a multiple before‐after–control‐impact design to programmatically evaluate the reach‐scale physical and biological effectiveness of a subset of restoration actions. A total of 65 projects in six project categories (fish passage, instream habitat, riparian planting, livestock exclusion, floodplain enhancement, and habitat protection) were monitored over an 8‐year period. We conducted habitat, fish, and macroinvertebrate surveys to calculate the following indicators: longitudinal pool cross section and depth, riparian shade and cover, large woody debris volumes, fish density, macroinvertebrate indices, and upland vegetation condition class. Results indicate that four categories (instream habitat, livestock exclusions, floodplain enhancements, and riparian plantings) have shown significant improvements in physical habitat after 5 years. Abundance of juvenile Coho Salmon Oncorhynchus kisutch increased significantly at fish passage projects and floodplain enhancement projects, but significant results were not detected for other fish species. Moreover, the biological response indicators of juvenile salmonid abundance and macroinvertebrate indices showed declines at instream habitat and habitat protection projects, respectively. Our results indicate that a subset of projects can be effectively evaluated programmatically, but power and sample size estimates indicate that two or more years of preproject data are necessary to adequately determine the effectiveness of many project types, particularly for fish. Programmatic evaluations of project effectiveness should include adequate preproject sampling and multiseason monitoring for fish species to address issues of variability that are likely to be encountered in large‐scale monitoring programs.Received September 16, 2015; accepted February 7, 2016 Published online June 6, 2016

Restoration Considerations of Large Woody Debris in the Elwha River Nearshore, Olympic Peninsula, Washington

Large Woody Debris (LWD) is a critical component of Pacific Northwest marine ecosystems and of growing interest for restoration. This study adds important empirical data to the limited pool of information on the dynamics of LWD at the interface of freshwater, human, and marine ecosystems. In Washington State, the Elwha River nearshore is significantly ecologically altered due to shoreline armoring and upstream dams. The Elwha dam removal project, begun September 2011, is anticipated to change the composition, delivery rate and volume of LWD. We describe baseline characteristics of LWD in the Elwha River’s drift cell relative to unaltered areas with intact hydrodynamic processes by landform type, discuss anticipated changes, and consider the need for future work to understand and promote LWD in this restoration event. Results indicate LWD volumes of the Elwha nearshore were significantly lower than certain comparison areas; average site volume on Elwha’s spit was 0.83 m³ versus 18.6 m³ of the comparison spit. Similarly, the average number of pinned and buried LWD pieces (0.5 vs. 13.7) and count of straight logs (6.5 vs. 36.5) (composition) were significantly lower than those in the comparison spit. Current lower volume and differing structure of LWD likely contributes to impairment of ecological functions in Elwha’s nearshore. While dam removals may result in partial restoration of nearshore processes, ongoing decreased wood recruitment attributable to early logging, harvesting, and shoreline armoring are likely to continue preventing LWD accumulation. Restoration efforts should prioritize actions such as the removal of armoring and reduction of wood harvest.

Multi-scale assessment of habitats and stressors influencing stream fish assemblages in the Lake Pontchartrain Basin, USA

This study determined if a spatial hierarchy existed with respect to reach-scale habitat, subwatershed-scale, and watershed-scale geomorphology and land use stressors on fish assemblages in southeastern U.S. coastal plain streams. During May–October 2009–2012, fishes were sampled by seine, and habitat was assessed at 50 reaches in the Lake Pontchartrain Basin (USA). Using partial redundancy analysis (pRDA) a variance decomposition procedure was used to partial out influences of confounding covariables at each spatial scale. Reach-scale habitat had the strongest association with the assemblage. Stream width, depth, aquatic vegetation and human debris cover, rapid habitat assessment score, and large woody debris volume were the most important variables. At subwatershed and watershed scales, natural and anthropogenic characteristics were important, including elevation, gradient, watershed area, wetland cover, stream density, road, dam and oil/gas well densities. Six species were associated most strongly with the watershed variables, compared to reach- and subwatershed-scale variables. These species had more “r-selected” life-history strategies (e.g., smaller eggs, shorter life spans, multiple broods, longer spawning season, and trophic generalists). In contrast, most species that were associated strongest with reach-scale variables exhibited more “k-selected” life-history traits (e.g., larger eggs, longer life spans, shorter spawning season, single brood, and trophic specialists).

