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Large Woody Debris –
The Common Denominator for Integrated Environmental Management of Forest Streams

C. Andrew Dolloff
 
 

Knowledge about ecology and environmental issues has exploded in the last half of the 20^th century. Concerns for environmental quality have become major political issues, and an increasingly informed public now demands comprehensive solutions to complex environmental problems. Such well publicized issues as preservation and recovery of individual endangered species have provoked the strongest reactions. Since passage of the Endangered Species Act, decision makers, scientists, and managers have been obliged to recognize that endangered species management may entail, among a host of other considerations, genetics research, captive breeding programs, and habitat manipulation. An integrated approach to resolving issues of environmental management should provide insights unavailable from the perspective of individual disciplines and help forestall-or at least foresee-potential future problems. The utility of an integrated approach to management extends far beyond concerns for the welfare of individual species to strategies for maintaining entire ecosystems. Nowhere is the need for integrated solutions greater than at the interface between terrestrial and aquatic systems, the riparian zone. And few features of riparian zones in forested areas, aside from water and trees, are as conspicuous as large woody debris (LWD).

Today most stream ecologists recognize that a variety of aquatic species depend on the natural accumulation of trees, branches, and root wads collectively known as LWD. In the past, however, many managers treated LWD as a liability. Many Federal and state land management agencies and some private corporations had policies that mandated debris removal from watercourses or supported programs of clearing and snagging. Agency decision-makers invoked these policies in the name of flood prevention, habitat improvement or simply because LWD was unattractive. Although careful removal of individual trees and debris accumulations can be justified for safe, efficient navigation of large rivers and to protect property or individual stream and river crossings (bridges, fords etc.), wholesale removal of LWD from rivers and small streams disrupts ecological processes and radically changes habitats for a multitude of aquatic species. In this chapter I summarize the many functions of LWD in streams and describe the role of LWD in creating and maintaining fish habitat. I also outline the implications of past management of LWD in streams and waterways in the southern Appalachians.
 
 

To many ecologists, any piece of wood 2.5 cm in diameter or greater is LWD. Although pieces of wood this size and smaller play significant roles in stream ecology, they are more readily dislodged and moved downstream by flowing water and thus, have less influence on stream channel morphology and fish habitat. Based on its potential to influence channel morphology, LWD is any piece of wood at least 10 cm in diameter at the small end and 1.5 m in length. LWD can be whole trees with tops and root wads, branches, snags, or detached tree boles. In general, the larger the piece (both in diameter and length), the more likely it is to stabilize and influence stream channel morphology. Because of the anchoring effect of roots, entire trees with root wads attached are most likely to make long term contributions to habitat.

Even pieces that are not in the water at low or average flows can make important contributions to instream habitat: both bankside and suspended debris "bridges" (pieces that span the channel) and "ramps" (broken bridges or pieces that do not span the width of the channel) have the potential to influence stream channel morphology by deflecting flow and encouraging scour when streamflows approach bankfull.² Debris dams, typically composed of one or more pieces of LWD and many smaller pieces, slow the flow of water, trap sediment and organic matter and create microhabitats for fish and benthic macroinvertebrates. In larger rivers, snags and deadheads provide cover and enhanced feeding opportunities, attracting both prey and predator species.

LWD is not slash-typical logging residue composed of small trees, tops, and branches.³ Except in the smallest of streams, slash tends to be unstable and contributes relatively little to instream habitat. Large amounts of fresh (green) slash and finely divided logging debris may even cause local depletion of dissolved oxygen or buildup of toxic residues.^1,5,6 However, individual whole trees that accidentally enter a stream during logging operations should probably be considered LWD.
 
 

There are several excellent reviews that explore the ecology of LWD in detail^1,5,7 and while no attempt has been made to duplicate or supersede those efforts in this chapter, a brief over-view of the roles played by LWD is necessary to appreciate its significance in stream and riparian ecology.

