Large Woody Debris Abundance Research Articles

Linking fish trait responses to in‐stream habitat in reconstructed valley‐plugged stream reaches of the Coastal Plain, U.S.A.

Valley‐plug formation is a challenging consequence of stream channelization especially in physiographic regions with highly erodible soils. Upstream channel degradation and incision results in accelerated sediment delivery processes wherein downstream aggradation decreases stream power and creates sand‐clogged channels. Channel reconstruction is now meeting hydrogeomorphic goals related to valley‐plug remediation, yet there exists a need to understand how this practice also facilitates ecological restoration. We evaluated fish trait response to in‐stream habitat conditions in channelized, recently restored, and “least‐disturbed” reference reaches of Coastal Plain streams in West Tennessee. Restored reaches were ecologically similar to channelized reaches, having higher proportions of nest‐guarding omnivores that were correlated with higher percentages of pool habitats and lower wetted width:depth ratios compared to reference reaches. Reference reaches had higher proportions of fast‐water dwelling and specialized insectivores that were correlated with high abundance of large woody debris, high‐wetted width:depth ratios, and low percentages of pool habitats. We conclude that in‐stream habitats in reconstructed channels have yet to promote reach‐scale ecological restoration relative to fish assemblage organization because trait‐habitat associations were not similar to reference conditions. However, our results lend to the development of ecological restoration targets that can be incorporated in future channel reconstruction projects in valley‐plugged, channelized streams of the Coastal Plain.

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.

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.

Large Woody Debris and Salmonid Habitat in the Anchor River Basin, Alaska, Following an Extensive Spruce Beetle (Dendroctonus rufipennis) Outbreak

Abstract A widespread and intense spruce beetle outbreak during the 1990s has killed most of the mature white spruce (Picea glauca) trees across many watersheds in south-central Alaska. To investigate the potential habitat impacts in a salmon stream, we characterized the current abundance and species composition of large woody debris (LWD), examined the linkages between LWD and salmonid habitat, and estimated changes in LWD abundance and associated pool habitat over time. LWD abundance was relatively low (97 pieces/km overall) and varied widely according to riparian vegetation typology, ranging from 15 pieces/km at sites with non-forested riparian zones to 170 pieces/km at sites adjacent to cottonwood forest. LWD provided significant fish cover in pools, especially in cottonwood forest stream reaches. LWD-formed pools were relatively rare (15% of total), but LWD abundance explained much of the variation in pool frequency (r2 = 0.86 in spruce forest reaches) and in the proportion of pool habitats (r2 = 0.8...

Identifying Linkages Between Land Use, Geomorphology, and Aquatic Habitat in a Mixed-Use Watershed

The potential impacts of land use on large woody debris (LWD) were examined in Sourdough Creek Watershed, a rapidly growing area encompassing Bozeman, Montana, USA. We identified six land classes within a 250 m buffer extending on either side of Sourdough Creek and assessed aquatic habitat and geomorphologic variables within each class. All LWD pieces were counted, and we examined 14 other variables, including undercut bank, sinuosity, and substrate composition. LWD numbers were generally low and ranged from 0 to 8.2 pieces per 50 m of stream. Linear regression showed that LWD increased with distance from headwaters, riparian forest width, and sinuosity in four of the six land classes. Statistically significant differences between land classes for many aquatic habitat and geomorphologic variables indicated the impacts of different land uses on stream structure. We also found that practices such as active wood removal played a key role in LWD abundance. This finding suggests that managers should prioritize public education and outreach concerning the importance of in-stream wood, especially in mixed-use watersheds where wood is removed for either aesthetic reasons or to prevent stream flooding.

Importance of large woody debris for juvenile chinook salmon habitat in small boreal forest streams in the upper Yukon River basin, Canada

The importance of large woody debris (LWD) in forested stream ecosystems is well documented. However, little is known about LWD in northern boreal forest streams. We investigated the abundance, characteristics, and function of LWD in 13 small tributary streams of the upper Yukon River basin, Yukon Territory, Canada. LWD abundance was similar to values reported from temperate regions, whereas LWD size and total volume were well below values for the Pacific Northwest. LWD formed 28% of the pools, which provide important habitat for juvenile chinook salmon (Oncorhynchus tshawytscha Walbaum). The median diameter of pool-forming pieces was 17 cm, and ring counts on fallen riparian trees indicated that pool-forming pieces were likely 70–200 years old when downed. Juvenile chinook salmon density was correlated with LWD abundance in our study reaches. We conclude that despite differences in climate and forest type, LWD in Yukon streams and LWD in temperate regions appear to perform a similar function in creating fish habitat. Resource managers should consider the relatively slow tree growth and thus potentially long recovery times following human disturbances in these watersheds.