Patterns of Riparian and In-stream Large Woody Debris Across a Chronosequence of Southern Appalachian Hardwood Stands

ABSTRACT: The density and volume of riparian and in-stream large woody debris (LWD) is hypothesized to be a function of forest disturbance and developmental processes. However, these relationships are poorly understood for many forest types, including hardwood forests of the southern Appalachian Highlands. We analyzed patterns of riparian and in-stream LWD in hardwood stands across three establishment classes (pre-1900s, 1930s, and 1950s) on the Cumberland Plateau to elucidate the relationships between forest development and LWD patterns. The stands were dominated by Fagus grandifolia, Quercus alba, and Lirodendron tulipifera. Density and volume of riparian LWD did not differ across the chronosequence. Density of riparian LWD ranged from 367 (1950s) to 407 (1930s) pieces ha-1 and volume ranged from 142.0 (pre-1900s) to 187.1 (1930s) m3 ha-1. Likewise, mean density and volume of in-stream LWD did not differ across the chronosequence. Density of in-stream LWD ranged from 20 pieces 100 m-1 (pre-1900s and 195...

Instream Woody Debris and Riparian Forest Characteristics in the Sabine River, Texas

We examined instream large woody debris (LWD) dynamics on the Sabine River, TX. All wood >10 cm in diameter and >2 m long was measured on four river meanders (meander wavelengths) below the dam on Toledo Bend Reservoir. We determined LWD species, degree of decay, bank orientation, jam association, and stage contact. We also measured riparian vegetation characteristics on each meander. LWD volumes were significantly greater at the site immediately below Toledo Bend Dam, due to the relatively steeper channel gradient and higher rates of channel erosion. Based on mass balance estimates, between 11 and 21% of total annual recruitment came from upstream fluvial transport, and the remainder resulted from bank erosion and tree mortality. We estimated average LWD residence time to be 12–14 years. The lower Sabine River is transport-limited for sediment, and the same is true for LWD. Based on these measurements, it is unlikely that Toledo Bend Reservoir is having a significant impact on LWD dynamics at the measurement reaches due to lacustrine wood storage. Of greater concern in the study system are riparian forest degradation and invasive species spread, which may dramatically affect future LWD loadings and residence times, and thus, riverine biota.

Millennial stocks and fluxes of large woody debris in lakes of the North American taiga

Summary Large woody debris (LWD) is an important cross‐boundary subsidy that enhances the productivity of lake ecosystems and the stability of aquatic food webs. LWD may also be an important carbon sink because LWD pieces are preserved for centuries in the littoral zone of lakes and rivers. However, a long‐term analysis of LWD stocks and fluxes in lakes, coupled with the reconstruction of past disturbances at the site level, has never been attempted. Large woody debris was sampled in five lakes of the Quebec taiga. Actual LWD stocks were described and residence time of the LWD pieces was established using tree‐ring and radiocarbon dating. LWD losses by decomposition and burial and other factors influencing LWD residence time were investigated using linear regressions. Impacts of wildfires on LWD fluxes during the last 1400 years were reconstructed separately for the five lakes using piecewise regression models. Fire years at each site were identified from the recruitment dates of charred LWD pieces. Large woody debris volume ranged between 0.92 and 1.57 m3 per 100 m of shoreline, and extrapolating these results to the landscape scale, it was concluded that LWD littoral carbon pools represent a minimal portion of boreal carbon storage. Large woody debris residence time in boreal lakes was confirmed to be very long. Tree‐ring dates of 1571 LWD pieces, mainly black spruce (Picea mariana (Mill.) BSP.), spanned the last 1400 years, while LWD specimens of older floating chronologies were preserved from decomposition for up to five millennia. The most influential variables explaining the variation in LWD residence time were the degree of burial and the distance from the shore. Large woody debris recruitment rates averaged 5.8 pieces per century per 100 m of shoreline. Fourteen wildfires were the primary cause for changes in the rates of tree establishment in the riparian forests and of LWD recruitment in the lakes. Synthesis. Interactions between terrestrial and aquatic ecosystems in northern boreal regions are strongly influenced by wildfires whose effects can last for centuries due to the slow large woody debris decay rate. Actual LWD stocks and carbon pools are a legacy of the past fire history.

