Scientific Literature Review of Forest

1
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

• 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

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 lt 30 feet
• Streamside landsliding 100-200?? feet
• Wind 75-130?? feet
• Treefall lt100 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

• 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

• 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
• Lots 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