Scientific Literature Review of Forest

1. Heat Exchange Functions • Stream temperatures affect the growth and mortality of salmonids • Too COOL: insufficient growth & lower ocean survival • Too HOT: lower abundance & risk of mortality • Riparian shade helps to control heat input to streams, but other factors are important too • No single, fixed-width buffer or canopy closure prescription can regulate heat objectives for salmon in all cases. • Effective shading can be provided by: • Lateral: buffer widths ranging from 30 to 100 ft • Longitudinal: generally within 500 to 650 ft upstream • Water temperature protection could be provided by varying the riparian shade requirements in relation to stream temperature sensitivity. • The relative importance and sensitivity of riparian vegetation to influence stream temperature varies by at least 11 site specific factors • Stream temperature targets can be helpful in managing to desired shade conditions • Timber harvest in or adjacent to riparian areas can influence microclimate, HOWEVER microclimate changes have not been demonstrated to translate to changes in water temperature. • Shade conditions inversely influence biotic and nutrient exchange functions. • Similarly, the canopy that provides shade also influences: • Water exchange functions • Wood exchange functions Scientific Literature Review of Forest Management Effects on Riparian Functions for Anadromous Salmonids by Mike Liquori, Dr. Doug Martin, Dr. Robert Coats, Dr. Lee Benda, Dr. David Ganz for the California State Board of Forestry and Fire Protection • Project Approach • This project was contracted through the State of California Board of Forestry and Fire Protection • Reviewed 185+ assigned scientific papers published after 1997 focused around 5 Riparian Exchange Functions • Biotic & Nutrient • Heat • Water • Wood • Sediment • Structured around Key Questions defined by a 12-member Technical Advisory Committee (TAC) • Document reviewed by TAC and 7 senior scientists during a day-long Technical Exchange Forum • Provides support for riparian rule revisions being considered by the Board of Forestry • Biotic & Nutrient Exchange Functions • Riparian leaf litter is an important food source • Litter quantity & quality is important • Highest: alder • Moderate: maple, willow and cottonwood • Low: conifers and oaks • Opening the canopy cover over some streams increases ecological productivity • Tradeoffs between nutrient exchange and other functions • Heat regulation • Water – response to flooding • Wood recruitment potential • A 100 foot wide no-cut buffer on both sides of a stream provides conditions similar to a “no harvest” level • No-cut buffers may forego opportunities to: • increase fish growth rate and biomass • address other beneficial functions • General Themes • Spatial context is important, as it influences functional response patterns. • Both longitudinal AND lateral controls are important in maintaining the watershed-scale ecosystem structure that maintains aquatic habitats. • Disturbances are an important mechanism for establishing conditions that support riparian functions by affecting factors like: • Stand structure • Vegetative succession • Wood recruitment • Nutrient exchange • Thermal regulation • Riparian zones can buffer a stream from direct management impacts, but they also alter the disturbance regimes in ways that can affect both short-term and long-term evolution of riparian areas. • There are dynamic interactions among and between riparian exchange functions that alter the importance of exchange functions for any particular setting. • Active and strategic riparian management can limit risks and benefit salmonids • temperature regimes • ecological productivity • woody debris recruitment • fuel loads and other disturbance risks • There are variations in the buffer width necessary to meet each function, and these variations depend on several factors • The reviewed literature offers many opinions, but limited hard data to evaluate the scientific effectiveness of any approach • Risks and benefits are inherently value judgments best determined by policy • Science can only provide the context • The geographic and watershed-scale variables for buffers requires a policy framework • Information in the literature is available, but inconclusive in the absence of a framework • Water Exchange Functions • Forest management activities in riparian areas might affect stream functions • effect is likely to be small • highly variable • strongly influenced by the watershed context • impacts are mixed • Management affects the riparian canopy • canopy interception • evapotranspiration • There is little direct evidence of riparian effects: • studied for entire watersheds • riparian zones alone have not been studied • The most sensitive hydrologic areas may be steep, zero-order basins (hollows) • This was not a focus of this review • Soil compaction in riparian areas can negatively affect hydrologic processes. • Suggests limits for heavy equipment near streams • Hyporheic flows are important ecologically • forest management effects are unclear • There is very little in the reviewed literature that can used to directly address the issue of buffer strip delineation relevant to the water function • Regional differences are likely to reflect: • Geology • topographic variation • dominant runoff mechanisms

