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7 Habitat Loss DIMENSIONS OF THE PROBLEM Salmon habitat in freshwater is defined by physical and chemical character- istics of the environment during the portion of the life cycle spent in streams, lakes, or estuaries. It is generally taken to include · Water quality: temperature, dissolved oxygen, turbidity, nutrients, and environmental contaminants. · Properties of flow: velocity, turbulence, and discharge. · Geological and topographic features of the stream and its valley: width and depth, streambed roughness, particle size composition, riffle and pool fre- quency, and floodplain characteristics. · Cover: shading, interstitial hiding spaces, undercut banks and ledges, woody debris and aquatic vegetation. For many of those features, streamside vegetation plays an important direct and indirect role in affecting local habitat characteristics. Some biotic compo- nents of the environment are influenced by physical habitat conditions, including prey, predators, competitors, and pathogens. In this report, altered habitat is habitat that has been changed by human activity but is still accessible to salmon; lost habitat is habitat that used to be accessible but is no longer. Habitat alteration and loss that lead to reduced salmon production can occur when either of two conditions exists: anthropo- genic perturbations transform freshwater spawning or rearing habitat to an un 164
HABITAT LOSS 165 natural or otherwise unproductive state or human intervention prevents natural disturbances from creating or maintaining habitat that is important for salmon production. Although most anthropogenic changes in habitat result in impair- ment of the productivity of aquatic ecosystems (Reice et al. l990J, some lead to increased production by improving survival or growth of one or more life-history phases. And some types of alterations do not directly affect salmon habitat but cause changes in the species composition of the aquatic community that might or might not be favorable to salmon (Reeves et al. 1987) or shift conditions from those favorable to one salmon species to those favorable to another (Lichatowich 19893. The important point is that habitat can be altered by the direct effects of human perturbations and by human prevention of natural disturbances (Sousa 1984, Wissmar and Swanson 1990~. Either can impair salmon production, espe- cially when its spatial or temporal scale differs fundamentally from that of the natural disturbance regime of an area. Habitat alterations can have positive or negative outcomes that are often difficult to predict. For example, removal of streamside vegetation, a frequent consequence of human alteration of riparian zones, results in increases in solar radiation and water temperature. Higher light levels and warmer water can promote algal growth (Gregory et al. 1987), which leads to increased invertebrate production and more food for rearing salmon (Hawkins et al. 1983~. Higher light levels also tend to enhance foraging efficiency of stream-dwelling salmon (Wilzbach 19853. The resulting increased growth rates might confer improved overwinter survival and increased smell size (Holtby and Scrivener 19893. Large smelts, in turn, might be better able to escape predation in nearshore environ- ments and have higher survival rates at sea (Pearcy 19921. All those processes potentially improve productivity. However, increased temperatures have also been shown to reduce growth efficiency when food is scarce (Brett et al. 1969) and to favor competitive dominance of cyprinid fishes, such as redside shiners (Richardsonius balteatus), over salmon (Reeves et al. 19871. And outcomes can be complicated by the presence of exotic species or pathogens, which also tend to be favored by higher temperatures (Li et al. 1987~. Those processes potentially limit salmon production. Because so many physical and biological factors, of which temperature is only one, are influenced by the removal of streamside vegetation and because interactions between these factors are still poorly understood, predictions of the specific consequences for salmon of altering stream temperatures to salmon are often prone to error. Models of the impact of habitat change on salmon generally suffer from an inability to predict the consequences of interacting ecological processes (Mathur et al. 1985, Fausch et al. 19883; this is especially true when models are extrapolated to geographical regions beyond those in which their quantitative relationships were developed (Shirvell 19891. Because habitat loss is widely acknowledged to have contributed to the decline of virtually every species of Pacific salmon in western North America
66 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST (Nehlsen et al. 1991), the lack of precise knowledge of relationships between various types of habitat change and salmon populations need not be a barrier to improved environmental management. Different land uses (e.g., forestry, agri- culture, grazing, mining, and urban and industrial development' are practiced at different locations in a river basin, but they share some effects with respect to habitat alteration and loss. This chapter identifies some important types of habi- tat alteration and loss, discusses how these changes influence the functioning of aquatic ecosystems, and identifies specific consequences for salmon. NATURAL VERSUS ANTHROPOGENIC DISTURBANCES AND WATERSHED PRODUCTIVITY Natural disturbances play a crucial role in the various life-history phases of salmon. Pacific salmon evolved in freshwater environments that included a variety of natural disturbances, including seasonal high flows and floods, gla- ciers, droughts, wildfires, volcanism, landslides and debris flows, and seasonally extreme temperatures. Their adaptations to life in frequently disturbed freshwa- ter ecosystems reflect, in part, a need to cope with unusual events. Such adapta- tions include relatively high fecundity and large eggs, which permit extended intragravel residence by alevins during periods of unfavorable stream conditions; excellent swimming abilities of both juveniles and adults; occasional straying from natal streams by adults; and differentiation into locally adapted populations. Salmon with prolonged freshwater life cycles appear to be somewhat more flex- ible in their habitat requirements than those with abbreviated or lacustrine fresh- water life cycles (Miller and Brannon 1982~. For example, Reimers (1973) identified five distinct life-history strategies involving different periods of river- ine and estuarine residence in a single population of fall chinook salmon in southern Oregon (Table 7-1~. Multiple life-history strategies within populations might be an effective means of hedging against unusual events. Not all disturbances result in diminished salmon production. Some cause short-term population declines but ultimately lead to increased productivity con- currently with habitat and trophic recovery (Gregory et al. 1987, Schlosser 1991~. Natural disturbances can alter habitat in ways that stimulate salmon production and maintain environmental heterogeneity (Neiman et al. 19921. Wildfires and some types of soil disturbances increase nutrient availability and so enhance primary production (Walstad et al. 1990~. Floods entrain particulate organic matter and both large and small woody debris from riparian zones. High flows cleanse spawning gravel of fine sediment and scour new pools. Wildfires open forest canopies, provide large woody debris, and create opportunities for early successional plant communities in riparian zones (Agee 19931. Windstorms and windthrow provide recruitment of large woody debris and increase the complex- ity of local habitats. Disturbances of many types increase the transport of nutri- ents. organic matter, and large woody debris to estuaries (Sibert 1979, Simenstad
HABITAT LOSS TABLE 7-1 Major Variations in Fall Chinook Salmon Life Histories in Sixes Rivera 167 Life-History Variation Description 1 2 3 4 Emerge from gravel? move directly downstream through main river and estuary and into ocean within few weeks. Emerge from gravel, move into main river (or possibly stay in tributaries) for rearing until early summer, move into estuary for short period, and finally move into ocean before period of high productivity in estuary during late summer and autumn. Emerge from gravel, move into main river (or possibly stay in tributaries) for rearing until early summer, move into estuary for extended rearing, and finally enter ocean after experiencing improved growth in estuary during late summer and autumn. Emerge from gravel, stay in tributary streams (or, rarely, in main river) until autumn rains, and then move directly to ocean. Emerge from ravel; stay in tributary streams (or, rarely, in main river) through summer, autumn, and winter, and then enter ocean during next . . spring as yearlings. aA coastal Oregon stream. Source: Reimers 1973. et al. 19821. All of those processes are important to maintaining fish production in aquatic ecosystems (Gregory et al. 1991) and are necessary for normal ecosys- tem functions and diverse aquatic communities (Poff and Ward 19901. Although a large natural disturbance can cause a temporary decline in salmon populations, productivity might rebound to exceed predisturbance levels for extended periods (Bisson et al. 1988~. Some types of natural disturbances that have beneficial long-term effects on salmon habitat, such as floods and wildfires, damage prop- erty and threaten lives and so are aggressively controlled and suppressed. It is therefore important to view human activity not only as a cause of habitat change, but also as potentially hindering natural disturbance patterns and recovery pro- cesses from creating and maintaining productive and diverse habitat. Productivity declines when habitat alteration and loss impair the successful completion of life-history stages in the context of a watershed's landscape, its natural disturbance regime, and its anthropogenic changes. If a salmon popula- tion exists close to the environmental tolerance limits of its species for ex- ample, at the edge of its range either geographically or with respect to riverine environmental gradients relatively minor changes in key habitat characteristics resulting from natural climatic events or from human activity can influence popu
68 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST ration viability or expression of full evolutionary potential (Table 7-2 and 7-3~. Many of the known extinctions of salmon populations over the last century have occurred near the edges of geographical ranges (Nehlsen et al. 1991, The Wilder- ness Society 1993), and many of these have apparently been caused or accentu- ated by human-related habitat losses. Understanding the effects of habitat alter- ation must include considering changes in the context of an area's natural disturbance regime (Table 7-2J. Habitat disturbances can be "cumulative" in the sense that different factors acting sequentially or concurrently can limit population size or growth during different phases of freshwater and estuarine rearing periods (Elliott 1985~. To some extent, populations can adjust to alteration in or loss of habitat in a compen- satory fashion; after a period of decreased survival, reduction in competition can lead to increased survival or growth (Chapman 19663. However, not all factors can be compensated in this manner and interactions between different types of habitat change may exacerbate the damage each would do independently (Niemi et al. 1990, Hicks et al. 1991~. Furthermore, anthropogenic changes to habitat may occur so fast that natural selection processes are unable to adjust and com- pensate. Human activities change the frequency or magnitude of disturbances (Table 7-2), and result not only in loss of or alteration in habitat but in substantial changes in natural recovery processes (see Figure 7-la). Natural disturbances large enough to have an important impact require recovery intervals that might include periods of high production followed by re-establishment of density-de- pendent regulating mechanisms and biological controls that cause a return to predisturbance levels. There have been relatively few long-term studies of stream- dwelling salmon after large natural disturbances (Hanson and Waters 1974, Wa- ters 1983, Elliott 1985, Bisson et al. 1988), but available evidence suggests that 10 years or more might pass after a large disturbance before salmon populations return to the normal range of predisturbance abundance. Frequent anthropogenic perturbations of various intensity superimposed on natural regimes of less-frequent disturbances (Table 7-2) can hinder recovery processes and prevent populations from returning to their former abundance (Fig- ure 7-11. Such perturbations gradually "ratchet" populations downward, a pat- tern typical of salmon populations in areas of progressive encroachment on ripar- ian zones or areas with chronic input of sediment (Cederholm et al. 1981~. Frequent, relatively small perturbations tend to increase the year-to-year variabil- ity of salmon populations. Hartman and Scrivener (1990) concluded that popula- tion instability was one of the most serious long-term consequences of logging for coho and chum salmon in Carnation Creek, British Columbia. Characteristic declines occur because populations do not have time to recover fully before the next large disturbance. Very large anthropogenic impacts can cause so much damage to salmon populations or their habitat that abundance declines precipitously and does not