Many ecological processes are associated with LWD in streams, ranging from providing sites and raw material for primary and secondary production and the formation of critical habitat for fish, to control of water and sediment yield from watersheds (Table 1).^1,5 LWD provides both a grazing surface and food source for a host of microbes and aquatic invertebrates. Seston and inorganic sediments trapped and stored by debris dams or around LWD accumulations are more readily available for instream processing by macroinvertebrates and microbes.⁸ During high flows sediments are trapped and stored, and downstream flood peaks may be delayed and damped by instream accumulations of LWD in the headwaters.

From the perspective of many fish species, pool formation probably is the most important function of LWD. Many species of fish are attracted to the lower water velocity and greater water depth in pools. In the pools of mountain streams, trout frequently occupy and defend positions in slow or slack water from which they make forays after insects and other food items in the faster flowing drift. Pools are especially important when fish are under stress, such as during conditions of extreme high or low flow.
 
 

Table 1. Overview of functions and processes in streams influenced by LWD.

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Physical		Biological
Habitat formation		Competition
	Type		Inter-and intraspecific
	Frequency	Predation
	Sequence		Aquatic
	Complexity		Terrestrial and avian
Water regime			Anglers
	Storage	Primary and secondary production
	Delivery		Substrate for microorganisms
	Quality		Source of fine organic material
Sediment regime
	Storage
	Delivery

__________________________________________________________________
 
 

Pools form around any material that creates friction and resists displacement by flowing water. While virtually everything in the channel creates friction, including the stream bottom and sides, LWD, boulders, and bedrock protrusions are the dominant pool forming elements. LWD is the most conspicuous of these elements, and may play a role in the formation of up to 100% of pools in small to medium sized streams flowing through undisturbed forests.¹ Many mountain streams in the southern Appalachians flow through old clearcuts or fields and have lost much of their LWD through the natural processes of decay and downstream transport. The percent of pools formed by LWD tends to be much lower in streams flowing through these second- and younger growth forests because the immature streamside vegetation is not yet able to contribute large amounts of LWD. Recent research in the southern Appalachians, however, suggests that LWD is a component in at least 50% of pools in streams flowing through riparian zones ranging in acre from 28 to over 300 years since establishment.⁹

Pools develop around LWD in a variety of ways.¹⁰ Plunge pools result when water flow scours sediment from the downstream side of LWD that spans the channel, dam pools form when water is backed up behind one or more pieces of LWD, and backwater pools are created by eddies where the ends of pieces or rootwads jut into the flow (Figure I). In general, the deepest pools form behind pieces that span the entire width of the channel near the water surface and are oriented perpendicular to flow.¹¹

In addition to its role in pool formation, LWD in the form of overhanging logs, debris jams, and especially root wads serves as complex cover, protecting fish from predation, excessive competition and physical displacement. Fish in pools with complex cover have greater opportunities to be visually isolated, which may decrease the number of behavioral interactions and permit greater numbers of fish to coexist.¹² Complex cover in deep pools is especially valuable during times of increased stress such as winter.^13-16 Fish find shelter from high streamflows in winter by moving into or behind LWD accumulations and rootwads.¹⁷

Removal of LWD typically results in loss of pool habitat¹⁸ and complexity¹⁹ and lower fish numbers, average size, and biomass for both warmwater²⁰ and coldwater fish species. ^12,21,22,23 Habitat simplification following timber harvest and subsequent decreases in residual LWD loading and input also has been linked to long term chances in the species composition (diversity) of fish communities, including shifts in dominance and the disappearance of formerly common species .²⁴