Simple measures of channel habitat complexity predict transient hydraulic storage in streams

Stream thalweg depth profiles (along path of greatest channel depth) and woody debris tallies have recently become components of routine field procedures for quantifying physical habitat in national stream monitoring efforts. Mean residual depth, standard deviation of thalweg depth, and large woody debris (LWD) volumes are potential metrics of habitat complexity calculated from these survey data. We used 42 intensive dye-transit studies to demonstrate the relevance of these easily measured channel habitat complexity metrics to transient hydraulic (“dead zone”) storage, a channel process important for biotic habitat as well as retention and “spiraling” of dissolved and particulate nutrients. We examined transient storage and channel morphology in small gravel and cobble-bedded upland streams (wetted width 2–5 m; slopes 2.6–8.3%) representing a wide range of flow stages, LWD loading, and channel complexity, including measurements before and after LWD was added to enhance fish habitat. While transient storage volume fraction decreased as flow stage increased in simple channels, those with complex morphology and well-developed riparian vegetation maintained high transient storage fractions even during storm flows. LWD additions increased transient storage and channel complexity over the 2 years of post-treatment measurements. We predict with considerable precision two different formulations of transient hydraulic storage fraction using single-variable linear regressions on residual depth (R 2 = 0.61–0.89), thalweg depth variance (R 2 = 0.64–0.91), or large woody debris volume (R 2 = 0.48–0.74). Demonstration of these likely causal associations contributes to understanding the process of transient storage and redefines the use of thalweg profile metrics as a new approach to quantifying morphologic and hydraulic complexity in streams.

Large Woody Debris Input and Its Influence on Channel Structure in Agricultural Lands of Southeast Brazil

Riparian forests are important for the structure and functioning of stream ecosystems, providing structural components such as large woody debris (LWD). Changes in these forests will cause modifications in the LWD input to streams, affecting their structure. In order to assess the influence of riparian forests changes in LWD supply, 15 catchments (third and fourth order) with riparian forests at different conservation levels were selected for sampling. In each catchment we quantified the abundance, volume and diameter of LWD in stream channels; the number, area and volume of pools formed by LWD and basal area and tree diameter of riparian forest. We found that riparian forests were at a secondary successional stage with predominantly young trees (diameter at breast height <10cm) in all studied streams. Results showed that basal area and diameter of riparian forest differed between the stream groups (forested and non-forested), but tree density did not differ between groups. Differences were also observed in LWD abundance, volume, frequency of LWD pools with subunits and area and volume of LWD pools. LWD diameter, LWD that form pools diameter and frequency of LWD pools without subunits did not differ between stream groups. Regression analyses showed that LWD abundance and volume, and frequency of LWD pools (with and without subunits) were positively related with the proportion of riparian forest. LWD diameter was not correlated to riparian tree diameter. The frequency of LWD pools was correlated to the abundance and volume of LWD, but characteristics of these pools (area and volume) were not correlated to the diameter of LWD that formed the pools. These results show that alterations in riparian forest cause modifications in the LWD abundance and volume in the stream channel, affecting mainly the structural complexity of these ecosystems (reduction in the number and structural characteristics of LWD pools). Our results also demonstrate that riparian forest conservation actions must consider not only its extension, but also successional stage to guarantee the quantity and quality of LWD necessary to enable the structuring of stream channels.

A critical review of field techniques employed in the survey of large woody debris in river corridors: a central European perspective

In forested watersheds, large woody debris (LWD) is an integral component of river channels and floodplains. Fallen trees have a significant impact on physical and ecological processes in fluvial ecosystems. An enormous body of literature concerning LWD in river corridors is currently available. However, synthesis and statistical treatment of the published data are hampered by the heterogeneity of methodological approaches. Likewise, the precision and accuracy of data arising out of published surveys have yet to be assessed. For this review, a literature scrutiny of 100 randomly selected research papers was made to examine the most frequently surveyed LWD variables and field procedures. Some 29 variables arose for individual LWD pieces, and 15 variables for wood accumulations. The literature survey revealed a large variability in field procedures for LWD surveys. In many studies (32), description of field procedure proved less than adequate, rendering the results impossible to reproduce in comparable fashion by other researchers. This contribution identifies the main methodological problems and sources of error associated with the mapping and measurement of the most frequently surveyed variables of LWD, both as individual pieces and in accumulations. The discussion stems from our own field experience with LWD survey in river systems of various geomorphic styles and types of riparian vegetation in the Czech Republic in the 2004-10 period. We modelled variability in terms of LWD number, volume, and biomass for three geomorphologically contrasting river systems. The results appeared to be sensitive, in the main, to sampling strategy and prevailing field conditions; less variability was produced by errors of measurement. Finally, we propose a comprehensive standard field procedure for LWD surveyors, including a total of 20 variables describing spatial position, structural characteristics and the functions and dynamics of LWD. However, resources are only rarely available for highly time-demanding surveys. We therefore include a set of core LWD metrics for routine baseline surveys of individual LWD pieces (diameter, length, rootwad size, preservation of branches and rootwad, geomorphological/ecological function, stability/mobility) and wood accumulations (number of LWD pieces, geometrical dimensions, channel blockage, wood/air ratio), which may provide useful background information for river management, hydromorphological assessment, habitat evaluation, and inter-regional comparisons.