HABITAT LOSS 169 recover (Figure 7-11. Such changes are characteristic of extensive habitat losses that might occur, for example, if a large portion of a river system were blocked. Sockeye salmon populations in the Fraser River underwent a major crash in 1913-1914 when rockslides caused by railroad construction in the canyon at Hell's Gate blocked much of the upper river, including most of the spawning grounds. Sockeye and other salmon that used the upper Fraser River remained at critically low densities until construction of fishways in the 1930s (Ricker 19875. Damage to or loss of habitat was so great that natural recovery was precluded until the fishways were completed. Many of the stock extinctions noted by Nehlsen et al. (1991) resulted from similar very large anthropogenic perturba- tions. The spatial and temporal scales of anthropogenic habitat alterations that are imposed on salmon populations often differ in both frequency and magnitude from natural disturbance regimes. It is the natural disturbance regimes to which local populations are adapted and that have historically powered the creation of new, productive habitat: These characteristics must be retained or replicated if freshwater salmon habitat is to be sustained (Hill et al. 19913. SEDIMENTATION Sediment can enter watercourses by various mechanisms, and inputs can be chronic or episodic. Mobilization of soil particles through surface and gully erosion delivers small particles (fine sediment) to the stream network. Surface erosion is normally associated with precipitation but can occur chronically if human activities generate continuous runoff of sediment-rich water to streams. The erosion of large volumes of hillslope material, a process termed mass ero- sion, occurs when large upper soil movements (often rapid), such as landslides, and deeply seated slope failures, such as earth slumps, deliver coarse and fine sediment, large woody debris, and fine organic matter to streams. . Both surface erosion and mass erosion are normal processes (Leopold et al. 19641; their frequency depends mostly on the geology and erosiveness of soils and underlying rock and on the intensity and duration of rainfall and snow melt (Swanson et al. 19875. Some areas have naturally high erosion rates; examples include sandstone-dominated coastal river basins in northern California and west- ern Oregon, granitic sediments in northern and central Idaho, and glacial-lacus- trine deposits in northwestern Washington. That kind of area is often among the most sensitive to erosion caused by anthropogenic perturbations, such as logging and road building (Figure 7-21. Improvements in road-construction and logging methods can reduce erosion rates. Rice (1992) documented an 80% reduction in mass erosion from forest roads and about a 40% reduction in mass erosion from logged areas in northern California due to improvements in forest practices beginning in the middle 1970s. However, the potential for continued alteration in and loss of salmon habitat
70 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST TABLE 7-2 Approximate Occurrence Rates of Different Types of Natural and Approximate Recurrence Interval (years) Type of Disturbance Natural Anthropogenic Daily to weekly precipitation and discharge patterns Seasonal precipitation and discharge; moderate storms; ice formation 0.01 - 0.1 0.001 - 0. 0.1 - 1.0 0.01 - 1.0 Major floods; storms; rain-on-snow events 10 - 100 1 - 50 Debris avalanches and debris torrents 1 Go - 1 coo 20 - 200
HABITAT LOSS Anthropogenic Disturbances 171 Physical and Chemical Factors Influenced by the Disturbance Habitat Effects Stream discharge; channel width and depth; storage and transport of fine particulate organic matter; fine sediment transport and deposition; nutrient concentrations; water current velocity Bank-full flows; moderate channel erosion; high base-flow erosion; increased mobility of sediment and woody debris; local damming and flooding; sediment transport by anchor ice; gouging of stream bed by ice movement; reduced winter flows with extensive freezing; seasonal nutrient concentrations Inputs of sediment, organic matter and woody debris from hillslopes, riparian zones and streambanks; localized scour and fill of streambeds; lateral channel movement; streambed mobilization resulting in redistribution of coarse sediment ant! flushing of fine sediment; redistribution of large woody debris; inundation of floodplains; transport of organic matter and large woody debris t`' estuaries Large, short-term increases in sediment and large woody debris inputs; extensive channel scour; large-scale movement and redistribution of substrate, fine particulate organic matter and large woody debris; damming and obstruction of channels at the terminus of the torrent track; accelerated streambank erosion, resulting in channel widening; destruction of riparian vegetation; very large short-term increase in suspended sediment; subsequent summer temperature increases from vegetative canopy removal Minor alteration of particle sizes in spawning ~ravels; minor variations in rearing habitat; minor temperature change; altered turbidity; altered primary productivity Changes in frequencies of riffles and pools; changes in particle sizes in spawning gravels; increased channel width; flooding of side channels; removal (or sometimes addition of) cover; relocation of holding areas. In areas affected by ice: decreased water temperatures; lower primary and secondary productivity; egg dewatering or scour during anchor ice formation and breakup Changes in the frequencies of riffles and pools; formation of large log jams; burial of some spawning sites but creation of new areas suitable for spawning; increased amounts of fine particular organic matter for processing by the benthic community, resulting in increased secondary production; destruction or creation of side-channels along the floodplain; increased secondary production and cover habitat in estuaries Extensive loss of pool habitat in the torrent track; loss of spawning gravels; loss of habitat complexity along edge of stream; destruction of side-channels and other overwintering areas; creation of new cover in the terminal debris dam; creation of new spawning areas in the sediment terrace upstream from the debris dam; short-term loss of aquatic invertebrates; possible damage to gills from heavy suspended sediment load; increased primary production
172 TABLE 7-2 Continued UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST Approximate Recurrence Interval (years) Natural Anthropogenic Type of Disturbance Beaver activity Major disturbances to vegetation Windthrow Wildfire Insects and disease Slumps and earthflows 5- 100 0 (removal of beavers) 100 - 500 50 - 150 (buffer strip blow-down) 100 - 750 50 - 150 (timber harvest rotation) 100 - 500 50 - 150 (timber harvest rotation) 1 00 - 1 ?0OO 50 _00
HABITAT LOSS 173 Physical and Chemical Factors Influenced by the Disturbance Habitat effects Channel damming; obstruction and redirection of channel flow; flooding of streambanks and side-channels; entrainment of trees from riparian zone; creation of large depositional areas for fine sediment; conditions that pr~'m<.~:e anaerobic decomposition and denitrification, resulting in nutrient enrichment downstream from the pond Increased sediment delivery to channels; decreased litterfall; increased inputs of large woody debris; decreased riparian canopy; increased retention of sediment and fine organic matter; reduced litterfall Increased sediment delivery to channels; inputs of large woody debris; loss of riparian canopy and vegetative cover; short-term increase in fine particulate organic matter and nutrients; decreased litterfall; increased peak discharge; short-term increase in summer flows from reduced evapotranspiration; short-term increase in biochemical oxygen demand in stream substrate Inputs of large woody debris; loss of . . . Spartan canopy and vegetative cover; decreased litterfall; short-term increase in summer flows from reduced evapo- transpiration Low-level, long-term contributions of sediment and large woody debris to streams; partial blockage of channel; local baselevel constriction below point of entry; shifts in channel configuration; long-term source of nutrients Enhanced rearing and overwintering habitat; increased water volumes during low :llows; refugia during floods; possible blockage to upstream migration by adults and juveniles; elevated summer temperatures and lower winter temperatures; local reductions in dissolved oxygen, including areas under ice in winter; increased production of lentic invertebrates in pond; increased primary and secondary production downstream from pond Increased pool habitat; localized sedimentation; increased in-channel cover; increased summer temperatures and decreased winter temperatures; creation of eddies and alcoves along channel mat gins; increased secondary production Increased sedimentation of spawning and rearing habitat; increased pool habitat and in-channel cover' increased water volume in summer; increased summer temperatures and decreased winter temperatures; increased secondary production; reduced dissolved oxygen in spawning gravels; scour of egos and alevins in spawning gravels Increased pool habitat and in-channel cover: increased summer temperatures and decreased winter temperatures; increased water volume in summer; increased primary and secondary production Sedimentation of spawning gravels; scour of channels below point of entry; accumulation of gravels behind obstructions; possible blockage of fish migrations; increased pool habitat in coarse sediment and large woody debris depositional areas; destruction of side channels in some areas, creation of new side channels in others; long-term maintenance of aquatic productivity
174 TABLE 7-2 Continued UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST Approximate Recurrence Interval (years) Type of Disturbance Natural Anthropogenic Volcanism Climate change 100- 1,000 1 ,000 - 1 00,000 1 0 - 1 00 (thermal discharges, riparian canopy removal, channelization) Source: Modified from Swanston 1991. resulting from forestry activities continues. The FEMAT report (1993) noted that federally owned forest lands within the range of the northern spotted owl contain about 180,000 km of roads, a substantial portion of which constitutes potential threats to riparian and aquatic habitats, mostly through sedimentation. An esti- mated 250,000 stream crossings are associated with the road system, and most of the crossing structures might be unable to withstand storms with a recurrence interval of less than 25 years (FEMAT 19933. Road failures often result in debris torrents in small streams and can be particularly damaging to coho, steelhead, and sea-run cutthroat habitat. Increased erosion from land use is not limited to the relatively steep forested terrain of the Pacific Northwest. For example, glacial sediment deposits in east- ern Oregon and Washington are widely farmed for the production of dryland crops. However, because extensive areas are left fallow (i.e., barren of vegetative cover) each winter, winter rainfall, particularly on frozen soils, causes much surface erosion and sediment movement to streams. Similarly, urbanization, mining, excessive grazing, and other land uses can increase sediment production well beyond background levels. Increased erosion can impair the reproductive success of salmon in several
