Common Even-Aged Systems

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Common Even-Aged Systems
Clearcut
Seed Tree
Shelterwood
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Clearcutting

• Clearcutting A method of regenerating an even
  aged stand in which a new age class develops in a
  fully exposed microclimate after removal, in a
  single cutting, of all trees in the previous
  stand.
• Regeneration is from natural seeding, direct
  seeding, planted seedlings, and/or advance
  reproduction.
• Silvicultural clearcuts differ from commercial
  clearcuts
• The first removes all trees, the second only
  merchantable trees

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Clearcutting changes the microenvironment

• Full sunlight conditions
• Air and soil temperature near the surface
  increases
• Humidity decreases and surface evaporation
  increases
• Soil moisture increases because transpiration
  decreases
• Precipitation interception decreases, more water
  reaches the surface
• Water infiltration and percolation increases
  subsurface flow increases
• Decomposition increases (warmer and wetter),
  releasing more nutrients
• Nutrients not taken up or bound to soil leach out
  of system

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Clearcutting

• Edge effect
• Moisture increases on a gradient for 30-40 feet
  into a clearing and then levels off
• Shade (in the northern hemisphere) is more
  pronounced on the south edge of the clearing.
  East to west shade depends on time of day.

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Clearcutting

• Alternate clearcutting arrangements
• Strip clearcut
• Block clearcut
• Patch clearcut
• Use of alternative methods
• Ensure good seed rain
• Manage shade patterns
• Protect against wind or ice/snow
• Improve aesthetics or meet policy-based
  constraints

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Alternative Clearcutting Approaches

• Block clearcutting
• All trees are removed in a single operation
• Size limitations are based on policy and site
  conditions, not on regeneration constraints

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Alternative Clearcutting Approaches
Progressive strip clearcut
Alternate strip clearcut
Strip clearcuts, alternate or otherwise, are best
oriented at right angles to prevailing winds. The
width of the strips will depend on seedfall
distances for the preferred species, wind hazard,
and other factors
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Alternative Clearcutting Approaches

• Patch clearcutting
• Stand is regenerated in a series of clearcuttings
  made in patches
• Patch size influences light availability within
  the patch and should be chosen to match species
  silvics

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Other considerations when using even-aged methods

• Stream Side Management Zones (SMZs)
• Typically leave an unharvested or partially
  harvest buffer
• Legacy trees
• Travel corridors for wildlife
• Management of viewscapes
• Orientation on landscape
• Aesthetic buffers
• Alter shapes, adjacencies
• Avoid straight edges and square corners
• Limit harvest size

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Clearcutting and Site Preparation

• Site preparation considerations for natural
  regeneration
• Some important questions
• Is it needed or would it be detrimental?
• Do you need it for a desired species?
• Does species need a mineral seedbed

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Site preparation and clearcutting Considerations
for natural regeneration

• Scarification ? mineral seedbed
• Control slash residues
• Partial shade or browse protection afforded by
  slash
• Control slash cover to manage seed eating mammals
• Mechanical or chemical vegetation control
• Competing vegetation that may inhibit or delay
  regeneration and effect subsequent growth rates

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• Advantages of the clearcutting method/system
• Commercially attractive
• Ease of administration and implementation of
  regulated forest
• Good method for most shade intolerant species
• Clean site eases site preparation and pest
  control
• Easy machine access eases harvesting
• Total overstory removal reduces some pests (e.g.
  dwarf mistletoe)
• Facilitates regeneration of species with
  serrotinous cones
• Precludes blow down
• Increases herbaceous cover (browse and cover for
  many wildlife species)

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Shortcomings of clearcutting with natural
regeneration

• Problems with dependable seed sources and
  seedling establishment
• Seed shortage limits regeneration to light seeded
  species
• Poor seed years may lead to regeneration failure
  or irregular stocking
• Overstory removal limits within stand seed
  production following harvest
• Density and uniformity of a species is difficult
  to control
• Issues associated with no high forest cover and
  high light environment
• Lack of cover may adversely impact some tree
  species and may increase competition by
  herbaceous and shrubs
• Dense competition may require costly site
  preparation
• Cold air drainage may damage reproduction
• Dry sites may not have sufficient surface
  moisture to support germination
• Reduced chance for genetic improvement

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Shortcomings of clearcutting with natural
regeneration

