Coarse Woody Debris in Streams of the Drift Creek Basin, Oregon

by

Curt N. Veldhuisen

A THESIS

submitted to Oregon State University

in partial fulfillment of the requirements for the degree of

Master of Science

Completed February 20, 1990

Commencement June 1990 AN ABSTRACT OF THE THESIS OF

Curt N. Veldhuisenfor the degree of Master of Science in Forest Engineeringpresented on February 27, 1990. Title: Coarse Woody Debris in Streams of the Drift Creek Basin. Oregon

Abstract Approved: Robert L. Beschta

This study examined the occurrence ofcoarse woody debris (i.e., pieces greater than 0.15m in diameter and 2.0 m in length) in first- through fifth-order streams located within the Drift Creek Basin of the Oregon Coast Range. Nine "tributary reachest were surveyed to determine how three land management treatments

(undisturbed, patch clearcut with buffer strip, and entirely clearcut) and/or geomorphologywere associated with CWD loadings or piece characteristics. An additional 45 km of third- to fifth-order channelswere surveyed to identify CWD distribution patternsover changing stream size. All surveys recorded channel characteristics and the dimensions and attributes ofeach CWD piece.

Coarse woody debris loadings varied greatly (11 to

62 pieces/lOOm, 0.3 to 4.3 m3/100m2 of inchannelvolume) between the tributary reaches, but were not significantly

(p > 0.10) related to harvest treatment. However, reaches associated with clearcut treatment containedless hardwood CWD and pieces were significantly shorter, and more decayed than in the other treatments. This suggested that little CWD recruitment had occurred in the

15 to 20 years since harvest. The undisturbed and buffer strip tributaries contained CWD that reflected continued recruitment of both hardwood and conifer trees.

Inchannel CWD loadings averaged 0.44 m3/100m2 and decreased significantly (p < 0.01, r2 = 0.68) with drainage area. Coarse woody debris frequency and total loadingaveraged 10 pieces/lOOm and 14 m3/lOOm, respectively, and were not significantly related to stream size. The percentage of total CWD volume within the channel increased with stream order and decreased with increasing channel gradient. "Large" debris pieces

(i.e., pieces greater than 0.5 m in diameter and10 m in length) were particularly frequent in the gorge-like reaches of the Drift Creek Wilderness. Over one third of the CWD pieces in larger channels occurred within debris j ams.

Coarse woody debris loadings in the Drift Creek Basin appear to be lower than other forested streams in the Pacific Northwest. It is concluded that past stream cleaning, harvesting, and basin geomorphology have influenced CWD loadings within the Basin. However, the effects of nineteenth century forest fires on stand characteristics and debris recruitment trendsappear to be a major cause of the observed CWD loadings. APPROVED:

Professor of Forest Engineering in charge of major

Head of department of Forest Engineering

Dean of Graduate School

Date thesis is presented February 27, 1990

Typed by ACKNOWLE DGEMENTS

Many thanks are due to the directors of Coastal

Oregon Productivity Enhancement (COPE) program for financial support and for selecting an intriguing study basin. Gordy Reeves, Jim Sedell, and Gordon Grant (from the PNW Forest Sciences Laboratory) were involved in conceiving the Drift Creek Basin survey, as were Tom McMahon and Stan Gregory (from OSU).

The fisheries crew at the PNW did an outstanding job collecting and processing habitat survey data. Special thanks in particular go to Kelly Burnett for coordination and Miranda Raugh for her conscientious work on the CWD inventory.

John Schwartz devoted enormous energy to the Drift Creek project, during our coordinated field surveys and interpreting observations from the Basin. You're almost there, John!

Thanks go to Ray Ayers of Georgia Pacific Corpora- tion, the Waldport Ranger District, Hank Froehlich, and Jim Kiser for information and recollections regarding

Basin history.

Bob Beschta, as major professor, was tireless in his contribution of patience, support and enthusiasm. Thanks also to Bill Atkinson, who encouraged me to enjoy gradu- ate school and to the "Bob Squad" who helped me do it! TABLE OF CONTENTS

SECTION PAGE

INTRODUCTION 1

LITERATURE REVIEW 5 STREAM FUNCTIONS OF COARSE WOODY DEBRIS 5 COARSE WOODY DEBRIS LOADING PROCESSES 7 Inputs 8 Losses 9 COARSE WOODY DEBRIS DISTRIBUTION PATTERNS 11 EFFECTS ASSOCIATED WITH FOREST MANAGEMENT 13 Harvesting 13 Stream Cleaning 14 Long-term Effects is

METHODS 18 STUDY AREA 18 Climate 18 Geology, Soils and Landforms 20 Vegetation 20 Resources and Management 22 SITE SELECTION 24 Tributary Reaches 24 Basin Survey Reaches 27 DATA COLLECTION 29 Channel Habitat Survey 29 Coarse Woody Debris Inventory 30 DATA ANALYSIS 35

RESULTS AND DISCUSSION 38 TRIBUTARY REACHES 38 Geomorphic and Vegetative Settings 38 Coarse Woody Debris 42 Spatial Distribution 42 Piece Characteristics 47 Forest Management and CWD in Tributaries 54

BASIN SURVEY 59 Geomorphic and Vegetative Settings 59 Coarse Woody Debris 61 Spatial Distribution 61 Piece Characteristics 64 Fluvial Influences on CWD Distribution 69 Forest Management and CWD in Survey 77 Reaches Effects of Valley Form on CWD 80 Distribution Comparing Drift Creek to other 86 Northwest Streams SECTION PAGE

CONCLUSIONS 94

LITERATURE CITED 97

APPENDIX 103 LIST OF TABLES

Table Page

A 5-class system of log decay based on 33 fallen Douglas-fir trees (from Robison 1988)

Physical characteristics of tributary 39 reaches, Drift Creek Basin

Management history of tributary watersheds, 41 Drift Creek Basin

Spatial distribution of CWD in tributary 43 reaches, Drift Creek Basin

Mann-whitney results of CWD comparisons 46 between sub-basin tributaries

Piece characteristics of CWD in tributary 48 reaches, Drift Creek Basin

Mann-Whitney results of CWD comparisons 49 between treatments

Physical characteristics of survey reaches, 60 Drift Creek Basin

Spatial distribution of CWD in survey 62 reaches, Drift Creek Basin

Piece characteristics of CWD in survey 67 reaches, Drift Creek Basin

Loadings and piece characteristics of 75 "large" CWD in Drift Creek survey reaches

Channel characteristics and spatial CWD 83 distribution for constrained and unconstrained stream segments, Drift Creek Basin

Forest type and management history for 87 streams in the Pacific Northwest

Al. Locations of Drift Creek survey reaches 103

A2. Coefficients and statistics of correction 104 equations for CWD piece dimension estimates Table Page

A3. Elevations, low flows, and vegetation of 105 tributary reaches, Drift Creek Basin

Additional piece characteristics of CWD 106 in tributary reaches, Drift Creek Basin

Elevations and vegetation of survey 107 reaches, Drift Creek Basin

Additional piece characteristics of CWD 108 in survey reaches, Drift Creek Basin

Species categories of CWD in tributary 109 and survey reaches, Drift Creek Basin LIST OF FIGURES

Figure Page

Location of Drift Creek Basin, Oregon 19

Longitudinal profile for (a) Drift Creek, and 21 (b) Meadow Creek sub-basin streams (profiles developed from USGS quadrangle maps).

Location of tributary reaches, Drift Creek 26 Basin

Location of survey reaches, Drift Creek Basin 28

Coarse woody debris piece measurements 31

Coarse woody debris influence zones 34

Channel loading of CWD per bankfull area 44 in tributary reaches, Drift Creek Basin (UD = undisturbed, BS = patch clearcut with buffer strip, CC = entirely clearcut)

Probability densities of CWD piece lengths 50 in (a) lower basin,(b) mid-basin, and (c) upper basin tributary reaches

Mean decay of CWD vs. harvest treatment of 52 tributary reaches, Drift Creek Basin (UD= undisturbed, BS = patch clearcut with buffer strip, CC = entirely clearcut)

Total volume loading of hardwood and conifer 53 CWD vs. harvest treatment of tributary reaches, Drift Creek Basin (UD = undisturbed, BS = patch clearcut with buffer strip, CC= entirely clearcut)

Average decay vs. percent hardwood CWD pieces 56 in tributary reaches, Drift Creek Basin

Relative frequency distribution for decay of 57 (a) hardwood and (b) conifer CWD pieces

Channel loading of CWD per bankfull area vs. 63 drainage area, Drift Creek Basin

Coarse woody debris volume in influence zones 65 vs. stream order, Drift Creek Basin Fiqure Page

Eighty-fourth percentile CWD piece lengths 68 vs. drainage area, Drift Creek Basin

Percent of CWD pieces with rootwads vs. 70 drainage area, Drift Creek Basin

Percent of total CWD volume in Zones 1 and 71 2 vs. channel gradient, Drift Creek Basin

Frequency of "large" CWD pieces (i.e., 76 pieces greater than 0.5 m in diameter and 10 m in length) and debris jams in Drift Creek reaches

Longitudinal profile of channel unit CWD 78 loading per bankfull area along Drift Creek

Cross-sectional view of typical (a) 81 constrained and (b) unconstrained valley forms

Channel CWD loading per bankfull area for 84 constrained and unconstrained stream segments, Drift Creek Basin

Channel loading of CWD for streams in the 88 Pacific Northwest (see Table 13 for stream descriptions)

Hypothetical CWD loadings over time fora 91 second-order Oregon Coast Range stream COARSE WOODY DEBRIS IN STREAMS OF THE DRIFT CREEK BASIN, OREGON

INTRODUCTION The presence of woody debris within Pacific Northwest streams has long been recognized, although perceptions of its function and value have changed. During the early years of settlement, waterways provided important avenues for transportation. Woody material in channels acted as an impediment to river navigation and the floating of logs to mills. In the mid-1900's, woody debris was blamed for damage to bridges and structures, and impeding fish migration (Sedell et al. 1985). All of these concerns have led to removal of large amounts of coarse woody debris (CWD) from northwest streams. It wasn't until the 1970's that the beneficial functions of CWD in stream systems became apparent to stream researchers and concern arose that streams were becoming depleted of CWD. Hence, recent interest has focused on methods for maintaining or increasing CWD loadings to enhance beneficial functions.

Over the past two decades, research has documented an array of stream functions associated with CWD, including fish habitat formation, control of sediment routing, and affects on channel stability (Keller and

Tally 1979, Bisson et al. 1987). The nature and extent of these functions in a given stream. are influenced by the configuration and loading ofCWD,which vary widely between sites.

Spatial patterns ofCWDdistribution are associated with stream characteristics, primarily stream size, geomorphology (i.e. valley form, channel features and slope), riparian vegetation, and land management history that affect the stream directly and indirectly through basin processes (Keller and Tally 1979). The importance of individual factors is often obscured by their interactions.

Recommendations designed to restore functions associated withCWDin streams, generally involve management of riparian stands to provide futureCWD input, or placement of trees or manufactured structures into channels. Ideally, such projects will be based on differences between presentCWDloading patterns and probable historic levels. However, the results of most

CWDresearch have limitations that reduce their applicability to riparian management planning:

NaturalCWDloadings vary dramatically between and within basins due to differences in geology, vegetation type, and stream size, making it

difficult to extrapolate optimal loading for the given basin.

Relatively little field research has been

conducted to indicate patterns ofCWDdistribution (both along the channel and within channel cross-

sections) and function for varying strean sizes. 3. Agencies and land owners are nanaging channels which may have been influenced by a range of past practices, while most studies are based on sites which are pristine or influenced by a single

"treatment" effect.

As a result of these limitations, basin-wide CWD studies are increasingly needed to evaluate the combined effects of a broad range of influences.

Several observations illustrate CWD processes operating at the basin scale. First, CWD loading at a site potentially integrates the effects of upslope and upstream events (Keller and Swanson 1979). Second, CWD is influenced by numerous natural and man-caused disturbances through time. Finally, anadromous and resident fish utilize CWD-influenced habitat in many parts of a basin in response to seasonal water level changes and during migration.

The focus of this study is to identify factors affecting spatial CWD patterns throughout the Drift Creek

Basin. More specifically, the objectives are to:

1. Compare the effect of three ianageinent options

(clearcut, patch clearcut with buffer strip, and undisturbed) upon CWD characteristics and loading

for streams within the basin. Analysis will investigate whether management history and/or geomorphic setting are associated with CWD and channel morphology.

