Large Woody Debris Recruitment Research Articles

Quantification of potential recruitment of large woody debris in mountain catchments considering the effects of vegetation on hydraulic and geotechnical bank erosion and shallow landslides

Large woody debris (LWD) exacerbates flood damages near civil structures and in urbanized areas and the awareness of LWD as a risk is becoming more and more relevant. The recruitment of “fresh” large woody debris has been documented to play a significant role of the total amount of wood transported during flood events in mountain catchments. Predominately, LWD recruitment due to hydraulic and geotechnical bank erosion and shallow landslides contribute to high volumes of wood during floods. Quantifying the effects of vegetation on channel and slope processes is extremely complex. This manuscript therefore presents the concepts that are being implemented in a new modelling framework that aims to improve the quantification of vegetation effects on LWD recruitment processes. One of the focuses of the model framework is the implementation of the effect of spatio-temporal distribution of root reinforcement in recruitment processes such as bank erosion and shallow landslides in mountain catchments. Further, spatio-temporal precipitation patterns will be considered using a probabilistic approach to account for the spatio-temporal precipitation variability to estimate a LWD recruitment correction coefficient. Preliminary results are herein presented and discussed in form of a case study in the Swiss Prealps.

Reach-scale characterization of large woody debris in a low-gradient, Midwestern U.S.A. river system

Addition of large woody debris (LWD) to rivers has increasingly become a popular stream restoration strategy, particularly in river systems of the Midwestern United States. However, our knowledge of LWD dynamics is mostly limited to high gradient montane river systems, or coastal river systems. The LWD-related management of low-gradient, Midwestern river systems is thus largely based on higher gradient analogs of LWD dynamics. This research characterizes fluvial wood loads and investigates the relationships between fluvial wood, channel morphology, and sediment deposition in a relatively low-gradient, semiconfined, alluvial river. The LWD and channel morphology were surveyed at nine reaches along the Big River in southeastern Missouri to investigate those relationships in comparison to other regions. Wood loads in the Big River are low (3–114m3/100m) relative to those of higher gradient river systems of the Pacific Northwest, but high relative to lower-gradient river systems of the Eastern United States. Wood characteristics such as size and orientation suggest that the dominant LWD recruitment mechanism in the Big River is bank erosion. Also, ratios of wood geometry to channel geometry show that the Big River maintains a relatively high wood transport capacity for most of its length. Although LWD creates sites for sediment storage, the overall impact on reach-scale sediment storage in the Big River is low (<4.2% of total in-channel storage). However, wood loads, and thus opportunities for sediment storage, have the potential to grow in the future as Midwestern riparian forests mature. This study represents the first of its kind within this particular type of river system and within this region and thus serves as a basis for understanding fluvial wood dynamics in low-gradient river systems of the Midwestern United States.

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.

Monitoring riparian restoration to ensure recruitment of large woody debris in Haida Gwaii, British Columbia

Monitoring is a fundamental aspect of restoration, as it determines when the restoration objectives have been met. As restoration objectives are not universal, monitoring needs to be included in the development and design of each restoration project. We assessed the effectiveness and efficiency of a forest stand dynamic monitoring plan, developed for use with riparian restoration occurring on Lyell Island, Haida Gwaii, British Columbia. The restoration objective is to accelerate the development of late-successional forests for the benefit of riparian wildlife species and recruitment of in-stream large woody debris, which specifically provides essential habitat for a variety of fish species. In this study large woody debris (LWD) is referred to as downed wood greater than 7.5 cm in diameter. Prior to the start of riparian restoration, two watersheds were quantified for their stand structure and composition using the forest stand dynamic monitoring plan. An error analysis of these data was used to assess the sampling efficiency of the monitoring plan. The design of the monitoring plan was found to be efficient at monitoring the riparian forest stand dynamics (with seven or eight plots per site sufficient to evaluate stand basal area and stem density to within 10%), but not woody debris volumes (for which deviations &gt;10% were found even with 14 plots per site). Incorporation of additional line transects or adoption of more efficient sampling methods for woody debris (such as diameter or length relascope methods) is suggested as a means of enhancing large woody debris sampling efficiency.

