Wood In Streams Research Articles

Effects of wood removal on stream habitat and nitrate uptake in two northeastern US headwater streams

Forested headwater streams play an important role in watershed nutrient dynamics, and wood is thought to be a key factor influencing habitat structure and nitrate-nitrogen dynamics in many forested streams. Because wood in streams can promote nitrogen uptake through denitrification, we hypothesized that nitrate uptake velocities would decrease following wood removal. We measured stream characteristics and nitrate uptake velocities before and after wood manipulation experiments conducted at Hubbard Brook Experimental Forest, NH, and the Sleepers River watershed, VT. The mean size of stream substrates and the amount of riffle habitat increased following wood removal. In contrast to our expectations, summer nitrate uptake velocities increased in the wood removal treatments relative to the reference treatments, possibly because wood removal increased the availability of stable substrates for periphyton growth, therefore increasing nitrate demand in these streams. Our results highlight that effects of wood on stream ecosystems occur through multiple pathways and suggest that the relative importance of these pathways may vary seasonally.

Does it make economic sense to restore rivers for their ecosystem services?

Summary Temperate forests managed to maximize sustainable yield of wood products can reduce the availability of dead wood on the forest floor and in adjacent streams, which in turn can impair ecological processes such as retention and transformation of organic matter. Lack of tools to link ecological processes with their effects on human well‐being leads forest managers to ignore the cost on other services from terrestrial and aquatic ecosystems. We examine how adding dead wood to restore stream channel complexity affects the provision and value of selected ecosystem services, mainly related to the retention and transformation of matter and cycling of nutrients, as well as to the effects on aquatic biota. Specifically, we evaluated the cost‐effectiveness of stream restoration through a comparative analysis of four reach‐scale projects in streams flowing through temperate forest and into a drinking water reservoir and two scenarios of active and passive restoration at the basin scale. Results indicate that the lack of dead wood in streams has an important economic cost because of the effects on fish provisioning, opportunities for recreation and tourism, water purification and erosion control. Active reach‐scale restoration resulted in a 10‐ to 100‐fold increase in the monetary benefits provided by streams, accounting as much as 1·8 € per metre of restored river length each year. Results of the reach‐scale cost–benefit analyses estimated that the time required to recover the active restoration investment ranged from 15 to 20 years in low‐ to middle‐order streams. Synthesis and applications. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services.

Effects of forest type and stream size on volume and distribution of stream wood: legacies of wildfire in a Euro-Mediterranean context

Downed wood pieces are key links between terrestrial and aquatic ecosystems. They promote organic matter retention, create habitat, and potentially increase stream productivity. The stock of downed wood in a river system is a product of the interaction between wood supply, transport, in situ losses, and retention characteristics of the system. Fire and forest management are important disturbances that influence the amount and organization of stream wood with boom-and-bust periods of recruitment and fluvial transport processes. We examined 1st- through 3rd-order Portuguese streams flowing through 3 common silvicultural systems in southern Europe: forests of cork oak, eucalyptus, and maritime pine. Our data set included 1483 pieces of wood in 27 streams, all of which had experienced extensive wildfires within the previous 6 y. We used binned neighbor-k analysis to assess wood organization (segregated, random, or aggregated). We then used linear mixed-effects modeling to evaluate the effects of stream order, forest type, and their interaction on wood volume and organization. The best predictor of wood volume and organization was the interaction between forest type and stream order. Most wood pieces were burned and organization was low, suggesting that arrangement of wood was largely a product of input dynamics rather than transport processes at this time. Potential drivers of across-system variability included vegetation obstructions, wood length∶channel width ratios, management actions, and effects of fire. Climate models predict more droughts in the Euro-Mediterranean region in the future, with implications for wood volume, transport, and function as terrestrial vegetation invades intermittent stream channels and plant communities shift from managed forests to shrublands with few trees.

Which stream wood becomes functional following wildfires?