Relationship between Large Woody Debris Characteristics and Pool Formation in Small Coastal British Columbia Streams

Abstract The characteristics and function of large woody debris (LWD) were measured in 41 small (1.2-11.2-m bank-full channel width), fish-bearing streams in coastal British Columbia to determine how total LWD abundance and the features of individual LWD pieces (diameter, length, orientation, and presence of a rootwad) influenced the effectiveness of pool formation. Pool spacing (the number of channel widths between channel-spanning pools) was a decreasing power function of total LWD abundance, but the relationship was relatively weak. Stratification of sites by channel gradient improved the model fit, steeper streams (≥2% gradient) having a significantly lower pool spacing than lower-gradient streams (<2%). The proportion of LWD that formed pools increased from 6% for pieces with a diameter of 15-30 cm to 43% for pieces with a diameter of more than 60 cm. Large woody debris more than 60 cm in diameter formed a higher proportion of pools across all channel widths. A simple, size-structured model of LWD ab...

Relationships of channel characteristics, land ownership, and land use patterns to large woody debris in western Oregon streams

Regression tree analysis was used to test the relationship of channel and aquatic habitat characteristics from 3793 stream reaches in western Oregon State to the abundance of large woody debris (LWD). Stream reaches were drawn from diverse ownerships and land uses – land cover types over a broad geographic extent. When all land uses – land covers were considered, ownership and land use patterns were related to LWD abundance. When nonforested land uses were excluded, however, these factors became less important. In forested streams, LWD abundance was predicted primarily by stream gradient and bankfull channel width, with the volume, frequency, and size of LWD pieces decreasing as channel size increased. Within forested lands, stand age and forest distribution were related to LWD size but had small correlations with LWD volume and abundance. The strong relationship of stream gradient and bankfull channel width with LWD suggests that in forested areas, the most significant factor related to LWD counts is the geomorphology of stream reaches and their surrounding areas. Land managers in western Oregon who want to improve aquatic habitat quality may want to direct their efforts to increasing LWD in larger streams, which typically include smaller quantities of LWD.

The Influence of Geomorphic Factors and Geographic Region on Large Woody Debris Loading and Fish Habitat in Alaska Coastal Streams

Large woody debris (LWD) and channel data from three Alaska coastal regions with varying geomorphic channel types were analyzed to document regional variability in LWD abundance, define geomorphic characteristics affecting LWD abundance, and identify relationships between LWD abundance and the formation of pools and gravel bars in streams. Large woody debris abundance was significantly lower at the northern edge of the coastal coniferous forest than in Southeast Alaska and was significantly greater in alluvial gravel-bedded channels than in contained boulder–bedrock channels. More pools and gravel bars were formed by LWD in alluvial channels than in contained channels. Pool spacing (the number of channel widths between pools) decreased with increasing LWD abundance (pieces/km) and was significantly influenced by the interaction between LWD abundance and channel width. As channel width increased, pool spacing was more strongly influenced by changes in LWD abundance, but the relative change in pool spacing diminished with increasing LWD load. The percentage of stream area in pools was insensitive to changes in LWD abundance and was best predicted by channel type. The percentage of habitat units with gravel as the dominant substrate was positively related to LWD abundance and negatively related to stream gradient.

Modeling Recovery Rates and Pathways for Woody Debris Recruitment in Northwestern Washington Streams

Abstract We modeled large woody debris (LWD) recruitment and pool formation in northwestern Washington streams after simulated stand-clearing disturbance using two computer models: Forest Vegetation Simulator for stand development and Riparian-in-a-Box for LWD recruitment, depletion, and pool formation. We evaluated differences in LWD recruitment and pool formation among different combinations of channel size, successional pathway, and stand management scenario. The models predict that time to first recruitment of pool-forming LWD is about 50% shorter for red alder Alnus rubra than for Douglas-fir Pseudotsuga menziesii at all channel widths. Total LWD abundance increases faster in red alder stands than in Douglas-fir stands but declines rapidly after 70 years as the stand dies and pieces decompose. Initial recovery is slower for Douglas-fir stands, but LWD recruitment is sustained longer. Total LWD abundance increases faster with decreasing channel size, and pool abundance increases faster with decreasing...

Relationships between Channel Characteristics, Woody Debris, and Fish Habitat in Northwestern Washington Streams

Relationships between large woody debris (LWD) and pool area or pool spacing varied with channel slope and channel width for streams in second-growth forests in northwest Washington. Pool spacing (expressed as the number of channel widths between pools) decreased as number of woody debris increased in both moderate-slope (0.02 < slope < 0.05) and low-slope (0.001 < slope ≤ 0.02) channels, but the relationship was stronger in moderate-slope channels. Percent pool was also more strongly correlated with woody debris volume in moderate-slope channels than in low-slope channels. Multiple-regression analyses showed that pool spacing and percent pool were correlated with an interaction term between LWD abundance and channel slope, suggesting that the influence of LWD on pool formation changes with channel slope. Analysis of pool-forming mechanisms indicated that low-slope channels are less sensitive to LWD abundance because pools are formed by mechanisms other than LWD when LWD abundance is low. Size of LWD that formed pools increased with increasing channel width, but was not related to channel slope. Percent gravel (proportion of the bed in patches of gravel 16–64 mm in diameter) was best explained by channel slope and channel width, and there was no significant relationship between woody debris and percent gravel. A regression between median particle size of sediment on the stream bed and basal shear stress showed that the relationships among percent gravel, channel width, and channel slope are adequately explained by the channelˈs capacity to transport particles of various sizes.