2. Quantify and characterize the spatial distribution of CWD along a continuous sequence of streams in the Drift Creek basin to evaluate if CWD characteristics and loadings vary in response to changing stream size. 5 LITERATURE REVIEW

Studies over the past two decades have indicated that coarse woody debris has an extensive range of ecological functions in streams. Detailed reviews have been published documenting CWD and stream ecosystems (Harmon et al. 1986, Sedell et al. 1988), fisheries habitat (Sedell et al. 1985, Bisson et al. 1987), and channel morphology (Keller and Swanson 1979). Although these functions will be reviewed briefly, research related to spatial and temporal patterns of CWD, and effects associated with forest management will be emphasized.

STREAM FUNCTIONS OF COARSE WOODY DEBRIS

In coniferous forest streams, CWD may contribute 70 percent of the organic input (Anderson and Sedell 1979), thus providing a major food source for aquatic organisms.

Although the compounds contained in CWD are not readily digestible, numerous microbes and invertebratesare able to process them (Harmon et al. 1986). Instream CWD also creates dams and log steps which improve retention and processing of the finer organic materials (Bilby 1980,

Gillilan 1989). Many organisms that subsist on woody debris are important food sources for salmonids.

Among the studies that have documented the affects 6 of CWD on salmonid production in the Northwest, early research focused on detrimental impacts. During the 1950's and 60's, fisheries biologists concluded that debris jams were major impediments to upstream ndgration, although subsequent research showed that CWD jams had rarely excluded fish from significant portions of spawning or rearing habitat (Sedell and Luchessa 1982). Other studies found that submerged debris can produce toxic leachates and deplete dissolved oxygen during microbial breakdown. Though such effects may be a valid concern in streams with extreme concentrations of slash, harmful levels are rarely reached in natural or managed watersheds (Sedell et al. 1985). More recent research has identified a number of means by which woody debris benefits fisheries, including the following:

CWD often provides inchannel cover that allows

fish to evade predation (Bryant 1983).

CWD provides refuge from high velocity flows in otherwise suitable habitat (Bustard and Narver

1975).

CWD may affect channel hydraulics, often

producing channel habitat. Specific habitat features include pool habitat for adult fish,

lateral habitat used by young and spawning gravel

deposits for reproduction (Bisson et al. 1987). 7 4. In some cases., pools created by CWD provide the last available-habitat during extreitie low flows (Hogan 1985, Lisle 1986a) A number of channel processes are associated with coarse woody debris.Large stable logs may provide sediment storage capacities inany tunes greater than the annual transport voluines (Marston 1982). Downstream water quality can be enhanced when sediment pulses from upstream landslides, debris torrents and erosion are trapped (Swanson and Lienkaemper 1978).Streain channel stability is enhanced by stable CWD that stores sediment, armors banks or anchors pool locations (Keller and Swanson 1979, Lisle 1986b). Woody debris can also initiate channel changes, particularly when pieces are unstable or deflect flow laterally into banks.Coarse woody debris jains have been observed to induce meander cutoffs and side channel formation (Keller and Swanson 1979).Janis occurring at culverts and bridges have lead to significant road and structure dainage (Swanson and Lienkaeinper 1978).

COARSE WOODY DEBRIS LOADING PROCESSES The loading and configuration of CWD in a stream reach reflects a balance of past inputs and losses (Keller and Swanson 1979).The relative importance of input and loss inechanisms varies between streams and is 8 influenced by specific geomorphic, hydraulic, and vegetation conditions for each site (Swanson et al.

1976). The following discussion is limited to natural processes.

Inputs

In many stream reaches, the adjacent riparian stand provides the major share of CWD via mortality, windthrow, and bank cutting. Studies of small streams in Northwest old-growth stands have identified windthrow (Keller and Swanson 1979) and mortality (Grette 1985) from the adjacent stand as predominant input mechanisiis. Larger streans acquire significant CWD by bank cutting, or access CWD during more drastic channel course changes

(Keller and Swanson 1979).

Significant CWD inputs can arrive from more distant sources as the result of floatation, debris torrents, earthflows and downslope movement by individual pieces

(Keller and Swanson 1979). Debris torrents are strongly controlled by channel gradient, and often deposit CWD and sediment at points of sudden decrease in slope or at tributary junctions (Swanson and Lienkaemper 1978). Large channels may receive substantial CWD that floats from upstream reaches, especially when obstructions are present to increase piece retention (Keller and Swanson

1979) In general, CWD input of streamside origin comes with branches and rootwad intact (Bisson et al. 1987), making it less subject to fluvial transport. Wood from upstream or upslope sources is often fragmented and/or

decayed, and is less likely to provide the functions in the manner of stable pieces (Swanson and Lienkaemper

1978)

Losses

Coarse woody debris losses from a reach typically result from fluvial export and gradual decomposition.

The probability of entrainment depends on CWD piece size and characteristics, channel characteristics and flow conditions. Debris pieces longer than average bankfull width are less mobile than shorter pieces (Bilby 1985,

Lienkaemper and Swanson 1987), indicating that bank

contact enhances stability of CWD. Debris pieces which have an attached rootwad, or that are partially buried in channel sediments (Toews and Moore 1982, Grette 1985,

Hogan 1985) are typically more stable. In some situations, burial of CWD in sediment or floatation to

infrequently flooded sites are seen as significant losses

(Keller and Swanson 1979, Grette 1985). Debris torrents may affect a stream infrequently, but can completely

deplete CWD from source channels. Though much of the CWD entrained in streams is subsequently trapped at 10 downstreamsites, some is carried to major rivers, estuaries, orultimately to the ocean (Gonor et al.

1988)

Coarse woody debris is also subject to breakdown by mutually enhancing processes of fragmentation and decay. Physical abrasion is a major breakdown mechanism, particularly in streams where wood or bedloadare especially mobile. Fragmentation occurs due to natural shrinking and cracking of trees after mortality, and boring insects or plant roots can accelerate thisprocess (Harmon et al. 1986).

Physical breakdown enhances decay efficiency by increasing surface area accessible to fungal and inicrobial consuiners, which are almost entirely restricted to surface layers. Studies report decay rate is inversely related to CWD piece diameter (Murphy and Koski, in press), and extent of submergence (Harmon et al. 1986). Depletion rates of CWD vary between tree species, because of differences in wood anatomy and constituent chemical compounds. In northwest streams, hardwoods decay more rapidly than conifers, with conifers (western redcedar and coast redwood in particular) being the slowest (Swanson and Lienkaemper 1978). Breakdown estimates for large conifers (partially submerged)range from 100 to 200 years, while red alder decays much faster (Harmon et al. 1986). 11 COARSE WOODY DEBRIS DISTRIBUTION PATTERNS

The River Continuum Concept (Vannote et al. 1980) characterizes headwater ecosystems as more profoundly affected by terrestrial processes than larger streams, which tend to be dominated by aquatic processes. Studies have observed that CWD loadings (expressed as volumeper channel area) decrease in larger channels (Keller and Tally 1979), suggesting that the spatial distribution of CWD conforms to this concept.

The occurrence of CWD may be influenced by a range of stream attributes, including stream size, channel roughness, as well as riparian vegetation and valley features. Keller and Swanson (1979) have proposed that differences in CWD loading result from the balance of input and loss mechanisms, and the relative importance of these mechanisms changes with stream sizes. Small streams (i.e. first-and second-order) are subject to many input mechanisms, but are not large enough tomove most pieces that enter, so piece longevity is determined primarily by rates of breakdown in place. Pieces remain in a nearly "random" distribution pattern.

Moderate-sized streams (third- and fourth-order)are generally large enough to redistribute smaller pieces into jams, which are anchored by larger pieces (Keller and Swanson 1979). Moderate-sized streams are often depositional sites for CWD and sediment from episodic 12 events such as debris torrents, which contribute to an aggregated distribution pattern. Abrasion and export losses are greater than in smaller channels (Harmon et al. 1986). Large streams (fifth-order and larger) are able to transport many pieces, and debris jams are larger though more widely spaced than upstream (Keller and Tally

1979)

In streams where fluvial redistribution of CWD is prevalent, channel features that provide anchoring for CWD accumulations may have great influence on CWD distribution. For small-to medium-sized streams, larger wood pieces can extend into or span the channel and trap smaller floating pieces (Bilby 1985). On larger streams, CWD rarely remains stable in mid-channel, so debris accumulations are more likely to occur along channel margins where their aquatic influence is limited to high

flow events (Keller and Swanson 1979). Debris jams are seen along the outside of channel bends, in side channels, on floodplains, or where anchored by stable logs or boulders. However, large streams with steep valley walls and few retention sites often retain very

little CWD (Bisson et al. 1987). Similarly, bedrock

streainbeds are sometimes observed to retain little CWD

(Bryant 1983, Bilby and Wasserman 1989). Woody debris piece sizes and their configuration in the channel cross section often varies with stream size. 13 Robison (1988) noted larger average piece volume in large channels than small ones. Two recent studies found that greater percentages of CWD volume occurs within the bankfull zones of larger streams, whereas the greater proportion of CWD was suspended over the channel and on banks for smaller streams (Long 1987, Robison 1988).

Streamnside stand composition often varies with channel size and can affect CWD loading. Studies in Washington and Alaska attribute the occurrence of young hardwood stands along large streams to disturbance caused by alluvial channel changes (Swanson 1982, Robison 1988). In second-growth riparian stands in the Oregon Coast Range, Long (1987) found that terraces along third- and fourth-order channels contained red alder, while conifers were more abundant along first- and second-order streams. Channel CWD volumes and piece characteristics were correlated to the species composition of the adjacent riparian stands (Long 1987).

EFFECTS ASSOCIATED WITH FOREST MANAGEMENT Harvesting

It is well established that streamnside logging influences CWD loading and piece characteristics.

Froehlich (1973) observed natural organic debris in small streams and changes that occurred after three separate logging treatments in western Oregon. Conventional 14 timber falling practices caused up to two-fold increases in CWD, while directional falling or buffer strips were associated with smaller increases or decreases

(attributed to salvage of merchantable CWD from the stream). In almost all cases, the abundance of fine woody material (less than 0.10 m in diameter) increased dramatically following logging.

Studies of post-logging CWD loading of streams in

British Columbia and southeast Alaska (Toews and Moore 1982, Swanson et al. 1984) have attributed the increases in smaller material to input of branches and tops, and breakage of pre-existing pieces. Although total debris volumes in different sites increased or decreased, post- logging CWD has almost always consisted of smaller pieces

(Bisson et al. 1987, Sedell et al. 1988). Small material is easily floatable, and may contribute to channel instability including CWD jam washout (Bryant 1980).

Individual pieces are often less stable after logging as well (Toews and Moore 1982, Hogan 1985).

Stream Cleaning

Historically, CWD was cleaned from many Northwest streams to improve navigation on large rivers, enhance transport of logs down small streams using splash dams, and to ensure access for anadromous fish (Sedell et al.

1985). Stream cleaning following logging began in the 15 1940's but was most extensively carried out on small streams in western Oregon between the mid-1950's to the mid-70's (H. Froehlich, O.S.tJ. Dept. of Forest

Engineering, Corvallis, Oregon, personal communication).

Although cleaning standards were directed toward removal of harvest-introduced debris, pre-existing CWD was often removed as well (Bisson et al. 1987).

Excessive stream cleaning has been associated with increases in sediment transport (Beschta 1979), reduced channel stability (Bilby 1984), and loss of pool habitat several years after cleaning (Bisson and Sedell 1984, Lisle 1986a). Most state forest practice regulations have been altered to protect stable CWD, but loadings remain low on many streams that were cleaned during this period (Sedell et al. 1985, Heimann 1988).

Long-Term Effects

Forest harvest and road building are associated with long-term basin changes that influence CWD loading. In some areas, road building and clearcut logging have increased the frequency of debris torrents and landslides, which provide large pulses of CWD and/or sediment (Swanson and Lienkaemper 1978). Streamside buffers, exposed to wind after nearby harvest, have experienced increased blow down (Froehlich 1973) and accelerated CWD input (Toews and Moore 1982, Sedell et 16 al. 1985). However, most research has found that CWD loadings some time after logging were lower than before harvest, and this is generally attributed to delayed input from the regenerating stand (Bisson et al. 1987). Following the loss of the riparian stand to logging or fire, residual CWD declines gradually, although it may continue to be important for 100 years or more (Heimann 1988). The level and duration of influence depends on the degree to which the disturbance reduced inchannel and riparian CWD (Swanson and Lienkaemper 1978).