Large wood is a critical element in stream ecosystems, but only a subset of wood pieces actually provide hydraulic, geomorphic, and ecological functions. We test the current paradigm that larger pieces provide more function, and examine the role wildfires may play in affecting functionality of recruited wood. We conducted a cross-basin analysis in nine central Portugal watersheds, obtaining a variety of measurements on 1483 wood pieces (diameter≥0.05m; length≥0.5m) in 27 streams burned within six years prior. We examined nonlinear relationships and indirect effects on function using Generalized Additive Modeling and Structural Equation Modeling. Variables with direct effects on function were piece diameter, rootwads, anchoring, position (bridging, ramping, loose), longitudinal distance along the stream continuum, and the ratio of piece length to channel width. The effect of length ratio on function was nonlinear. Relatively long pieces were more likely to be functional until they were ∼3 times the channel width, at which point longer pieces became less likely to be functional. Post-fire wood likely lacked complexity and longer pieces were more likely to be bridging; both conditions may have prohibited them from interacting with the wetted area. Wildfires had indirect effects on function. Burned pieces were more likely to be large in diameter (thus more likely functional) but not anchored (thus less likely functional); these antagonistic effects may be the reason burned status had no direct effect on function. Our results challenge the well-established idea that the function of wood in streams is simply a matter of wood size, along with indicators of longevity (e.g. stability and decay status). Relatively long pieces may in fact provide less function to the stream, at least until they break or are transported further downstream. Practitioners installing wood to streams should consider pieces with wide diameter and rootwads, approximately 3 times the channel width, and anchored but not bridging the channel.

Association of brook trout andOncorhynchusspp. with large wood jams in a Lake Superior tributary in a northern old‐growth watershed

AbstractWood in streams functions as fish habitat, but relationships between fish abundance (or size) and large wood in streams are not consistent. One possible reason for variable relationships between fish and wood in streams is that the association of fish with wood habitat may depend on ecological context such as large‐scale geomorphology. We studied the relationship between salmonid assemblages and large wood jams (LWJ) in four settings that differed geomorphically at the scale of the stream corridor along a tributary toLakeSuperior in old‐growth conifer–hardwood forest in northernMichigan. The focal fish species of this study were brook trout (Salvelinus fontinalis), which were wild in the stream. Relocation efforts for coaster brook trout (an adfluvial life history variant of brook trout) were ongoing in the study stream. We measured fish abundance and length in pairs of pools of similar size and substrate, but varying in the presence ofLWJ; this allowed us to evaluate associations of fish simply with the presence ofLWJrather than with other channel or flow‐shaping functions ofLWJ. The length ofOncorhynchusspp. and young introduced brook trout was not strongly correlated withLWJpresence; however, the presence ofLWJin pools was positively correlated with larger wild brook trout. We also found that the correspondence ofLWJwith the abundance of salmonids appears to be moderated by the presence of alternative habitat in this relatively natural, old‐growth forest stream.

Annulatascus aquatorba sp. nov., a lignicolous freshwater ascomycete from Sirindhorn Peat Swamp Forest, Narathiwat, Thailand

As part of a long term study of fungi colonizing submerged wood in freshwater streams a new Annulatascus species, A. aquatorba, is described and illustrated from Erythrophleum teysmannii test blocks from Sirindhorn Peat Swamp Forest, southern Thailand. It differs from other species in the genus in ascospore measurements, thickness of the cell wall, 1–3-septate, fusoid to lunate shape, with central brown cells and subhyaline end cells and without a mucilaginous sheath. Asci are cylindrical, pedicellate, with a distinct, wedge-shaped and non-amyloid apical ring. Phylogenetic relationships of this species, based on the combined partial 18S and 28S rDNA, place it in the same clade as A. velatisporus (type species), A. hongkongensis and A. nilensis.