SPATIAL PATTERN, DENSITY AND CHARACTERISTICS OF LARGE WOOD IN CONNECTICUT STREAMS: IMPLICATIONS FOR STREAM RESTORATION PRIORITIES IN SOUTHERN NEW ENGLAND

ABSTRACTMany streams have been modified so extensively that river managers do not have clear reference conditions to frame targets for stream restoration. Large woody debris (LWD) has long been recognized as an important influence on both geomorphic and ecologic processes in stream channels; however, there have been few studies of LWD dynamics in New England. Although this region is heavily forested today, the forest is predominantly young (70–90 years old) regrowth following a historical episode of severe deforestation. This study presents the results of an extensive census of LWD and associated stream characteristics in over 16 river kilometres of northeastern Connecticut streams and represents the first reported inventory of wood loading and sorting in Southern New England. Results of this study indicate that wood loading and jam frequencies in the study region are low: 2.5–17.8 and 0.5–5.51 per 100 m, respectively. Orientation of LWD is predominantly parallel to flow, an indication that these streams are not retaining organic matter or sediment, which has important geomorphic and ecologic implications. Results imply that stream recruitment of LWD is still lagging from the massive forest conversions of the 18th and 19th centuries. Given the low wood loadings observed in the study reaches, manual wood addition and continued forest regeneration would likely improve both habitat diversity and organic matter and fine sediment retention in these systems. Copyright © 2011 John Wiley &amp; Sons, Ltd.

A LIDAR‐DERIVED EVALUATION OF WATERSHED‐SCALE LARGE WOODY DEBRIS SOURCES AND RECRUITMENT MECHANISMS: COASTAL MAINE, USA

ABSTRACTIn‐channel large woody debris (LWD) promotes quality aquatic habitat through sediment sorting, pool scouring and in‐stream nutrient retention and transport. LWD recruitment occurs by numerous ecological and geomorphic mechanisms including channel migration, mass wasting and natural tree fall, yet LWD sourcing on the watershed scale remains poorly constrained. We developed a rapid and spatially extensive method for using light detection and ranging data to do the following: (i) estimate tree height and recruitable tree abundance throughout a watershed; (ii) determine the likelihood for the stream to recruit channel‐spanning trees at reach scales and assess whether mass wasting or channel migration is a dominant recruitment mechanism; and (iii) understand the contemporary and future distribution of LWD at a watershed scale. We utilized this method on the 78‐km‐long Narraguagus River in coastal Maine and found that potential channel‐spanning LWD composes approximately 6% of the valley area over the course of the river and is concentrated in spatially discrete reaches along the stream, with 5 km of the river valley accounting for 50% of the total potential LWD found in the system. We also determined that 83% of all potential LWD is located on valley sides, as opposed to 17% on floodplain and terrace surfaces. Approximately 3% of channel‐spanning vegetation along the river is located within one channel width of the stream. By examining topographic and morphologic variables (valley width, channel sinuosity, valley‐side slope) over the length of the stream, we evaluated the dominant recruitment processes along the river and often found a spatial disconnect between the location of potential channel‐spanning LWD and recruitment mechanisms, which likely explains the low levels of LWD currently found in the system. This rapid method for identification of LWD sources is extendable to other basins and may prove valuable in locating future restoration projects aimed at increasing habitat quality through wood additions. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Post-harvest windthrow and recruitment of large woody debris in riparian buffers on Vancouver Island