HABITAT LOSS 175 Physical and Chemical Factors Influenced by the Disturbance Habitat effects Increased delivery of fine sediment and organic matter; scour of channels from mudflows; formation of mudflow terraces along rivers; destruction of riparian vegetation; damming of streams with creation of new lakes; increased nutrients Major changes in channel direction, gradient and configuration; stream capture; lon:,-term changes in temperature and precipitation regimes Sedimentation of spawning gravels; loss of pool habitat from mudflows, but creation of pool habitat in areas with tree blowdown; creation of new overwintering habitat and side channels along mudflow terraces; short-term potentially lethal sediment and temperature levels during eruptions; long-term increases in primary and secondary production; formation of migration blockages; long-term benefits to lake-dwelling species Major changes in frequencies of dominant habitat types; shifts in species composition related to preferences for temperatures, substrates, and streamflows; faunal transfers from stream capture; reproductive isolation may lead to stock differentiation; founder effects ways. Spawning areas can be buried by large quantities of coarse and fine sedi- ment, and spawning migrations can be blocked by landslides (Swanson et al. 19871. Intrusion of fine sediment into the egg pocket of reads can cause smoth- ering of eggs and entrapment of alevins (Chapman 1988~. Likewise, the rearing capacity of streams is often damaged by increased erosion (Hicks et al. 19911. Fine sediment can fill interstitial spaces and prevent their use by juvenile salmon for cover (Platte and Megahan 1975~. Turbidity impairs foraging efficiency (Noggle 1978), causes emigration (Bisson and Bilby 1982), and disrupts social behavior (Berg and Northcote 19851. Long-term increases in sediment in con- junction with other impacts on riparian systems can result in pool-filling. Sedell and Everest (1991, see also FEMAT 1993) surveyed streams in national forests in Washington and Oregon that had been originally surveyed from 1935 to 1945 (Figure 7-3~. They found that there had been about a 60% reduction in the frequency of large, deep pools (greater than 2 m deep and 43 m2 in surface area), a loss attributed to filling with sediments and decrease in pool-forming processes. Nickelson and Hafele (1978) found a statistically significant correlation between densities of juvenile coho and the volume of pools in western Oregon streams. Bjornn et al. (1977J added sand to a natural pool in an Idaho stream, experimen
76 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST TABLE 7-3 Spatial Scales, Recovery Times, and Some Biological Recovery Mechanisms of Stream Organisms Following Natural and Anthropogenic Disturbances in the Pacific Northwest Nature of Disturbance Spatial Scale Examples Natural Anthropogenic Small Large Acute sublethal Small Large Acute lethal Small Large Chronic sublethal Small Large Chronic lethal Small Large Flood on:< 1- to 3-year recurrence interval; local windstorm; minor landslide Major wildfire; dam-break flood (small streams); flood of 50- to 100- year recurrence interval (large streams) Minor landslide or streambank erosion; short-lived toxicant (local use); temporary water withdrawal Short-lived toxicant (widespread use); various flood-control practices Short-lived toxicant (e.g., spill); major debris torrent Introduction of pathogen to drainage system; channelization Point-source sediment inputs; local thermal change; migration blockage in tributary Increased erosion at the watershed level; widespread loss of riparian vegetation; habitat simplification; multiple water withdrawals; dams Frequent discharges of long- or short- lived tox~cants; chronic anoxia; temperature or flows beyond tolerance . · . Helmets Frequent introductions of pathogens; frequent discharges of long- or short- lived toxicants; chronic anoxia; temperature or flows beyond tolerance . . 1lmlts Source: Modified from Poff and Ward 1990. tally reducing pool volume by half and water deeper than 0.3 m by two-thirds, and found that fish numbers declined by about two-thirds. However, stream habitat can be improved if mass erosion delivers coarse sediment to streams that have little structural roughness, thereby creating new cover and increasing channel complexity (Everest et al. 1987, Swanson et al.
HABITAT LOSS 177 Relative Recovery Time Biological Recovery Mechanisms Short Moderate to long Fast Long Moderate to long Long Moderate to long Long Very long Very long Behavioral avoidance and refuge-seeking; increased growth among survivors; rapid recolonization of disturbed area Adjustment of populations and community structure to new habitat conditions; species migrations and new population establishment Behavioral and physiological avoidance; refuge-seeking; rapid recolonization Physiological acclimation; selection for tolerant species; behavioral avoidance and ref~uge-seekin:,; shifts in community organization Behavioral avoidance; recolonization; new species establishment Population and community adjustments; selection for tolerant species Local population and community adjustments; colonization by tolerant species; behavioral and physiological . . acclimation Population and community adjustments throughout system; selection for tolerant species; species migrations Selection for tolerant species Colonization by rare, resistant species 19873. Thus, the specific effects of accelerated erosion depend on the nature and timing of sediment delivery (i.e., magnitude and frequency), the size of the par- ticles eroded into the stream, and the prior condition of the stream itself. Some watershed studies have clearly shown that sedimentation lowers sur- vival of salmon eggs and alevins in the gravel (Hartman and Scrivener 19901.
178 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST A M Direct mortality| Habitat loss Reduced food Increased primary and secondary production Reduced competition Reduced predation ~` Habitat recovery \K I i~ / Recovery of competitors /\, and predators / Return of primary and secondary /\/ production to normal range R Natural ~ /` disturbance' C 1 ~ A/ ~ ~ / i ~- 1 1 1 1 Frequent small anthropogenic disturbances ~ 1 D Very large /\\ /\ ~ ~ anthropogenic disturbance Natural | disturbance l Time FIGURE 7-1 Hypothetical response of fish populations to natural disturbances of moder- ate to large intensity (b), frequent small anthropogenic impacts superimposed on natural disturbance regime (c), and single very large anthropogenic impact superimposed on natural disturbance regime (d). Box (a) above graphs shows some natural biophysic~al processes that operate during initial depression and later recovery stages of disturbance response.
HABITAT LOSS Queen Charlotte Isl., BC Cascade Mountains, WA Cascade Mountains, OR Coast Range, OR Klamath Mountains, OR Queen Charlotte Isl., BC Olympic Mountains, WA Cascade Mountains, WA Cascade Mountains, OR Coast Range, OR Klamath Mountains, OR 179 __ ~N=4 N = 4 N = 1 j ~ ~I . . . N = 3 N = 2 . . · . . - ' 1 ' , ~I I I I 0 1,000 2,000 3,000 Percent Increase in Landslides Due to Clear-Cutting N = 2 N = ~ I I I I 1 1 1 1 1 1, I I 1 1, I I 1 1 l 0 5,000 10,000 15,000 20,000 N = 4 N = 4 N = 3 N= 1 Percent Increase in landslides Due to Roads Pl(JU~ 7-Z increased frequencies of landslides caused by clear-cutting and roads in Pacific Northwest. Each bar is mean of results of existing studies of erosion rates on forested watersheds. Source: variety of sources summarized by Pentec Environmental, Inc. 1991, for Washington Department of Natural Resources. Bjornn and Reiser (1991) summarized studies of spawning requirements of Pa- cific salmon and noted that the area used by each spawning pair ranged from less than 1 m2 for pink salmon to 20 m2 for chinook salmon. They concluded that substrate-particle size composition does not constitute a comprehensive measure of the suitability of stream gravel for spawning; water depth, velocity, and prox- imity to cover were also important in determining suitability. Citing unpublished data of R. A. House (Bureau of Land Management), Bjornn and Reiser (1991)
180 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST reported that although gravel made up about 25% of the total substrate of an Oregon stream, only about 30% of the gravel-i.e., 8% of the total area was suitable for spawning by coho salmon. It appears unnecessary for all stream gravels to be relatively free of fine sediment for successful spawning to occur. Furthermore, salmon have the ability to purge spawning areas of fine sediments during the spawning act itself (Everest et al. 19871. Thus, the proportions of fine sediment needed to decrease salmon production in streams are not known with certainty. Most research has been limited to the effects of fine sediment on reproductive success, with the result that the effects of sedimentation on other aspects of stream habitat and the food web of streams are poorly known. STREAMBANK EROSION Erosion of streambanks can affect fish habitat by introducing new sediment into the stream, by eliminating undercut streambanks and other types of cover along the margin of the channel, and by altering the width and depth of the channel. Localized streambank erosion is a natural consequence of channel meandering for most streams and rivers (Dunne and Leopold 1978), but damage caused by excessive erosion of streambanks and riparian zones can affect virtu- ally all physical and biological processes in streams (Platte 19911. The frequency and extent of streambank erosion in a watershed can be exac- erbated by several types of anthropogenic perturbation. Among the most com- mon are disturbances to streambanks resulting from livestock grazing and water- ing. Livestock grazing in semiarid regions of eastern Oregon, Washington, and Idaho continues to be very destructive to riparian vegetation in streams that support salmon populations (Beschta et al. 1991, Kauffman et al. 1993~. The area affected by grazing can be considerable. Federal and nonfederal range land accounts for about one-third of the total land area of the Pacific Northwest (Table 7-41. A 1984 U.S. Department of Agriculture report of stream and riparian conditions in southeastern Washington (cited by Palmisano et al. 1993) indicated that about 1,100 km of the 1O,600 km of streams on nonforested range land was severely eroded because of grazing. Platts (1991) compared the results of 21 studies of the effects of livestock grazing on riparian zones and fish populations in western North America and found that 20 documented substantial damage to rip arian vegetation and 18 found substantial decreases in fish populations. Resis- tance of streams to damage from large storms was also seriously impaired where grazing had reduced or eliminated vegetation along streambanks. Although dam- age to riparian zones and streambanks has diminished with improvements in grazing practices in recent years (Platte 1991), many streams in range land still contain severely degraded habitat. In forested areas, damage to streambanks can be caused by the removal of streamside vegetation. The root systems of forest vegetation are important for providing long-term bank stability and resisting the erosive effects of high flows
