Salmon Versus Timber: Considering Reciprocal Service Flows in Harvest Management of Riparian Forests


Abstract

Growing empirical evidence suggest that spawning salmon populations provide measurable nutrient flows back to riparian forest systems, further complicating the dilemma of optimizing harvest management of both timber and fisheries in salmon-rearing watersheds.  Such a co-dependent relationship between these two high-value resources begs reconsideration of existing resource management strategies, where frequently timber production is prioritized.  Here, I review recent research on salmon benefits to forest growth, all of which focus on the Pacific Northwest region of North America and the endemic timber and salmon species.  Additionally, I consider the implications from this ecological co-dependency for existing timber harvest and conservation payment policies.  As an example, I apply them to the findings by Zorbrist and Lippke (2007) on Oregon and Washington riparian timber harvesting limits for fish protection, whose economic analysis predict that such restrictions decrease soil expectation value for small landowners.

Keywords: ecosystem services, salmon, marine-derived nutrients, forestry economics

Submitted as an economics course term paper on 2008/12/14.  This report has not been published in a peer-reviewed journal.

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Background

Two important natural resources in the Pacific Northwest region of North America (extending from northern California to southeast Alaska) are timber and salmon.  However, due to the natural, overlapping distribution of timber forests and Pacific salmon, management and harvesting of timber has historically come into conflict with the successful production of wild salmon stocks.

About seven species of Pacific salmon (Salmonidae: Oncorhynchus) rear in the coldwater rivers of the Pacific Northwest, and all are economically important as commercial and recreation fisheries.  All seven species include regional populations which are listed as threatened or endangered under the United States Endangered Species Act.  Having an anadromous life history, adult salmon return to the freshwater ecosystem after one to five years of maturation in the open ocean, the duration depending on the species.  Adults may swim up river over 200 kilometers upstream before creating a gravel nest (termed a “redd”), pairing off, spawning, and then death.  After hatching, juvenile salmon commence development in their birth streams, before moving down river to undergo physiologic changes to adapt to saltwater chemistry and then finally entering the marine ecosystem.

Juvenile salmon require several specifications in their stream habitat for optimal growth and development, many of which may be negatively impacted by timber harvesting activities in the riparian.  Salmon eggs laid in the interstitial spaces of the stream bed gravel must have access to oxygenated water flow, and high sediment loads caused by erosion and soil disturbance from logging can block this access and suffocate developing eggs and recently hatched fry (Cederholm and Reid 1987).  Eggs, fry, and juveniles also require cool temperatures for optimal physical development; streams in warmer climates normally cooled by riparian canopy shade can exceed this temperature range if the canopy has been thinned or fully harvested.  Natural timber falls from the riparian canopy also provide optimal stream habitat patterns.  Large woody debris (LWD) influence flow and stream bed morphology to form riffles and deep pools, with the former a preferred habitat for foraging juveniles, and the latter a preferred aggregating habitat for larger juveniles or returning adults; an overabundance or absence of LWD would have negative impacts to salmon stream habitat (Harford 2008).  Finally, the terrestrial ecosystem supported by riparian forests provide a constant flow of allochthonous nutrients that catalyze the processes of the immediate aquatic ecosystem, which either directly benefit salmon (juveniles feeding on terrestrial insects and organisms) or the lower trophic levels that support the salmon (algae and aquatic insects utilizing fallen leaves and other decomposing terrestrial plant matter) (Naiman, et al. 2002; Kiernan 2007).

Resource economics and management theory over the past decades have considered salmon as a non-timber use of forest stands and the dependence of salmon life history on standing timber.  Calish et al. (1978) considered the optimization of cutthroat trout production with timber production, postulating that given sufficient value of cutthroat trout (a species of Pacific salmon), timber rotations should be lengthened to take advantage of trout economic returns.  Numerous nonmarket valuation studies since then have estimated the worth of recreational salmon fishery in various regions of the Pacific Northwest (Olsen et al. 2001; and others); the value per area of salmon habitat (Knowler et al. 2003; and others); the willingness to pay for salmon habitat restoration or accept forgoing harvest (Kline et al. 2000a; Kline et al. 2000b; and others); and the passive and existence values of salmon populations (Loomis 1999; and others).

Qualitative reports on the regional economic benefits of salmon population restoration programs have been produced in the past two decades (Niemi, et al, 1999; CH2M Hill 2000; and others), and quantitative cost-benefit analysis of varying degrees of detail on salmon fisheries itself have also appeared (Schwindt 2000), though none extensively incorporate social opportunity costs in all economic sectors affected by salmon and timber industries.  Nonetheless, the relative importance of salmon to the economy and natural capital of the Pacific Northwest has been strongly promoted and eventually acknowledged through recent regional legislation, notably the “Fish and Forest Rules” of Washington state imposing timber harvest limits within riparian corridors, and similar laws in Oregon.