Large woody debris (LWD) provides structural complexity to small streams. Riparian buffers are intended to provide long-term vegetation cover and supplies of LWD, but post-harvest windthrow often occurs. To evaluate the impacts of windthrow in riparian buffers and identify the components for a small stream LWD recruitment model, we sampled 26 streams in immature and older stands in wind-exposed areas of southwestern and northern Vancouver Island. These treed buffer strips had been exposed following clearcut harvest of adjacent timber on both sides 1–20 years previously. For stream sections 100 m long in each buffer, all logs greater than 7.5 cm diameter that spanned at least part of stream channel were measured. A total of 658 logs were recorded. Windthrown trees were comparable in characteristics to the trees that made up the buffer. The majority of logs derived from windthrown trees were oriented perpendicular to the stream channel and were suspended above the stream channel. Even 20 years after harvesting, two-thirds of the logs were still suspended above the stream. Logs in older buffers were more decayed, and the decay rate depended on tree species and initial diameter. Log height above stream was negatively correlated with log decay class and time since logging. Log length declined with time since harvest exposure and decay class. Sediment was exposed on upturned roots and within mineral soil pits. The volume of soil retained on upturned rootwads declined over time, but some soil remained even after 20 years. Very little of this exposed sediment was close enough to the creek to result in sediment delivery.

Windthrow and recruitment of large woody debris in riparian stands

To document the impacts of windthrow in riparian leave strips and identify the components needed for small stream large woody debris (LWD) recruitment modeling, we monitored nine small streams at a temperate rainforest site in coastal British Columbia. This study was a component of a larger integrated study of forest management impacts on small streams. A series of small clearcuts were harvested in 1998 in a 70-year-old second growth stand that had regenerated naturally following logging and wildfire. Three cutblocks each were assigned to 10 m and 30 m buffer width treatments and three areas were assigned as unharvested controls. Seven years after the 1998 logging, all logs greater than 10 cm diameter that spanned at least part of stream channel width were measured. A total of 179 logs were recorded. Post-harvest windthrow was higher in the 10 m buffer treatment, while competition-related standing tree mortality was higher in the controls. The major windthrow events had occurred in the first and second years after logging of adjacent stands. There was no significant difference in the number of spanning and in-stream logs in the 10 m, 30 m buffer and control treatments. More than 90% of the LWD was in the 10–30 cm diameter classes. The majority of logs were oriented perpendicular to the stream channel. At the time of measurement, the majority of these trees were still suspended above the stream channel, indicating that the recruitment of logs into the stream channel is a long-term process. Time to recruitment into the channel is dependent on log and valley geometry, log size, species, and log condition prior to toppling. Log height above stream was negatively correlated with log decay class and valley width. Log length was negatively correlated with state of decay, and many windthrown logs were in an advanced state of decay before they entered the stream.

Linking upstream channel instability to downstream degradation: Grenada Lake and the Skuna and Yalobusha River Basins, Mississippi

AbstractUnstable fluvial systems are characterized by actively migrating knickpoints, incising channel beds, failing banks, and recruitment of large woody debris and it would appear that river corridors downstream of these processes would be adversely affected or impaired because of higher fluxes of sediment and other riverine products. In north‐central Mississippi, the Yalobusha River is one such system and the characteristics of two downstream locations are examined to explore this geomorphic linkage between upstream instability and downstream degradation. For the large woody debris plug along the Yalobusha River, it is found that (1) the deposit is composed mostly of sand covered with a veneer of silt and clay, (2) agrichemicals and enriched concentrations of elements are prevalent, and (3) excessive sedimentation and wood accumulation have forced river flow entirely out‐of‐bank. For Grenada Lake, it is found that (1) the impounded sediment is predominantly clay, (2) agrichemicals and elements observed throughout the reservoir show no spatial variation, (3) little difference exists in the amount and quality between the sediments deposited in Skuna and Yalobusha River arms, and (4) only a small fraction of the reservoir's storage capacity has been lost because of sedimentation. While excessive sedimentation and large woody debris recruitment have had a marked affect on stream corridor function in the area of the debris plug, the high sediment loads associated with the unstable portions of the Yalobusha River and their associated products have not been communicated to Grenada Lake. The fish consumption advisories within Grenada Lake and its tributaries due to bioaccumulated trace elements and agrichemicals, appear to be independent of the pervasive river channel instability occurring upstream. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Temporal dynamics of large woody debris in small streams of the Alberta foothills, Canada