HABITAT LOSS Western Washington Cascades Lower Columbia Basin Middle Columbia Basin Coastal Oregon 181 - ~r 1 ' 1 1 1 1 -100 -75 -50 -25 0 25 Percent Change in Pools from 1935-1945 to 1987-1992 FIGURE 7-3 Changes in occurrence of large, deep pools in 3rd- to Sth-order streams in selected river basins in Pacific Northwest. Sample size refers to the number of river basins surveyed. Source: Data of Sedell and Everest 1991, and FEMAT 1993. (Sedell and Beschta 1991~. Hence, the logging of riparian trees particularly those close enough to the channel, where their roots help to reinforce and bind streambank sediments can initiate widening of stream channels and concurrent loss of undercut banks. Damage to streambanks can also result from urban development and recre- ational activities adjacent to streams. Clark and Gibbons (1991) listed types of recreational activities that potentially affect riparian vegetation and streambanks. They included hiking, horseback riding, use of on- and off-road vehicles, camp- ing, fishing, boating, water sports (swimming and use of temporary dams), re- moval of debris, bathing, and dish-washing. In heavily used recreational areas, damage to streambanks and riparian zones can be severe. STREAMBANK ARMORING AND CHANNELIZATION Just as streambank erosion can alter fish habitat, prevention of all lateral channel movement can change the pattern of responses to natural disturbances in streams. To prevent bank erosion and lateral channel adjustments, streambanks are often armored with erosion-resistant materials such as rocks, concrete, or logs to protect property or bridges from damage during high flows. Streams and rivers with armored banks commonly appear as straightened channels with few breaks in the current, particularly along the margins. The energy of the flow in channelized streams is focused along the thalweg (the deepest part of a chan- nel), where high rates of downcutting can occur. Channelized streams typically have little physical complexity, because large roughness elements (e.g., woody
82 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST TABLE 7-4 Area and Percentages of Oregon, Washington, and Idaho in Different Land Uses Oregon WashingtonIdahoTotal k~m2 ~0 km2 % km2 % km2 % Federal lands Commercial forests 559 22.3 211 12.0 387 17.4 1,157 17.8 Other forestsa 198 7.9 172 9.8 291 13.1 661 10.2 Range land 532 21.2 68 3.9 635 28.5 1,234 19.0 National parks 7 0.3 73 4.1 4 0.2 84 1.3 Non-federal lands Crop land 176 7.0 314 17.8 264 11.8 754 11.6 Irrigated land 71 2.8 66 3.7 142 6.4 278 4.3 Commercial forests 480 19.1 511 29.0 165 7.4 1,156 17.8 Pasture 77 3.1 58 3.3 55 2.5 190 2.9 Range land 370 14.8 226 12.8 267 12.0 863 13.3 Urban and industrial 38 1.5 63 3.6 19 0.9 121 1.9 Total 2,508 100.0 1,762 100.0 2,229 100.0 6,498 100.0 aAreas assigned to this category were estimated before designation of additional federal forest lands in late successional and old-growth reserves, spotted owl and murrelet conservation reserves, and npanan reserves in Apnl 1994 Record of Decision for Amendments ~o Forest: Service and Bureau of Land Management Planning Documents Within the Range of the Northern Spotted Owl; effect or new policy is to increase area of "Other forest" and decrease area of "Commercial forests" on federal lands in Oregon and Washington. Source: Modified from Pease 1993. debris) that obstruct the flow are typically transported downstream during peri- ods of high discharge. Some types of armoring materials can provide habitat for juvenile salmon. For example, rock riprap consisting of large boulders with many interstices is used for cover in both summer and winter by salmon and steelhead in middle Columbia River tributaries (Mullen et al. 19921. Where streambanks are armored with smooth, continuous structures, there are no hiding places for young fish, no eddies that serve as holding areas in swift currents, and few suitable rearing sites. INSTREAM MINING In the late 1800s, mining of gold and silver was a major industry in the Pacific Northwest. Placer deposits were heavily worked, thus stream and riparian alterations were not only locally devastating, but resulted in vast quantities of sediment being washed downstream. Johnson (1984) indicated that late 1800s gold mining activities in the Rogue River basin destroyed large areas of coho
HABITAT LOSS 183 habitat. Similarly, hydraulic mining along the Sacramento River had so damaged fish runs by 1866 that the region's first cannery, which had opened only two years previously, was shut down and moved to the Columbia River (see Chapter 39. Even today, evidence of channel alteration from early mining operation persists throughout streams and rivers of the Pacific Northwest. While instream mining operations generally cause significant modification to channel morphology, streambanks, bed material composition, water quality, and other habitat features, few studies have addressed their direct effects upon salmon. Although present-day mining impacts on fisheries are largely not known, they are probably relatively minor compared to historical turn-of-the-century impacts (Kaczynski and Palmisano 1993, Palmisano et al. 19931. Another form of instream mining that has become relatively common over the last half century is aggregate extraction for sand, gravel, and cobbles. Palmisano et al. (1993) indicated that mining of sand and gravel occurs along or in nearly every major salmon stream in Washington. The extraction of aggregate material from streams and rivers has local effects, such as altering bed elevations and channel morphology, that in turn affect other characteristics (e.g., spawning habitats, streambank morphology, channel patterns, riparian vegetation) and pro- cesses fe.g., bedload transport rates, connectivity of hyporheic and subsurface water zones). The persistent removal of aggregate material, particularly when rates of removal exceed rates of replenishment, can cumulatively result in major changes to a stream or river system (Collins and Dunne 19873. Stream protection regulations associated with the removal of aggregate ma- terial from channels of the Pacific Northwest were generally absent until recent decades, with the exception of U.S. Army Corps of Engineers Section 10 permits for work in navigable waters. In Oregon, there were no state stream protection regulations for gravel removal operations before 1965 (Kaczynski and Palmisano 1993~. While Oregon has issued over 4,000 permits for gravel removal since 1967, with a total permitted volume of over 800 million cubic yards, there has been essentially no environmental monitoring and assessment by state agencies of resulting environmental impacts (WRRI 1995 a, b); most regulatory efforts by the state have simply focused on managing on-site impacts. Furthermore, little research has been undertaken to evaluate the short- or long-term effects of aggre- gate removal upon either channel characteristics (Collins and Dunne 1987) or anadromous salmon (Kaczynski and Palmisano 1993, Palmisano et al. 19931. DIKING, DRAINING, AND FILLING Diking, draining, and filling primarily for urban and industrial develop- ment, agriculture, and creation of pasture land are most common in estuaries and tidal sloughs but also occur in wetlands and floodplains. Loss of estuarine and riverine wetland habitat can potentially affect all salmon. Those most likely to be affected are coho, which can use riverine wetlands and estuaries for over
184 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST wintering (Tschaplinski and Hartman 1983), and chum, chinook, and sea-run cutthroat trout, which rear in estuaries for extended periods (Simenstad et al. 1982, Trotter 1989, Healey 1991, Salo 1991~. Loss of estuarine habitat from draining and filling can result not only in loss of rearing area but in substantial alteration of the food base of estuarine commu- nities. Sherwood et al. (1990) estimated that 77% of the 10,500 ha of tidal swamps, 63% of the 6,500 ha of tidal marshes, and 7% of the 17,000 ha of tidal flats of the Columbia River estuary were diked or filled between 1870 and 1970. They suggested that those activities reduced production of emergent vegetation by about 80~o and benthic algal production by about 15%. Placement of struc- tures (rock jetties and pile dikes), in addition to diking or filling, to improve navigation had reduced the tidal prism (salt wedge) by about 15%, simplified the complex network of tidal channels, and focused the flow into navigation chan- nels. Such changes, with alterations in sediment and water transport characteris- tics resulting from upstream impoundments and water uses, have had a profound effect on benthic invertebrates that contribute substantially to the biological pro- ductivity of the Columbia River estuary for salmon (Simenstad et al. 1992~. Loss of estuarine habitat through filling has been proportionately greater in some rivers than in the Columbia River. Although highly variable (Table 7-5), losses of estuarine habitat have exceeded 90% of the historical area of some Puget Sound river systems (Simenstad et al. 19821. And reductions in estuarine tidal marshes by diking and filling have exceeded 50% of the historical area in seven of the 15 Oregon coastal estuaries examined by Boule and Bierly (19873. The greatest losses have occurred in areas that are heavily industrialized and urbanized, particularly in rivers with shipping ports at their mouths. Reductions have probably been less in coastal rivers without large cities and shipping ports (Palmisano et al. 1993~. Small streams in urban areas can also be altered by land-filling. Lucchetti and Fuerstenberg (1993) analyzed the drainage network of Thornton Creek, a third-order tributary to Seattle's Lake Washington, between 1893 and 1977. They found that Thornton Creek had lost all major wetlands and 60% of the open channel network, including all first-order tributaries, to urban development. The remaining stream system was constrained by loss of riparian vegetation, streambank armoring, and an extensive series of culverts and underground pipes. Although cutthroat trout continued to survive in Thornton Creek, the last adult coho salmon was reported in 1979, and none has appeared since then despite repeated fry plantings by school and volunteer groups. Conditions in this stream might be typical of small streams in heavily urbanized areas, where habitat loss has been extensive and permanent (Booth 19911. Conversion of riverine wetlands to agricultural fields and livestock pasture and navigation improvements along rivers have transformed river valleys from marshy, densely vegetated areas with highly complex river channels to simplified drainage systems most of whose flow is confined to the mainstem (Sedell and
HABITAT LOSS 185 Luchessa 19821. Overall wetland losses in some areas have been great; for example, only about 9% of the wetlands present before Euro-American coloniza- tion remain intact in California (Dahl 19905. Beechie et al. (1994) estimated that 54% of the riverine slough and wetland habitat available to coho salmon in Washington's Skagit River was lost from the floodplain because of diking, drain- ing, and filling for agriculture and creation of pasture. The total area of lost slough habitat was about twice the combined losses of tributary habitat due to water withdrawals, impassable culverts, and inundation by a major reservoir. Estimated annual losses of juvenile coho salmon caused by elimination of rearing habitat in Skagit River valley sloughs ranged from 220,000 to 560,000. FLOOD CONTROL Prevention of damage by flooding is usually achieved through the use of flood-control dams, dredging to increase channel capacity, and dikes and levees to prevent rivers from overtopping their banks and spilling out onto the flood- plain. Specific effects of dams are discussed in Chapter 9, but flood-control measures can have a serious effect on salmon habitat. Dikes along river channels impair connections between rivers and floodplains that supply large woody de TABLE 7-5 Changes in Areas of Selected Puget Sound Estuanes (Including Hood Canal) and Grays Harbor (a Coastal Washington Estuary) from 1 800s to 1970s Area (ha) Estuary PredevelopmentAmount in 1970sChange (%) Puget Sound Nooksack445460+3 Lummia58030-95 Samisha19040-79 Skagit1.6001,200-25 Stillaguamish300360+20 Snohomisha3,9001,00-74 Duwamisha2604-98 Puyallupa1,00050-95 Nisqually570410-28 Skokomish210140-33 Dungeness50500 Washington Coast Grays Harbora19,50013,600-30 aEstuaries with substantial industrial development. Source: Simenstad et al. 1982 as cited in Palmisano et al. 1993.