Heimann (1988) studied Oregon Coast Range streams in forests at differing stages of development following disturbance (clearcut logging or wildfire) and found that red alder provided moderate amounts of CWD after age 30 but conifer did not produce significant input until 80 years after harvest. Only after 120 years past disturbance was new CWD more abundant than residual material (Heimann 1988), and at that time, total loads were much below those associated with old-growth streams. A study of CWD in an Oregon Cascade stream 140 years after wildfire resulted in a very similar conclusion

regarding replacement of residual debris (Swanson and

Lienkaemnper 1978). A study of upslope Douglas-fir stands in Oregon and Washington suggests that forest floor CWD loadings are lowest around 100 years after new stand

establishment, but continue to increase until a stand age 17 of approximately 400 years (Spies et al. 1988). Coarse woody debris inputs from young stands typically consist of smaller pieces and greater hardwood proportions (Bisson et al. 1987). Grette (1985) found a greater percentage of alder CWD, and smaller average piece sizes in streams in second-growth (20 to 60years old) than in old-growth stands. The conclusion of Heiinann (1988), Grette (1985) and others is that riparian harvest rotations of less than 100 years would greatly reduce input of coniferous CWD to similar streams. As residual material declines, stream CWD loadings will remain at significantly lower levels than in old-growth settings. 18 STUDY METHODS

STUDY AREA

The study was conducted within the Drift Creek basin which is centered about 16 km northeast of Waldport,

Oregon (Figure 1). Drift Creek was chosen as a study basin for COPE (Coastal Oregon Productivity Enhancement) research because its characteristics (salmonid fish habitat, high forest productivity and diverse management history) are representative of the central Coast Range. Drift Creek is about 50 km long and is a fifth order stream when it flows into the Alsea River estuary. The Drift Creek Basin has an area of about 180 km2, with elevations ranging from sea level to 860 m.

Climate

The basin's climate is characterized by mild temperatures and relatively abundant moisture. The average annual precipitation is about 250 cm, almost exclusively falling as rain. Ninety percent of the annual precipitation generally falls between October and May, due to long-duration, low- to moderate-intensity frontal storms that approach from the Pacific. The orographic effect of the Coast Range causes precipitation to be somewhat greater for higher elevations in the drainage. Peak flows typically occur in late fall and 19

/ ( N

Approximate scale 024 kflometers \ £ I a q) 0U /

U Wald p ort U a Alsea R.

Figure 1. Location of Drift Creek Basin, Oregon 20 winter while lowest flows occur in latesummer or fall.

Geology. Soils, and Landforms

The basin is almost entirely underlain by the Tyee formation of bedded marine sandstone and siltstone.

Broader valley bottoms along mainstem Drift Creek contain thick deposits of alluvial silt, sandor gravel (Snavely et al. 1976). Predominant soil series in the basinare gravelly loams and gravelly clay loams of the Bohannon-

Slickrock association. Soils are sandstone-derived, well drained, and often subject to slumping (Corliss1973).

Hillslopes vary from moderate to steep (20to 80 percent). Channel gradients are typically less thanone percent for fifth order channels, though small firstand second order channel gradients range fromone to ten percent. The transition from flatter to steeperreaches is not always continuous, and alternatinggentle and steeper reaches produce a "stair step" patternassociated with some channels (Figure 2). Alluvial bed material derived from local sandstone is notably incompotentand weathers rapidly into sand and silt.

Vegetation

Forests in the Basin fall within the Picea sitchensis and Tsuga heterophyllazones, based on potential climax overstory species (Franklinand Dyrness 21

300 (a) 250

200

150

100 Drift Cr. 50

I I I I I I I I I I I I I I I II I II II I I I I I 10 20 30 40 5 15 25 35 45 Distance frcm Alsea River (krr-i)

225 b 200 Flyrm Cr. 175 Horse Cr. Needle 150 Br. ecdow Crc' 125 Drift Cr. 100

75 18 22 26 20 24 28 Distance frcm Alsea River (km)

Figure 2. Longitudinal profile for(a) Drift Creek,and (b) Meadow Creek sub-basinstreams (prof iles developed from USGSquadrangle maps) 22 1973). Present forest overstory is dominated by Douglas- fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and red alder (Alnus rubra), which is especially abundant in riparian stands. Western redcedar (Thula plicata), sitka spruce (Picea sitchensis), and bigleaf maple (Acer macrophyllum) are less abundant components of riparian stands. TJnderstory communities along streams typically include shrub species, including salmonberry (Rubus spectabilis), stink currant (Ribes bracteosum), willow (Salix spp.) and swordfern

(Polystichum munitum). Common herbaceous species include Oregon oxalis (Oxalis oregana), tall sedge (Carex obnupta), and stinging nettle (Urtica doica).

Historical records suggest that most of the central Coast Range (including most of the Drift Creek Basin) burned during extensive wildfires around 1850 and 1870 (Juday 1977). As a result, the majority of undisturbed stands are less than 150 years old, although isolated patches of older forest remain (Juday 1977).

Resources and Management

The basin has had a complex management history.

Approximately 60 percent of the basin is under government ownership. The majority of this is administrated by the U.S. Forest Service, with small portions owned by the State of Oregon and the Bureau of Land Management. 23 Unmanaged areas in the basin include the Drift Creek

Wilderness which occurs along 10 km (six miles) of the lower mainstem, and the Flynn Creek Research Natural Area

(2.2 kin2). Most government ownership has undergone dispersed clearcut logging. About 35 percent of the watershed is industrially owned forest land, which has been progressively harvested since 1960, and is now vegetated with young conifers, alder, and shrub species. A minor portion of the basin consists of rural farinsteads which are located along valley bottoms below

"Mile 9" (15 kin) and near the Meadow Creek confluence.

Cattle grazing occurring on streamside terraces is the predominant land use on these ownerships. There is some evidence that more people lived in the basin in the past, although their extent and location remain unrecorded.

Stream and riparian activities on government land have included stream cleaning, log jam removal, and recently, placement of logs in Drift Creek for fish habitat. Streams in industrial lands logged during the l96Os and 70's underwent stream cleaning which included salvaging merchantable logs from streams (Ray Ayers, Georgia Pacific Corp., Toledo, Oregon, personal communication). It does not appear that "splash_dammingit has occurred in the basin.

Drift Creek and its tributaries supporta productive fishery, that includes coho and chinook salmon 24 (Oncorhyncus kisutsch and Q. tshawytscha), steelhead

(Oncorhyncus gairdneri) and cutthroat trout (Q. clarkii). Angling for these species attracts many sport fishermen to the Basin

Concern for forestry impacts on fisheries led to the Alsea Watershed Study, carried out between 1958 and 1973 on three small tributaries. That project monitored the responses of fish abundance and water quality to forest harvest and road building operations in 1965, 1966 and

1967. The watersheds involved were Needle Branch, which was entirely clearcut, Deer Creek, which was patch clearcut with buffer strips along channels, and Flynn Creek which served as an undisturbed control watershed (Moring and Lantz 1975).

SITE SELECTION

Tributary Reaches

To evaluate effects of forest management on CWD loadings and characteristics, nine low-order streamswere surveyed. They included the study streams from the Alsea

Watershed Study (AWS). The six additional streams were chosen to provide two more sets of reaches with similar treatment histories.

Because the AWS tributaries are located in the middle part of the Drift Creek basin geographically, the two "replicate" sets were chosen from small tributaries 25 in the upper and lower portions of the basin. Additional tributaries provided a larger range of geoniorphic and vegetational settings, besides improving the spatial representation within the Basin.

The priorities for tributary selection were:

Tributaries within a "sub-basin" should be located close to one another, and include one clearcut basin, one patch clearcut with buffer strip, and one undisturbed.

For the tributaries within a "treatnient", the

riparian practices eniployed and the dateson which they occurred should be as siniilar as possible to

the AWS stream(each set of three will be termed a "treatment", even though the upper and lower basin sites were not formally "treated").

Stream orders and drainage areas should

approximate those of the AWS streams.

Tipper sub-basin tributaries chosen included upper

Drift Creek (clearcut; CC), North Fork Drift Creek (patch clearcut with buffer strip; BS), and South Fork Drift

Creek (undisturbed; liD). Lower sub-basin tributaries included Bear Creek (CC), Trout Creek (BS), and East Fork

Trout Creek (liD). Locations of tributary reach are shown in Figure 3. Although the entire lengths of Alsea Watershed Study streams were surveyed, one study reach was surveyed on each of the additional six tributaries. Approximate sca'e MidBasin 0I - -kilo meters 2 4 DeerCr. FlynnNeedleUpper Cr. Bronch BasinLowerBear Trout Cr. TroutEost Cr. Fork Upper South NorthDrift Fork Cr. Cr. DriftFork Cr. Upper Basin DriftCr.Upper Figure 3. Alsea R. Location of tributary reaches, Drift Creek Basin 27 Basin Survey Reaches

The basin survey reaches were chosen to provide a continuous survey of first- through fifth-order channels.

The AWS streams were the smallest channels sampled. The basin survey also included reaches that connected AWS streams to Drift Creek (i.e. Horse Creek, Meadow Creek and lower Flynn Creek) (Figure 4). The lowest two kilometers of the South Fork of Drift Creek was surveyed, and the mainstem of Drift Creek was surveyed from the South Fork confluence to near "Mile 5" (8 km above the Alsea River confluence) on the USGS "Tidewater" quadrangle. This location appeared to be the upper limit of daily tidal influence and submerged CWD became difficult to see downstream from here because waterwas brackish.

The Drift Creek CWD survey data was divided into 12 reaches based on the following criteria:

Reaches should be fairly similar in length.

This was typically about 100 to 200 times bankfull

width.

Reach endpoints should occur at:

Major tributary junctions, which are easily located and indicate abrupt increases in

drainage area.

Major changes in valley form.

Boundaries of distinct human impacts, such 0 Approximate scale 2 4 Horse Cr. Flynn Cr. kilom eters N SH So. Fk. LowerHI Figure 4. Alsea R. Location of survey reaches, Drift Creek Basin 29 as CWD anchored into the channel or abrupt management boundaries.

Reach endpoint locations are described in Table Al.

DATA COLLECTION Channel Habitat Survey

A quantitative assessment of channel dimensions and habitat features was completed for all survey reaches and tributary sites (except for Drift Creek reaches TD and

LO). This provided a common longitudinal basis for comparing channel habitat, fish inventories, and CWD. Methods and results of the fish survey will be reported in Schwartz (in progress). This report will describe the channel habitat survey briefly and the CWD survey in greater detail.

Channel habitat was surveyed using the "calibrated visual estimation technique" (Hankin and Reeves 1988). With this method, channel dimensions and habitat features were addressed for each "channel unittt (i.e. pool, glide, riffle, cascade, and side channel). The field crew estimated channel dimensions (i.e. unit length, wetted width and depth), and recorded physical features

(gradient, substrate types, terrace heights, valley width) and riparian vegetation characteristics, for each channel unit. Because estimates were obtained during the summer months, they represent low flow conditions. A 30 sample of channel units were measured to developa "calibration factort to correct for estimator bias. Bankfull widths were also estimated by considering indicators of past high flows, such as margins of perennial vegetation, scour, or floated debris. Bankfull width was the only channel characteristic collected for

Drift Creek reaches TD and LO.

Coarse Woody Debris Inventory

The coarse woody debris inventory collected

information on each piece of dead woody material

occurring in or above the bankfull channel. Pieces greater than 0.15 in in diameter and 2 in in lengthwere inventoried (Figure 5). For each CWD piece, the length and diameters at large and small endswere estimated. For pieces with an attached rootwad, the large diameter

was measured at DBH (diameter at breast height, 1.4 in

above ground line), and any root volumewas not included.

For irregularly shaped pieces, a representativecross section was chosen for the diameter estimate. A

calibration test was used for both of the CWDsurveyors (Table A3).

Each CWD piece was identified by species whenever

possible, or as hardwood (i.e. deciduous)or conifer. This identification was determined from bark

characteristics, wood color, bole form, and branch 31

"Length" - must be at least 2 m

/ "Large diameter "SmaM diameter" - end of piece - end of piece or "DBH" or where less - must be at than 0.10 m least 0.15 m

Figure 5. Coarse woody debris piece measurements 32 configuration. Decay classes were based on a five class system (Robison 1988) (Table 1).