An integrated analytical framework for quantifying the LCOE of waste-to-energy facilities for a range of greenhouse gas emissions policy and technical factors

This study presents a novel integrated method for considering the economics of waste-to-energy (WTE) facilities with priced greenhouse gas (GHG) emissions based upon technical and economic characteristics of the WTE facility, MSW stream, landfill alternative, and GHG emissions policy. The study demonstrates use of the formulation for six different policy scenarios and explores sensitivity of the results to ranges of certain technical parameters as found in existing literature. The study shows that details of the GHG emissions regulations have large impact on the levelized cost of energy (LCOE) of WTE and that GHG regulations can either increase or decrease the LCOE of WTE depending on policy choices regarding biogenic fractions from combusted waste and emissions from landfills. Important policy considerations are the fraction of the carbon emissions that are priced (i.e. all emissions versus only non-biogenic emissions), whether emissions credits are allowed due to reducing fugitive landfill gas emissions, whether biogenic carbon sequestration in landfills is credited against landfill emissions, and the effectiveness of the landfill gas recovery system where waste would otherwise have been buried. The default landfill gas recovery system effectiveness assumed by much of the industry yields GHG offsets that are very close to the direct non-biogenic GHG emissions from a WTE facility, meaning that small changes in the recovery effectiveness cause relatively larger changes in the emissions factor of the WTE facility. Finally, the economics of WTE are dependent on the MSW stream composition, with paper and wood being advantageous, metal and glass being disadvantageous, and plastics, food, and yard waste being either advantageous or disadvantageous depending upon the avoided tipping fee and the GHG emissions price.

Water, Wind, Wood, and Trees: Interactions, Spatial Variations, Temporal Dynamics, and their Potential Role in River Rehabilitation

AbstractRecent Australian research has quantified the role of large wood (wood of any origin and length with a diameter greater than 0.1 m) in dissipating stream energy, forming pool habitats by local bed scour, protecting river banks from erosion, and damming rivers with long rafts causing avulsions. Large wood in Australian streams is sourced by a range of processes from the nearby riparian zone which has usually been degraded by post‐European settlement vegetation clearing. Large wood loadings within the bankfull channel are dependent not only on the type and quality of the riparian plant community but also on bankfull specific stream power, channel width, and the processes of large wood delivery to the stream. While bank erosion and floodplain stripping by catastrophic floods are obvious and important delivery mechanisms, treefall and trunk and branch breakage by strong winds during tropical cyclones and severe storms are also significant in the tropics. Furthermore, wood decay and downstream transport produce temporally dynamic large wood distributions. The longevity of natural large wood structures in rivers, such as rafts, debris dams, and log steps, requires determination. River rehabilitation programs need to not only include the reintroduction of large wood, but also carefully plan the spatial distribution of that wood, the most appropriate type and range of large wood structures, and, most importantly, the revegetation of the riparian zone to ensure a natural long‐term source of large wood. Exotic species management is an essential part of river rehabilitation.

Anthropogenic controls on large wood input, removal and mobility: examples from rivers in the Czech Republic

Anthropogenic controls on large wood in streams and rivers, and its wider geomorphological and ecological consequences, have come under increasing scrutiny in recent years. However, while the anthropogenic controls on riparian vegetation have been extensively studied, the direct effect of removal of wood from rivers and its mobility have not been widely assessed. This paper specifically considers anthropogenic input, removal and mobility of large wood in rivers. The analysis is based on data from ten semi‐natural rivers in the Czech Republic. An increase in number of large wood pieces because of anthropogenic activity was documented in all of the river reaches studied. Anthropogenic activity was responsible for on average 9 per cent of large wood pieces within rivers, rising to over 20 per cent in extreme cases. Large wood unintentionally recruited to rivers by human activity was of smaller dimensions than natural large wood and therefore does not significantly contribute to total large wood volume. Deliberate removal of large wood was also a significant process and in some river reaches natural large wood loads have been reduced by almost 50 per cent. Large wood removal tends to target the largest wood pieces. All pieces of wood bearing signs of anthropogenic impact were susceptible to transport. This may have a negative effect on the public perception of in‐channel large wood. Despite the fact that the river reaches examined were classified as natural or semi‐natural (based on channel morphology and riparian vegetation), the human impact on large wood loads and dynamics (mobility) was surprisingly high. The results suggest that determination of natural large wood loads and dynamics in rivers flowing through the Central European cultural landscape remain difficult to quantify.