86 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST bris, fine organic matter, and dissolved nutrients to the drainage network (Pinay et al. 19901; these materials are important habitat elements, providing both refuge and major food sources for riverine and estuarine communities (Vannote et al. 1980). Juvenile salmon can spend large portions of their freshwater residence in floodplain environments (Levy and Northcote 1982; Brown and Hartman 1988), especially in winter. Survival and growth are often better in floodplain channels, oxbow lakes, and other river-adjacent waters than in mainstem systems (Peterson 19821. Isolation of rivers from floodplains can in some instances be extensive (Sedell and Froggatt 1984~. The Pacific Northwest River Basins Council (1972; as quoted in Kaczynski and Palmisano 1993) estimated that some 3,000 km of dikes, 5,000 km of bank protection, and 5,800 km of channel modifications (dredging) for flood control had been completed by the early 1970s, and the numbers are likely greater today. Sedell and Luchessa (1982) used maps and river-clearance records from the 1800s to document that coastal river valleys then were filled with mazes of floodplain sloughs, beaver ponds, marshes, and wet- lands. Flow was channeled into river mainstems away from floodplains to im- prove river navigation and for flood control. ALTERED STREAMFLOW Human activities can increase or decrease flows, cause streamflows to be- come more or less variable than the natural discharge regime, and alter the timing of seasonal runoff patterns. Changes in flow result from water impoundments, water withdrawals, enlargement or shrinkage of the effective drainage network (an example might be a watershed in which many roads effectively function as first-order channels), increasing the imperviousness of the soil surface, altering the rapidity of runoff, altering groundwater quantities or movements, altering the depth of coarse and fine sediment in the stream (which can affect the amount of surface discharge relative to subsurface flow), altering streamside and hillslope vegetation via forest-management practices (which can affect evapotranspiration, snow interception, and fog drip), and the conversion of forest land to other uses (such as agriculture and urbanization). Salmon are very sensitive to changes in streamflow and time their life-cycle movements according to local discharge regimes (Northcote 1978, Groot and Margolis 1991). Increases in peak discharges are often a concern when sensitive eggs and alevins are still in stream gravels because bedload movement can cause mortality (Everest et al. 1987, Chamberlin et al. 19911. Juvenile salmon might seek cover in interstices of stream gravels to avoid predators or when conditions for feeding become unfavorable in winter (Chapman and Bjornn 1969, Hillman et al. 19871. Recently emerged fry can occupy the interstices of 2- to 5-cm gravel, and year- ling and older salmon require particles larger than 7.5 cm (Bjornn and Reiser
HABITAT LOSS 187 19911. Mobilization of gravel and cobble substrates during peak discharges can kill salmon directly if they happen to be present. In small- to medium-sized channels, high flows can alter pool and riffle habitat and can flush sediment and organic matter from streams (Sullivan et al. 19871. Some flushing is beneficial in that it removes fine sediment from the streambed, but excessive flushing can remove much of a stream's organic matter and adversely affect secondary productivity (Sedell et al. 1978, Murphy and Meehan 19913. Frequent movement of large woody debris during periods of peak discharge can deposit logs on upper streambanks, where habitat benefits are minimized (Bisson et al. 19873. Many human activities contribute to increasing peak flows. For example, the seasonal removal of vegetation and litter cover from agricultural lands usually leaves them prone to surface runoff, which is generally more rapid than subsur- face flow. Similarly, soil compaction can increase the amounts of precipitation that enter streams through surface runoff. Although soil compaction can occur with almost any type of land use, effects are often most pronounced in urban and industrial settings, where extensive roads and paving can effectively double the frequency of hydrologic events that are capable of mobilizing stream substrates (Booth 1991 J. Logging affects surface and groundwater hydrology in complex ways (Chamberlin et al. 1991), and studies have indicated that the frequency and magnitude of stream discharge peaks are sometimes increased after harvesting (Beschta et al. 1995~. Forestry activities including road construction, timber falling and yarding, slash burning, and mechanical scarification-can all cause water to reach streams more rapidly (Herr et al. 1975, Harr and McCorison 19791. Internal changes in soil structure occur after logging as water is piped along channels of decaying tree roots and moves faster downslope (Hetherington 1988J. Logging roads and landings form relatively impermeable surfaces. Roadside ditches collect water from roads, and subsurface flow is intercepted by road cuts (Herr et al. 1975~. Forest canopies intercept snowfall, shade the snowpack on the ground, and decrease ground-level wind velocities. Clearcutting contributes to increased snow accumulation in logged areas because snow is no longer retained in forest canopy. In areas with snow-dominated hydrology (e.g., forested areas of Idaho, eastern Oregon, and Washington,, the timing and rate of snowmelt are generally advanced in clearcuts, and this effect persists for several decades. In- creased snowmelt peaks during warm rains are especially pronounced in the transient snow zone the zone of alternating rain and snowfall at intermediate elevations in coastal and western Cascade Range watersheds (Herr 19863. Rain- on-snow runoff exacerbated by logging can generate extremely high streamflow peaks and can contribute to extensive streambed scour and habitat alteration (Herr et al. 1989~. At the other extreme, changes in discharge regimes from a wide variety of land uses can result in unnaturally low streamflows. Water withdrawals for
88 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST irrigation, hydroelectric production, urban and industrial consumption, and other uses can shrink stream channels and reduce or eliminate fish spawning and rear- ing habitat. Logging can have a variable effect on summertime flows (Hicks et al. 1991). Redd dewatering or reduced intragravel flows can also be caused by reduc- tions in discharge, which can lead to egg and alevin desiccation or to reductions in water exchange rates in the environment of the embryos. Salmon eggs can survive exposure to low flows, and even some periods of no surface-water flow, but survival rates depend on intragravel permeability, humidity, temperature, and dissolved oxygen (Bjornn and Reiser 19911. Redd dewatering can contribute to freezing conditions in the egg pocket during cold periods a further cause of death. Salmon often select spawning sites in areas of subgravel water upwelling, which helps to buffer the risk of dewatering or freezing and ensure adequate water movement past embryos. However, if no upwelling areas exist naturally or if human activities have eliminated them, flow reductions can reduce reproduc- tive success. Effects of reduced discharge on streams' capacity for rearing juvenile salmon are complex. Reduced flows can lower stream volume and lead to crowding, which might cause increased aggression, competition emigration, and predation (Chapman 1962, 1966~. Although the relationship between stream volume and salmon carrying capacity is often unclear, there is some evidence that densities of salmon can be influenced by the amount of water present in streams. Kraft (1972) diverted water from a Montana stream during summer to cause a 90~o reduction in discharge. Many brook trout moved from runs to pools; average numbers of trout in partially dewatered runs decreased by about 60%. Smoker (1955) found a positive correlation between the 1935-1954 commercial catch of coho salmon and summer streamflows two years previously (the time when juve- niles resided in streams). However, a significant positive correlation between summer flows and coastal Oregon coho was not detected by Scarnecchia (1981~. In most instances, the potential effects of flow reductions on rearing salmon will be mediated by the amount of pool habitat and by biological factors, such as food availability, population levels, competitors, and predators. Altering the flow regime of a stream can interfere with the upstream migra- tion of adult salmon. Salmon runs are often timed to take advantage of particular streamflows in smoothing fish passage and avoiding predators (Northcote 1978~. Upstream migration can occur on both rising and falling portions of storm hydrographs (Shapovalov and Taft 1954), or it can be timed to coincide with low or high flows to surmount potential passage barriers. Flow alteration can inter- fere with environmental cues that trigger run timing for species that spawn in both large rivers, such as chinook (see Healey 1991), and small streams, such as coho (see Sandercock 19911. Salmon often congregate near stream mouths when spawning is near and are stimulated to migrate upstream by their reproductive condition, changes in water discharge, and appropriate stream temperatures. In
HABITAT LOSS 189 species that enter freshwater shortly before spawning, such as chum salmon (Salo 1991), long periods of unfavorable flow can reduce reproductive success. Murphy (1985) and Heard (1991) documented large mortality in pink and chum salmon caused by a combination of anoxia and low flow in intertidal reaches of south- eastern Alaska streams. It is not known whether these die-offs were related to flow changes caused by human disturbance. ALTERED GROUNDWATER The role of groundwater in maintaining the productivity of stream ecosys- tems has only recently become appreciated; for a particularly thoughtful review, see Stanford and Ward (19921. Interactions between terrestrial and aquatic eco- systems are often strongly influenced by subsurface water movement and bio- genic nutrient transformations (Gilbert et al. 19901. Rivers and their valleys are linked by exchanges of water between phreatic (true groundwater) and hyporheic (river-influenced groundwater) zones, and these linkages influence nearly all aspects of the physical and chemical habitat of aquatic organisms (Ward and Stanford 19895. Particularly important are nutrient transformations that occur in hyporheic and phreatic zones; these transformations ultimately regulate nutrient availability to primary producers in streams and rivers. Interchanges between surface water and groundwaters are critical to maintaining productivity in both large and small lotic systems and can be strongly disrupted by human activities that remove groundwater or inhibit the movement of water into or out of rivers and floodplains. The specific effects on salmon of groundwater alteration by anthropogenic perturbations are poorly known. Sites of groundwater upwelling in streams are preferred spawning areas for chum salmon (Lister et al. 1980) and can become less suitable if upwelling characteristics are changed. In the Olympic Peninsula, spring-fed streams originating as groundwater seeps at the base of hillslopes serve as important overwintering areas for coho salmon (Peterson and Reid 1984, Cederholm et al.19889. Roads crossing hillsides often cut into soils and intercept subsurface water, transporting it quickly downslope in ditches (Ziemer 1981', and might prevent it from draining to springs and streams along the valley floor. Warming of groundwater after logging in the Carnation Creek watershed raised late-winter stream temperatures (Hetherington 1988) and accelerated egg devel- opment; this caused early emergence of coho salmon fry and losses due to exces- sive downstream movement in years with frequent early-spring freshets (Holtby 19881. Loss of riparian vegetation and associated channel changes in arid regions through livestock grazing lower the zone of water-saturated soil and reduce sub- surface storage of water; these effects can allow small streams to run dry in summer (Elmore 19921. Other than those few case-study reports, little is known about how altered groundwater affects salmon. It is likely, however, that some of the greatest impacts of alterations in groundwater on salmon habitat result from