Recent research on ecological disturbance and refugia - areas that remain habitable during extremes of drought, flood, or other disturbance - has emphasized the importance of maintaining connectivity among stream channels, accessory or side channels and riparian zones as sources of LWD.²⁵ Refugia are fail-safe habitats from which fish and other aquatic organisms recolonize following disturbances; the quality and frequency of refugia greatly influences the stability and resilience of aquatic systems. LWD is a major feature of refugia across a multitude of habitat types and spatial scales, from individual pieces in pools to large accumulations distributed across stream channels and floodplains of entire drainage basins. The variety and availability of refugia for aquatic organisms is greatly reduced in streams and rivers that have been channelized, cut off from their floodplains, or lack significant amounts of LWD. Fish assemblages in several flood-damaged watersheds in the Blue Ridge Mountains of Virginia, for example. become isolated in individual pools when streams become intermittent because of low flows. Fish of several species pack into these residual pools, where they survive until flows return to normal, but are vulnerable to predation and deteriorating water quality.²⁶ Researchers are attempting to increase survival by decreasing fish densities per pool in a small stream on the George Washington National Forest by adding LWD to encourage the formation of additional refuse pools. Similar efforts are underway in other parts of the country to benefit trout, salmon and other native fish species.
 
 
 
 

 
 
 
 

Most LWD enters streams from a relatively narrow band on either bank; over 70% of the LWD in streams flowing through mature and old-growth riparian zones in western Washington and Oregon originated within 20 m of the stream bank.²⁷ Debris can be introduced from more distant sources on floodplains and hillslopes, however, when transported by floods or debris torrents. ^1,2,28,29 Large woody debris enters streams as the soil surrounding toot systems is eroded by flowing water. Bankside trees are then easily toppled by further undercutting, windthrow or the extra weight of rain, ice or snow. Rates of LWD input vary depending on factors such as size of receiving stream, age, species and health of trees in the surrounding riparian zone, and historical land use.² When widespread, disease can directly influence LWD loading. In the Eastern United States a blight has virtually eliminated the formerly common American chestnut, resulting in atypically high LWD loads (except where valuable chestnut logs were salvage logged) composed primarily of blight-killed chestnut trees.⁹

The greatest inputs of LWD can usually be traced to specific catastrophic events such as debris flows, floods, tornadoes and hurricanes.^1,5 LWD loading in the Basin Creek watershed, for example, more than doubled over previous levels - from 39 to 88 pieces per kilometer of stream channel- after Hurricane Hugo swept over northwestern North Carolina in 1989. Much of this, however, was relatively small LWD reflecting the short time interval (~60 years) since the riparian zone began reverting to a forested condition.

In general, the proportional loading of LWD is higher and its contribution to structure and function is greater in headwater tributaries than major rivers.³⁰ Some low gradient large rivers in the southeastern United States, however, display trends of increasing instream LWD loading with increasing steam order.³¹ The observed lack of LWD in many other large rivers is at least in part an artifact of river management. Over 800,000 snags (average length 40 m) were removed from the lower 1,650 km of the Mississippi River between 1830 and 1880 to improve navigation.¹ In later years, many other rivers across the United States received similar treatment.^1,32

The particular arrangement of instream LWD is influenced by the dynamics of the addition process, stream size, and geomorphic characteristics of the site.^1,5 In small streams (first and second order), many patterns are possible but generally pieces do not move after input because small streams have little power to move larger pieces. The arrangement appears to be random but is determined by the source; pieces stay where they fall or move very little after input. Complex debris dams, composed of smaller LWD and wood fragments, leaves and forest litter are prominent features of small headwater streams in forested watersheds.³³

Accumulations of LWD in streams of intermediate size (second to fourth order) tend to be clumped along the margins or at channel constrictions, creating secondary channels or meander cutoffs. Stream power is sufficient to float pieces from streambanks and upstream accumulations but many pieces may still span the width of the channel. Submerged pieces can remain in place for many years, influencing channel morphology and habitat formation by trapping or scouring sediments. In larger channels (4th order and greater), LWD forms tightly clumped accumulations at the heads of point bars and secondary channels, islands, and along the outside curve of meander bends.

