Woody Debris In Streams Research Articles

Effects of woody debris and the supply of terrestrial invertebrates on the diet and growth of brown trout (Salmo trutta) in a boreal stream

Summary Changes to the riparian vegetation of forest streams during timber harvesting may have considerable impacts on stream biota, but few studies have attempted to separate the effects of individual factors that are altered during clear‐felling operations. We studied the effects of large wood and terrestrial invertebrate supply, two factors affected by forest harvesting, on the growth and diet of two size classes of brown trout (Salmo trutta) during a two‐month (June–August) field enclosure experiment. Twelve 20‐m‐long enclosed stream reaches were used in a 2 × 2 factorial design, with large wood either absent or added to mimic pre‐modern forestry conditions, and terrestrial invertebrate inputs either reduced or maintained at ambient levels. The addition of large wood had a positive effect on the growth of large trout but no effect on small trout, whereas terrestrial invertebrate input had no effect on the growth of either size class. Growth rates were highest in the treatment with ambient terrestrial invertebrate inputs and added wood, were lowest in the treatment with reduced terrestrial invertebrate inputs and no added wood and were intermediate in the other two treatments. Dietary analyses showed no difference in treatments with and without added wood, perhaps because instream wood influences growth by producing profitable stream positions for trout, rather than by acting as a source of prey. Terrestrial invertebrate inputs affected the diet, as trout in enclosures with reduced inputs had a lower proportion of terrestrial invertebrate biomass in the diet than trout in enclosures with ambient terrestrial inputs. Our results suggest that leaving woody debris in streams when harvesting forests may enhance trout growth and that this is probably due to the physical changes in depth and current velocity caused by the wood rather than to changes in dietary prey composition.

The use of floating overhead cover by warmwater stream fishes

Increasing the amount of woody debris in streams has often increased population size of one or more focal species whereas clearing a stream of woody debris has often reduced populations. Alterations of the amount of woody debris change multiple aspects of the habitat simultaneously, so it is very difficult to know what particular stimulus or combination of stimuli evoked the changes in the fish populations. The purpose of this research was to alter habitat by the addition of overhead cover alone, and to see whether or not that single change would affect the distribution of stream-dwelling fishes. The addition of solid, floating cover objects 1.8 m by 2.4 m resulted in increased local populations of bluntnose minnow (Pimphales notatus), creek chub (Semotilus atromaculatus), and longear sunfish (Lepomis megalotis) five to six weeks later, but did not change the distribution of four other species: white sucker (Catostomus commersoni), green sunfish (Lepomis cyanellus), bluegill (Lepomis macrochirus), and largemouth bass (Micropterus salmoides). These results showed that for some species at least, changes in channel morphology, visual isolation, and amelioration of flow produced by adding three-dimensional complex woody debris were not essential for making locally attractive habitat changes in a warmwater stream. The effectiveness of overhead cover as used here would be expected to vary for different species and depend on such things as predation threat, flow, and food levels.

Comparisons of the Colonisation by Invertebrates of Three Species of Wood, Alder Leaves, and Plastic “Leaves” in a Temperate Stream

AbstractSmall woody debris in streams is abundant, and may be a food source or may provide a substrate on which other food sources such as biofilm may develop, both of which may be significant to invertebrates in times of food scarcity. We examined patterns of invertebrate colonisation of small woody debris (veneers of red alder, Douglas‐fir, and western red cedar), red alder leaves, and plastic (as an inert substrate to mimic leaves). Invertebrate colonisation was high on alder leaves, but low on wood substrates and plastic, controlling for the available surface area. Detritivorous invertebrates had significantly higher colonisation rates of alder leaves versus the other four substrates, whereas predators and collectors did not (consistent with their use of these as substrates and not food). All wood decreased in mass by <15% and leaves by ∼50% over the 75 days of the experiment. For all taxa tested, there was no significant difference in their colonisation of the wood veneers versus the plastic sheets. These results suggest that wood was not directly used by these invertebrates as a food source, or that there could be similar biofilm development on the surfaces of these substrates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simulating the Effects of Forest Management on Large Woody Debris in Streams in Northern Idaho