A piece's location within the channel was described by estimating the percentage of that piece's volume in four "influence zones" (Figure 6). "Zone 1" lies within the summer low flow channel and affects flow and habitat during low and high flows. "Zone 2" is the additional

CWD volume submerged during bankfull flow. Both Zone 1 and 2 volumes affect flow patterns during higher flows. "Zone 3" is debris volume directly above the bankfull channel and "Zone 4" is the portion of a CWD piece that extends beyond Zones 1, 2, or 3. Coarse woody debris volumes in Zones 3 and 4 do not affect flows, though Zone 3 is likely to eventually enter the channel due to breakage and/or decay. Zone 4 volume may anchor the CWD piece to the bank. Only debris pieces that had at least part of their volume in Zones 1, 2, or 3 were surveyed.

Coarse woody debris pieces which were partly buried or with an attached rootwad were noted. Pieces in contact with other pieces were noted as grouped in an

"aggregation" (two to four pieces), or a "jam" (five or more). When large concentrations of CWD pieces were encountered, only a representative sample of them were characterized individually. The total number of pieces in the grouping was then counted, and the non- characterized pieces were assumed to have characteristics 33

Table 1. A 5-class system of log decay based on fallen Douglas-fir trees (from Robison 1988)

Characteristic of fallen tree Decay class

1 2 3 4 5

Bark Intact Intact Trace Absent Absent

Twigs (3 c& Present Absent Absent Absent Absent

Texture Intact Intact Some abrasion Abraded surface Vesicular with on wood, sur4ace with some holesnumerous holes still smooth and openings and openings

Shape Round Round Round Round to oval Irregular

Color of wood Original Original Original color Darker Darker color color or darkening 34

Zone 4 Zone 3 Zone 4

Terrace height BankfuH Zone 2 flow Low flow Zone

Figure 6. Coarse woody debris influence zones 35 similar to the sample.

Each CWD piece was recorded by channel unit. Thus, a piece's location within the reach could be determined by referring to channel unit locations within the channel habitat survey information.

DATA ANALYSIS

Computer spreadsheet software (LOTUS 1-2-3 and QUATTRO) was used for storage and editing of field data. Statistical analysis (data description, distribution analyses, and graphics development) utilized STATGRAPHICS and QUATTRO. Data for each stream or reach was stored in a separate spreadsheet file. A sequential channel unit numbering system was developed to allow interineshing of CWD and habitat survey information.

A sample of CWD pieces estimated by each observer were measured in the field to determine precision and accuracy. Regression analysis was used to develop

"correction equationst which were used to obtain

"corrected" values for all CWD piece dimension estimates.

Coefficients and statistics associated with these equations are included in Table A2. Piece volumes were calculated using corrected lengths and diameters using the standard formula for a "truncated coneti in Swanson et

al.(1984).

Data analysis typically consisted of comparisons 36 between streams or reaches. Distribution patterns for all CWD piece dimensions were strongly skewed, and resembled either a lognormal or negative exponential distribution. Attempts to "normalize" the dimension distributions using various arithmetic transformations

(natural log, square-root, and arcsin) were not successful.

Because distributions were skewed, medians were used to describe piece dimensions within a reach. The84th percentile piece lengths (analogous to an observation that is greater than the mean by one standard deviation for a normal distribution) were calculated to characterize the longer pieces within a reach.

Statistical comparisons utilized a non-parametric test to identify significant differences between treatments or sub-basins. The Mann-Whitney test requires that compared distributions are similar in shape and spread.

Statistical test results with p-values less than 0.10 and 0.01, were interpreted as "significant" and

"highly significant", respectively. Regression analyses were used to correlate CWD with stream size or other attributes. However results should be viewed with caution because CWD loads in adjacent stream reachesmay not be strictly independent due to fluvial transport of

CWD. 37 Analysis was also undertaken to view changes in CWD loading at a finer level of spatial resolution than inherent in reach comparisons. A computer program was developed to determine CWD loadings at the "channel unit" scale. The longitudinal profiles of CWD loading were used to compare spatial distribution patterns (i.e. "dumpiness") and to determine if any channel units had consistent CWD loading tendencies. 38 RESULTS AND DISCUSSION

TRIBUTARY REACHES Geomorphic and Vegetative Settings Although the tributary streams are similar in size, each reach has a unique combination of channel and basin characteristics (Table 2).Among Drift Creek tributaries, channel gradient often indexes various aspects of landforin of the watershed and generally reflects the overall steepness of the terrain.It also determines stream energy available to move CWD and erode banks, thus influencing substrate and channel features. Although channel gradient typically varies within each reach, larger streams. usually have lower overall gradients.Gradients are steepest among lower basin tributaries, more moderate for upper basin 'reaches, and relatively gentle for maid-basin tributaries (Table 2). Channel substrate for the upper and lower basin groups are predominantly cobbles and boulders, while maid- basin streams are mainly gravel-bedded (Table 2).Mid- basin tributary watersheds have moderate side slopes and extensive valley-bottom terraces, while the upper and lower basin tributaries have steeper side slopes and minimal valley-bottom terraces.The geomorphic variability within and between sub-basins made it difficult to identify differences in CWD or channel 39

Table 2. Physical characteristics of tributary reaches, Drift Creek Basin

Manaqe- Reach Gtrea Drainaqe Bankfull Channel Dominant Sub-ba5in Tributary menU lenqth order area* width qradient&sedimentQ () (kmA2) () (fl

E.Fk. Trout Cr. UD 670 2 3.0 4.4 5.6 7, 8, 4 Lower Trout Cr. BS 750 3 6.4 5.5 3.9 8,7

Bear Cr, CC 500 1 0.5 3.1 8.9 7, 3,5

2.5 2.3 6,5 I Upper Flynn Cr. UD 1130 2 2.2

Mid Deer Cr. BS 2350 2 3.1 7.1 2,2 5, 6,8

Needle Branch CC 1140 1 0.9 3.4 1.3 6,5

So.Fk. Drift Cr. UD 1110 3 3.7 5.0 3,0 7, 6 Upper No.Fk.Drift Cr. BS 1030 2 2.0 5.5 4.4 8, 6 7 Upper Drift Cr. CC 880 2 3.5 4.5 3.5 8,6! 7

- UD is undisturbed3 '8S is patch clearcut with buffer 5trip, andCC is entirely clearcut. * - Drainage areas were determined for lower end of each reach. & - Gradients determined using a hand clinometer. - Doiinant sediient sizes, 3 - silt, 4 - 5and, - sa1l qravel (3-10 mm), 6 - large qravel (10-100 im), 7 - cobble (100-300 me), 8 - boulder (>300t&. 40 responses to treatment.

Within the lower and mid-sub basins, drainageareas range from 0.5 to 6.4 km2, while the upper basin tributaries only vary from 2.0 to 3.7 km2 (Table 2). For this reason, differences in CWD loadings and characteristics among upper basin tributaries may more clearly reflect treatment effects, and be less affected by the confounding effects of stream size.

Current riparian vegetation appeared to be strongly influenced by past management. An overstory of conifer and hardwood trees predominate along undisturbed and buffer strip reaches, while forb/brush and hardwood vegetation classes were most abundant along clearcut reaches (Table A3). Alder was observed to be more abundant on mid-basin watersheds, while the conifer densities were greatest (i.e. for unharvested stands) along the upper basin tributaries.

Buffer strip reaches generally have greater proportions of hardwood in the overstory than undisturbed reaches, though this is more likely due to growing site differences than treatment effects. Buffer strips are generally 30 m or wider and the vegetation within the buffer resembled pre-logging conditions for the most part. Watersheds of clearcut reaches were logged around 15 to 20 years ago, and treatment probably involved cleaning and/or salvage of substantial CWD (Table 3). Table 3. ManagementDrift Creek history Basin of tributary watersheds, Sub-basin Tributary Manage- ment* Year(s) of harvestnearest (iost likely) activityChannel Present riparian vegetation Approx. percentof watershedharvested Information source lower I BearTroutE.F. TroutCr. Cr. Cr. CCBSUD 196,'72,'89 19691973 cleanednone none CCBSLiD w. onew. 200 side, foot LiD opening other few lEave trees 100X CC3010 CC Ranger District Wal dport (USFS) Mid NeedleDeerUpper Cr FlynnBranch Cr. CC85LiD 196 and later 1966none cleaned (most) none part wide BS,complete part UDCC w. burn undisturbed 100X CC50X CC o, H. Froehlich (OSU)Moring and lantz 1975, & Upper UpperNo.Fk.So.Fk. Drift Drift Cr. Cr. CCBSliD early 1980'smidmid 1970's 1970's cleaned/salvaged none CC w. fewmostly leave treesliD, part BS undisturbed 1O CC,100 20 BOX CC CC CT& & aerial photographyGeorgia Pac. Corp. (USFS) & -* UCTI - MUD" is undisturbed,- Some evidence of riparian cedar salvage. is comffiercial thin of overstory. BS is patch clearcut with buffer strip, and "CC' is entirely clearcut. 42 Coarse Woody Debris

Spatial Distribution

Coarse woody debris loading in a stream can be scaled several ways. Three loading expressions were chosen to illustrate different aspects of CWD loadings and to facilitate comparison with CWD studies elsewhere.

Coarse woody debris "piece frequency" is simply the number of pieces per unit of stream length. "Total volume loading" is defined here as the total CWD volume per unit of stream length. This expression includes CWD volume that extends above and beyond the bankfull channel

(Zones 3 and 4). "Channel loading" is the debris volume in Zones 1 and 2 per unit of bankfull channelarea. Because this loading is scaled by channel surface area rather than length, "channel loading" incorporates differences in channel widths, and ismore relevant for comparisons that involve different sized channels. Coarse woody debris loadings varied substantially between tributaries. The highest and lowest CWD frequency values differed by five-fold, while total volume loading and channel loading both varied by about

15-fold (Table 4, Figure 7). Coarse woody debris loadings were highest among upper basin tributaries, somewhat smaller for the lower basin, and smalleston mid-basin tributaries (Tables 4). In many cases, differences in CWD loading between sub-basinswere 43

Table 4. Spatial distribution of CWD in tributary reaches, Drift Creek Basin

Total Channel Manage- Piece volume (Zone 1+2) Total volume Sub-basin Tributary ment* frequency loading loading Zone 1Zone 2 Zone 3 Zone 4 (pcs/100m) (w3/100m) Ca3/100mA2) (7) (%) (/)

E,Fk. Trout Cr. UD 20 33 1.1 3 12 43 42 Lower Trout Cr. BS 36 56 2.3 5 17 39 39 Bear Cr. CC 15 23 1.0 4 9 47 40

Upper Flynn Cr. UD 22 27 2.6 6 18 27 50 Mid Deer Cr. BS 11 7 0.3 8 22 30 40 41 Needle Branch CC 1 12 0.9 5 20 34

So.Fk. Drift Cr, UD 30 107 4.3 4 16 46 34 Upper No.Fk. Drift Cr, BS 62 105 2,7 3 11 4 32 Upper Drift Cr. CC 47 39 3.4 13 26 46 15

Average 29 45 2.1 6 17 41 37

* - UD is undisturbed BS° is patch clearcut with buffer strip, and flCCN is entirely clearcut. ccBSUD Lower Subbasin Mid Upper Figure 7. patchreaches,Channelclearcut) clearcut loadingDrift withCreek of CWDbuffer Basin per strip,(UDbankfull = undisturbed,CC area= entirely in tributary BS = 45 statistically significant (Mann-whitney sub-basin results are in Table 5).

In most cases, clearcut reaches had lower CwD loadings than undisturbed reaches. within each sub- basin, CWD volume loadings (total and channel)were greater for the undisturbed reach than the clearcut in all cases (Table 4), and CWD frequency for undisturbed was greater than clearcut for two of three sub-basins. Only in the upper sub-basin, was CwD frequency greater in the clearcut reach than the undisturbed. However, treatment differences of CWD loading and frequencywere not statistically significant.

Influence zone percentages among tributarieswere more consistent than were loading levels. On average, six percent of total CWD occurred in the wetted channel (Zone 1) and 17 percent was located in the bankfull channel above low flow (Zone 2) (Table 4). The only two streams in which greater than 25 percent of CWD volume occurred in Zones 1 and 2 (i.e. Deer Creek and Upper Drift Creek), contained the most extensive beaver ponds.

Reaches with beaver ponds would be expected to have considerably more water volume at low flow (Zone 1), hence greater stream volume to contain CWD.