Once in the channel, LWD may persist only until the next high flow or for hundreds of years depending on the attributes of the site (stream order, presence of channel constrictions, etc.) and relative size and quality (resistance to decay) of the LWD. Among other characteristics, smaller pieces have relatively higher surface area to volume ratios and lower proportions of decay resistant heartwood than large pieces; consequently, rates of fragmentation, abrasion and decomposition or disappearance through floatation may be higher for small versus large LWD.¹ LWD tends to exhibit a continual cycle of loss and replenishment in systems that have been undisturbed for a long time. As some pieces are lost or moved about, new pieces take their place, preserving the state of dynamic stability.

The highest loads of LWD usually are associated with coniferous forest types in riparian zones adjacent to streams in the Pacific Northwest;¹ up to 4500 m³/ha were estimated in a stream flowing through a redwood stand in northern California.³⁴ Outside of redwood country, typical LWD loads range from 2.5 to 1700 m³/ha. Estimates of LWD loading tend to be lower in southeastern streams (40-300 m³/ha),¹ owing in part to the long history of settlement and land clearing in the East. The most comprehensive inventory of LWD in southern Appalachian watersheds showed that loadings were highly variable depending on land use and disturbance histories, the number and variety of riparian tree species that contributed to LWD accumulations, and the dynamics of American chestnut input relative to the chestnut blight.⁹ LWD loadings, particularly those originating in mature and old-growth forests, were lower than expected and considerably lower than those in comparably sized Pacific Northwest streams.

In the absence of anthropogenic disturbances, streams flowing through Eastern forests probably would have substantial loads of LNVD. Streams in unloggedwatersheds in the Great Smoky Mountains National Park contain, on average, four times more LWD (338 vs. 84 m³/ha) than streams of comparable size in watersheds logged before the Park was established in the 1930s.³⁵ Elsewhere in the southern Appalachians, Flebbe and Dolloff³⁶ found higher loads of LWD in unmanaged (unlogged) versus managed (logged within the last 60-80 years) wilderness watersheds (Figure 2).
 
 
 
 

Of the many factors that affect LWD input to streams, perhaps the most significant is the legacy of past land use. Since antiquity, engineers have regarded LWD as a hindrance to navigation and commerce on large rivers and an impediment to efficient drainage of small watersheds. In more recent times, biologists have advocated debris removal on the grounds that it might degrade water quality, harm fish habitat or block fish migration.^37,38 And even the most casual observers agree that wood debris in streams is unsightly.

We now understand the important role that LWD plays in stream ecosystems. Under natural conditions, LWD would be a key ecological component in most if not all river systems flowing through forested regions of the world. But centuries of forest and river management worldwide have changed the composition and appearance of most forested watersheds so that it is difficult for most people to appreciate the importance of LWD. Rivers and streams in Asia³⁹ and Europe¹ were cleared of boulders and debris hundreds of years ago to facilitate log driving. On the North American continent, land clearing and development of waterways as transportation networks began in the late 1600s. From 1867-1912, the U.S. Army Corps of Engineers oversaw the clearing and removal of many hundreds of thousands of snags, logs and debris piles from rivers all across the United States.¹

Nearly all of our larger streams, rivers and lakes have been used to raft or drive logs to sawmills at some time over the last 300 years.^40,41 While the actual drives were responsible for significant damage to sensitive stream beds and banks and riparian areas, the stream improvements that preceded these drives were equally if not more destructive. Side channels and backwaters were blocked to keep logs in the main channel and ensure high water levels, and obstructions of all types were hauled, burned, or blasted out of the way.