Forest Seral Stage and Large Woody Debris Abundance in an Allegheny High Plateau Foreststream System

Large woody debris (LWD) in the form of standing dead trees and down logs is an important structural and functional component of forest ecosystems and is a key factor linking riparian forests and streams. We examined the influence of forest seral stage (old-growth vs. second-growth forest) on terrestrial (snags and down logs) and in-stream LWD abundance in a riparian forest-stream system in Cook Forest State Park, Pennsylvania. Snag density, but not basal area, was significantly greater in second-growth forest due to elevated mortality of eastern white pine (Pinus strobus L.). Abundance of both terrestrial and in-stream LWD was significantly greater in the old-growth forest-stream system than in second-growth. Eastern hemlock, Tsuga canadensis (L.) Carr., strongly dominated the volume of both terrestrial and in-stream LWD in the old-growth stand and adjacent stream reaches. Terrestrial and in-stream LWD loadings that we recorded are similar to loadings occurring in forest-stream systems elsewhere in the eastern United States, especially the Appalachian region, suggesting that these values may be useful targets for LWD enhancement projects for Allegheny High Plateau forest-stream systems.

Assessing the relations between aquatic habitat indicators and forest harvesting at watershed scale in the interior of British Columbia

Selection of appropriate aquatic habitat indicators is important for supporting sustainable forest and watershed management. To date, many identified watershed indicators have not been well tested. To address this issue, we sampled 28 stream reaches in the central and south interior of British Columbia, Canada. The selected reaches were similar with respect to gradient, watershed and topographic characteristics but with various levels of forest harvesting. Aquatic habitat indicators were derived based on a field survey, involving substrates, channel dimensions, pools, and large woody debris (LWD), together with some ratios and derivatives generated from them. Timber harvest disturbance at the watershed scale was quantified by calculating historical forest clear-cut area based on the BC vegetation resources inventory database. To account for the subsequent forest recovery, equivalent clear-cut area (ECA) was calculated based on the dominant species of each stream watershed and its regrowth since being logged. Pearson correlation coefficients showed that percent ECA and percent historical clear-cut area could effectively quantify the cumulative logging disturbance by limiting the effect of factors not related to logging activity (i.e., watershed area and elevations). These two variables were then related to the aquatic habitat indicators. Pearson correlation analyses found that relative width (ratio of D to bankfull width) ( D is the b axis diameter of the largest substrate particle found in the reach), relative roughness (ratio of D to bankfull depth), pool frequency and per piece LWD volume are sensitive to percent ECA, i.e., significant ( p < 0.01) while independent of influence from non-forest logging activity related factors and spatial clustering of samples. This relationship also holds true for the last two indicators when related to percent historical clear-cut area, though with a reduced degree of correlation. In addition, mean LWD diameter also showed significant relationship with percent historical clear-cut area, but not with percent ECA. Overall, per piece LWD volume was considered as the best aquatic habitat indicator. The performance of mean LWD diameter was comparable to per piece LWD volume if percent historical clear-cut area was used to quantify forest disturbance. Implications of these findings for forest management strategies are discussed.

Spatial distribution and influence of large woody debris in an old-growth forest river system, New Zealand

A field survey was undertaken to determine the quantity, spatial distribution and influence of large woody debris (LWD) in a fifth-order river system in old-growth forest in New Zealand. LWD attributes were assessed at 25 sites distributed in the headwaters and along the main stem of the Whirinaki River system (73 km 2). LWD volume, number of pieces, piece length and piece size, were positively correlated with bankfull width, whereas the number of pieces/unit area, LWD/unit area, number of pieces suspended across the channel and LWD influence on channel morphology, were negatively correlated. Pieces influencing channel morphology were larger, longer and more stable than average. We identified four key zones in the river system based on LWD spatial distribution patterns and influence on habitat complexity. Zonal boundaries occurred where there were changes in the transport capacity, fluvial processes, channel width and geomorphic structure of the channel. The results of this study highlight the need to understand the characteristics, spatial distribution patterns and influence of LWD at the catchment level when undertaking protective, management or rehabilitation programmes in forested river ecosystems.