In most tributaries, over three-fourths of total CWD volume was located outside of the bankfull channel in

Zones 3 and 4. Differences in influence zone percentages 46

Table 5. Mann-Whitney results of CWD comparisons between sub-basin tributaries *

CWD load Sub-basin characteristic Upper basin Lower basin Mid-basin

Piece a b b frequency

Total CWD c d loading

Channel CWD f q q loading

Median piece h h volume

Percent j k k hardwood

* - Common letter indicates no significant difference (alpha 0.10). 47 were not related to treatments, though they were associated with geomorphic differences between sub-basins

(see "Effects of Valley Form on CWD" section).

Piece Characteristics

Median piece volumes and median diameters for all tributary reaches averaged 0.50 m3 and 0.40 m, respectively (Table 6). Piece volumes were the most variable CWD dimension within reaches, and therewere no statistical differences between treatments for piece volumes or diameters. However, median piece volumes from mid-basin reaches were significantly smaller than either the upper or lower sub-basin reaches (Table 6).

The association between CWD piece length and treatment is strong. Piece lengths (median and 84th percentile) were significantly (p < 0.10) shorter for clearcut reaches than the buffer strip or undisturbed reaches (Table 7). Probability density curves for CWD piece lengths (Figure 8) show that debris greater than 10 m constitutes a substantial proportion of pieces in buffer strip and undisturbed reaches compared to those clearcut.

Research in other locations has attributed decreased CWD piece lengths following harvest to breakage during harvest (Toews and Moore 1982), and stream cleaning and/or salvage activities (Sedell et al. 1988). In the 48

Table 6. Piece characteristics of CWD in tributary reaches, Drift Creek Basin

Number CWD piece sizes Average Manage- of Volume Diameterfl Length ---- decay -- Species -- Sub-basin Tributary ent pieces median ethan median 84 pctl.& class hard. con.

(mA3 (a) (m) Cm) (7) (7)

E.Fk. Trout Cr. lID 131 0.50 0.40 5.6 11.7 3.7 38 62 Lower Trout Cr. BS 271 0.45 0.40 5.3 11.1 3.5 36 64 Bear Cr. CC 76 0.62 0.48 3.8 9.4 4.3 20 80

Upper Flynn Cr. UD 254 0.49 0.40 4.7 13.2 3.7 50 50 Mid Deer Cr. 85 250 0.28 0.31 5.0 13.2 3.3 74 Th

Needle Branch CC 173 0.32 0.37 3.2 6.5 4.2 6 94

So.Fk. Drift Cr. liD 339 0.72 0.43 5.9 15.0 3.7 22 78

Upper No.Fk. Drift Cr. 85 638 0.65 0.43 5.2 12.0 3.9 21 79 Upper Drift Cr, CC 413 0.43 0.43 4.1 8.3 4.1 15 85

- UDM is undisturbed, BS is patch cut with buffer strip, andCC is entirely clearcut

I - Means and standard deviations aren Table 4. H- Diameter at the larger end. - Length greater than 84 percent of pieces in reach. - Decay class criteria detailed n Table 1. 49

Table 7. Mann-Whitney results of CWD comparisons between treatments *

CWD load Treatment characteristic UndisturbedBuffer Strip Clearcut

Median piece a a b length

84th pctl. c c d piece Iength*

average decay e e + class

Percent 9 g h hardwood

Hardwood loading

* - Common letter indicates no significant difference (alpha 0.10). * - Length greater than 84 percent of pieces in reach, 50

0.25

0.2

0 15

0.1

0.05

0

0 25

e.a

0 15

0.1

0.05

0

0 25

o.a

0 15

0.1

0 05

0

0 5Piece length (m)10 15

Figure 8. Probability densities of CWD piece lengths in tributary reaches of (a) lower basin, (b) mid- basin, and (c) upper basin tributary reaches 51 Drift Creek Basin, post-harvest stream cleaning would have consisted of bucking many instream logs for removal.

Instream salvage would have removed the largest, soundest conifer CWD. Each of these activities have probably impacted one or more of the clearcut tributaries studied

(Table 3).

A sizeable proportion of CWD pieces in several tributaries occurred in groups (Table A4). Differences between percentages of CWD pieces buried, grouped,or with a rootwad for survey reaches were not associated with sub-basin or treatment effects.

Because CWD decay and species composition are determined subjectively, these attributesmay be less consistent and precise than measured attributes. As a result, pieces classed as "partly" and "mostly" buried were combined, and the range of hardwood and conifer species identified were combined into "hardwood" and

"conifer" categories for analysis (percentages of pieces classified by individual speciesappears in Table A7). Levels of CWD piece decay and debris species composition were significantly related to treatment (Table 7).

Clearcut reaches contained more decayed pieceson average

(Figure 9), and had lower hardwood debris volume thanthe other treatments (Figure 10). Average decay and species composition were not statistically different (p> 0.10) between buffer strip and undisturbed reaches. 5.0 4.5 /1//I//Il//A BSUD 4.0 PAiAWAAtAYA!JAYAYaYJ cc 3.5 3.0 Treatment Figure 9. strip,undisturbed,tributaryMean decay CC reaches,= ofentirely BS CWD = patchvs.Drift clearcut) harvest clearcutCreek treatmentBasin with (liD buffer of= 4050 / Hardwood Conifer 30 <'ITIlht 11111 2010 Il UD :7 Treatment BS CC Figure 10. CWDTotalentirelyBSreaches, vs.= volumepatch harvest clearcut)Drift clearcutloading treatmentCreek of withBasin hardwood ofbuffer (UDtributary = and strip,undisturbed, conifer CC = 54 Forest Management and CWD in Tributaries In this study, questions regarding management effects on CWD loadings and characteristics were addressed by comparing smaller streams within the Drift Creek Basin. This emphasis on small tributary streams was due to several concerns, including the following:

Because small streams are more numerous than large ones within a basin, similarly-sized

tributaries with differing characteristics (i.e.

valley form or treatment history) can be selected from a single basin.

Because CWD in small channels is less subject to fluvial import and export of CWD (Keller and Swanson 1979), debris loads are more likely to reflect influences from the immediately adjacent hillslope

than would a larger stream.

Despite these advantages, it remains difficult to precisely identify "cause and effect" relationships because tributaries vary from each other in many respects.

Loadings of coarse woody debris varied greatly between the nine tributaries and were not significantly influenced by past harvest practices. Loading similarities observed within sub-basins (Table 5) suggest that other factors, possibly valley form and/or the influence of pre-harvest vegetation, have had a greater 55 impact on CWD loadings.Yet, differences in debris lengths, decay and species composition suggest that harvest treatment is associated with systematic changes in CWD loads.The inferences that have been drawn from these differences are based on an assumption thatall tributary reaches had roughly similar CWD loads priorto harvest, and that CWD surveyed in undisturbed sites resemble these loads. Interpretation of decay differences was confused by the fact that hardwood and conifer CWD have different decay distributions.Figure 11 indicates thataverage decay is significantly (p < 0.10, r2= 0.59) related to the percent of hardwood CWD.Therefore, hardwood and conifer CWD pieces were separated tocompare decay between treatments.Decay class distributions of CWD pieces in clearcut reacheswere compared against undisturbed and buffer strip (TJD/BS) reaches whichwere combined because decay and hardwood percentageswere not significantly different. Debris loads in clearcut reacheswere predominantly in greater levels of decay for both hardwoodand conifer classes, while CWD in TJD/BS reacheswere more evenly distributed between decay levels (Figure 12).Classes 1, 2, and 3 consistently represented higher percentagesof CWD in TJD/BS reaches than in clearcut reaches.It is particularly notable that the clearcut reachescontained 4.24.4 UD 3.84.0 cc 3.43.6 3.2 0 10 20 30 40 50 60 70 80 Figure 11. Averagetributary decay streams, vs. percent Drift hardwoodCreek Basin CWD Percent hardwood pieces in 57

60 (a) UD/BS 50

40 cc

30

20

10 V.' 0 3 4 5 Decay doss

80 J...... 70 UD/BS 60 cc 50 I 40 30 I 20 10 0

1 2 3 4 Decay class

Figure 12.. Relative frequencydistribution for decay of (a) hardwood and (b) coniferCWD pieces 58 no conifer CWD in decay classes 1 and 2.These results suggested that recruitinent of new CWD has been virtually elilninated after harvest. The treatinent differences between CWD decay and species coinposition indicate that these streanis have undergone a series of processes since harvest that reflect teinporal CWD trends suggested by other studies (i.e. Grette 1985 and Heiinann 1988).Since harvest, hardwood CWD niay have been lost inore rapidly than conifer, because pieces decay faster andare inore subject to export, being snialler.The one or two decades since the harvest of the clearcut reaches is not adequatefor regenerating trees to provide significant CWD (Heiniann 1988).Without fresh input, CWD would consist of residual pieces in nioderate to advanced states of decay, as was observed.In contrast, undisturbed and buffer strip sites would have received continued input ofCWD froni riparian stands, as reflected by theniore even distribution of decay classes of CWD in the UD/BS treatnients. Although CWD froni buffer strip reaches did not differ significantly froni undisturbed reaches,several buffer strip reaches appeared to have received additional input froni landslides associated with roads and/or blowdown following harvest.Although these processes contribute to current CWD loading, standing trees 59 available for future recruitment have been reduced.

BASIN SURVEY Geoniorphic and Veqetative Setting Physical and biological aspects of the stream environnient were observed to change with streani size. Although channel gradient typically decreases for reaches with increasing drainage area, several reaches in the basin deviate from this pattern (Figure 2).The unusually gentle reaches (Horse Creek, Lower Flynn Creek) may result froni a pre-settlenient landslide(s)(R. Beschta, OSU Dept. of Forest Engineering, Corvallis, Oregon, personal communication) immediately upstreani of the relatively steep section along lower Meadow Creek in Figure 2b.Fine sedinient is abundant in these low- gradient reaches, though coarse substrates (i.e. boulders and bedrock) dominate most larger channels (Table 8). Headwater streams contain more diverse combinations of substrate sizes (Table 2). Hardwoods were observed as the niost common riparian vegetation along niost larger (third-order and larger) channels (Table A5).Riparian terraces which are common along large streams contain alder almost exclusively, a pattern observed on a similar basin by Long (1988).Forb and shrub vegetation were most abundant where channel terraces have been affected by grazing or beaver 60

Table 8. Physical characteristics of survey reaches, Drift Creek Basin

Reach Stream DrainageBankfull Channel Dominant Percent Stream lenqth order area width radient& substrate# bedrock

Cm) tkm2) Cm) CX)

Lower Flynn Cr, 2930 3 6,4 4.0 0.68 4 3 5 0

Lower So.Fk. Drift 1670 3 8.1 10.3 3.0 7, 6

Horse Cr. 2890 3 10 .3 0.42 4 0

Meadow Cr. 2720 4 19 13 0.84 3 8, 4 3

Drift Creek Reach

SV 3220 4 24 13 1.91 7, 9

FL 1240 4 28 15 1.10 9,8 47

HI 1500 4 36 15 0.65 9,8 30

2270 4 38 15 0.67 8, 9 34

SH 2120 4 56 18 0.62 8, 9, 7 33

SG 4140 5 86 20 0.44 84 91 7 24

3710 5 102 24 0.49 8, 9 31 BL 3930 108 27 0.70 8, 9 29 CS 2720 5 121 32 0.62 8, 9 22 EL 5150 5 136 30 0.50 9, 8 62 LU 4650 5 160 24 0.33& ID 2130 5 170 24 0.21&

* - Drainaqe area determined at downstream end of reach

& - Gradients determined from USGS map, all others mea;ured with clinometeror hand level. - Sediment izes 3 - silts 4 - sands 5 - small gravel <30 mm), 6 - larQe qravel (30-100 sm), 7 - cobble (100-300), 8 - boulder (>300 9 - bedrock. - Reach locations shown in Figure 4 and end points described in Table Al. 61 activities. Lower Flynn Creek and reach SH on Drift

Creek contained examples of terraces grazed currentlyor in the past. Mature conifers were often found where sideslopes ended at the stream bank and/or within unlogged riparian zones.

Coarse Woody Debris

Spatial Distribution

Coarse woody debris loading trends were fairly consistent throughout larger channels in the basin, except for two reaches (i.e. Lower South Fork of Drift Creek and Drift reach HI) that contained unusually high loadings. Excluding these two reaches, debris frequencies ranged from 4 to 13 piecesper 100 m of channel length, and were not associated with channel size

(Table 9). The pattern for total volume loading was similar, with most reaches containing around 10 m3per 100 m.