Abstract Existing models for simulating large woody debris (LWD) loads of forest streams were adapted for forest conditions in northern Idaho. Effects of riparian management prescriptions implemented for streams within a habitat conservation planning area for bull trout and other sensitive species were evaluated based on riparian and instream LWD conditions observed along 58 randomly selected stream segments. A wood budgeting system presented by Welty et al. (2002. Riparian aquatic interaction simulator (RAIS): A model of riparian forest dynamics for the generation of large woody debris and shade. For. Ecol. Manage. 162:299–318) was employed through use of observed starting instream LWD loads and generalized depletion rates. LWD recruitment estimates were based on locally relevant growth and yield simulators, taper equations, and adjustments for tree fall directional bias. LWD loading, expressed as the number of qualifying pieces per 1,000 ft of stream, was examined under two scenarios: a no-harvest scenario and a harvest scenario. Results indicated no significant difference in the frequency distribution of simulated LWD loading between the no-harvest and harvest scenarios over a 100-year prediction period. Examination of our assumptions indicated that LWD loading was likely underestimated and less variable than would be expected. However, these assumptions had equal effects on each scenario, enabling us to confidently interpret the effects of timber harvest. The nature and extent of riparian forest harvesting evaluated in this simulation is similar to levels being considered elsewhere in the region. Therefore, simulation techniques demonstrated here could be applied elsewhere in the region for evaluating the potential effects of riparian management on fisheries resources.

A quantitative framework for evaluating the mass balance of in-stream organic debris

A quantitative framework is developed for analyzing the mass budget of in-stream woody debris. Wood budgets are necessary for defining the relative importance of different recruitment processes over short and long periods, for designing spatially explicit simulation models, and for estimating the range of variability. The framework is used to analyze century-long patterns of large woody debris in streams that are governed by episodic forest death (fire and wind), forest growth and chronic mortality, bank erosion, mass wasting, decay, and stream transport. Simplified mathematical expressions are used to represent climatic, hydrologic, geomorphic, and biotic processes. Results are expressed in terms of time series and probability distributions. Predictions include that in areas of longer fire rotation (500 years) toppling of fire-killed trees comprises only 15% of the long-term wood budget yet chronic stand mortality that affect the large standing forest biomass ensures continuous large volumes of wood in streams. In contrast, toppling of fire-killed trees in forest environments with shorter fire rotations (150 years) comprise about 50% of the wood budget and indicates that field observers have a significantly higher chance of encountering low wood volumes in streams. Wood recruitment by bank erosion should increase irregularly downstream and bank erosion recruitment should exceed mortality recruitment at a bank erosion rate of approximately 5 cm per year. Recruitment from debris flows represents the single largest point source of woody debris to streams. The rarity of debris flows, in conjunction with a 3% per year annual decay rate, limits the contribution of wood from debris flows to about 12% of the long-term wood budget. Fluvial transport of wood promotes an increase in both inter-jam spacing and jam volume downstream. The proportion of woody debris transported into a reach in comparison to lateral recruitment approaches an asymptotic maximum of 50% when tree height approaches channel width. The relationships among process rates, their spatial variance across landscapes, and the resulting probability distributions of long-term patterns of wood abundance are proposed as a set of general theoretical principles. New data on wood supply and storage at the network scale are needed to fully test the predictions made in this analysis.

Experimental provision of large woody debris in streams as a trout management technique

Abstract The natural stock of large woody debris (LWD) in the afforested Douglas River (Fermoy, Co. Cork) is very low relative to old‐growth forests, which seems to arise from deficiency both of supply and retention. Woody debris is important to the ecology and physical structure of forest streams, so its abundance is relevant to aquatic conservation and the maintenance and size of salmonid fish stocks. The physical characteristics and fish stocks of 16 contiguous segments of two 200 m stream reaches were surveyed in spring 1998 prior to the installation of 12 partially spanning debris structures on four of the segments. This study investigated the effect of debris structures on the heterogeneity of flow and substratum, and the distribution of brown trout (Salmo trutta), and assessed the potential use of woody debris manipulation as a tool in the management of forest streams. Surveys of stream habitat conditions over a 2 year period following the installation of woody debris showed a change in stream architecture. This created more suitable habitat for trout through development of additional pools in which beds of fine sediment developed, and constraining the main current, increasing the amount of eddies and slack water areas. There were significant increases in trout density and biomass in the debris segments relative to control segments without debris dams 1 and 2 years after debris addition, although trout condition was not modified by the addition of LWD. These results suggest that the addition of woody debris offers a positive and practical management technique for enhancing fish in plantation forest streams. Copyright © 2002 John Wiley & Sons, Ltd.