Large woody debris (LWD) is a key link between riparian forests and streams; however, the temporal dynamics of in-stream wood remains poorly quantified. Using dendrochronology, we evaluated the dynamics of five Pinus -dominated and five Picea -dominated riparian forests in the foothills of Alberta and cross-dated the ring widths of 186 pieces of LWD. Time since death of LWD ranged from 2 to 143 years, with maximums of 86 and 143 years for Pinus and Picea, respectively. Recruitment of Pinus LWD was influenced by stand-replacing fires followed by self-thinning about 40 years after stand establishment. In uneven-aged Picea-dominated forests, tree mortality and LWD recruitment were due to fine-scale disturbances. Time since death increased significantly with decay and position classes, which resulted in changes in LWD function through time. LWD persisted in the bridge position for about 30 years. Bridged LWD was least decayed, was significantly longer, and had greater volume than LWD in other positions. LWD remained in partial bridge and loose positions about 15 years and &gt;80 years when submerged in water and buried in sediment. Given the persistence of LWD, we conclude that management that alters wood abundance and recruitment has short- and long-term implications for the structure and function of small streams.

Dynamics of large woody debris in small streams disturbed by the 2001 Dogrib fire in the Alberta foothills

We investigated the temporal dynamics of large woody debris (LWD) in five headwater streams before and after the 2001 Dogrib fire in the foothills of Alberta. The density of LWD varied from 5 to 41 logs per 50 m of stream reach and accounted for 19.4 ± 5.1 m 3 ha −1 (mean ± standard error) of wood in the riparian zones and 114.1 ± 30.1 m 3 ha −1 of wood in the bankfull margins of the stream channel. Individual logs averaged 18.9 ± 1.15 cm in diameter, 5.5 ± 0.7 m in length, and 0.2 ± 0.02 m 3 in volume. Logs became significantly shorter in decay classes II–IV. Bridges were longer than partial bridges, which were longer than loose and buried LWD. Individual log volume was greatest for bridges, but not significantly different among other position classes. Bridges and loose LWD contributed little to stream morphology and function; however, 55% of partial bridges and all buried logs contributed to sediment storage, channel armouring, or riffles and pools in the stream channel. Using dendroecological methods, we estimated the year of death of 108 of 115 spruce logs. LWD resulted from tree deaths that occurred between 1874 and 2001, so that time since death ranged from 5 to 132 years. Time since death increased from decay class II to III to IV and bridges were younger than LWD in all other position classes. Due to high rates of recruitment after fire, 16.5% LWD recruited between 2001 and 2006, most of which were bridges or partial bridges in decay class II. We anticipate a delay of 30–45 years before newly recruited logs contribute significantly to stream morphology and function. Depletion rates of LWD were exponential, such that 50% of LWD would be lost to decay, erosion or downstream transport within 30 years of tree death and <12% of LWD would persist more than 100 years. Since recruitment of new LWD in post-fire lodgepole pine stands is delayed by ca. 40 years while trees establish and stands develop, we anticipate periods of ca. 70 years between stand-replacing fires and recruitment of new, functional LWD into stream channels. During this time, fire-killed snags are an important source of LWD to small streams. For headwater streams in environments susceptible to floods and erosion we recommend that buffer zones comprised of snags to be established after fires. The goal of these post-fire buffers is to ensure a supply of LWD into streams for years to decades after a stand-replacing fire.