Threshold-induced complex behavior of wood in mountain streams

The geomorphic complexity of streams influences the residence time of carbon by creating storage sites for organic matter. Instream wood increases complexity, particularly where logjams initiate multithread channels, as documented previously for lowland alluvial channels. Analogous processes in mountain streams can substantially increase the residence time of organic matter in streams otherwise characterized by high transport capacity and limited storage. Thresholds in wood mobility that reflect valley and channel geometry and wood dimensions determine the distribution of multithread channels and the mechanics underlying these thresholds. Valleys must have a lower gradient and less lateral confinement to develop multithread channels, but also larger volumes of riparian and instream wood. Hydrostatic forces that mobilize jams increase more slowly in low-gradient, unconfined channels, facilitating jam persistence. Treefall can thus initiate complex behavior that results in a self-enhancing feedback between wood recruitment and channel geometry. Patches of old-growth forest and multithread channels were formerly more widespread. Carbon retention has likely decreased as multithread channels have become less common.

Tree type and forest management effects on the structure of stream wood following wildfires

Wildfires are an increasingly common disturbance influencing wood recruitment to streams, and thereby affecting their physical and biological condition. Mediterranean countries such as Portugal, where more than 25% of the land area has burned since 1990, are ideal areas to study impacts of wildfire effects on streams. We evaluated the physical structure of 2206 downed wood pieces (DWP) across 27 first- to third-order streams in central Portugal, all of which had experienced recent wildfires. The streams flowed through monospecific upland forests of Eucalyptus, Maritime pines, or Cork oaks and were fringed by a mixture of riparian tree species. DWP structure differed between tree types and between burned and unburned pieces. Post-fire timber-production forests (Maritime pines and Eucalyptus) contributed a higher quantity of thinner, longer and straighter DWP to streams than Cork oak stands. Pieces from Maritime pines had more rootwads and branches than DWP from the other tree types. Pieces from Cork oak and riparian species generally had a bent form, were shorter and had no rootwads. Burned DWP in streams were often from riparian trees. Relative to unburned DWP, the burned DWP occurred more frequently, were larger and straighter, had branches less often, and were more decayed. With more complex branches, rootwads, and a larger diameter, inputs from burned Maritime pine forests are more likely to change stream hydraulics and habitat complexity, relative to inputs from Eucalyptus forests with their simpler structure. This study shows that, less than a decade after wildfires, structure of downed wood in and near streams is strongly influenced by wildfire, but also still reflects intrinsic species characteristics and respective silviculture practices, even after the effects of fire have been accounted for. Under an anticipated shift in landscape cover with higher shrubland proportions and more mixing of Maritime pine and Eucalyptus forests, our results suggest that instream large wood will become scarcer and more structurally homogeneous.

Niches and neutral processes contribute to the resource-diversity relationships of stream detritivores

Summary 1. Explaining resource–diversity relationships is a long-standing goal in ecology, and there is currently little consensus as to the relative contributions of neutral versus a variety of proposed niche-related mechanisms. 2. The resource–diversity relationship of insect detritivores was examined in a survey of 25 small, parallel streams flowing into the Bay of Fundy in eastern Canada, with the objective of determining whether neutral processes (sampling effects) could account for the observed patterns. 3. Detritivore taxonomic richness showed a positive, but decelerating relationship with quantity of detritus. Richness also increased with catchment area and with stream permanence. 4. Species distribution patterns were significantly nested, and low resource streams (little detritus) tended to have species with large ranges (i.e. found in many or most streams). 5. Sampling effects could explain only part of the positive relationship between richness and detrital resources, but accounted for the species richness–area relationship. 6. Two mechanisms that could potentially increase niche space as resource abundance increased were rejected: there was no evidence that riparian forest diversity or beta diversity increased with detrital resources. 7. Two niche-related mechanisms were consistent with existing data, but will require further testing. First, flood disturbance may decrease species richness by eliminating species that require benign habitat, and lowering detritus retention, producing a positive correlation between detritivore richness and resources. Second, large wood in streams located in older riparian forest may increase habitat heterogeneity (number of niches) and the retention of organic matter, again leading to a positive relationship between detritivore diversity and detrital resources. 8. It was concluded that the positive ‘productivity–diversity’ relationship for stream detritivores was most likely produced in part by sampling effects, but also by ecological processes (disturbance and succession) that simultaneously influence resource level and niche availability.