The pattern of land clearing in the southern Appalachians generallv proceeded from downstream to upstream. With the depletion of timber from floodplains and readily accessible lowlands adjacent to larger rivers, lumber companies were obliged to penetrate further into the mountains for supplies of their raw material. There they encountered rough country and small streams not well suited to traditional log driving activities. As was true in New England⁴² the Great Lakes states,^43,44 parts of the Intermountain west,⁴⁵ and the Pacific Northwest,⁴⁶ splash dams, flumes and slides were common in parts of the southern Appalachians.^42,47,49

One of the best documented examples of stream modification occurred from about 1907-1910 on the Russell Fork of the Big Sandy River in southwest Virginia.^47,50 There, near the Virginia-Kentucky State line, the Yellow Poplar Lumber Company constructed a 110 meter long, 7.5 meter high splash dam to help transport its supply of yellow poplar timber through the Breaks of Sandy into Kentucky and on to its mill in Coal Grove, Ohio. Over 50 million board feet of yellow poplar logs (average diameter 63.5 centimeters, length 0.5- 11.5 meters) passed through bays of the dam and down the Russell Fork during the few brief seasons of operation. Forty men labored for two months and used nearly 10,000 kilograms of dynamite to remove all obstructions in the 24 kilometers of stream immediately below the dam. The effect of the initial stream improvements and subsequent repeated torrents of wood and water totally transformed the character of the river; at the present time, the stream channel upstream and downstream of the dam (the main supports of which survive as the piers for a highway bridge) superficially resembles a u-shaped channel of glacial origin.

Many other rivers with headwaters in the Appalachians suffered similar fates, including the Tellico in Tennessee and West Fork Chattooga in Georgia. On a weekly schedule until, after a few brief seasons the supply of logs was exhausted, water and logs were simultaneously released from behind three dams, each 122 meters long and 12 meters high, on the major forks of the Tellico.⁵¹ Despite its current status as a Wild and Scenic Waterway, much of the watershed of the West Fork Chattooga River was logged and its timber transported by splash dams long before it received protective status or was included in the National Forest system.

Mountain streams continued to play an important role in resource extraction even after railroads had taken over much of the job of log transporrtation. Transportation by rail was more expensive than by water, which was used whenever conditions permitted. Companies frequently ran short lines to transport timber from remote coves and small drains to railways and log dumps on the larger rivers. Transportation by rail did little to protect even the small streams, as stream gravels were mined to build roads and rails were frequently laid directly over stream channels.

Much of the cutover lands in the southern Appalachians eventually were acquired by the Federal Government in the 1920s and 30s. These "lands that nobody wanted" and the streams that drain them have largely reforested and are managed by the U. S. Departments of Interior and Agriculture in national parks and forests.⁴⁸ With the return of the forest, however, knowledge and understanding of the changes caused by past land use are fading from memory.
 
 

If we accept the premise that LWD is and will likely continue to be in short supply in many streams and rivers, then restoring loads and ensuring the future supply of LWD should be of major concern to managers. Arguments for maintaining or supplementing LWD loads include promotion of channel and habitat stability, habitat enhancement (holding, hiding areas), habitat restoration, and enhanced recreational use, primarily angling. On the minus side are the potential for localized damage from flooding, particularly at stream crossings, interference with fish passage, and conflicts with recreational uses such as canoeing and rafting. Because it influences so many ecosystem functions, criteria for LWD management should be based on input from many different disciplines, including (but not necessarily limited to) fisheries, stream and landscape ecology, geomorphology, hydrology, silviculture, and engineering. At all stages in the development of management plans, the public must be informed and given opportunities to voice concerns and opinions.

Of course, LWD is but one of a host of considerations in the broader domains of riparian and watershed manacrement.^52,53 Riparian zones influence temperature, sedimentation, and basic ecological processes such as nutrient uptake and cycling. Many plant and animal species depend on the unique characteristics of riparian zones and wetlands to fulfill virtually all of their life history functions. Still other species rely on the relative security of riparian zones for nesting or rearing young or to facilitate movements and migration among habitats. Along with an appreciation of the various natural functions and values of riparian zones has come increased human use. Riparian zones are now being managed for their ability to sequester nutrients, filter sediments, and grow specific agricultural and forest crops.^54,55 Lastly, because riparian zones form the highly visible boarders of streams and rivers, physical appearance is a major concern of managers who must respond to public perceptions and demands for recreation in aesthetically appealing settings.⁵⁵