Factors controlling the fluvial export of large woody debris, and its contribution to organic carbon budgets at watershed scales

The fluvial export of large woody debris (LWD) was monitored in 131 reservoirs throughout Japan. Published data on the fluvial export of dissolved and particulate organic carbon were used to estimate the contributions of LWD in carbon budgets. Of all variables tested, watershed area was most important in explaining LWD carbon (LWDC) export, followed by annual precipitation. LWDC export per unit area was relatively high in small watersheds, highest in intermediate‐sized watersheds, and decreased in large watersheds. In small watersheds, a large proportion of LWD retained on narrow valley floors may fragment or decay and eventually be exported in forms other than LWD. In intermediate‐sized watersheds, LWD supplied from upstream and recruited by bank erosion is consistently transported downstream. In large watersheds, LWD recruitment is limited and LWD transported from upstream is stored on large floodplains. These differences in LWD recruitment, retention and transport in watersheds of different sizes lead to the proportion of LWDC in organic carbon exports to be maximum in intermediate‐sized watersheds and decline rapidly in large watersheds.

Large woody debris influences vegetation zonation in an oligohaline tidal marsh

The amount of large woody debris (LWD) in Pacific Northwest estuaries has declined dramatically since Euro-American settlement in the mid 19th century. Little is known about the ecological significance of estuarine LWD. This ignorance impairs protection and restoration of habitat critical to threatened Chinook salmon (Oncorhynchus tshawytscha), as well as other fish and wildlife. This study investigates whether LWD affects the distribution of estuarine shrubs, particularly nitrogen-fixingMyrica gale L. (sweetgale), which dominates the tidal shrub community of the Skagit River estuary, Washington, U.S.A. LWD,M. gale, and other shrubs were surveyed along line transects in an oligohaline tidal marsh and in abandoned agricultural land whose dikes failed more than 50 years ago and which has reverted to marsh. The results demonstrate a strong association between LWD andM. gale. M. gale was very rare on LWD<30 cm in diameter, increasingly more common for LWD between 30 and 75 cm, and always present on LWD≥75 cm. The marsh surface was generally 45 cm below mean higher high water (MHHW), suggesting LWD benefitsM. gale by providing a growth platform at an elevation near MHHW and reducing flooding stress. The largest and most abundant tree in the marsh,Picea sitchensis, averaged only 35.8 cm in diameter, which suggests LWD recruitment from upstream sources is necessary to sustainM. gale populations in the geomorphologically dynamic Skagit marsh. By affecting the distribution and abundance ofM. gale in the estuary, LWD may indirectly affect nitrogen dynamics in the marsh and secondary production of detritivores and herbivores.

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.

Forest change and stream fish habitat: lessons from ‘Olde’ and New England

The North Atlantic region has a long history of land use change that has influenced and will continue to influence stream ecosystems and fisheries production. This paper explores and compares the potential consequences of changes in forest cover for fish production in upland, coldwater stream environments in New England, U.S.A. and the British Isles, two regions which share important similarities with respect to overall physical, biotic and socio‐economic setting. Both regions were extensively deforested and essentially no extensive old‐growth forest stands remain. In New England, recovering forests, consisting almost entirely of naturally‐regenerated native species, now cover &gt;60% of the landscape. Associated with this large‐scale reforestation, open landscapes, common in the 19th and first half the 20th century, are currently rare and declining in this region. In the British Isles, forests still cover &lt;20% of the landscape, and existing forests largely consist of exotic conifer plantations stocked at high stand densities and harvested at frequent rotations. While forest restoration and conservation is frequently recommended as a fisheries habitat conservation and restoration tool, consideration of the way in which forests affect essential aspects of fish habitat suggests that response of upland stream fish to landscape change is inherently complex. Under certain environmental settings and reforestation practices, conversion of open landscapes to young‐mature forests can negatively impact fish production. Further, the effects of re‐establishing old‐growth forests are difficult to predict for the two regions (due to the current absence of such landscapes), and are likely to depend strongly on the extent to which critical ecosystem attributes (large‐scale disturbances, fish migrations, keystone species, large woody debris recruitment) are allowed to be re‐established. Understanding these context‐dependencies is critical for predicting fish responses, and should help managers set realistic conservation, management and restoration goals. Management may best be served by promoting a diversity of land cover types in a way that emulates natural landscape and disturbance dynamics. This goal presents very different challenges in New England and the British Isles due to differences in current and predicted land use trajectories, along with differences in ecological context and public perception.