90 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST changes in nutrient dynamics and consequent loss of aquatic productivity (Triska et al. 1989, Stanford and Ward 1992) and are expressed as reductions in growth rates and species diversity in streams and rivers. ALTERED RIPARIAN VEGETATION Removal of vegetation along streambanks and floodplains can be caused by a variety of human activities. Like several other types of habitat alteration, loss of streamside vegetation can affect salmon in a variety of ways. Riparian vegeta- tion mediates key interactions between aquatic and terrestrial ecosystems and in many respects controls the productivity of streams by influencing water, sedi- ment, and nutrient dynamics; shading; inputs of fine particulate organic matter and woody debris; and the stability of streambanks and floodplain terraces (Beschta 1991, Gregory et al. 1991~. The direct influence of riparian vegetation on streams declines with increas- ing distance from the channel and with the height of the dominant tree species. Ecological functions provided by riparian vegetation are achieved at different distances, depending on the type of function and the width of riparian vegetation needed for the function to take place naturally. The height of dominant trees influences the potential distance over which riparian vegetation directly affects stream channels, e.g., tall trees potentially contribute shade, particulate organic matter, and large woody debris at greater distances from streams than do short trees. Areas capable of producing large, tall trees thus possess wider functional riparian zones than areas in which trees do not grow as large. For this reason, FEMAT (1993) used the height of dominant late-successional tree species that would naturally grow in a particular rip arian zone as the basis for recommending streamside buffers needed to safeguard ecological functions instead of suggesting a fixed linear distance from the streambank to the outer margin of the buffer strip that would not allow for differences in potential tree growth between regions. According to FEMAT (1993) estimates, the width of vegetated buffers needed to achieve greater than 90% effectiveness for different ecological functions ranges from as low as 0.5 tree heights for protection of streambank root strength to about three tree heights for some microclimate characteristics (Table 7-6~. In coastal regions of the Pacific Northwest, late-successional trees in riparian zones typi- cally reach 70 m or more in height; therefore, protection of the full range of ecological functions and characteristics provided by riparian vegetation might require intact buffers of natural vegetation in excess of 70 m. The buffer widths summarized in Table 7-6 are applicable to protecting ecological functions whether streams contain fish or not. However, many current land-use regulations maintain a higher level of riparian protection based on the presence of fish at a particular site or on whether there are important fish re- sources or public water supplies downstream. In areas next to streams, termed streamside management zones, some level of activity, such as logging or grazing,
HABITAT LOSS 191 is permitted as long as minimum requirements for environmental protection are met. These requirements are often related to shading and streambank integrity (Bisson et al. 1992) but do relatively little to safeguard other processes. The width of streamside management zones required by state land-use laws is much less than the width of natural vegetation needed to provide full ecological protec- tion. For example, the forest-practice regulations of California, Oregon, and Washington (Table 7-7) require narrower buffers next to streams than would be needed to fulfill the buffer requirements of Table 7-6 for aquatic and microcli- mate functions. Although streams on federally owned lands are protected by federal standards and guides for forestry practices, the level of protection given to non-fish-bearing permanent and intermittently flowing headwater streams is usu- ally less than that afforded fish-bearing streams. Protection of forested riparian zones on federal lands is generally greater than on state-owned and privately owned lands (Robinson 1987, FEMAT 19931. Thus, there are two sets of double standards for protection of riparian forests: one set for fish-bearing and non-fish- bearing streams and the other set for federal lands and state or private lands.There is a third set of double standards: Riparian protection requirements on federally owned, state-owned, and privately owned commercial forests, taken in the aggre- gate, are far more restrictive than requirements along streams where agricultural and urban or industrial land uses are dominant. In California, Oregon, and Washington, state environmental regulations concerning forestry practices have been in place since the early 1970s, but until recently none of those states has enacted an agricultural-practices act explicitly protecting riparian vegetation. Rather, agricultural activities are limited by the water-quality requirements of the Clean Water Act, state water-quality standards, and voluntary compliance with best management practices. Although forestry-practice regulations deal, how- ever incompletely, with riparian-zone protection, agricultural-practice regula- tions tend to emphasize meeting water-quality thresholds for drinking water and protection of aquatic biota but do not address riparian protection. Urban and industrial wastewater discharges are also regulated according to water-quality requirements, and protection of riparian zones in urban areas is often left up to local ordinances. Much of the historically most productive salmon habitat exists in lower river valleys and coastal lowlands where riparian zones are given the least protection (Sedell et al. 19901. ALTERED THERMAL REGIME The amount of thermally altered habitat in Pacific Northwest streams and rivers is not known, but it is probably proportional to the extent of water im- poundments, riparian canopy alteration, heated discharges, and channel changes, such as widening and shallowing. In small streams, temperatures potentially lethal to salmon were measured after logging and burning in an Oregon coastal watershed during the 1960s (Hall and Lantz 19691. In the Salmon Creek drainage
92 UPSTREAM: SALMON AND SOCIETY lN THE PACIFIC NORTHWEST TABLE 7-6 Estimated Widths of Riparian Forests Needed To Achieve > 90% of Full Function Provided by Streamside Vegetation to Stream Ecosystems in Forested Watersheds of Pacific Northwest. Ecological Characteristic Distance from Channel (in late-successional dominant tree heightsa) Needed to Achieve > 90% Effectiveness Functions directly affecting stream ecosystems Contribution of leaf litter and other material Shading Contribution of large woody debris Intact root systems along streambanks Protection of microclimate Soil moisture Radiation Soil temperature Air temperature Wind speed Relative humidity 0.7 1.0 1.0 0.5 0.5 1.0 1.5 2.0 3.0 3.0 a About 70 m for late-successional coniferous forests in coastal regions. Source: FEMAT 1993. of the Oregon Cascades, summertime stream temperatures at the mouth of the basin underwent a long-term increase during a period of increased harvest activ- ity (Beschta and Taylor 19883. The FEMAT report (1993) presented current and historical summer temperatures in 46 forested watersheds in western Oregon and Washington. Maximum temperatures in recent years had risen more than 2°C above historical maximums in 85% of the watersheds, and modal summer tem- peratures were beyond the range of historical conditions in 54%. Maximum temperatures exceeded 20°C (potentially stressful for salmon) in 70% of the streams and 25°C (potentially lethal) in 20%. It is likely that river basins in the Pacific Northwest are now thermally altered on a scale that under natural condi- tions would exist only in the presence of an exceptionally large climate change. Effects of temperature changes on salmon and their habitat are summarized in several reviews (Beschta et al. 1987, Bjornn and Reiser 1991, Hicks et al. 1991~. Thermal alterations potentially affect the survival and growth of virtually every stage of the freshwater life cycle. Clear patterns have yet to be established, but increased temperatures at northern latitudes along the West Coast have tended to benefit salmon production in small, naturally cold streams by increasing avail- able food resources (e.g., Holtby 1988), whereas salmon productivity at southern latitudes usually declines when temperatures extend into thermally stressful
HABITAT LOSS TABLE 7-7 Current Requirements for Riparian Protection on State-Owned and Privately Owned Forests in California, Oregon, and Washington 193 Stream Classification Minimum Riparian Protection Zone Width Each Side `~f Stream (m) Californian Class I (fish-bearing) Class II (non-fish-bearing) Classes III & IV (no aquatic life) OregonC Type F (fish use or fish and domestic use together Type D (domestic use only) Type N (no fish or domestic use) Washingtonf Types I-III (fish-bearing) Type IV (non-fish-bearing) Type V (intermittent or ephemeral) 23-46b 15 30b None 15 30d 6-2ld o-2le 7-30g Noneh None amp to 50% of overstory and 50% of understory may be removed; exceptions for greater removal are given. bDetermined by slope steepness. CThe Oregon Rules permit timber harvest within npanan management zones as long as conifer basal requirements are met. dDifferent ripanan management area widths are specified for small, medium, and large Type F and Type D streams. eFor some small Type N streams, understory vegetation and nonmerchantable conifers must be left within 3 m of the stream. fWidths of npar~an zones along Washington's streams are determined by process called watershed analysis; some timber harvest is allowed within r~par~an management areas. "Designed to recruit, on average, 70% of historical levels of large woody debris. hVegetative buffers may be required along lower reaches of Type IV waters for temperature protection and to buffer streams from applications of forest fertilizers. Source: FEMAT 1993. ranges (e.g., Burns 19711. Unless food is extremely plentiful (a situation that rarely occurs in nutrient-poor coastal river systems', higher temperatures de- crease lower salmon growth efficiencies (Brett et al. 1969, Bisson and Davis 1976, Wurtsbaugh and Davis 1977), which must be offset by increased food production for temperature increases to be beneficial. Increased temperatures can influence the migratory behavior of spawning adults. Bjornn and Reiser (1991) cited several studies that show delays in the upstream movement of sockeye, chinook, and steelhead adults because natal streams became too warm. Berman and Quinn (1991) found that adult chinook salmon behaviorally regulated their body temperature by pausing in areas of cool