Other values notwithstanding, providing both current and future LWD for instream habitat is a legitimate objective of riparian management. In contrast to policies and practices that once allowed harvest of all streamside trees and mandated removal of all debris from stream channels, public land managers and some private industrial landowners have established standards and guidelines for riparian management and have even set goals for LWD recruitment. This abrupt about-face has created some credibility problems for managers and biologists, who for many years demanded that loggers remove all debris, frequently including natural debris, from stream channels. Now they are told that not only is debris removal nearly always unwarranted but also that we should expend time and effort to deliberately put debris back in. The term "stream improvement," at one time used by loggers and rivermen to mean removal of any hindrance to free flow, including LWD and large rocks or boulders, now has exactly the opposite meaning.

Management of LWD will be most effective when approached from an entire watershed rather than an individual stream reach perspective. Examination of conditions at the watershed scale may expose stream reaches of exceptionally high or low quality that on the ground are indistinguishable from adjacent reaches. Information from aerial photographs, topographic maps, and around-based inventories of habitat, riparian vegetation and LWD can be computerized in a Geographic Information System (GIS) and manipulated to produce graphic images of watershed conditions. A comprehensive plan for LWD management can then be developed with site specific goals and objectives.

How does one determine if LWD loading is "too low?" Where they exist at all, criteria for LWD loading are highly variable, depending on historic conditions, local topography, size and availability of tree species, and the composition and needs of the aquatic community. To date, there have been very few attempts to manipulate and link specific amounts of LWD to fish production. In general, however, LWD loadings are too low when the number and quality of pools and cover is low and the stream lacks hydraulic complexity.⁵ Although the optimal amount and frequency of habitat types in mountain streams is probably unique for every stream, an approximate 1:1 ratio of pools to riffles is generally considered desirable.⁵⁶ The determination of what constitutes sufficient amounts of LWD is even more uncertain, but may be based on historic records or inventories of loadings in undisturbed watersheds. If such records or undisturbed areas do not exist, then loadings can be approximated by comparison with LWD loads in similar streams that appear to have "brood" habitat, or by inference based on the outcome of controlled experimentation with different LWD loads in reference watersheds.

Techniques to modify stream structure range widely in expense and complexity. Engineered stream improvements such as wing deflectors, cribs, and sills that are carefully designed to promote specific hydraulic action such as channel constriction or pool scouring are usually stable and effective but costly in both labor and time.⁵⁷ It also is possible to temporarily restore LWD by adding logs and rootwads, pulling or pushing over trees with winches or heavy equipment,⁵⁷ or toppling trees with strategically placed explosives.⁵⁸ But clearly, placement of individual stream improvement structures or trees is not feasible on a large scale. Alternatively, given enough time, many disturbed riparian areas will recover on their own, retain the characteristics of mature forest, and once again provide LWD. Unfortunately, "enough time" may mean at least 50⁵⁹ or as long as several hundred years. A flexible approach is therefore necessary, employing a mix of techniques to address both specific current conditions and long term goals for natural LWD recruitment.

In contrast to the relatively simple, if costly, techniques for actively inputting LWD, arriving at strategies for long term recruitment of LWD will tax the abilities of experts in many disciplines. The diversity of riparian zone functions and values suggests that advocates for LWD must compete for their future raw material (trees) with proponents of other uses. It may be necessary to limit salvage of storm, fire or insect killed trees, for example, to a specified distance from the streambank to preserve sources of LWD until understory trees mature.⁶⁰

Width of streamside management zones (SMZs) should be based on objective criteria including the probability of LWD recruitment. Except as a result of catastrophic additions such as debris flows or landslides, most LWD in the coniferous forests of the Pacific Northwest enters from a 20-30m wide band of riparian forest on both sides of the stream.¹⁶ Similar relationships, although incompletely described, probably exist in other parts of the country as well. Robison and Beschta⁶¹ suggest that a SMZ should be wide enough so that if a tree in the SMZ falls perpendicular to the stream channel, the portion of the tree that intersects the channel has the minimum diameter and height necessary to qualify as LWD. Models for LWD recruitment, such as those developed for watersheds in the Cascade Mountains of Oregon⁶² and the coastal forests of southeast Alaska⁶³ can be valuable tools for deciding the width of SMZs.

