George R. Pess

The Network Dynamics Hypothesis: How Channel Networks Structure Riverine Habitats

Abstract Hierarchical and branching river networks interact with dynamic watershed disturbances, such as fires, storms, and floods, to impose a spatial and temporal organization on the nonuniform distribution of riverine habitats, with consequences for biological diversity and productivity. Abrupt changes in water and sediment flux occur at channel confluences in river networks and trigger changes in channel and floodplain morphology. This observation, when taken in the context of a river network as a population of channels and their confluences, allows the development of testable predictions about how basin size, basin shape, drainage density, and network geometry interact to regulate the spatial distribution of physical diversity in channel and riparian attributes throughout a river basin. The spatial structure of river networks also regulates how stochastic watershed disturbances influence the morphology and ages of fluvial features found at confluences.

A Review of Stream Restoration Techniques and a Hierarchical Strategy for Prioritizing Restoration in Pacific Northwest Watersheds

Abstract Millions of dollars are spent annually on watershed restoration and stream habitat improvement in the U.S. Pacific Northwest in an effort to increase fish populations. It is generally accepted that watershed restoration should focus on restoring natural processes that create and maintain habitat rather than manipulating instream habitats. However, most process-based restoration is site-specific, that is, conducted on a short stream reach. To synthesize site-specific techniques into a process-based watershed restoration strategy, we reviewed the effectiveness of various restoration techniques at improving fish habitat and developed a hierarchical strategy for prioritizing them. The hierarchical strategy we present is based on three elements: (1) principles of watershed processes, (2) protecting existing high-quality habitats, and (3) current knowledge of the effectiveness of specific techniques. Initially, efforts should focus on protecting areas with intact processes and high-quality habitat. Fol...

Pool Spacing in Forest Channels

Field surveys of stream channels in forested mountain drainage basins in southeast Alaska and Washington reveal that pool spacing depends on large woody debris (LWD) loading and channel type, slope, and width. Mean pool spacing in pool-riffle, plane-bed, and forced pool-riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1 channel width with increasing LWD loading, whereas pool spacing in generally steeper, step-pool channels is independent of LWD loading. Although plane-bed and pool-riffle channels occur at similar low LWD loading, they exhibit typical pool spacings of greater than 9 and 2–4 channel widths, respectively. Forced pool-riffle channels have high LWD loading, typical pool spacing of <2 channel widths, and slopes that overlap the ranges of free-formed pool-riffle and plane-bed channel types. While a forced pool-riffle morphology may mask either of these low-LWD-loading morphologies, channel slope provides an indicator of probable morphologic response to wood loss in forced pool-riffle reaches. At all study sites, less than 40% of the LWD pieces force the formation of a pool. We also find that channel width strongly influences pool spacing in forest streams with similar debris loading and that reaches flowing through previously clear-cut forests have lower LWD loading and hence fewer pools than reaches in pristine forests.

Process-based Principles for Restoring River Ecosystems

Process-based restoration aims to reestablish normative rates and magnitudes of physical, chemical, and biological processes that sustain river and floodplain ecosystems. Ecosystem conditions at any site are governed by hierarchical regional, watershed, and reach-scale processes controlling hydrologic and sediment regimes; floodplain and aquatic habitat dynamics; and riparian and aquatic biota. We outline and illustrate four process-based principles that ensure river restoration will be guided toward sustainable actions: (1) restoration actions should address the root causes of degradation, (2) actions must be consistent with the physical and biological potential of the site, (3) actions should be at a scale commensurate with environmental problems, and (4) actions should have clearly articulated expected outcomes for ecosystem dynamics. Applying these principles will help avoid common pitfalls in river restoration, such as creating habitat types that are outside of a sites natural potential, attempting to build static habitats in dynamic environments, or constructing habitat features that are ultimately overwhelmed by unconsidered system drivers.

Setting River Restoration Priorities: A Review of Approaches and a General Protocol for Identifying and Prioritizing Actions

Abstract Implicit in the question, “How should I prioritize restoration actions?” is often the unstated question, “What should I restore?” Distinguishing between these questions helps clarify the restoration planning process, which has four distinct steps: (1) identify the restoration goal, (2) select a project prioritization approach that is consistent with the goal, (3) use watershed assessments to identify restoration actions, and (4) prioritize the list of actions. A well-crafted restoration goal identifies the biological objective of restoration, addresses underlying causes of habitat change, and recognizes that social, economic, and land use objectives may constrain restoration options. Once restoration goals are identified, one of six general approaches can be selected for prioritizing restoration actions: project type, refugia, decision support systems, single-species analysis, multispecies analysis, and cost effectiveness. Prioritizing by project type, refugia, or a decision support system requir...

Evolutionary history of Pacific salmon in dynamic environments.