Mapping the spatial and temporal distributions of woody debris in streams of the Greater Yellowstone Ecosystem, USA

The objectives of this study were: (1) to document spatial and temporal distributions of large woody debris (LWD) at watershed scales and investigate some of the controlling processes; and (2) to judge the potential for mapping LWD accumulations with airborne multispectral imagery. Field surveys were conducted on the Snake River, Soda Butte Creek, and Cache Creek in the Greater Yellowstone Ecosystem, USA. The amount of woody debris per kilometer is highest in 2nd order streams, widely variable in 3rd and 4th order streams, and relatively low in the 6th order system. Floods led to increases in woody debris in 2nd order streams. Floods redistributed the wood in 3rd and 4th order streams, removing it from the channel and stranding it on bars, but appeared to generate little change in the total amount of wood throughout the channel system. The movement of woody debris suggests a system that is the reverse of most sediment transport systems in mountains. In 1st and 2nd order tributaries, the wood is too large to be moved and the system is transport-limited, with floods introducing new material through undercutting, but not removing wood through downstream transport. In the intermediate 3rd and 4th order channels, the system displays characteristics of dynamic equilibrium, where the channel is able remove the debris at approximately the same rate that it is introduced. The spatial distribution and quantity of wood in 3rd and 4th order reaches varies widely, however, as wood is alternatively stranded on gravel bars or moved downstream during periods of bar mobilization. In the 6th order and larger channels, the system becomes supply-limited, where almost all material in the main stream can be transported out of the central channel by normal stream flows and deposition occurs primarily on banks or in eddy pool environments. Attempts to map woody debris with 1-m resolution digital four-band imagery were generally unsuccessful, primarily because the imagery could not distinguish the narrow logs within a pixel from the surrounding sand and gravel background and due to problems in precisely coregistering imagery and field maps.

Transport and deposition of large woody debris in streams: a flume experiment

Large woody debris (LWD) is an integral component of forested streams of the Pacific Northwest and elsewhere, yet little is known about how far wood is transported and where it is deposited in streams. In this paper, we report the results of flume experiments that examine interactions among hydraulics, channel geometry, transport distance and deposition of floating wood. These experiments were carried out in a 1.22-m-wide×9.14-m-long gravel bed flume using wooden dowels of various sizes as surrogate logs. Channel planforms were either self-formed or created by hand, and ranged from meanders to alternate bars. Floating pieces tended to orient with long axes parallel to flow in the center of the channel. Pieces were deposited where channel depth was less than buoyant depth, typically at the head of mid-channel bars, in shallow zones where flow expanded, and on the outside of bends. We hypothesize that the distance logs travel may be a function of the channel's debris roughness, a dimensionless index incorporating ratios of piece length and diameter to channel width, depth and sinuosity. Travel distance decreased as the ratio of piece length to both channel width and radius of curvature increased, but the relative importance of these variables changed with channel planform. Large pieces can move further than our debris roughness models predict if greater than 50% of the active channel area is deeper than the buoyant depth of the piece, or if momentum is high enough to carry pieces across shallows. Our debris roughness model allows first-order prediction of the amount of wood transport under various channel geometries.

Effectiveness of large woody debris in stream rehabilitation projects in urban basins

Urban stream rehabilitation projects commonly include log placement to establish the types of habitat features associated with large woody debris (LWD) in undisturbed streams. Six urban in-stream rehabilitation projects were examined in the Puget Sound Lowland of western Washington. Each project used in-stream log placement as the primary strategy for achieving project goals; none included systematic watershed-scale rehabilitation measures. The effectiveness of LWD in these projects was evaluated by characterizing physical stream conditions using common metrics, including LWD frequency and pool spacing, and by sampling benthic macroinvertebrates. In all project reaches where pre-project data existed, pool spacing narrowed after LWD installation. All project sites exhibited fewer pools for a given LWD loading, however, than has been reported for forested streams. In project reaches where the objective was to control downstream sedimentation, only limited success was observed. At none of the sites was there any detectable improvement in biological conditions due to the addition of LWD. Our results indicate that, although LWD projects can modestly improve physical habitat in a stream reach over a time scale of 2–10 years, they apparently do not achieve commensurate improvement in biological conditions.