The geomorphic function and characteristics of large woody debris in low gradient rivers, coastal Maine, USA

The role, function, and importance of large woody debris (LWD) in rivers depend strongly on environmental context and land use history. The coastal watersheds of central and northern Maine, northeastern U.S., are characterized by low gradients, moderate topography, and minimal influence of mass wasting processes, along with a history of intensive commercial timber harvest. In spite of the ecological importance of these rivers, which contain the last wild populations of Atlantic salmon ( Salmo salar) in the U.S., we know little about LWD distribution, dynamics, and function in these systems. We conducted a cross-basin analysis in seven coastal Maine watersheds, documenting the size, frequency, volume, position, and orientation of LWD, as well as the association between LWD, pool formation, and sediment storage. In conjunction with these LWD surveys, we conducted extensive riparian vegetation surveys. We observed very low LWD frequencies and volumes across the 60 km of rivers surveyed. Frequency of LWD ≥ 20 cm diameter ranged from 15–50 pieces km − 1 and wood volumes were commonly < 10–20 m 3 km − 1 . Moreover, most of this wood was located in the immediate low-flow channel zone, was oriented parallel to flow, and failed to span the stream channel. As a result, pool formation associated with LWD is generally lacking and < 20% of the wood was associated with sediment storage. Low LWD volumes are consistent with the relatively young riparian stands we observed, with the large majority of trees < 20 cm DBH. These results strongly reflect the legacy of intensive timber harvest and land clearing and suggest that the frequency and distribution of LWD may be considerably less than presettlement and/or future desired conditions.

MATURE AND OLD-GROWTH RIPARIAN FORESTS: STRUCTURE, DYNAMICS, AND EFFECTS ON ADIRONDACK STREAM HABITATS

Riparian forests regulate linkages between terrestrial and aquatic ecosystems, yet relationships among riparian forest development, stand structure, and stream habitats are poorly understood in many temperate deciduous forest systems. Our research has (1) described structural attributes associated with old-growth riparian forests and (2) assessed linkages between these characteristics and in-stream habitat structure. The 19 study sites were located along predominantly first- and second-order streams in northern hardwood-conifer forests in the Adirondack Mountains of New York (U.S.A.). Sites were classified as mature forest (6 sites), mature with remnant old-growth trees (3 sites), and old-growth (10 sites). Forest-structure attributes were measured over stream channels and at varying distances from each bank. In-stream habitat features such as large woody debris (LWD), pools, and boulders were measured in each stream reach. Forest structure was examined in relation to stand age using multivariate techniques, ANOVA, and linear regression. We investigated linkages between forest structure and stream characteristics using similar methods, preceded by information-theoretic modeling (AIC). Old-growth riparian forest structure is more complex than that found in mature forests and exhibits significantly greater accumulations of aboveground tree biomass, both living and dead. In-stream LWD volumes were significantly (alpha = 0.05) greater at old-growth sites (200 m3/ha) compared to mature sites (34 m3/ha) and were strongly related to the basal area of adjacent forests. In-stream large-log densities correlated strongly with debris-dam densities. AIC models that included large-log density, debris-dam density, boulder density, and bankfull width had the most support for predicting pool density. There were higher proportions of LWD-formed pools relative to boulder-formed pools at old-growth sites as compared to mature sites. Old-growth riparian forests provide in-stream habitat features that have not been widely recognized in eastern North America, representing a potential benefit from late-successional riparian forest management and conservation. Riparian management practices (including buffer delineation and restorative silvicultural approaches) that emphasize development and maintenance of late-successional characteristics are recommended where the associated in-stream effects are desired.

A watershed scale assessment of in-stream large woody debris patterns in the southern interior of British Columbia