Contemporary evolution of Pacific salmon (Oncorhynchus spp.) is best viewed in the context of the evolutionary history of the species and the dynamic ecosystems they inhabit. Speciation was complete by the late Miocene, leaving c. six million years for intraspecific diversification. Following the most recent glacial maximum, large areas became available for recolonization. Current intraspecific diversity is thus the product of recent evolution overlaid onto divergent historical lineages forged during recurrent episodes of Pleistocene glaciation. In northwestern North America, dominant habitat features have been relatively stable for the past 5000 years, but salmon ecosystems remain dynamic because of disturbance regimes (volcanic eruptions, landslides, wildfires, floods, variations in marine and freshwater productivity) that occur on a variety of temporal and spatial scales. These disturbances both create selective pressures for adaptive responses by salmon and inhibit long‐term divergence by periodically extirpating local populations and creating episodic dispersal events that erode emerging differences. Recent anthropogenic changes are replicated pervasively across the landscape and interrupt processes that allow natural habitat recovery. If anthropogenic changes can be shaped to produce disturbance regimes that more closely mimic (in both space and time) those under which the species evolved, Pacific salmon should be well‐equipped to deal with future challenges, just as they have throughout their evolutionary history.

Modeling Recovery Rates and Pathways for Woody Debris Recruitment in Northwestern Washington Streams

Abstract We modeled large woody debris (LWD) recruitment and pool formation in northwestern Washington streams after simulated stand-clearing disturbance using two computer models: Forest Vegetation Simulator for stand development and Riparian-in-a-Box for LWD recruitment, depletion, and pool formation. We evaluated differences in LWD recruitment and pool formation among different combinations of channel size, successional pathway, and stand management scenario. The models predict that time to first recruitment of pool-forming LWD is about 50% shorter for red alder Alnus rubra than for Douglas-fir Pseudotsuga menziesii at all channel widths. Total LWD abundance increases faster in red alder stands than in Douglas-fir stands but declines rapidly after 70 years as the stand dies and pieces decompose. Initial recovery is slower for Douglas-fir stands, but LWD recruitment is sustained longer. Total LWD abundance increases faster with decreasing channel size, and pool abundance increases faster with decreasing...

Biological Impacts of the Elwha River Dams and Potential Salmonid Responses to Dam Removal

Abstract The Elwha River dams have disconnected the upper and lower Elwha watershed for over 94 years. This has disrupted salmon migration and reduced salmon habitat by 90%. Several historical salmonid populations have been extirpated, and remaining populations are dramatically smaller than estimated historical population size. Dam removal will reconnect upstream habitats which will increase salmonid carrying capacity, and allow the downstream movement of sediment and wood leading to long-term aquatic habitat improvements. We hypothesize that salmonids will respond to the dam removal by establishing persistent, self-sustaining populations above the dams within one to two generations. We collected data on the impacts of the Elwha River dams on salmonid populations and developed predictions of species-specific response dam removal. Coho (Oncorhynchus kisutch), Chinook (O. tshawytscha), and steelhead (O. mykiss) will exhibit the greatest spatial extent due to their initial population size, timing, ability to maneuver past natural barriers, and propensity to utilize the reopened alluvial valleys. Populations of pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon will follow in extent and timing because of smaller extant populations below the dams. The initially high sediment loads will increase stray rates from the Elwha and cause deleterious effects in the egg to outmigrant fry stage for all species. Dam removal impacts will likely cause a lag in recolonization and population rebuilding. These negative sediment effects will be locally buffered by the extent of functioning floodplain, and management attempts to minimize sediment impacts. Resident life forms of char (Salvelinus confluentus), rainbow trout (O. mykiss), and cutthroat (O. clarki) will positively interact with their anadromous counterparts resulting in a positive population level response.

The Importance of Beaver Ponds to Coho Salmon Production in the Stillaguamish River Basin, Washington, USA

Abstract The use of beaver Castor canadensis ponds by juvenile coho salmon Oncorhynchus kisutch and other fishes has been well established. However, the population-level effects on coho salmon resulting from the widespread removal of millions of beaver and their dams from Pacific Coast watersheds have not been examined. We assessed the current and historic distributions of beaver ponds and other coho salmon rearing habitat in the Stillaguamish River, a 1,771-km2 drainage basin in Washington and found that the greatest reduction in coho salmon smolt production capacity originated from the extensive loss of beaver ponds. We estimated the current summer smolt production potential (SPP) to be 965,000 smolts, compared with a historic summer SPP of 2.5 million smolts. Overall, current summer habitat capacity was reduced by 61% compared with historic levels, most of the reduction resulting from the loss of beaver ponds. Current summer SPP from beaver ponds and sloughs was reduced by 89% and 68%, respectively, co...

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

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