FLOW DISTURBANCE CAUSED BY CROSS-STREAM COARSE WOODY DEBRIS

Coarse woody debris affects many streams in forested regions throughout the world. These effects include lateral channel migration, bank slumping, and aggradational or erosional features related to flow redirection. The extent of effect is dependent on the ability of the system to resist the new forces derived from flow redirection. This study on the Pine River, Ontario, looks at how obstructions that are perpendicular to downstream flow modify fluid behavior. Results show that fluctuations in speed and approach azimuth vary considerably depending on the position of the sample relative to the obstruction. The use of time-averaged (1 sec., 30 sec.) recordings of fluid speed and azimuth at selected channel locations shows how flow adjusts to external controls as it moves away from the obstruction zone, giving an indication of the spatial extent of the obstruction influence. These data are represented as a function of the diameter of the obstruction relative to the surrounding flow depth (obstruction ratio), and then are compared to results found in other debris obstructions on the Pine River and Wilmot Creek. Flow obstruction dimensions in the study site equal 26.5 trunk diameters (the average diameter of the tree trunk measured five times along its length), and range between 16.9 and 56.7 trunk diameters on the Pine River (n = 48) and between 7.4 and 63.5 trunk diameters on Wilmot Creek (n = 1066). Knowledge of these spatial relationships may allow for better management of woody debris in streams, primarily from the perspective of aquatic habitat. Multiquadric interpolation formed the basis for plotting fluid vector fields, showing the behavior of flow as it approached and moved through the obstruction zone. This is compared to studies of flow in unobstructed meanders in an attempt to quantify obstruction influence, and is used to provide a depiction of flow under these circumstances. [Key words: flow patterns, woody debris, influence zones, stream management.]

Applying geostatistics to quantify distributions of large woody debris in streams

Large woody debris (LWD) strongly influences morphology and aquatic habitat in streams within forested watersheds. Previous studies have used data to describe spatial distributions of LWD in qualitative terms. We used high-resolution spatial data collected from a forested stream in western Oregon to conduct three geostatistical analyses. The data were collected at five time periods prior to and following the addition of LWD into the stream. Each analysis is examined for its potential and shortcomings in quantifying distributions. Our findings indicate that semi-variograms, when used with a raster spatial data structure, can be useful quantitative descriptions of LWD distributions.

Function and dynamics of woody debris in stream reaches in the central Sierra Nevada, California

In 1993, we located, measured, and tagged almost 1700 woody debris pieces on six streams in California’s central Sierra Nevada. The stability, geomorphic function, and use by fish for cover of each piece were recorded. In 1994 and 1995, piece movement was quantified and new debris pieces were measured. In the 60 study reaches, debris was not influential in shaping channel morphology and fish cover. Although woody debris was often associated with habitat units, few pieces deflected flow or contributed to the formation of pools or steps. Fish used deep water as cover more often than debris or any other cover type. Medium-sized debris was, however, used in a greater proportion than its availability to fish. Little sediment was stored by debris, and five large pieces stored 85% of the sediment volume measured. Debris frequency and volume did not differ significantly by channel type. After a low stream flow year (1993–1994), few pieces had moved and few new pieces were identified. After a high-flow season (1994–1995), 31% of the pieces had either moved or were not found and new pieces represented over 5% of the originally surveyed volume of wood.

Changes in the quantity and characteristics of large woody debris in streams of the Olympic Peninsula, Washington, U.S.A. (1982-1993)

We assessed the changes in large woody debris (LWD) abundance and composition at 28 sites in 27 low-gradient Olympic Peninsula streams between 1982 and 1993. The average number of pieces of debris was virtually identical (P = 0.98) in both years (50.7 versus 50.6). However, we found a significant (P <= 0.01) reduction in the total volume of LWD material in the stream sites surveyed (51.7 m3 ·100 m-1 in 1982 to 38.2 m3 ·100 m-1 in 1993). While the mean volume of second-growth derived LWD increased from 3.6 to 10.9 m3 ·100 m-1 (P < 0.01), the increase was insufficient to offset the loss of old-growth derived LWD. The mean volume of old-growth derived LWD for all sites decreased from 48.1 to 27.4 m3 ·100 m-1 between sample years (P < 0.01). The mean diameter of second-growth derived LWD was significantly larger in 1993 than in 1982, although still smaller than old-growth derived pieces. We measured a significant increase in the percentage of LWD pieces rated as highly decayed from 1982 to 1993. The results indicate that the loss of old-growth derived LWD following the removal of old-growth riparian forests is initially very rapid, followed by a slower rate of depletion associated with watershed destabilization. Inputs of LWD from second-growth riparian forests up to 73 years old were characterized by small diameter, high mobility, and high decay rates.

Function and dynamics of woody debris in stream reaches in the central Sierra Nevada, California

Function and dynamics of woody debris in stream reaches in the central Sierra Nevada, California

Changes in the quantity and characteristics of large woody debris in streams of the Olympic Peninsula, Washington, U.S.A. (1982-1993)

Changes in the quantity and characteristics of large woody debris in streams of the Olympic Peninsula, Washington, U.S.A. (1982-1993)