Channel volume loadings decreased fairly consistently from about 0.70 m3/100m2 for third-order streams, to 0.20 m3/100m2 for large fifth-order reaches

(Figure 13). The correlation between channel loading and drainage area (excluding the two anomalous reaches)was highly significant (p < 0.01, r2= 0.68). Given that

Drift Creek and its larger tributaries flow througha broad range of vegetation types and valley fonns, these 62

Table 9. Spatial distribution of CWD in survey reaches, Drift Creek Basin

Total Channel Drainaqe Piece volume (Zone 1+2) Total volume Stream areal frequency loading loadinq Thne 1 'one 2 Zone 3 Zone 4 (hA2) (pcs/100) (3/100m) (mA3/1002) (7.)

Lower F]ynn Cr. 6 8 5 0.70 25 33 17 25

Lower So.Fk. Drift 8 44 54 1.33 2 23 54 21

Horse Cr. 10 10 8 0.62 41 30 27 2

Meadow Cr. 19 5 8 0.47 18 60 10 12

Drift Creek Reach

SV 24 13 18 0.37 6 21 41 31

FL 28 5 4 0.11 2 36 34 27

HI 36 23 44 1.46 9 42 18 31

GO 38 7 11 0.32 3 40 28 29

SH 56 6 7 0.22 8 48 13 31

S6 86 7 8 0.19 14 38 23 26 GL 102 10 11 0.19 6 37 26 32 BL 108 6 16 0.29 8 43 43 6

C6 121 5 14 0.26 9 51 12 29

EL 136 5 13 0.25 9 48 28 15

LO 160 4 2 0.05 18 24 36 22

TU 170 9 6 0.20 36 31 7 26

- Drainage areas determined at downstream end of survey reach. - Reach locations shown in Figure 4 and end points described in Table Al. 1.251.50 - Lower South Fork Drift Reach HI 0.751.00 0.250.50 + + + + + 0.00 0.75 1.00 1.25 I + 1.50 I 1.75 2.00 I + 2.25 Figure 13. drainageChannel loading area, Driftof CWD Creek per bankfullBasin area vs. Drainage area (log km2) 64 results suggest that drainage area (or associated variables such as discharge and stream power) is related to much of the variation of inchannel CWD loading.

The two outlier reaches in Figure 13 (i.e. the lower South Fork of Drift Creek and the HI reach) have received the majority of CWD volume from atypical sources. The lower South Fork of Drift Creek contains a series of CWD accumulations that may be debris torrent deposition(s).

Several hundred logs were placed in reach HI of Drift Creek to enhance fish habitat.

The location of CWD volume within the channel cross section, changes with stream order (Table 9). Figure 14 illustrates the percentages of volume in influencezones for all stream orders represented by tributary andsurvey reaches. Among low-order streams, Zones 1 and 2 contain the smallest percentages of CWD volume. The proportion of CWD volume occurring within the channel (Zones 1 and 2) increases with stream size and constitutes over half of total volume for the largest channels (Figure 14). Zone 3 and 4 percentages decrease correspondingly for larger streams.

Piece Characteristics

Each survey reach contained CWD pieces with a broad range of dimensions and attributes. Pieces recorded in Drift Creek reaches BL, CG and EL had greater piece 1 L 3 4 Figure 14. Coarsestream woody order, debris Drift volume Creek inBasin influence zones vs. Stream order 66 volumes and diameters than other reaches (Table 10), though differences may result from input from nearby conifer stands (these reaches flow through the Drift Creek Wilderness) or from the selective export of small pieces from these relatively high-gradient reaches.

There was no indication that median piece volumes or diameters were related to stream size.

Although median piece lengths were not related to stream size (Table 10), 84th percentile piece lengths increased with drainage area (Figure 15). The HI reach was anomalous due to artificial CWD loading and the lowest reach (TD) is tidally influenced. Excluding these two reaches the relationship illustrated in Figure 15 was highly significant (p < 0.01, r2 = 0.46).

The percentage of hardwood CWD pieces ranged from 24 to 74 percent (Table 10). On average, CWD in survey reaches were more decayed and contained greater percentages of grouped pieces than in the tributary reaches. For the Drift Creek reaches, jams (groups of five or more pieces) often represented one-third to one- half of all CWD pieces (Table A6). Reach differences in these piece attributes (percent hardwood, decay, percent grouped) were not significantly correlated with stream size. Although pieces with rootwads did not constitute more than 17 percent of the pieces in any survey reach (Table 10), rootwad percentages increased significantly 67

Table 10. Piece characteristics of CWD in survey reaches, Drift Creek Basin

Number CWD piece sizes* Avera9e Pieces of Voluae Diaffieter** Length decay -- Species -- with Stream pieces median median median 84 pctl.*class& hard. con. roatad

(mA3) Cm) (ffi} (%} (%) IX)

Lower Flynn Ck. 243 0.21 0,29 4.1 8.0 3.3 68 32 3

Lower Sa.Fk. Drift 727 0.46 0.40 4.7 9.5 3.5 37 63 7

Horse Creek 283 0.4 0.41 5.2 8.3 4.0 73 27 5

Meadow Creek 148 0.80 0.50 5.7 9.3 4.2 76 24 11

Drift Creek Reach

SY 405 0.48 0.37 5.0 10.4 3. 26 74 9

FL 65 0.40 0.34 5.6 11.1 2.9 45 55 8

HI 348 0.50 0.34 6.8 17.1 2.1 55 4 9

GO 166 0.72 0.37 7.0 13.5 3.1 51 49 12

SH 118 0.49 0.40 4.7 12.6 3.4 43 57 16

SG 276 0.32 0.31 5.6 12.9 2.9 51 49 10

GL 356 0.41 0.37 5.0 11.0 3.0 49 51 15

BL 245 1.35 0,58 7.3 13.3 4.1 68 32 6 C6 125 1.70 0,58 7.3 15.8 4,1 48 52 17 EL 235 1.41 0.58 5.8 12.3 4.0 37 63 12

LO 168 0.26 0.34 3.9 9.5 3.3 4 46 13 ID 196 0.29 0.34 3.8 7.1 3.7 52 48

* - Means and standard deviations are in Table A4. U- Diameter at the larger end. * - Length greater than 84 percent of pieces in reach. & - Decay class criteria detailed in Table 1. - Reach locations shown in Figure 4 and end points described in Table Al. 1618 Reach HI + 1214 + + + + + + + 10 B + + + + + 0.756 1.00 1.25 1.50 1.75 2.00 TD 2.25 Figure 15. drainageEighty-fourth area, percentile Drift Creek CWD Basin piece lengths vs. Drainage area (log km2) 69 (p < 0.01, r2 = 0.48) with stream size (Figure 16).

Because rootwads often enhance anchoring (Sedell et al. 1988), this increase may result from the selective export of pieces without rootwads. Stabilizing characteristics (such as a rootwad or piece length) are important factors for piece retention in larger streams which are increasingly able to entrain unstable debris pieces.

Fluvial Influences on CWD Distribution

Coarse woody debris in the bankfull channel (Zones 1 and 2)is subject to hydraulic forces that may lead to movement in place (i.e. rotation), downstream transport, abrasion and/or breakage. The magnitude of these forces (often indexed by "stream power") increases with flow and channel gradient. Less CWD would be expected at channel locations where these hydraulic forces are great.

Among all tributary and survey reaches in the basin, the percent of CWD volume in the active channel (Zones

1+2) was inversely related to the logarithm of channel gradient (Figure 17). The relationship was highly significant (p < 0.01, r2 = 0.62) and indicates that the percent of total CWD volume that occurs within the active channel of a stream decreases with increasing channel gradient, regardless of total loading. This correlation may also reflect the association between stream gradient and valley geometry, rather than simply channel gradient. 1518 + + + 12 9 + + + + + I 36 -I- -I- Reach +TD 0750 1.00 1.25 150 I 2.00 I 2.25 Figure 16. area,Percent Drift of CWDCreek pieces Basin with rootwads vs. drainage Drainage area (log km2) 0 100 Ea) 6080 2040 0.2 i 0.5Channe) gradientI (log percent) I i 1.0 2.0 5.0 10.0 Figure 17. channelPercent ofgradient, total CWD Drift volume Creek in BasinZones 1 and 2 vs. H 72 A regression of the percent of total volume in Zones 1 and 2 against drainage area was not significant.

Hydraulic forces also influence longitudinal patterns of CWD distribution via fluvial transport. In the Drift Creek Basin, the percentages of grouped CWD pieces are greater for larger channels. Although the factors involved in piece grouping vary, two conditions are generally required: (1) a "roughness element" (such as a boulder or large log) to provide stability to the debris accumulation and (2) sufficient CWD pieces from upstream to become stabilized in the jam. In small streams, CWD pieces are commonly longer than channel width, thus allowing them to span the channel and provide a stable obstruction (Bilby 1985). Yet the stream must contain a sufficient number of CWD pieces of floatable size (shorter than bankfull width) for groupings to occur. The East Fork of Trout Creek,

Bear Creek and Upper Flynn illustrate this situation,as the median piece lengths are shorter than bankfull width and few pieces are grouped (Tables 2, A6). Streams that contain many CWD pieces shorter than bankfull width, but with some long enough to span the channel (i.e. 84th percentile piece length greater than bankfull width),are likely to have many grouped pieces (e.g. Trout Creek,

Needle Branch, and Upper Drift). A stream with very few pieces long enough to span the channel is likely to have 73 few grouped pieces (e.g. Meadow Creek) unless other roughness elements are present to stabilize CWD and block downstream export.

When CWD loads consist of shorter pieces following harvest and/or stream cleaning, the rate of grouping or export should become greater than where piece lengths are unaltered. The generalization by Sedell et al.(1988) that stream CWD is more "clumpy" in harvested than unlogged basins may reflect this response. Although debris pieces among Drift Creek tributaries were shortest

in clearcut reaches, longitudinal profiles of CWD loading that would illustrate aggregation patterns on each of the tributaries, did not differ noticeably between

treatments.

Coarse woody debris groupings are not entirely controlled by channel processes, because groups of CWD

are deposited by lateral input events such as landslides

and debris torrents, windthrow and bank erosion. The high percentages of grouped pieces on North Fork Drift

and the Lower South Fork Drift Creek reaches (Table A4) appear to result from such episodic input processes.

For relatively large channels, CWD pieces rarely span the channel because they are not long enough and

flows are powerful. Still, length appears to contribute

to a piece's tendency to be trapped by a boulder, alonga meander bend or in a side channel. A separate analysis 74 was made of "large" CWD pieces (i.e., greater than 0.5 m in diameter and 10 m in length) in survey reaches (Table 11) because of the important physical effects that they provide (Sedell et al. 1988). Most debris jams (85 percent) in Drift Creek contained one or more "large" CWD piece, and reaches with frequently occurring "large" CWD pieces typically contained more jams (Figure 18). Most jams that contained significant Zone 1 volume were observed to consist of very long pieces. Many CWD jams were anchored by large boulders or occurred at changes in gradient, such as falls, cascades or rapids. It appears that many of these accumulations of large pieces are seldom moved.

Sixty percent of the CWD pieces in Drift Creek reach HI occur in jams, a higher percentage than any other

Drift Creek reach. This reach retains CWD in part because it contains a large number of pieces longer than stream width that function in a manner similar to pieces

in smaller channels. Numerous CWD pieces in this reach are longer than the bankfull width (the 84th percentile length is greater than bankfull width) and capable of trapping smaller CWD pieces. The many shorter pieces that are trapped in these jams might have been carried downstream if they had not been stabilized by the longer pieces. Most of the large pieces that were added to this reach have been manually anchored to streamside trees or 75

Table 11. Loadings and piece characteristics of "large"CWD in Drift Creek survey reaches

Percent Percent CWD Piece Sizes Drift Creek o4 pcs. o4 vol. Piece Volume Diaeter& Length Reach in reach in reach frequency mean mean mean

CX) (X) (no/lOOm) (mA3) (ia) ()

By 11 45 1,37 5.9 0,80 16.0

FL 9 42 0.48 3.5 0.73 12.1

HI 18 70 4.07 7.6 0.76 28.3 60 25 73 1.81 4.5 0.75 12.4

911 14 60 0.80 5.1 0.71 16.8 SG 12 58 0.82 5.4 0.73 17.7 SL 9 47 0.86 5.8 0.77 16.4 BL 26 63 1.60 6.2 0.75 16.5 CG 34 67 1.54 6.1 0.53 17.4

EL 26 61 1.18 6.7 0.79 15.1

LO/TD* 3 38 0.13 11.6 0.9 15.6

* - Larqe' CWD includes pieces that are greater than 0.5 m in diameter and 10 m in length. - Reach locations shown in Figure 4 and end points described in Table Al. - Diameter at larqer end o4 Diece, - Reaches LU and TD combined because o small nuffiber of pieces. 45 23 01 sv FL HI GO SH Reach SC GL BL CG EL LO/TD Figure 18. length)greaterFrequency thanand of debris0.5"large" jams CWD in pieces Drift (i.e.,Creek reachespieces In in diameter and 10 in in 77 introduced boulders, so are less subject to movementor export.