94 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST water during upstream migrations; they concluded that reduced availability of cool areas could potentially reduce spawning success. Altered thermal regimes might have an even greater effect on the production of salmon through effects on interspecific interactions between salmon and non- salmon fishes, principally competition and predation. Reeves et al. (1987) dem- onstrated that juvenile steelhead in laboratory streams were aggressively dis- placed from preferred foraging sites by juvenile redside shiners, a species of minnow, when experimentally increased temperatures became physiologically less favorable for steelhead. In a forested river system in southern Oregon, they found that the outcome of steelhead-redside shiner competition followed a ther- mal gradient in which stream warming resulted in the retreat of steelhead to higher-elevation, cooler tributaries. Many river systems in the Pacific Northwest contain a variety of introduced species that originated in warmer waters in eastern North America (Li et al. 1987), which were planted to provide a greater diversity of recreational angling opportunities. Their effects on native salmon populations are often poorly under- stood, but many species are known to prey on young salmon or compete with them for food or rearing sites at some stage in their life history. Temperature increases whether caused by riparian canopy removal, water impoundment, agricultural and urban runoff, or heated industrial discharges-create conditions favorable to many warm-water game species and might enable them to gain a competitive advantage or facilitate their predation on juvenile salmon. Altered thermal regimes can change other characteristics of habitat in streams, rivers, and estuaries by altering the structure of plant and invertebrate communities (Bisson and Davis 1976~. Aquatic plants and macroinvertebrates have specific temperature preferences. Changes in thermal regime can alter species composition in ways that might or might not be favorable to salmon production. DECREASED LARGE WOODY DEBRIS Perhaps no other structural component of the environment is as important to salmon habitat as is large woody debris, particularly in coastal watersheds. Nu- merous reviews of the biological role of large woody debris in streams in the Pacific Northwest (e.g., Harmon et al. 1986, Bisson et al. 1987, Gregory et al. l991J have concluded that woody debris plays a key role in physical habitat formation, in sediment and organic-matter storage, and in maintaining a high degree of spatial heterogeneity ("habitat complexity") in stream channels. Loss of large woody debris from streams usually diminishes habitat quality and re- duces carrying capacity for rearing salmon during all or part of the year (Hicks et al. 1991~. As with temperature, the exact manifestation of the effects of woody- debris loss on salmon is often difficult to predict. Two general trends with respect to loss of woody debris are clear. First, the
HABITAT LOSS 195 distribution and abundance of large woody debris have been extensively altered in most river systems. Headwater streams have lost woody debris through sev- eral processes, most related to logging activity. Years of splash damming, a method of floating logs from upland logging sites to downstream mills, have scoured channels and removed much of the instream woody debris that was present. Sedell and Luchessa (1982) found that some coastal river systems in Oregon and Washington contained hundreds of active splash dams from the early to middle 1900s. In some areas without splash dams, increased frequency of landslides caused large debris torrents (Figure 7-2), scoured stream channels, and created conditions similar to those resulting from splash dams and log drives. When it became apparent that accelerated hillslope erosion had caused numerous debris torrents culminating in large, impassable logjams, fishery management agencies in the middle 1900s undertook aggressive programs of debris removal to facilitate adult salmon spawning migrations. In addition to removing the log- jams, stream-cleaning crews often removed large woody debris after logging even when there was little evidence that the debris actually constituted a migra- tion barrier (Narver 1971 J. Harvest of timber from riparian zones in coastal and western Cascade water- sheds created ideal conditions for early-successional tree species, such as red alder, which replaced late-successional conifers as the dominant form of riparian vegetation over large areas (Kauffman 1988~. Recruitment of new debris to streams from alder-dominated riparian zones was more rapid than from conifer- dominated stands, but the hardwood debris was smaller, was more prone to breakage, and decomposed faster than conifer debris (Bilby 1988), so streams in second-growth forests became progressively debris-impoverished after removal of the old-growth stand (Grette 1985, Veldhuisen 19901. Rotational harvest ages of forests on many industrial forest lands (40-60 years) have been short enough to preclude re-establishment of dominant conifers in rip arian zones (Andrus et al. 19883. The combined effects of those anthropogenic perturbations have led to a large-scale reduction in the quantity and quality of large woody debris in many forested headwater tributaries and to a substantial decline in woody debris floated downstream to lowland streams (Sedell et al. 1988~. Mainstem rivers and estuaries historically also contained great amounts of large woody debris (Gonor et al. 1988J. Some of the debris was produced in uplands and fluvially transported to depositional sites along rivers and their flood- plains, but woody debris was also recruited from riparian zones adjacent to rivers and estuaries and entered channels through natural processes of floods, wind- storms, fires, and beaver activity. Often, the lower reaches of rivers contained massive accumulations of debris that formed huge drift dams. Much of the wood in Pacific Northwest river systems was removed for navigational improvements and flood control in the late 1800s and early 1900s; for example, 368 km of the Sacramento River, 88 km of the Willamette River, and 24 km of the Chehalis River (Washington) were cleaned for river navigation from 1867 to 1912 (Sedell
96 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST et al., 19901. Rivers and estuaries containing large volumes of woody debris were characterized by spatially complex and diverse channel systems and highly productive salmon habitat, but many of these areas were lost in the early twenti- eth century. The second trend related to alteration of large woody debris abundance has been simplification of stream channels and loss of pool habitat (Figure 7-3~. Simplification occurs when loss of small-scale spatial heterogeneity leads to channel conditions characterized by uniform substrate, depth, and velocity; loss of sediment and organic-matter retention capacity; elimination of backwaters, eddies, and side channels; and loss of instream cover. In other areas of North America where habitat simplification has taken place, streams support fewer species and are less resistant to community disruption from natural disturbances (Kerr et al. 1985, Schlosser 19911. Pacific Northwest streams have fewer species than most other regions (Moyle and Herbold 1987) but have a great diversity of locally adapted populations. Streams with simplified channels usually contain fewer species than streams with structurally complex channels (Bisson et al. 1992), or they might be suitable for one age group but not multiple age groups- an important factor for salmon rearing two years or more in streams. Reeves et al. (1993) demonstrated that Oregon coastal watersheds with histories of forest management had lower salmon diversity than unmanaged watersheds. Typically, simplified channels with scarce woody debris support abundant populations of underyearling salmon but contain few yearling and older fish (Bisson and Sedell 1984, Hartman and Scrivener 1990, Reeves et al.1993~. Reduction in numbers of older salmon in simplified streams is often related to loss of pool habitat and winter cover resulting from elimination of large woody debris (Bisson et al. 1987~. Of the 43 intermediate-size tributaries with histories of forest manage- ment examined in the FEMAT report (1993) for western Oregon and Washing- ton, two-thirds had modal pool frequencies below the range of frequencies be- lieved to have existed historically (generally 25-60%~. In about half the watersheds, pools comprised less than 20% of channel areas. MIGRATION BARRIERS Dams are an important class of migration barriers and are discussed in Chap- ter 9. Many smaller barriers to migration are probably unknown. Nehlsen et al. (1991) noted that a substantial fraction of 106 stock extinctions might have resulted from migration blockages. They quoted from a story told by a Twana Indian who was born about 1865 but referred to the extinction of a sockeye run in southern Puget Sound in 1852: There were some sockeye in Mason Lake, south of Hood Canal Puget Sound area. These ran up Sherwood Creek from Allyn on Case Inlet. They'd hang around the lake till ripe, then run up the creeks from there. The Squaxon got them with a weir in Sherwood Creek. Finally a pioneer named Sherwood built
HABITAT LOSS a little dam in the creek and stopped the fish, and they named the creek after him. 197 Many small populations might have been extirpated by similar activities in the 1800s and early 1900s. Although historical records are infrequent and usually rely on anecdotal information from people with little ability to identify salmon species, small dams probably contributed to the extinction of many local breed- ing populations, as in the case of Atlantic salmon in eastern North America. Likewise, landslides that blocked migratory routes eliminated some runs before the middle 1900s, but records were often poorly kept or lost. In many instances, nonnative stocks of salmon have been introduced into formerly blocked river systems (Johnson et al. 1991~. Rearing habitat of juvenile salmon can also be lost to blockages. Some of the most productive rearing sites in streams are located in backwaters along the edge of the channel and in side-channel areas (Sedell et al. 1984, Sedell and Beschta 19913. Highways built next to streams and rivers often disrupt access to these off-channel sites by physically isolating them from the main channel or by in- cluding culverts that are impassable for juvenile salmon. Culverts that are de- signed to pass adult salmon might create speeds that exceed the sustained swim- ming abilities of juveniles. Furniss et al. (1991) give the sustained swimming speeds of juveniles of several salmon species; they range from about 20 cm/s for juvenile coho 5 cm long to 70 crn/s for juvenile sockeye 13 cm long. Water speeds in many culverts are too great to allow juvenile passage at any time except during periods of low streamflow; in others the outfall of the culvert might be suspended too high above the water for juveniles to enter. Unscreened water diversions constitute a potential migration blockage if downstream-migrating juvenile salmon are entrained in diverted water. Nichols (1990) identified over 3,000 unscreened water diversions in Oregon, including 1,300 on coastal rivers, that potentially affected salmon-rearing streams. In addition to blocking migrations, water withdrawals potentially influence avail- able rearing habitat. Kaczynski and Palmisano (1993) reported that about 60~o of the water diversions in Oregon were for irrigation and 20% for urban uses. Palmisano et al. (1993), citing several studies by the National Marine Fisheries Service, stated that about 70% of Washington's water diversions lacked proper screening in the late 1970s and that 30% continued to be improperly screened or designed even after efforts to improve screening. WATER POLLUTION Before enactment of the federal Water Pollution Control Amendments to the Clean Water Act in the 1970s, fish kills in the United States occurred with some regularity. Dissolved-oxygen concentrations in Oregon's Willamette River in the 1940s and 1950s often dropped to anaerobic levels because of sewage and