Wood in different stream types: Epixylic biofilm and wood-inhabiting invertebrates in a lowlandversusan upland stream

Colonization of incubated wood samples by invertebrates and biofilm was compared between a lowland and an upland stream over a 15 month period. Invertebrate densities increased during the first weeks of incubation and then decreased to rather stable densities during the remaining investigation period in both streams. Within the first incubation weeks invertebrate numbers were significantly higher in the lowland stream. Higher dissolved nutrient concentrations and water temperatures accelerated initial epixylic biofilm development in the lowland stream. Lowest invertebrate numbers on incubated branches in the lowland stream coincided with increased discharge. Extreme low flows in the upland stream resulted in lowest invertebrate numbers on incubated wood during the study. Temporal patterns of biofilm and invertebrates indicated some interactions, but statistical significance was low, which might be caused by the variety of interacting effects. Additionally, invertebrate assemblages of in-stream wood samples were collected from four lowland and four upland streams to examine differences of epixylic invertebrate assemblages between the two stream types. Invertebrate densities were significantly higher on submerged wood from lowland streams than wood from upland streams. However, no clear differences in invertebrate assemblages found between the stream types. The study results show that introduced wood in lowland and upland streams is rapidly colonized by aquatic invertebrates and provided an attachment site for biofilms. Invertebrate numbers during the first two months of incubation significantly overestimate the invertebrate numbers found on resident in-stream wood in lowland and upland streams. Analyses of taxonomic composition of wood-inhabiting invertebrate assemblages from natural wood from lowland and upland streams revealed that each stream displayed a rather specific epixylic fauna.

Wood retention and transport in tropical, headwater streams, La Selva Biological Station, Costa Rica

Wood in tropical streams has the potential to be more mobile than wood in otherwise similar temperate streams because of the warm and humid conditions that promote decay and the more frequent and flashier floods of the tropics. To test this hypothesis, we monitored all large wood pieces for 2.3 years in 10 50-m-long reaches of old-growth headwater streams in La Selva Biological Station, Costa Rica. Annual wood retention rates for pieces ranged from 0.55 to 0.91 among the sites, and retention rates by volume ranged from 0.67 to 0.99. Assuming steady state wood load, which is reasonable for La Selva, these rates are equivalent to mean residence times of 2.2–10.6 years for pieces, and 3.0–83.2 years for a volume of wood. Calculating mean residence time from the weighted average of retention rates gives an average residence time of 4.9 years for a piece of wood and 6.9 years for a volume of wood. These values are less than those reported for old-growth temperate forests, supporting our hypothesis. Mobility of individual pieces was best predicted by piece length relative to stream width ( l r, higher l r led to lower mobility), channel gradient ( s, higher s led to higher mobility), and piece integration into the channel (unattached pieces were 2.6 times more mobile than attached, ramp, or bridge pieces). Temporal variation in retention rates was well explained by variation in peak flow. All four of these factors have also been observed to influence mobility in the temperate zone. The higher mobility of wood in our study site relative to the temperate rainforest of the Pacific Northwest may be explained by the flashy and frequent floods, the high decay rate, or the branching morphology of the native trees; but differentiating the role of these factors, particularly flow and decay, will be complicated by their covariation across climates.