The appropriate species or mixture of species to be managed for LWD is an open question, depending on site suitability, resistance to decay, and other riparian management objectives. For example: in the southern Appalachians, northern red and white oak have high aesthetic value and produce hard mast and other benefits for wildlife, high quality timber, and decay-resistant LWD.⁵⁵ Eastern hemlock, while of lesser value for timber, provides thermal cover during both winter and summer and is very resistant to decay.

The emergence over the last 20 years of knowledge of the many roles played by LWD has contributed greatly to both the science and practice of riparian ecosystem management. Armed with this knowledge and an appreciation for the benefits of interdisciplinary, integrated approaches to management, present and future generations of managers will be better able to meet the increasing demands for traditional and potential new uses of riparian ecosystems.
 
 

A variety of aquatic species depend on the natural accumulation of trees, branches, and root wads known as large woody debris (LWD). LWD slows the flow of water, dissipates energy, traps sediment and organic matter, and creates microhabitats for fish and macroinvertebrates. LWD in the form of overhanging logs, debris jams, and especially root wads forms pools and provides complex cover. Removal of LWD typically results in habitat simplification and fewer, smaller fish. Habitat simplification resulting from timber harvest and subsequent decreases in residual LWD loading and input has been linked to long term changes in the species composition of fish communities. LWD is a major feature of refugia across a multitude of habitat types and spatial scales.

Most LWD enters streams from a relatively narrow band on either bank. Debris can be introduced from more distant sources on floodplains and hillslopes, however, when transported by floods or debris torrents. Rates of LWD input vary depending on factors such as size of receiving stream, age, species and health of trees in the surrounding riparian zone, and historical land use. The greatest inputs of LWD can usually be traced to specific catastrophic events.

The particular arrangement of instream LWD is influenced by the dynamics of the addition process, stream size, and geomorphic characteristics of the site. Once in the channel, LWD may persist only until the next high flow or for hundreds of years. The highest loads of LWD usually are associated with coniferous forest types in undisturbed riparian zones adjacent to streams in the Pacific Northwest. Estimates of LWD loading tend to be lower in southeastern streams, owing in part to the long history of settlement and land clearing in the East.

Centuries of forest and river management worldwide have changed the composition and appearance most forested watersheds so that it is difficult for most people to appreciate the importance of LWD. As was true in other parts of the country, log driving and splash dams were common in parts of the southern Appalachians.

Riparian zones are now being managed for their ability to sequester nutrients, filter sediments, grow specific agricultural and forest crops and provide recreation as well as LWD. Criteria for LWD management should be based on input from many different disciplines, including morphology, hydrology, silviculture, and engineering. Management of LWD will be most effective when approached from an entire watershed rather than an individual reach perspective.

Engineered stream and direct additions of LWD can be effective stream improvements but are costly in both labor and time. Many disturbed riparian areas if allowed to recover on their own will regain the ability provide LWD, given enough time. A mix of techniques is necessary to address both specific current conditions and long term goals for natural LWD recruitment.

The diversity of riparian zone functions and values suggests that advocates for LWD must compete for their future raw material (trees) with components of other uses. Width of streamside management zones (SMZs) should be based on objective criteria including the probability of LWD recruitment. Because of the different values associated with individual tree species, riparian species composition can be manipulated to meet specific management objectives.

Large woody debris is an effective model for implementing integrated environmental management.