Historical fires in Douglas-fir dominated riparian forests of the southern Cascades, Oregon

Despite the ecological importance of fire in Pacific Northwest forests, its role in riparian forests is just beginning to be documented. This study reconstructed the historical occurrence of fire within riparian forests along different stream sizes in coast Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirbel] Franco) dominated forests within the drier western hemlock (Tsuga heterophylla [Raf.] Sarg.) forest series of the Upper Steamboat Creek watershed of the Umpqua National Forest, Oregon. Fire dates were determined from a total of 194 fire-scarred wedges from stumps sampled at 15 riparian and 13 upslope one-hectare plots. Fire was common historically in both the riparian zones and upslope forests of this study area. Riparian Weibull median probability fire return intervals (WMPIs) were somewhat longer (ranging from 35–39 years, with fire return intervals ranging from 4–167 years) than upslope WMPIs (ranging from 27–36 years, with fire return intervals ranging from 2–110 years), but these differences were not significant. Fires were probably mixed in severity and likely patchy, considering the high incidence of fires occurring only at a riparian plot or only at an upslope plot within a pair, but not at both. Finally, fire return intervals showed a non-significant trend of decreasing length from west to east to north aspects. An increased sampling effort may have shown this decrease to be significant. Based on the results from this study, it is evident that restoring fire will be necessary to protect riparian forest health in this study area. Historical recruitment of large woody debris was likely patchy and pulsed for these mixed-severity fire regime forests.

Sensitivity of a Riparian Large Woody Debris Recruitment Model to the Number of Contributing Banks and Tree Fall Pattern

Abstract Riparian large woody debris (LWD) recruitment simulations have traditionally applied a random angle of tree fall from two well-forested stream banks. We used a riparian LWD recruitment model (CWD, version 1.4) to test the validity of these assumptions. Both the number of contributing forest banks and predominant tree fall direction significantly influenced simulated riparian LWD delivery, but there was no apparent interaction between these factors. Pooled across all treatments, the average predicted 300-year cumulative LWD recruitment was 77.1 m3/100 m reach with both banks forested compared to 49.3 m3/100 m reach when only one side was timbered. Total recruitment within bank cover categories (one versus both forested) depended on the directionality of the falling stem. When only one bank was forested, the CWD model predicted the same riparian LWD recruitment for the random and CWD default tree fall patterns (∼39 m3/100 m reach), the pattern biased toward the channel yielded twice this volume, a pattern quartering toward the channel produced 64% more LWD, and the pattern paralleling the channel contributed almost 30% less than random. With both banks forested, the random, default, and quartering simulations resulted in similar delivery (about 78 m3/100 m reach), the pattern biased toward the channel contributed almost 14% more LWD, and the parallel pattern yielded 26% less. Because CWD is similar in design and operation to other riparian LWD recruitment models, it follows that any simulation of wood delivery to streams should be checked for their consistency with local forest cover and tree failure patterns. West. J. Appl. For. 19(2):117–122.

A practical scientific approach to riparian vegetation rehabilitation in Australia