Wood-inhabiting filamentous fungi in 12 high-altitude streams of the Western Ghats by damp incubation and bubble chamber incubation

The diversity and distribution of fungi on naturally submerged wood from 12 high-altitude streams of the Western Ghats in India were studied by damp chamber incubation and bubble chamber incubation. The damp chamber incubation of wood samples yielded 29 fungal taxa (17 anamorphs, 11 ascomycetes, 1 basidiomycete). Acrogenospora sphaerocephala, Canalisporium sp., Dictyosporium heptasporum, Leptosphaeria ginimia, L. typharum, Massarina australiensis, Sporoschisma saccardoi, and Sporoschismopsis australiensis were the most common taxa and were widely distributed on wood in streams of the Western Ghats. The bubble chamber incubation of bark and cambium revealed 30 aquatic hyphomycetes (bark, 28; cambium, 18). Anguillospora longissima, Flagellospora curvula, F. penicillioides, and Lunulospora curvula were most common in bark as well as cambium. There was only 1 species (Helicomyces roseus) that was identified following both incubation methods, indicating that methodology influences the detection of fungal communities. It is recommended that studies on freshwater fungi should incorporate both damp incubation and bubble chamber techniques.

Wood-inhabiting filamentous fungi in 12 high-altitude streams of the Western Ghats by damp incubation and bubble chamber incubation

The diversity and distribution of fungi on naturally submerged wood from 12 high-altitude streams of the Western Ghats in India were studied by damp chamber incubation and bubble chamber incubation. The damp chamber incubation of wood samples yielded 29 fungal taxa (17 anamorphs, 11 ascomycetes, 1 basidiomycete). Acrogenospora sphaerocephala, Canalisporium sp., Dictyosporium heptasporum, Leptosphaeria ginimia, L. typharum, Massarina australiensis, Sporoschisma saccardoi, and Sporoschismopsis australiensis were the most common taxa and were widely distributed on wood in streams of the Western Ghats. The bubble chamber incubation of bark and cambium revealed 30 aquatic hyphomycetes (bark, 28; cambium, 18). Anguillospora longissima, Flagellospora curvula, F. penicillioides, and Lunulospora curvula were most common in bark as well as cambium. There was only 1 species (Helicomyces roseus) that was identified following both incubation methods, indicating that methodology influences the detection of fungal communities. It is recommended that studies on freshwater fungi should incorporate both damp incubation and bubble chamber techniques.

English

This paper presents the restoration design process and construction activities associated with the Big Hanaford Creek restoration project. The project was completed as part of required wetland mitigation to compensate for adjacent plant and mine activities requiring state and federal wetland permits. Big Hanaford Creek is a tributary to the Skookumchuck River in Lewis County, Washington, with its headwaters in the foothills of the Cascade Mountains, and with lower reaches in low gradient floodplain valleys. Within its lower reaches, a 4800-meter portion of the creek was straightened and deepened approximately 90 years ago when the valley was drained for agricultural purposes. Most recently, the floodplain surrounding the creek was used for grazing and mowing of pasture grasses for hay production. In an effort to rehabilitate in-stream habitat, reconnect the creek to the floodplain, and return native floodplain vegetation to the valley, a 61-hectare restoration project is underway. The project includes excavating 63,460 cubic meters of soil to relocate 2,286 linear meters of the stream back to a historical channel alignment; installing in stream wood structures for fish habitat; creating a new channel cross section with a bench at spring water surface elevations; planting willows along the reconfigured channel; creating low lying floodplain swales, and planting over 290,000 native trees, shrubs, and sedge plugs in the floodplain. Aerial photographs were used to identify a past historical meander pattern to serve as the new stream alignment and Government Land Survey Office field notes from 1867 were used to identify the historical wetland floodplain plant community. Construction occurred over an 18-month period to allow for channel excavation and included construction of approximately 150 in- stream wood structures during the dry season; and installation of plants the following spring. A 10-year monitoring program is being developed to monitor hydrologic performance and establishment of the native vegetation. This project is located immediately west of the TransAlta Centralia Generation Plant and Mine operations on land currently owned by the TransAlta Corporation.