l9S UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST industrial discharges, creating an uninhabitable zone along a substantial reach of the river until nutrient discharges were controlled (Warren 19713. Anaerobic conditions often occurred in upper Grays Harbor, the estuary of Washington's Chehalis River system, during the 1920s and 1930s in response to effluents from two sulfite pulp mills, three municipal sewage-treatment plants, and agricultural runoff (Eriksen and Townsend 19401. One pulp mill, built in 1928 near the mouth of the Hoquiam River in Grays Harbor, exerted a biochemical oxygen demand of 115,000 kg/d, a load equivalent to the raw sewage produced by 1.4 million people (Seller 1989~. Water quality was degraded during low river dis- charges from May to October in Grays Harbor and was severely damaging to chinook, coho, and steelhead; but it apparently did not substantially affect chum salmon, which emigrated earlier than the other species and did not rear in the upper estuary. Pollution-abatement efforts have reduced sewage and industrial discharges over the last two decades and the upper estuary is no longer anaerobic in summer, but experimental releases of smells from hatcheries upstream have shown that a pollution block still exists in Grays Harbor and that exposure of smolts to water of poor quality has reduced seawater adaptation, increased infes- tation by a trematode parasite, lowered disease immunity, and possibly increased vulnerability to predation by birds and squawfish. Smolts in the Chehalis River system survive at roughly half the rate of smelts from a nearby, relatively unpol- luted river (Seller 19891. The case study of Grays Harbor has been well docu- mented and might be representative of the effects of water-quality degradation on salmon in lower rivers and estuaries with heavy urban and industrial develop- ment. Although the concentration of pollutants in wastewaters is now regulated more strictly than before, the volume of pollutants in water could be equal to or greater than volumes existing before water-quality laws were enacted. Servisi (1989) estimated that the volume of wastewater discharged into the Fraser River had tripled since 1965. Mining is another source of water pollution in Pacific Northwest rivers. Nelson et al. (1991), citing a study by the Environmental Protection Agency, reported that in 1961-1975 at least 10 million fish were killed nationally by mining-related water pollution, although the number of salmon included was not given. Nelson et al. (1991) provided a thorough discussion of the different types of water pollution resulting from mining activity: in western North America, metals and radionuclides from mining wastes can be highly toxic to salmon; some highly toxic metals, such as copper and zinc, are also highly synergistic- their combined effects greatly increase lethality. Furthermore, metals can "bio- accumulate" in fish tissues, causing long-term stress and posing potential health threats to people consuming the fish. Sediment can be an important byproduct of mining activity. In an Idaho tributary of the Salmon River, Konopacky et al. (1985) found that dredging for rare earths generated 500,000 m3 of sediment, which smothered important downstream spawning and rearing areas of chinook salmon and steelhead. Spaulding and Ogden (1968) estimated that hydraulic
HABITAT LOSS 199 mining for gold in the Boise River, Idaho, generated 116.5 million kilograms of sediment in 18 months. LOSS OF REFUGES Because natural disturbances were an important part of the freshwater envi- ronment of Pacific salmon, many populations, particularly those at the edges of the range, underwent periodic expansion and contraction in response to local extinctions and periods of recolonization. That process fostered genetic diversity and versatility and enabled salmon to be resilient and locally variable (Scudder 1989~. Over the last century, many small populations have become extinct as a result of human activity (Nehlsen et al. 1991, Frissell 1993), and the geographical distribution of some species has become highly fragmented (The Wilderness Society 19931. Within the confines of a river basin, the ability of salmon to recolonize areas of local population loss, such as a third- to fourth-order tributary system, might depend on the presence of refugia (survival areas) containing high quality habitat and relatively stable populations (Sedell et al. 19901. At present, watersheds without substantial anthropogenic perturbations are limited almost solely to national parks and designated wilderness areas, and in the Pacific North- west states these are usually at elevations above the occurrence of anadromous salmon. High-quality habitat might exist in small patches within river basins that are subject to land and water management, but often habitat refugia widely dis- tributed throughout the system there are insufficient for colonization of nearby disturbed sites (Sedell et al. 19901. Concern for the continued viability of Pacific salmon on federally owned forest lands has led to the establishment of "key watersheds" in which high priority is given to protecting stream habitat (Figure 7-4) (Reeves and Sedell 1992, FEMAT 19933. Protection of habitat watersheds will be achieved by controlling erosion and by leaving large riparian buffers adjacent to both fish- bearing and non-fish-bearing streams. However, the distribution of key water- shed reserves is limited primarily to headwater drainages where national forests are located (FEMAT 19933; few are in lower river valleys and coastal lowlands. In the Pacific Northwest landscape, the latter kinds of environment lack refugia with high-quality habitat for salmon (Frissell 1993), and there seems to be little hope of future establishment of such areas without considerable public resolve and financial commitment. SUMMARY Habitat for salmon in Pacific Northwest river basins has been lost or exten- sively altered over the past 150 years. As a result of alteration and degradation of biophysical conditions, many salmon populations have been extirpated or de
200 Key Watersheds Tier ~ Tier 2 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST ? \ FIGURE 7-4 Key watersheds in the Pacific Northwest identified in the president's forest plan. The shaded area indicates the known range of the northern spotted owl (Strix occidentalis caurina). Source: FEMAT 1993.
HABITAT LOSS 201 pleted. Although the full extent of the modifications of salmon habitat will never be known, some generalizations are possible. As a result of human development, the current condition of most river basins in California, Idaho, Oregon, and Washington is significantly different from the conditions in which salmon evolved. Stream-habitat alterations and losses asso- ciated with many types of land uses have included increased sediment loading, higher and more variable water temperatures, reduced amounts of large woody debris, reduced and simplified riparian plant communities, new barriers to migra- tions, lower streamflows during some periods and higher peak flows at other times, loss of stream-bank integrity, simplified channel structure, and reduced small-scale habitat heterogeneity. These changes have generally reduced the productivity of river basins for salmon, although some changes have occasionally increased production. Anthropogenic habitat disturbances have often resulted in simultaneous changes in a wide variety of functions, processes, and habitat characteristics. It has usually been impossible to identify which habitat changes have had the greatest effect on salmon. Human-caused disturbances have interacted with natu- ral ones: for example, effects of widespread removal of riparian vegetation, loss of ground cover, or decreased stability of hillslopes have sometimes not been manifested until after a heavy rainfall or snowfall. The simultaneous alteration of many factors had important implications for habitat rehabilitation. First, it is important to avoid attempting only to improve individual aspects of habitat (e.g., pools in streams) without addressing other aspects that might be equally degraded and are critical to salmon production. It is not enough to improve a pool in a stream, for example, if the water is too warm to support salmon. In many cases, these single-factor approaches are not effective (NRC 1992a). Second, rehabili- tating watershed processes to the extent possible given human development, including the re-establishment of riparian functions such as providing shading, organic matter, and large woody debris-is probably more effective in improving salmon habitat over the long-term than substituting artificial structures for eco- logical functions. Habitat changes caused by human activities have occurred at far different spatial and temporal scales than natural disturbances in the Pacific Northwest. These differences between anthropogenic and natural disturbance patterns have interfered with the abilities of salmon to survive and recover from changes in their habitat. Anthropogenic perturbations have been significant causes of direct mortality for juvenile and adult salmon. Examples include excessive sediment inputs, scouring of reads, creation of migration blockages, high water tempera- tures, and toxic discharges. Catastrophic habitat loss can also occur as a result of natural disturbances, but the frequency and spatial scale of natural disturbances- unlike those of many human-caused disturbances are such that salmon's behav- ioral and physiological characteristics allow their populations to be resilient. Human activities have prevented natural disturbance regimes from creating
202 UPSTREAM: SALMON AND SOCIETYIN THE PACIFIC NORTHWEST or maintaining productive salmon habitat. In addition to imposing new distur- bance regimes, the land- and water-management actions of an increasing human population have systematically prevented natural disturbances from providing crucial raw materials for productive habitat. Examples include flood control and wildfire suppression, both of which have interfered with processes that provide woody debris and nutrients to river systems. In addition, stream processes have been altered to the extent that they cannot respond to natural disturbances in a normal manner. Rehabilitating ecologically productive watersheds will require allowing natural disturbances to occur to the greatest extent possible. Habitat alteration has changed the outcome of interactions between salmon and other species. Increased water temperatures, for example, have favored warm-water species at the expense of cold-water species such as salmon. In addition, many Pacific Northwest river basins contain nonnative fishes intro- duced from eastern North America and elsewhere, which are often better adapted to warm temperatures than salmon and which can prey on or outcompete young salmon. Some habitat alterations unfavorable for salmon have resulted from exotic animals or plants. Habitat protection-especially with respect to riparian zones has been very uneven across different types of land uses and ownerships. Overall, streams on public lands receive greater protection than those on private lands; those on forested lands often receive greater protection than those on agricultural and range lands; and streams and sloughs in urban and industrial areas have generally received the least protection. Water-quality requirements also differ according to the predominant use or according to various federal, state, and local discharge regulations. There often are large variations in the degree of protection afforded in different places within a river basin. Habitats on private and public lands are important to salmon, and rehabilitation programs that focus only on public lands will be less effective than those involving private lands as well (NRC 1995b). Therefore, cooperation between private and public landowners is important to protecting and rehabilitating habitat at a watershed scale. Development of coop- erative habitat-conservation agreements between public and private landowners and resource managers will help identify critical habitat areas in need of rehabili- tation while providing site-specific flexibility for landowners to provide different types of protection measures (see also Chapter 13 and NRC l995b). So much habitat has been lost or altered that relatively few areas of high- quality habitat remain, especially in large river valleys and in coastal lowlands- typically home to large numbers of people. Therefore, protecting and rehabilitat- ing enough habitat to provide refuges for salmon and sources for recolonization of other areas that might be improved in the future will entail operating in a context of human development in other words, ways must be developed for people and salmon to live together. Although many of the best remaining sites are in forested headwaters, nodes of good habitat are also needed in large river valleys and coastal lowlands. These sites can be identified and locally based
HABITAT LOSS 203 protection measures can be developed. In some cases, landowner incentives can be used as a financial carrot in place of the more traditional regulatory stick. An example of such a program is King County's Waterways 2000, an aquatic conser- vation program funded from county real-estate taxes. It provides with tax reduc- tions to landowners for dedicating part of their property to riparian protection, outright purchases of important greenways and conservation easements, and pub- lic education emphasizing good stewardship of the county's streams. The initial phase of the program has already helped to protect good habitats in six important salmon watersheds in this urban area, which includes Seattle (King County Sur- face Water Management Division 19959.