The clearance of indigenous riparian vegetation and removal of large woody debris (LWD) from streams combined with the planting of exotic plant species has resulted in widespread detrimental impacts on the fluvial geomorphology and aquatic ecology of Australian rivers. Vegetation exerts a significant influence on fluvial geomorphology by affecting resistance to flow, bank strength, sediment storage, bed stability and stream morphology and is important for aquatic ecosystem function. As the values of indigenous riparian vegetation are becoming better recognised by Australian river managers, large amounts of money and resources are being invested in the planting of indigenous riparian vegetation as part of river rehabilitation programs. This paper summarises the results of an investigation into the survival, growth and regeneration rates of a series of trial native riparian vegetation plantings on in-channel benches in the Hunter Valley of southeastern Australia. The trials were poorly designed for statistical analysis and the paper highlights a number of shortcomings in the methods used. As a result, a new approach to riparian vegetation rehabilitation is outlined that promotes the use of scientific principles and understanding. Appropriate species should be selected using a combination of remnant vegetation surveys, historical records, palynology and field trials. A number of important factors should be considered in the rehabilitation of riparian vegetation to achieve worthwhile results. These include flood disturbance, vegetation zonation, vegetation succession, substrate composition, corridor planting width, planting techniques, native plant regeneration, LWD recruitment and adaptive ecosystem management. This approach, if adopted, revised and improved by river managers, should result in greater success than has been achieved by previous riparian vegetation rehabilitation efforts in Australia.

Riparian aquatic interaction simulator (RAIS): a model of riparian forest dynamics for the generation of large woody debris and shade

Streams depend on riparian forests to supply many important functions such as delivery of large woody debris (LWD), organic matter, and nutrients into the aquatic ecosystem and to provide shade to help maintain cool water. Both forests and streams are dynamic, and inputs from the riparian forest are constantly replenished as organic matter and nutrients are processed and transported. Forest stand dynamics have been intensively studied and foresters have developed a good understanding of tree growth and mortality to support commercial forest management. In recent years, the relationships between aquatic functions and adjacent forest stand characteristics have been increasingly quantified by ecologists. Management of riparian forests to protect aquatic functions and water quality has received considerable attention in the Pacific Northwest and elsewhere. For scientific knowledge to be useful to decision-makers, the complex set of riparian relationships, increasingly well understood individually, need to be collectively and objectively linked in a form that can be easily used by scientists and non-scientists alike to develop management strategies for riparian forests. In this paper we describe an analytical system that quantitatively links widely used forest growth forecasting systems for coastal Pacific Northwest forest types to the riparian ecological functions of large woody debris recruitment and shade. The riparian aquatic interaction simulator (RAIS), with its user-friendly interface, allows managers to forecast aquatic functions for up to 300 years. RAIS provides these forecasts over a range of critical input variables and produces realistic estimates of riparian functions when compared with published research. RAIS is available at http://www.weyerhaeuser.com/rais.html

Patterns of Instream Wood Recruitment and Transport at the Watershed Scale

A wood budget was constructed for the Game Creek basin (132 km2) in southeast Alaska to identify spatial and temporal controls on the abundance and distribution of large woody debris (LWD). Field measurements of wood storage, size, and age were used to estimate volumetric rates of LWD recruitment and transport. Mortality recruitment did not follow a spatial pattern and ranged from 0.1 to 8.1 m3·km−1·year−1 (recruitment corresponded to forest mortality rates of 0.1–2.6% per year). Wood recruitment by bank erosion increased with increasing drainage area and ranged from 1 m3·km−1·year−1 at the smallest drainage areas to about 16 m3·km−1·year−1 at 60 km2. Bank erosion recruitment exceeded the maximum mortality recruitment at a drainage area of approximately 20 km2 (about 10-m-wide channel). Recruitment from land-sliding was only locally significant. The contribution of fluvial transport (flux) to total LWD storage increased with drainage area to an asymptotic maximum of 50% at about 50 km2 (about 20-m-wide channel). Mean predicted transport distances for mobile LWD over the lifetime of individual pieces ranged from about 200 m in small, jam-rich streams to about 2,500 m in larger channels with fewer jams. Fluvial transport of LWD increased interjam spacing and jam size and decreased jam age with increasing distance downstream. Constructing LWD budgets at the watershed scale has numerous geomorphic and ecological implications, including identifying spatial controls on the abundance and diversity of aquatic habitats. In addition, information on LWD budgets may be useful for determining how and where to protect LWD sources to streams.