2. Wood Exchange Functions • Wood functions vary by stream type and geomorphic context • There are three dominant sources of instream wood in California second-growth forests • bank erosion: ~40-60% • streamside landslides: ~30% • treefall: ~10-30% • The zone that can contribute 90% of observed wood recruitment varies depending on the dominant processes • Bank erosion: < 30 feet • Streamside landsliding: 100-200?? feet • Wind: 75-130?? feet • Treefall: <100 feet • The major factors that are reported to influence wood recruitment conditions include: • Existing Stand Density, Composition And Structure • Stream Type, Order and Watershed Context • Vegetation Type and Soil/ Site Index • Regional Context • Disturbance Context • Instream wood can move downstream through: • Flood: in larger streams • Debris-flow: in steep, low-order streams • Wood recruitment potential depends upon: • Existing stand conditions • Successional pathway • Disturbance Regime • Forest management appears to influence natural disturbance regimes by affecting • How often disturbances occur • How large the disturbances are • Which type of disturbances are likely • Active forest management can influence wood functions by manipulating riparian stand structure in ways that: • a) affect the growth and mortality dynamics for the stand and • b) influence the types, qualities and risks of disturbances • Sediment Exchange Functions • Sediment Best Management Practices (BMPs) typically address sediment primarily in three general ways: • Source Controls • Runoff Controls • Treatment Controls • Sediment sources from forest management include: • surface erosion processes (rills and sheetwash) • skid trails • yarding ruts • gullies • soil piping • roads • fire • mass wasting processes • bank erosion • windthrow • legacy forest management practices • Riparian buffers are mostly effective at limiting sediment delivery to streams • In the absence of buffers, ground disturbances that are near streams have the potential to deliver sediment • Selective forest management within buffers does not appear to substantially increase sediment production or delivery • The extent that riparian buffers along headwater streams are necessary to prevent sediment delivery is not clear from the reviewed literature. • Despite the lack of evidence for direct sediment delivery, instream sediment yields tend to increase following logging • Sources of such sediment are not clear • Source distance relationships for sediment also appear to vary with the dominant processes and site conditions • The reviewed literature did not provide a sufficient guidance for the various landscape situations in California, although a more detailed analysis of data may lead to more definitive specifications for buffer width. • Riparian sediment management objectives include mitigating for: • Harvest-Related Sediment • Hydrologic Link to Sediment Delivery • Road Sediment • Mass Wasting Impacts • Synthesis of Exchange Functions & Management Implications • The current scientific basis for defining buffer widths in fish-bearing streams is often based on source distance relationships, HOWEVER, there are several important challenges associated with this approach. Source distance relationships: • Ignore the trade-offs between functions • Downplay the importance of the quality of contributed inputs • Only capture the effects of some disturbances • Describe the relative contribution, but not the total contribution • Ignore changes over time • Ignore the longitudinal context • Have not established instream biological responses • Management should consider both lateral (width) and longitudinal (network) variation, which requires an understanding of how different ecosystem processes act to form and maintain habitats throughout the channel network. Important factors include: • River Continuum v. Network Dynamics • Geomorphic Context is Important • Biological Hotspots • Disturbance Cascades • There are dynamic interactions among and between riparian exchange functions that alter the importance of exchange functions for any particular setting • While riparian zones can buffer a stream from some direct management impacts, buffers do not protect streams from disturbances, but in fact alter the disturbance regimes in ways that can affect the functional response expressed by both short-term and long-term evolution of riparian areas. Bank Treefall Landslides Erosion Windthrow • Policy Inferences • Lot’s of good detail available from literature that supports specific rule-making elements • But limited information about the effectiveness of different buffer strategies • Suggests the need for management decision-support tools that help integrate science with management • Decision-support tools • Models & mapping capabilities • Resource targets • Riparian management specifications • Design tools • A science-based management framework will provide the necessary policy direction • Establish value positions regarding various management approaches • Identify clear functional goals and performance measures that define the decision space for science-based management • Outline a planning approach that provides a policy-oriented framework (i.e. based in regulations, planning processes, etc) • Develop Adaptive Management structures and procedures For a Free Copy of the report, go to: http://www.soundwatershed.com/BOF.htm