Benefits of Salmon Carcasses to the Riparian Aquatic Ecosystem

That riparian forests provide essential services and benefits for salmon life history has been widely accepted.  However, research in the past decade suggests that salmon also return benefits to the riparian ecosystem, both to the aquatic component and the terrestrial.   Wipfli, et al. (2003) and other authors have provided experimental evidence that young salmon grew significantly faster in length and mass with the seeding of adult salmon carcasses in the stream, where aquatic invertebrate densities were also significantly higher.  Higher prey item density and faster time to size are intuited as traits for greater survival and fitness for juvenile salmon.  Adult salmon, in essence, are perpetuating a positive feedback loop for their offspring, with each generation of returning adults laying the nutritional foundation for increased fitness of successive generations of juveniles.

Postulating that the nutrients released by adult carcasses can be traced in organisms that uptake them, subsequent research set out to seek evidence proving the causal relationships between carcasses and improved juvenile fitness and riparian ecosystem productivity.  Fortunately, a reliable tracer exists to determine whether stream ecosystem nutrients have originated from adult salmon carcasses.  While in the ocean, young salmon feed on plankton, fish, and other prey items to gain more than 95 percent of their adult mass, up to 10 to 40 kilograms, depending on the species (Groot and Margolis 1991).   As a result, a typical adult salmon is substantially comprised of marine-origin molecules, which can be distinguished from those of terrestrial and freshwater origin.  In particular, salmon are significantly comprised of 15N isotopes and “omega-3” polyunsaturated fatty acid chains, molecules which have been observed to naturally occur in higher abundance in marine ecosystems than in terrestrial ecosystems (Schindler, et al. 2003).   This phenomenon implies that a typical riparian ecosystem would have significantly lower ratios of 15N isotopes and omega-3 fatty acids, unless sufficiently seeded with biomass comprised of those marine-derived nutrients (MDN).  It is also thought that 15N in particular would be more influential and readily uptaken by a nitrogen-limited ecosystem, and there is acknowledgement that many coastal, riparian forest systems in the Pacific Northwest are nitrogen-limited (Naiman, et al. 2002).

Research attempting to link salmon carcass benefits to the inland ecosystems have relied on identifying proportionally higher ratios of MDN in the riparian food web.  Preliminary findings from recent research by Kiernan (2007) detected MDN at various trophic levels, including algae, aquatic insects, and juvenile salmon in experimental treatments with carcass seedings, with differences in MDN ratio, juvenile salmon fitness, and aquatic invertebrate species composition noted between treatments with and without carcasses.

Evidence that returning adult salmon provide nutrient benefits and increased fitness to successive generations of salmon has translated into a number of innovative carcass seeding projects in the Pacific Northwest, aimed to stimulate the health of salmon stocks.  A number of local watershed coalitions and citizens groups in Oregon and Washington organize “carcass throws” and “salmon tosses” where volunteers throw frozen hatchery carcasses from the beds of pickup trucks into the riparian zone (McOmie 2008).  Washington State’s Department of Fish and Wildlife has also organized annual distributions of over 10 tons salmon carcasses in tributary systems under restoration efforts (WDFW 2000).  Perhaps the most noteworthy are the U.S. Forest Service projects in Washington and Oregon where salmon carcasses are loaded onto helicopters and distributed in densities up to 4 tons per mile (AP 2005; U.S. Forest Service 2006).

Benefits of Salmon Carcasses to the Riparian Terrestrial Ecosystem

More directly relevant to the salmon versus timber debate, however, are research efforts focusing on the presence of MDN in the terrestrial component of riparian systems.  Several pathways have been observed for the movement of carcass MDN to the terrestrial ecosystem.  Schindler, et al. (2003) lists several physical actors that bring carcass matter directly onto stream banks and deeper into the riparian zone, including natural flooding and flow patterns, as salmon naturally spawn along very shallow streams and banks, and already readily strand or beach themselves as they die post-spawning.  More notable are the roles of terrestrial predators and scavengers, such as bears, wolves, and eagles, which readily congregate and depend on seasonal influxes of salmon as a food source.  These megafauna can rapidly and regularly relocate high numbers of fresh, partially-consumed carcasses some distances into the forest, where remains are further distributed and consumed by smaller predators.  This is a major nutrient dispersion function in wilderness where high densities of large carnivores still occur.