HYDRAULIC GUIDELINES FOR THE RE‐INTRODUCTION AND MANAGEMENT OF LARGE WOODY DEBRIS IN LOWLAND RIVERS

The volume of large woody debris in most of the world's lowland rivers has been depleted, either through persistent de-snagging or clearance of the riparian vegetation from which it is naturally recruited. The now recognized important environmental role of debris in rivers, the established environmental value of vegetated riparian buffer strips and the movement towards rehabilitation of degraded riverine habitats demand more objective procedures for the management of woody debris in streams. In some instances it may be centuries before the process of natural recruitment of wood from rehabilitated riparian strips achieves an ecologically adequate volume and quality of instream debris. To accelerate this process, the re-introduction of debris is being considered. This paper presents the results of laboratory and field hydraulic investigations relevant to the problem of managing debris in lowland rivers. The laboratory experiments were used to develop a model, based on the momentum principle, of the effect of debris on afflux, or the increase in water surface elevation. Debris drag was found to be less affected by position and shape than by orientation to the flow and blockage ratio, or the proportion of the channel occupied by the debris. Debris aligned at 20–30° to the flow produced an afflux one-third of that produced by debris which was perpendicular. Significant loss of conveyance occurs only for debris which is large relative to the channel dimensions (greater than about 10% of the channel area blocked by debris). Wake interference acts to reduce the hydraulic effect of debris so that if spaced within two diameters, multiple in-line items of debris produce an afflux no greater than that of a single item. The models of debris hydraulics presented here can be used to predict the effect of removing, lopping, rotating or re-introducing debris to rivers.

Environmental Hydraulics of Large Woody Debris in Streams and Rivers

Although awareness of the habitat value of large woody debris in streams has promoted a more environmentally sensitive approach to its management, present guidelines are largely intuitive and do not contain advice for conducting quantitative hydraulic investigations. This review of the literature provides information to assist management, and highlights deficiencies in current knowledge. Hydraulically, debris act as large roughness elements that provide a varied flow environment, reduce average velocity, and locally elevate the water-surface profile. This can significantly increase flood travel time. The significance of debris is scale-dependent. For example, the hydraulic effects are often drowned out in a large flood on a large river. Some hydraulic models can be used to predict the effect of debris removal or reinstatement. A challenge for research is the development of a hydraulically and biologically meaningful definition of debris geometry that can be readily used in the field. When more is known about the physical and biological significance of debris in rivers, a detailed cost-benefit analysis on its management should be undertaken.

Distribution and abundance of coarse woody debris in some southern New Zealand streams from contrasting forest catchments

Abstract Greater amounts of coarse woody debris (CWD) occurred in streams from old native forests than in streams from young native and pine forests in southern New Zealand. The size of CWD in the streams generally reflected the age of the surrounding vegetation. More wood was present in pool than in non‐pool sections of old native forest streams and the frequency of pools per unit length formed by woody debris was greatest in these streams. The volumes of pools formed by wood and those formed by inorganic substrates were similar. Amounts of woody debris in these streams were relatively small compared to values recorded from North America.

Spatial distribution of coarse woody debris dams in the Lymington Basin, Hampshire, UK

Abstract Debris dams of coarse woody debris have a significant influence on channel processes in forested areas but few detailed studies have been made of variations within a single basin. Results from previous research are standardised and show that average variations throughout basins include densities of debris dams up to 40 per 100 metres of channel and can involve a loading value of up to 225 kg per m2 of channel. Variations have been ascribed to distance downstream, to channel width, to land-use effects, to felling, and to the management of coarse woody debris in streams. This study of the Lymington Basin, 110.4 km2 in drainage area, shows that the input of storm debris resulting from blowdown accounts for 45% of the gross load. The remaining 55% net load varies to distance downstream, to land use with the greatest loads in deciduous woodland areas, and according to management removal of debris from streams and multiple regression equations are provided. It is deduced that as a consequence of long-term management the present channel debris may be as little as 7% of the total net load that could have been present if no management had occurred.

Woody Debris, Channel Features, and Macroinvertebrates of Streams with Logged and Undisturbed Riparian Timber in Northeastern Oregon, U.S.A.

Macroinvertebrate communities and several aspects of fish habitat were examined for 16 northeastern Oregon stream segments, 11 with undisturbed riparian forests and five where 26–54% of the riparian forest had been harvested 6 to 17 yr previously. Amounts of woody debris in streams and pools formed by the debris were similar between undisturbed and logged sites. Pool volume was inversely related to stream gradient and directly related to the amount of woody debris in the stream. Stream surface substrate composition was not significantly different between streams in logged and undisturbed areas. Macroinvertebrate density was 20 to 113 percent greater at the logged sites and diversity was similar at logged and undisturbed sites. Macroinvertebrates were most abundant at lower elevation streams and at streams that were shaded less by the surrounding vegetation. Timber harvesting activities do not appear to have damaged aquatic insect habitat and pool abundance was not altered, suggesting the habitat's carrying capacity for fish was not affected.