The lowest Drift Creek reach (TD) has a low channel gradient, abundant fine sediment, and frequent small CWD that are predominantly non-grouped (Table 10). Many of the CWD pieces observed in this reach are partially buried or have sunk below the water's surface. This material might identify where a depositional slackwater zone is caused when stream discharge meets tidewater during peak flows, which typically transport CWD from upstream channels.

Forest Management and CWD in Survey Reaches

Although it is more difficult to associate CWD loadings on large streams with management of adjacent slopes, differences among Drift Creek reaches may indicate responses to land management. The reaches of Drift Creek flowing through the Wilderness (BL, CG, and EL) contained greater CWD loadings than other fifth- order reaches (Table 9), and pieces were larger (Table

10) than in all other reaches (except for the HI reach in

Drift where CWD was artificially installed). Figure 19 shows channel CWD loading per channel unit for the majority of Drift Creek from slightly below the wilderness, upstream to the Bohannon Ranch (reaches EL to

FL). The many peaks that identify high CWD 0.2 I' I -I_-1---1 0.16 Drift(reaches Creek Wilderness BL, CC. EL) E j :::0.04 0 15 18 21 I 24 27 38 33 36 39 42 Figure 19. loadingLongitudinal per bankfull profile areaof channel along Driftunit CWDCreek Distance ?rm Alsea Riuer (km) 79 concentrations within the Wilderness reaches indicate that CWD loadings are greater and/or more aggregated.

The very high peak near 39 kin represents a small channel unit with a large amount of channel CWD.

"Largett CWD represent a disproportionate percentage of total volume in all survey reaches, especially those in the Wilderness (Table 11). The average volume per tlargets piece is similar in all reaches. Reaches above and below the wilderness have a great many more small pieces, which may result from input of smaller pieces by riparian alder stands along reaches above and below.

The relatively high loadings of "largett CWD associated with wilderness reaches may alternately be attributed to the geomorphic setting of these reaches, which are somewhat anomalous. The wilderness reaches are steeper than the reaches above and below them, and most CWD occurs in large jams, often anchored by boulders.

Large boulders appear to be more frequent in wilderness reaches than other parts of Drift Creek. Depositions of boulders and large CWD appear to have been brought to the channel by landslides. Landslides in this area are more likely to introduce large CWD, since conifersare relatively abundant along these reaches. In these settings, it appears that a riparian stand characteristics and geomorphic features interact to contribute to the relatively high loadings. 80 Effects of Valley Form on CWD Distribution

Distinct differences in valley form were noted between tributaries and within channels in the Basin. During the field survey, high CWD loads were recorded in sections of channels flowing through valleys with steep slopes adjacent to the channel, which were termed as

"constrained" (Figure 20). Reaches in which terraces separate valley slopes from the channel (i.e.

"unconstrained") contained less CWD. The association between valley form and CWD loading provided a potential explanation for CWD loading differences observed between tributaries. The upper basin and lower basin tributaries were predominantly constrained, and had significantly higher CWD loadings than the relatively unconstrained mid-basin streams. However, valley form differences between sub-basins were based on field observation, and were not adequately docunented to quantify the level of constraint for each of the tributaries.

A comparison of channel segments from constrained and unconstrained valleys was made to quantify the relative significance of valley form on CWD loadings. Mid-basin streams were used for this conparison because survey reaches were longer than for the upper and lower basins, and included geomorphic data (terrace locations and their heights). Flynn Creek and Deer Creek each contain a distinct constrained segment that contrasts 8].

Figure 20. Cross-sectional view of typical (a) constrained and (b) unconstrained valley forms 82 with unconstrained segments occurring above and below.

Similar constrained segment sets were identifiedon

Meadow Creek and lower Drift Creek (reach BL)so that CWD loadings and influence zone percentages could be assessed from a range of stream sizes. Paired constrained and unconstrained segments were located adjacently, thus effects of management and stream size variation within segment sets were minimized.

Coarse woody debris frequencies were higher for constrained segments than unconstrained segments, and total volume loadings were typically twice as high (Table

12). Channel CWD loadings were greater in constrained reaches (Figure 21), even though inchannel percentages

(Zone 1 and 2) represented smaller percentages of total volume than on the unconstrained (Table 12). Differences between constrained and unconstrained segmentswere not as great among larger channels, suggesting that valley wall influences are less related to CWD loadingson large streams than small.

Influence zone volumes appeared to be associated with relative valley constraint as well. The greatest percentages of CWD located in Zone 3 generally occurred in the constrained segments and tributaries (upperand lower sub-basins) (Tables 4 and 12). Debris surveyed in constrained channels were often suspended between side slopes or grouped above bankfull water level (Figure20). Table 12. DriftChannelfor constrainedCreek characteristics Basin and unconstrained and spatial streamCWD distribution segments, Stream Con- Reach fullBank- Channel Piece TotalCWD loading vol. Channel Percentages strained (X YWI) length (ml width (m) gradient frequency (X) (no/lOOm) (vol/lOOm)loading (m3/lO0a'2) loading Zone 1 CL) Zone 2 (7.) Zone 3 (7.) Zone 4 (7.) Flynn Cr. yes (82) no (6)(8) 692333575 2.12.53.3 2.24.21.3 231612 301716 1.312.461.76 10 53 271217 332622 574642 Deer Cr. yes (94) no (7)(0) 574483395 7.37.77.5 4.01.4 1710 8 13 4 0.170.400.28 1617 3 232142 152928 464812 Meadow Dr. no (0) 1624 12.613.4 0.41.2 74 12 5 0.32 1131 55 9 6 BL Drift yes (79) no (50) 1100 936 29.2 0.3 4 7 0.180.68 6 7362 1810 16 3 * - Constrained reaches have qreatr psrcentage of adjacent valley walls1 indicated by N7. VW. yes (100) 1087 27.1 0.8 8 16 0.50 16 69 11 4 2.53.0 unconstr 2.01.5 constr 0.51.0 0.0 Deer Cr. Meadow Cr. Drift (BL) Figure 21. DriftconstrainedChannel Creek CWD Basinandloading unconstrained per bankfull stream area segments, for 85 In contrast, unconstrained segments typically contained more CWD volume in Zone 4 than Zone 3. It appears that the terraces along unconstrained segments provide stable, Zone 4 sites for debris delivered by windthrow or from upslope. Although CWD volume in neither Zone 3 nor 4 affect channel hydraulics directly, volume in Zone 3 is more likely to enter the channel in the future.

Other research has described interactions between valley sideslopes and CWD recruitment. Keller and Swanson (1979) suggest that earth flows and debris torrents are more likely to contribute CWD if steep terrain is adjacent to the channel. This valley form

(which would be classed as constrained) effectively hasa broader uphill source area for CWD input (Keller and

Swanson 1979). Riparian terrace surfaces intercept CWD from upslope sources, delaying or preventing entry to the channel.

Constrained channels may also contain more CWD because of differences in the vegetation occurring adjacent to the channel. In the Drift Creek Basin as elsewhere in the Oregon Coast Range, conifersare more abundant along constrained channels, while alder and brush typically dominate streamside terraces (Long 1988).

This may be attributed to growing site preferences,or reflect that terraces have been more accessible to logging or clearing for grazing. Regardless of the 86 cause, the conifer CWD in constrained channels would be larger and longer-lasting than hardwood debris recruited to unconstrained channels.

Comparing Drift Creek to other Northwest Streams

Results of this study have illustrated that CWD loadings in streams within the Drift Creek Basinvary greatly. Data from other locations in the Northwest indicate that loadings differ even more drastically between forest types as well (Bisson et al. 1987), yet such data provide a regional perspective for CWD loading in the Drift Creek Basin.

Coarse woody debris loading data was summarized from published data for comparably sized streams from forested watersheds from coastal and Cascade Range streams in the

Pacific Northwest (Table 13). While three of the studies represent CWD loadings in "pristine" settings, the other two are from second-growth watersheds in Washington and

Oregon which like Drift Creek, have been partlyor entirely harvested. Bankfull width classes were used as a common scale of channel size, though not every class was represented in each study. Figure 22 illustrates the inchannel CWD loadings for these five published studies and for Drift Creek.

Coarse woody debris loadings from the Drift Creek Basin are substantially lower than other basins in each 87

Table 13. Forest type and management history for streams in the Pacific Northwest

Number Forest type Stand history Location Source

Coast redwood unlogged California Harmon et al. northwest 1986 Douglas-fir unlogged Oregon - Harmon et al, Cascades 1986 Sitka spruce/heilock unlogged Alaska - Robison 1988 southeast lder/Douq1as-fir harvested Washington - Grette 1985 20-60 years Olympic Pen. lder/spruce/heffilock harvested Oregon - Lonq 1988 50 years Coast Range 20 "AWAYJ$AYAAYiA 15 21 10 Will/il/h 34 Drift Cr. 5 1-5 5-10 Channel width (m) 10-15 15-20 20-35 Figure 22. descriptions)PacificChannel Northwestloading of (see CWD Tablefor streams 13 for instream the - 89 channel width class.The most comparable loadings were recorded in the Big Creek basin, which is about20 kilometers southwest of Drift Creek, andwas harvested and burned about 50 years before the CWDsurvey (Long 1988).Although forest sites in the Drift Creek Basin are capable of producing woody biomass at rates comparable to other forest sites, several circumstances may contribute to the apparently wood-impoverished state of surveyed channels. The effects of natural forest disturbancesover the past 150 years in conthination with more recentmanagement practices are probably the major factors associatedwith the low CWD loadings in the basin.Extensive wildfires around 1850 and 1870 burned most of the basin (Juday 1977).Only a few unburned areas remained, resulting in relatively little forestedarea with trees older than 120 years.Heimann's (1988) research indicates that120 years after a major disturbance, most pre-disturbanceCWD has been depleted.Recruitment of large conifer debris to streams is much lower during the firstcentury after disturbance than in subsequent centuries.During early stages of stand development, red aldermay produces substantial CWD (Heimann 1988), though piecesare relatively sirrall and decay rapidly. A hypothetical scenario of the effects ofseveral riparian disturbances conthined with projectedrecruitirrent 90 trends that would follow is illustrated in Figure 23.

The tinting of disturbances are based on historical events in Needle Branch (Moring and Lantz 1975). Stream cleaning was assumed to reduce loads toone half of pre- harvest levels. Depletion rates of pre-f ire debris are from Murphy and Koski (in press), and recruitment trends are from research by Heimann (1988). Pre-f ire CWD loading are based on levels found in similar streams in undisturbed forests, although the loading level before the fire and post-fire debris input patternsare difficult to quantify.

During the 1960's and 70's, when much of the harvesting in the Basin took place, stream cleaning and/or salvage were often intensive. In addition, riparian stands probably contain greater percentagesof hardwoods than the stands they have replaced. Inchannel retention of small material produced by alder would depend partially on larger CWD for stabilization (Heimnann

1988). During this period, residual conifer material in Drift Creek and many larger tributaries would have declined substantially since the fires, in additionto losses resulting from stream cleaning and salvage activities. Indeed the Drift Creek Basin survey suggests that large channels currently contain fewer large CWD

(Table 11) than observed in streams elsewhere (Sedellet al. 1988). 6 Stream 5 Wildfire 'if,I cleaning/Harvest Postfire hardwoodPrefire residual 4 '1 I, ' Postfire conifer Total CWD 3 cwD 2 Survey '1, 18500 1 1890 1930 1970 2010 -- 2050 Figure 23. second-orderHypothetical OregonCWD loadings Coast Rangeover timestream for a Year 92 An additional explanation of the low CWD loadings in Drift Creek is that valley forms in this basin are not conducive for either CWD recruitment or retention. As discussed earlier, steep channel walls can enhance CWD recruitment (Swanson and Lienkaemper 1978), yet most of Drift Creek is bordered by terraces (except for the reaches BL and CG). Low gradient reaches in other basins often recruit CWD via bankcutting and during channel rerouting (Robison 1988). However, along Drift Creek there is relatively little evidence of recent lateral channel movement.