Work by Reimchen (2002) suggests a direct linkage between salmon spawning density and enrichment of 15N in the humus soil, terrestrial scavenging beetles, and shrubs in the riparian, as well as finding significantly higher values of 15N in Western hemlock (Pinaceae: Tsuga heterophylla) wood samples taken within 7 meters lateral to a salmon spawning stream than those farther, more than 34 meters away.  Bilby et al. (2003) described significantly higher values of 15N in salmonberry shrubs (Rosaceae: Rubus spectabilis) within 100m of a stream with historically dense salmon spawning (incidentally, a collaborated study between Weyerhaeuser and U.S. Forest Service).  Finally, work by Naiman and colleagues (notably, Helfield and Naiman 2001) detects elevated 15N in Sitka spruce (Pinaceae: Picea sitchensis) highest within 25 meters of a salmon spawning stream but up to 100 meters into the riparian zone.  Furthermore, mean annual basal area growth of Sitka spruce within 25 meters of a spawning stream were triple that of reference, non-spawning streams, although the data did not suggest a direct correlation between 15N and accelerated growth.  Finally, the detection of 15N in the growth rings of riparian trees has prompted investigations into whether tree rings can be used to estimate the relative abundance of spawning salmon over historic seasons, assuming that greater runs and densities of returning salmon would inject greater doses of MDN into the riparian each growing season, and in turn cause riparian forests to uptake greater ratios of 15N (Drake and Naiman 2007; Kiernan 2007).

To date, there is a strong body of evidence that enhanced productivity and juvenile salmon fitness is correlated with seeding by adult salmon carcasses, and growing support that MDN’s are significantly correlated with this benefit to the riparian ecosystem.  There is also support for significantly higher 15N presence in terrestrial vegetation adjacent to salmon spawning streams, inversely proportional to the distance away from the stream.  Relevant to the discussion at hand is whether MDN’s can be correlated with and determined as a casual factor for accelerated growth of economically important timber species such as Sitka spruce, but additional work is needed to support this hypothesis.

Implications of MDN Benefits for Forest Management Policies

Additional support is needed to directly correlate salmon-contributed MDN to enhanced riparian timber growth.  It may be that any significant influences of salmon MDN on riparian timber growth in the Pacific Northwest have been dampened due to historic depletions of both salmon and timber in more heavily harvested regions such as Washington and Oregon.  Still, it is clear that adult salmon returns have significant aggregate benefits to riparian forest ecosystems, and repeatedly demonstrated that marine-derived nitrogen is a prominent component of riparian vegetation and timber.

We can consider both the hypothetical impact of MDN on riparian timber growth and the known benefits of MDN to riparian forest health, and conceive several consequences for forest management policies:

  1. Infinitely extending timber rotations: Calish et al. (1978) considers the lengthening rotation time of timber given a sufficiently high value of salmon as a competing resource cohort, and infinitely delaying harvest if non-timber value is the sole management priority.  Given recent opinion on “stacking” or “bundling” of ecosystem services, the sum of ecosystem benefits that salmon populations return to the riparian forest system may justify non-timber uses as management priorities.  If holding timber stands preserve future runs of returning adult salmon, the injection of salmon MDN can enhance an aggregate of non-timber services, such as:
    • Improved ecosystem health and associated passive use value (aesthetics and cultural heritage, the latter particularly important for the Pacific Northwest region)
    • Improved ecosystem health and associated indirect use value (improved vegetative ecosystem health and associated water quality benefits)
    • Improved non-game wildlife health and associated direct use value (eco-tourism for charismatic predator species)
    • Improved game species health and associated direct use value (big game hunting)
    • Improved salmon population health and associated direct use value (recreational and commercial fishery stocks)
  2. Shortening timber rotations: If a timber company manages several tracts drained by several, separate tributary systems, it may have the luxury to tailor harvest rotations to logging and fallowing alternate tracts as single, total harvests.  If indeed salmon MDN can accelerate timber growth, it may be beneficial to initially completely delay harvesting on a tract to maximize the annual returns of salmon and in turn accelerate the production of timber.  Increased growth rate will normally shorten rotation, regardless of discount rate, and owners can turn a profit in a shorter time.  After harvest, the tract can be restored and planted for the next harvest, and it can even be stocked with salmon fry and seeded with imported adult carcasses, as management shifts to salmon production for this tract.  Meanwhile, another tract on an alternate timeline may be ready for its timber harvest. Rotations will need to be optimized between the timber species and salmon species life cycle.  Granted, this is the most fanciful of potential options:  While salmon do generally imprint on their natal stream, there is no guarantee that the juvenile cohorts, stocked or natural, will return to the very same drainage in expected densities.  Also, a variety of federal environmental impact laws today could prohibit this style of rotating harvest and direct exploitation of riparian habitat on salmon streams.
  3. Increase conservation payment credit value: A number of existing payments for ecosystems services (PES) programs incent landowners to preserve a riparian buffer zone where farming or logging is prohibited, in hopes that natural riparian vegetation would be allowed to function normally as wildlife and gamefish habitat and water quality filters.  As we realize the even greater importance of salmon as nutrient conveyors and critical fertilizers of coastal ecosystems, the ecosystem service value of salmon runs should be acknowledged and appropriately increased, in addition to their market, recreation, and cultural value.  An overall rise in salmon value should also proportionately increase the value of any conservation measures designed to restore and protect salmon stock, including conservation buffer programs.  In salmon-rearing streams, enrolled buffer zones should then be accordingly valuated at a higher compensation.
  4. Increasing carbon credit value: Related to conservation payment credits are carbon credits, specifically those harnessing reduced emissions from deforestation and forest degredation (REDD).  If salmon MDN’s enhance a forest stand’s rate of growth and accordingly its rate of annual carbon sequestration, there may be justification to rate salmon-populated timberland at a higher credit price than timberland without salmon.
  5. Increased political capital for salmon-timber management negotiations: Establishing the reciprocal, beneficial relationship between salmon and timber production should at the least provide resource managers and private owners with more information to make policy agreements and decisions.  There is some controversy over the efficiency of salmon restoration efforts in context of alternate funding and investment opportunities, and of the fisheries economy supported itself (Schwindt, et al. 2000; Wu, et al. 2003).  Realizing the additional benefits salmon populations have to other natural resource commodities, such as timber, will inform better funding decisions and management priorities.

Several caveats are common to the above considerations.  Market demand for timber may continue to outweigh the aggregate non-timber values of a riparian system, and careful quantification of social benefits of non-timber uses may not be available to use in an economic cost-benefit analysis.  Uncertainties in the non-forest life stages of Pacific salmon (predation, atmospheric and climate cycles in the open ocean) may affect the size and health of the returning adults, partially severing the linkage between forest management goals and salmon population health outcomes and nullifying returns from the investment decision of not harvesting timber.

Finally, any direct, positive benefits of MDN to timber health will be limited to the frequency and distance that salmon carcasses are distributed inward throughout the riparian zone.  Likewise, it is difficult to excise the negative effects of timber harvesting from salmon production activities on the same tract of land.  While incentives may promote the selective management of a riparian buffer zone, any harvesting activity legally or contractually safely away from the stream may still have direct, negative effects on the rearing salmon.  Sediment runoff can be generated far upslope of the riparian zone and reach the stream, and roadways necessary for logging operations to reach timber stands may continue to contribute sedimentation and canopy clearing to the stream, simply at another junction in the watershed.

Implications of MDN Benefits for Timber Management Policies: Fish and Forest Rules of Washington State as an Example

Still, we can take some of the concepts from the above thought exercise and observe how they might apply to a real-world management policy currently seeking to co-manage fish and timber.  Revised Code of Washington 77.85, the “Fish and Forest Rules” (FFR), was passed by the Washington State Legislature in 1999 to balance the growing needs of both Washington’s timber industry and salmon resources, while conforming to the goals and provisions of the federal Endangered Species Act.  In essence, the Rules require private landowners to commit to harvesting prohibitions on riparian land adjacent to salmon-rearing streams, intended to provide these streams relief from pollution and other damages caused by riparian logging.  In exchange, private landowners are afforded a certain degree of immunity from the Endangered Species Act, which has strict limits on the degree of disturbance or mortal harm that can come to species listed as endangered or threatened (James 2008).  In Washington, this includes select populations of chinook, coho, chum, and sockeye salmon and cutthroat trout.

In western Washington, the FFR requires a three-zone riparian management zone for any salmon-bearing stream, to prevent timber harvests from taking place directly adjacent to a stream and to serve as a buffer to mitigate logging activities upslope. The total buffer width is 1 site-potential tree height (SPTH), which ranges from 30 meters (90 feet) to 80 meters (200 feet). The first zone is a 15 meter (50 feet) no-harvest core zone, followed by an inner zone, which extends to two-thirds and three-quarters of the SPTH for small and large streams, respectively and allows for various partial harvest options.  To compensate for economic value lost in timber dedicated to the buffer zones, Washington state offers a cost-sharing, conservation payment plan called the Forest Riparian Easement Program (FREP).  FREP pays landowners 50 percent of the value of timber that must be left in riparian buffers.  If the value of riparian buffer trees exceeds an upper-cost threshold of 19.1 percent, the value in excess of this threshold is compensated at 100 percent. (Zorbrist and Lippke 2007).