In-stream large woody debris (LWD) is a structurally and functionally important component of forested stream ecosystems. To assess the role played by LWD in sustaining aquatic ecosystems at the watershed scale, the amount, distribution, dynamics and function of LWD within channel networks have to be determined. We surveyed 35 sites in first- through fifth-order streams within forested watersheds in the southern interior of British Columbia, and the spatial variation and distribution of LWD characteristics (frequency, density, volume, biomass, orientation, submersion, and decay state) were quantified based on four stream size categories. We found that the average diameter, length, volume and biomass of individual LWD pieces increased as a function of increasing bankfull width. However, LWD density (piece per 100 m 2 of the stream area) decreased with an increase in bankfull width. LWD volume ranged from 0.78 to 1.58 m 3/100 m 2 of stream area, with intermediate sized streams (sizes II and III) having the largest value and large sized streams (size IV) having the lowest values. Results showed that LWD biomass averaged 383 kg/100 m 2 (range 265–651 kg/100 m 2) in stream size I, increased to 491 kg/100 m 2 (range 81–1254 kg/100 m 2) in stream size II, and slightly decreased to 465 kg/100 m 2 (range 247–938 kg/100 m 2) in stream size III and further decreased to 250 kg/100 m 2 (range 88–533 kg/100 m 2) in stream size IV. The large majority of LWD pieces in the smallest sized streams was orientated perpendicular to streamflow and was located in spanning the channel. Conversely, most LWD pieces in intermediate sized streams were orientated parallel to the direction of flow and were situated below the bankfull height of the channel. With a difference in the orientation and position, LWD pieces within different sized streams are expected to have varying potentials to affect streamflow and channel habitats. These results highlight the need to recognize spatial variation of in-stream LWD loading and function through channel networks when maintaining suitable LWD pieces and making riparian management decisions at watershed scales.

Effects of prescribed fire on a Sierra Nevada (California, USA) stream and its riparian zone

Concerns about the effects of fire on ecologically sensitive habitats have limited the use of prescribed fire in the management of forest riparian areas. Using a beyond-BACI (Before-After-Control-Impact) experimental design, we examined the effects of a 26-ha prescribed fire that burned upland and riparian areas of a first-order watershed, and compared this to five unburned sites examined from 1 to 7 years pre-fire and 1 year post-fire. We monitored pre- and post-fire riparian vegetation, large woody debris, sediment, water chemistry, periphyton, and benthic macroinvertebrates. The prescribed fire in the riparian zone was patchy in terms of intensity, consumption, and severity; it consumed 79% of the pre-fire fuel in the riparian zone, 34% of the total surface fuel, and 90% of the total ground fuel. The prescribed fire significantly reduced percent cover of surface vegetation and plant taxa richness in comparison to unburned sites but not plant diversity (Simpson's D). Community composition of understory riparian vegetation changed post-fire, most likely as a result of the reduction in taxa richness and cover. Riparian tree mortality (>11.5 cm DBH) was only 4.4% post-fire. Similarly, there was no post-fire change in large woody debris volume and recruitment, or fine sediment in pools ( V *). Post-fire, there were increases in some water chemistry parameters (SO 4 −, total P, Ca 2+, and Mg 2+) and a decrease in periphyton biomass; however, these changes were short-term, and recovery occurred in ≤1 year. Macroinvertebrate community composition but not density, richness, or diversity was affected 10–19 d post-fire; composition recovered within 1 year. The trends observed in this study examining multiple abiotic and biotic parameters suggest that this prescribed fire either had no or short-lasting (≤1 year) impacts on Dark Canyon Creek and its riparian zone. The limited observed impacts are at least partially a result of the small portion (<20%) of the watershed area burned, moderate topography, the low- to moderate-severity of the fire, and the relatively low precipitation (and thus, stream flow) that occurred post-fire.

Post-flooding distribution and characteristics of large woody debris piles along the semi-arid Sabie River, South Africa

The formation of large woody debris (LWD) piles has a profound impact on channel patterns and riparian succession in temperate rivers. The opportunity to study LWD along the Sabie River, a river in the semi-arid region of Kruger National Park, South Africa, arose in February 2000 after a significant flood (c. 100-year return interval) removed a large proportion of the fully mature riparian forest and other plant communities. Much of the uprooted vegetation was deposited as LWD piles (woody vegetation accumulations deposited on the ground > 0.1m 3) throughout the riparian and upland zones. In this article we describe the spatial distribution patterns of LWD as related to geomorphic channel type and flood frequency zone, and assess pile composition characteristics six months after the flood. Within the areas surveyed there were 68 LWD piles per hectare, the median size of LWD piles was 4.6 m3 but pile sizes (by volume) varied widely. Pool/rapid geomorphic channel types had the highest density of LWD piles (79 ha-1) and the largest piles (by volume) were in the bedrock anastomosing channels (mean = 124 m3). Piles were larger in the seasonal and ephemeral flood frequency zones (mean = 54 m 3 and 55 m3) than piles in the active zone (c. 2 m3). The patterns of distribution and volume of LWD will affect the subsequent development of vegetation communities as debris piles form a mosaic of patches of surviving organisms and propagules that can strongly influence the initial trajectory of succession. The amount, distribution, and subsequent decomposition of LWD are different from that reported for temperate rivers, suggesting that the role of LWD may be different on non-floodplain rivers such as the Sabie in semi-arid South Africa.