Floatation from upstream is typically a major source of input to larger streams, though retention sites are needed to retain floated debris. Channel roughness elements (i.e. large logs and boulders) are not common in Drift Creek and much of the streambed (37 percent) of

Drift Creek is bedrock. Bedrock channels are subject to accelerated debris export (Murphy and Koski, in press) and have been observed to contain little CWD (Bilby and

Wasserman 1989). The abundance of bedrock also reflects less bed area composed of finer sediment, which stabilizes CWD pieces in other large streams (Grette

1985, Robison 1988).

In conclusion, the Drift Creek Basin and the streams therein, embody many physical, biological and temporal characteristics that have been associated with low CWD 93 loadings elsewhere. Many or all of these attributes and events appear to be reflected in current CWD loading levels observed in the Basin. 94

CONCLUS IONS

The extensive data collected on coarse woody debris occurring in streams of the Drift Creek Basin provide the basis for the following conclusions:

For small streams (first- to third-order), riparian

forest history and geomorphology are major

determinants of CWD loading. Forest harvest/stream cleaning practices are more clearly associated with

piece characteristics than CWD loadings. Reaches flowing through clearcut riparian zones contain pieces which are shorter and more decayed than streams within forested riparian zones (i.e. undisturbed and buffer strip reaches) and smaller

loadings of hardwood CWD.

The clearcut treatments evaluated in this study were

affected by practices prevalent in 1960's and 70's

(i.e., intensive stream cleaning and CWD salvage) which probably would not occur under contemporary harvest activities.

Stream reaches with buffer strips contained CWD

loads that were similar to undisturbed reaches in terms of loading levels and characteristics.

For streams of increasing size, channel CWD loading I per bankfull area decreases. However, the percentage of total CWD volume occurring within the 95 channel (Zones 1 and 2) increases.

For streams of increasing size, "large" CWD pieces

(i.e. greater than 0.5 m in diameter and 10m in length) and those with an attached rootwadoccur more frequently, because they are more resistant to fluvial export.

Stream reaches which are constrained (i.e.a large percentage of banks adjacent to valley walls) had greater inchannel and total CWD volume loading than did unconstrained channels (i.e. where terraces separate the channel from the valley walls).

Debris volume in constrained reacheswas more frequently situated above the channel than unconstrained reaches, in which CWD volumewas predominantly within the channel andon the banks.

The percentage of the total CWD load thatoccurs within the bankfull channel is significantly and inversely correlated with channel gradient.

Because CWD input patterns vary over time, evaluation of loading at any given time should consider past input trends to providea temporal perspective.

Results from this study indicate that additional research is needed to address the following topics: a. Do buffer strips provide CWD to streams at rates similar to input from undisturbed 96 riparian zones?

How do artificially installed debris pieces influence CWD distribution and channel morphology?

What channel features (i.e., land use, valley form, roughness elements, magnitude of recent peak flows) determine the distribution of CWD in large channels?

To what extent and for how long do landscape-

scale forest disturbances (i.e. fires)

influence stream CWD loads.

12. Future research on stream CWD would benefit from the use of standardized survey methods, which would

improve validity of comparisons. These methods might include:

Common minimum diameter and length (or sets of

dimensions for sub-classes) used to define coarse woody debris.

A system to describe the position of a piece in the channel cross section, such as influence

zones (Robison 1988).

A standard decay class criteria for CWD within aquatic ecosystems.

These methods would improve validity of comparisons

between stream CWD in different forest types and geographic areas. 97 LITERATURE CITED

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Table Al. Location of Drift Creek survey reaches

Source of Reach Location of reach end point Reach name length D15t. from Alsea R. Description Cm) (miles) (km)

5.3 8.5 Eastward curve just below Lyndon Creek ID TiDal 2130 (top of daily tidal influenc&

influence 6.6 10.7 Near arsh" on USGS 'Tideater" ap LO LOwer 4650 (top of occasional tidal influence) Drift Cr. 9.5 1.3 Start of 1988 survey EL ELlen Cr. 51 0 (near ford' on Tidewater ifiap) con4luence 12.7 20.5 Cougar Creek con4luence CG CouGar Cr. 2720 confluence 14.4 23.2 Boulder Creek confluence BL BouLder Cr. 3930 confluence 16.8 27.1 Slickrock Creek confluence GL GoLd Cr. 3710

con4luence 19.2 30.8 Lowest concrete bridge on Drift Cr. 96 "Staff Gages 4140 bridge 21.7 3.0 Meadow Creek confluence SH "SHotqun 2120 bridge (GP1000) 23.0 37.1 Gopher Creek confluence GO GOpher Cr. 2270 confluence 24.5 39.4 Lower end of habitat enhaceent' HI HabItat 1500 structures (as of 7/1988) ehancemet 25.4 40.9 Upper end of Nhabitat enhaceffient" FL Fish Ladder 1240 structures (as of 7/1988) 26.2 42.1 Falls/fish ladder near sy Section seVenD 3220 'Bohannon Ranch (1989 survey) 28.2 45.3 South Fork Dri4t Creek confluence 104

Table A2. Coefficients and statistics of correction equations for CWD piece dimension estimates.

A (slope) B (intercept) R- G.E. of

Piece squared estiffiate

dimension coeff. p-value$ coeff. p-value (7.)

Surveyor :C. Veldhuien n 68

Large dia. 1.092 0.000 -0.742 0.388 90 0.09

Sffiall dia. 0.945 0.000 0.984 0.128 99 0.06

Length 0.992 0.000 0.557 0.475 96 1,01

Surveyor : M. Raugh n = 50

Large dia' 0.884 0.000 0.054 0.262 76 0.11

Small dia. 0.821 0.000 0.048 0.258 72 0.11

Length 1.006 0.000 0.216 0,569 94 1,24

4 - P-values for all slope estimates are less than 0.000001. - P-values for intercepts are not significantly different from zero (for alpha 0.10) but are retained in the equations to improve fit.

COMMENTS

Simple hnear re9ression was used to determine the correlation

betieen estimated and measured CWD piece dimensions. Calibration

equations were o the following for;.

C = (A* E) + B

where: C = corrected dimension A regression line slope E estimated dimension B V-axis intercept 105

Table A3. Elevations, low flows, and vegetation of tributary reaches, Drift Creek Basin

Riparian vegetation Average Suier forb/ hrd/con

Sub-basin Stream elev. low flow shrub hardwood ix conifer

( (us) () CX) () ()

E.Fk. Trout Cr, 80 26,1 0 0 37 63 Lower Trout Cr. 110 44.8 0 60 40 0

Bear Cr. 100 1,3 90 10 0 0

Upper Flynn Cr. 200 4.6 0 0 39 61 Mid Deer Ck. 200 8,5 3 36 59 2 Needle Branch 150 1.0 63 27 0 10

Go.Fk. Drift Cr. 370 20.9 17 27 7 49 Upper No.Fk. Drift Cr. 290 19.6 0 80 0 20 Upper Drift Cr. 300 21.6 16 83 0 1

* - Flow measured at lower end of reach in September, 1988. 106

Table A4. Additional piece characteristics of CWD in tributary reaches, Drift Creek Basin

CWD piece sizes Pieces Yoiue Diameter* Length -- Grouped& -- Buried with Sub-basin Streaii Ave. (s.d.) Ave. (s.d.) Ave. Cs.dJ 2-4 5+ pcs rootwad

(m.3) () (m) () (7.) (%) ())

E.Fk'. Trout Cr. 1.7 (4.0) 0.45 (0.26) 7.2 (5.1) 0 0 4 6

Lower Trout Cr. 1.6 (2.9) 0.47 (0.27) 6.9 (4.7) 1 38 7 7

Bear Cr. 1.5 (24) 0.53 (0.29) 5.6 (4.9) 0 0 7 9

tipper Flynn Cr. 1.2 1.9) 0.44 (0.21) 7.3 5.7) 4 0 6 4

Mid Deer Cr. 0.7 (1.0) 0.33 (0.16) 7.0 5.4) 20 8 21 16

Needle Branch 0.8 (1.9) 0.41 (0.21) 4.3 (3.2) 5 24 7 2

So,Fk. Drift Cr. 3.5 7.5) 0,56 (0.38) 8.2 (6.3) 3 32 8 6

tipper I No,Fk. Drift Cr. 1.7 (2.8) 0.48 (0.25) 6.9 (.2) 1 36 9 5

Upper Drift Cr. 0.B (1.2) 0.44 (0.19) 5.0 (2.5) 2 42 7 1

* - UD is undisturbed, 'BS' is patch clearsut with buffer strip, and TMCC" is entirely clearcut. * - Piece diameters measured at the larger end. & - Includes both 'partly and umostlyl buried pieces. - Percentages of pieces occurring in groups this size. 107

Table A5. Elevations and vegetation of survey reaches, Drift Creek Basin

Riparian vegetation Average forb/ hrd/con Stream elev. shrub hardwood mix conifer

(m) (%} () (7.) (7.)

Lower Flynn Cr. 160 46 0 0

Lower So.Fk. Drift Cr. 240 39 50 11 0

Horse Cr. 160 0 100 0 0

Meadow Cr. 140 4 90 6 0

Drift Creek Reach

SV 210 20 61 11 8

FL 180 13 82 0 5

HI 170 0 88 0 9

60 150 7 75 0 13 SH 140 30 68 0 0

96 120 10 78 0 11

GL 100 13 70 0 14

BL 70 0 44 52 0

CG 60 20 43 27 0

EL 40 0 30 65 0 LO 10 TD 5

- Reach locations shown in Figure 4 and described in Table AL 108

Table A6. Additional piece characteristics of CWD in survey reaches, Drift Creek Basin

CWD piece sizes Volume Diaeter& Length -- Grouped* -- Buried

Stream Ave. (s.d.) Ave.(s.d.) Ave. (s.d.,) 2-4 5+ pcs I (A3) () (7) 7) (7)

Lower Flynn Cr. 0.59 (1.25) 0.34 (0.19) 5.2 3.5) 5 7 19 Lower So.Fk, Drift 1.24 2.56) .45 (0.24) 6.2 (4.6) 6 70 l

Horse Cr. 0.83 (1.02) 0.45 (0.17) 5.7 (3.2> 25 21 2

Meadow Cr. 1.42 (1.86) 0.53 (0.24) 6.4 (3.6) 25 14 1

Drift Creek Reach

SY 1.42 (2.30) 0,46 (0.26) 6.7 (5.0) 13 43 11

FL 0.78 (1.04) 0.38 (0.18) 6.6 (3.8) 0 0 3 HI 1,91 (4.77) 0,42 (0.26) 9.4 (7.4) 6 62 1

60 1.51 (2.31) 0.44 (0.24) 8.1 4.4) 13 32 2

SH 1,23 (2.32) 0.42 (0.21) 7.3 (6.1) 19 14 6

SG 1.16 2.31) 0.39 0.22) 7.8 6.2) 3 17 7

GL 1.11 (2.32) 0.42 (0.23) 6.8 (5.0) 9 37 9 BL 2.52 3.26I 0.59 0.19} 8.9 (6.3) 18 58 8

CG 3.03 (3.91) 0.63 (0.19) 9.7 (7.0) 27 41 0

EL 2.85 (4.37) 0.66 (0.25) 7.8 (5.3) 19 1 0 LO 0,78 (2.46) 0,36 (0.22) 5.5 (3.9) 30 12 29

ID 0.75 (2.80) 0.40 (0.22) 4.7 (3.5) 13 0 41

& - Piece diameters measured at the larger end * - Includes pieces partly and mostly buried1. - Reach locations shown in Figure 4 and end points described in labble Al. 109

Table A7. Species categories of CWD in tributary and survey reaches, Drift Creek Basin

Tributaries Survey UD PC/SB CC Reach

Number of pieces 724 1159 662 3903

Species X) (7.) ()

Conifer (unknown) 0 0 0 10 Douglas-fir 46 35 67 29

Western hemlock 4 1 0 1

Western redcedar 12 27 16 14

Sitka spruce 5 1 2 0

Hardwood (unknown) 0 1 0 11 Red alder 33 34 15 35

Sigleaf maple 0 1 0 0