Zorbrist and Lippke (2007) hypothesized that the economic costs of FFR would be greater to small landowners than to large landowners.  FFR’s mandate a certain width of buffers must be maintained for the length of a salmon-bearing stream.  In terms of surface area, however, the percentage of land dedicated to the buffer versus to harvestable land would be very different between small and large landowners.  Owners of very large property may have a single stream coursing through its boundaries, and the ratio of timberland allocated to the buffer of the requisite wideth is relatively low compared to land available for harvesting.  In contrast, the owner of a small tract encompassing a segment of the same stream within its borders would stand to lose much more land proportionally, because much of the previously available timberland must be dedicated to a riparian buffer zone of the same width.

To illustrate the disparity, Zorbrist and Lippke modeled soil expectation values (SEV) for ten different small timberland owners in Washington state, ranging from 33 to 310 acres, using buffer limits imposed by the FFR and also comparing to similar regulations from Oregon state.  Modeling SEV of land planted with Douglas fir (Pinaceae: Pseudotsuga menziesii) at harvest after 50 to 55 years, the authors estimated that these small landowners would experience a 23- to 145-percent loss in SEV if a Washington FFR buffer is implemented.  If owners participated in the FREP conservation payment program, the losses are significantly lowered.  However, Zorbrist and Lippke note that few landowners may qualify for FREP due to limited program funding; worse, those owners are only compensated for the value of lost timber, but not the permanent loss in land value and opportunity costs.  In closing, the authors raise the fear that faced with diminished property value due to the FFR, small landowners may take advantage of alternate opportunities, such as selling their tract to real estate developers.  Suburban development would lead to further degradation of salmon habitat and relegate FFR’s to ultimately backfire in its intent to protect salmon while giving timber owners a viable, compensatory solution.  Additional irony lies in the fact that it is usually the smaller landowners who are more ecologically conscientious, harvesting only occasionally and at much longer rotations than commercial plots, and tend to keep timberland within generations (James 2008).

Washington’s FFR was composed and passed prior to the recent research on the reciprocating benefits salmon have for riparian forests.  With our expanding understanding of marine-derived nutrient cycles and benefits, a number of policy adaptations may help retain the efficacy and benevolent intent of the FFR plans, while more providing small landowners with economically sound options.  FREP credit values should increase to reflect the value that salmon runs add to the riparian ecosystem.  Another option would be to allow greater entry into FREP, and link the payment program with a state-run ecosystem services bank, routing credit purchases by mitigating parties back to FREP credit sellers.  If a particular watershed is densely populated with small landowners who are all equally disadvantaged by the FFR – that is, essentially forming a privately owned commons – perhaps an alternate ecosystem services bank can assist landowners to sell credits or participate in cost shares with the state fisheries industry or a state proxy fund.  This latter arrangement would recognize the intricate, positive feedback cycles where salmon and riparian forests enhance the population health of one another, and at the same time, providing a setting where market producers (land owners producing habitat quality) and market consumers (fisheries harvesting salmon) of the same good can balance their respective needs.

Lastly, if marine nutrient subsidies can be shown to accelerate the growth of riparian timber, small owners of salmon-rich streams in the Pacific Northwest may find enough incentive to organize and form their own REDD credit auction market.

Conclusion

Coastal riparian forests are dynamic ecosystems, frontiers where biochemical processes from motile, open seas far away can interact and influence the ecology of comparatively sedentary timber groves.  The example of salmon and coastal timber clearly illustrate that nominally separate resource uses in the same ecosystem may in fact be much more inexorably linked.  Both forestry and fisheries economists should stay apprised of continuing ecological research on the tracing and impact of salmon-derived nutrients in riparian forests of the Pacific Northwest.  Further ecological findings may require adjustments of bioeconomic models currently used to forecast timber growth and design timber management plans, and consider the complementary life cycle of salmon.  New analysis of non-convexities that account for the intimate relationship between salmon and timber will surely be revealing.  Most importantly, regional governments will need to revisit resource policies on the optimal co-management of these two valuable natural commodities, to ensure that both resource industries remain sustainable for the future.

References

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