Dynamics of wood recruitment in streams of the northeastern US

Wood is an important component of forested stream ecosystems, and stream restoration efforts often incorporate large wood. In most cases, however, stream restoration projects are implemented without information regarding the amount of wood that historically occurred or the natural rates of wood recruitment. This study uses a space-for-time analysis to quantify large wood loading to 28 streams in the northeastern US with a range of in-stream and riparian forest characteristics. We document the current volume and frequency of occurrence of large wood in streams with riparian forests varying in their stage of stand development as well as stream size and gradient. Linear models relating stream wood characteristics to stream geomorphic and forest characteristics were compared using Akaike's Information Criterion (AIC) model selection. The AIC analysis indicated that the volume and frequency of large wood and wood accumulations (wood jams) in streams was most closely associated with the age of the dominant canopy trees in the riparian forest (best models: log10(large wood volume (m3100m−1))=(0.0036×stand age)−0.2281, p<0.001, r2=0.80; and large wood frequency (number per 100m)=(0.1326×stand age)+7.3952, p<001, r2=0.63). Bankfull width was an important factor accounting for wood volume per unit area (m3ha−1) but not the volume of wood per length of stream (100m−1). The empirical models developed in this study were unsuccessful in predicting wood loading in other regions, most likely due to difference in forest characteristics and the legacy of forest disturbance. However, these models may be applicable in other streams in the northeastern US or in streams with comparable riparian forests, underlying geology, and disturbance regimes—factors that could alter long-term wood loading dynamics. Our results highlight the importance of understanding region-specific processes when planning stream restoration and stream management projects.

Large versus small wood in streams: the effect of wood dimension on macroinvertebrate communities

Conventionally, most research and restoration involving in-stream wood focuses on large wood (> 0.1 m diameter), excluding any smaller pieces. However, this may neglect a major component of in-stream habitat, as small wood can constitute the majority of pieces, particularly in small streams. The ecological benefi t of large wood is well established, but corresponding benefi ts associated with small wood (0.05-0.1 m diameter) have not been demonstrated. To test the effect of wood dimension on macroinvertebrate community composition, we compared the fauna occupying large wood habitats with that occupying small wood at eight streams in south-eastern Australia. The relationships between wood dimensions and its macroinvertebrate fauna were complex. Community composi- tion did not vary with wood dimension, and no signifi cant correlations were found between other macroinvertebrate attributes (including family richness and evenness) and wood dimension, including diameter. However, analysis of covariance suggested that large wood supported a greater diversity and abundance of macroinvertebrates, indicat- ing that the method of analysis could infl uence the result. Adjustment for differences in sample dimension using rarefaction determined that these fi ndings were likely to be a result of the surface area and volumes sampled varying with the dimension of the wood. Per unit surface area, and per unit volume, small wood supported a similar number of families to large wood. Thus we conclude that, relative to the available surface area, small and large wood can be equivalent in their contribution to the available habitat in a stream. Therefore, the potential value of small wood as a habitat resource warrants its explicit consideration for inclusion in ecological and rehabilitation studies.

A conceptual model for the longitudinal distribution of wood in mountain streams

AbstractWood load, channel parameters and valley parameters were surveyed in 50 contiguous stream segments each 25 m in length along 12 streams in the Colorado Front Range. Length and diameter of each piece of wood were measured, and the orientation of each piece was tallied as a ramp, buried, bridge or unattached. These data were then used to evaluate longitudinal patterns of wood distribution in forested headwater streams of the Colorado Front Range, and potential channel‐, valley‐ and watershed‐scale controls on these patterns. We hypothesized that (i) wood load decreases downstream, (ii) wood is non‐randomly distributed at channel lengths of tens to hundreds of meters as a result of the presence of wood jams and (iii) the proportion of wood clustered into jams increases with drainage area as a result of downstream increases in relative capacity of a stream to transport wood introduced from the adjacent riparian zone and valley bottom. Results indicate a progressive downstream decrease in wood load within channels, and correlations between wood load and drainage area, elevation, channel width, bed gradient and total stream power. Results support the first and second hypotheses, but are inconclusive with respect to the third hypothesis. Wood is non‐randomly distributed at lengths of tens to hundreds of meters, but the proportion of pieces in jams reaches a maximum at intermediate downstream distances within the study area. We use these results to propose a conceptual model illustrating downstream trends in wood within streams of the Colorado Front Range. Copyright © 2009 John Wiley &amp; Sons, Ltd.