• Impacts on soils and hydrology
• wet sites may become wetter
• wet soils may become unstable on steep slopes
• mineral soil exposure may increase soil erosion
• in case of regeneration failure, increased
  decomposition rates may affect soil productivity
• Decreased visual aesthetics
• Increased fuel loading and fire danger
• Decreased wildlife habitat for some species

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Coppice Silviculture
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Coppice

• The term "coppice" is commonly applied to any
  regeneration arising from sprouts or
  suckerstypically hardwoods of young to moderate
  age
• As a method, it is where regeneration is solely
  from sprouts or root-suckers
• Associated with short rotation production of
  pulpwood or fuelwood
• Historically associated with charcoal iron
  production

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Coppice

• Some coppice principles
• Low stumps produce better quality sprouts
• Best sprouts originate from the root collar
• Sprouting vigor tends to decline with age and
  size of stems
• smaller stems, better sprouting
• Sprouting is most vigorous from dormant season
  cutting
• Least vigorous from late spring cutting

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Coppice

• Coppice for energy, bioremediation, environmental
  cleanup
• Repeated crops without replanting
• Vegetative propagation maintains genetic
  integrity of plantation
• Increased growth rates allow large volume
  production on limited land base
• Short cycle provides quick return on investment
• Second and third rotation often produces greater
  biomass in shorter time frame due to multiple
  stems from sprouts

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Coppice

• The cutting cycle is set by when the MAI
  intersects PAI

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• General shortcomings of coppice systems
• Financial success depends on access to markets
  for small diameter wood
• Serve limited set of management goals
• Frequent entry requires extra caution to minimize
  soil disturbance and may increase loss of soil
  nutrients after repeated harvests
• Coppices susceptible to freezing and browse
• It takes time to convert from coppice to high
  forest methods
• Coppice stands have limited non-market values
• General shortcomings of short-rotation biomass
  plantations
• Require guaranteed markets
• Require fertile soils with abundant moisture as
  well as fertilization to maintain critical
  nutrients
• May require protection from browse
• Mechanized systems needed for efficient
  harvesting require fairly level sites with
  uniform surfaces and highly trafficable soils.

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Coppice with standards scattered, individual
stems allowed to grow on through several coppice
cycles
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Seed Tree Method

• Definition even-aged method retaining widely
  spaced, uniformly distributed seed bearing trees
• Reproduction source from seeds disseminated from
  trees left after harvest

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Seed Tree Method

• Remaining seed trees may be removed after
  suitable regeneration is established, but this is
  not necessary to the method's application
• Produces an even-aged stand
• Inherently works well for wind dispersed species,
  but not hard seeded trees such as oaks and
  hickories
• The method removes size constraints on the
  regeneration area (also shape and orientation
  issues)

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Seed Tree Regeneration Method

• Regeneration must be established in a short
  period of years, or else the site will be
  occupied by other plants
• Produces early successional conditions on the
  site (the same as a clearcut)
• High light levels, high exposure to wind, and
  extremes in temperature at ground level.
• Retained trees do not provide enough canopy cover
  to alter the stands microenvironment in
  comparison to open condition
• Density of retained trees that would alter
  microenvironment is species-specific

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Key considerations for the seed tree method

• Number and spacing of seed trees depends on
• Size and species of seed trees
• Amount of viable seed per tree
• Percent of seed trees that may survive
• Percent of seed that produces an established
  seedling

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• Considerations for number and spacing
• Distance to which seed from desired species can
  be dispersed to fully stock an area
• Do not exceed maximum dispersal distances
• Nature of the seedbed
• If unfavorable (e.g., heavy duff or sandy
  topsoil), leave more seed trees (but, better to
  prepare it by fire or disking)
• Anticipated competition level
• Increase the number of seed trees if there will
  be a high competition level with no or inadequate
  competition control
• Above all, know the silvics of species to be
  retained

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• Considerations for number and spacing
• In general
• Light seeded trees can disseminate 2 to 5 times
  their height
• Amount of viable seed is usually limiting factor
• Influence of spacing on pollination alter total
  seed production
• Because of year-to-year variation in seed
  production, it is best to ensure enough reserve
  trees to restock area in one moderate seed year
• Usually, 4 to 20 trees per acre retained.

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8 seed trees per acre in a loblolly-shortleaf
pine stand. Arkansas.
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Recommended minimum number of seed trees for major southern pines, by DBH class. Number per acre. (Average distance between trees, in ft, shown in parentheses). Will provide value for commercial removal Recommended minimum number of seed trees for major southern pines, by DBH class. Number per acre. (Average distance between trees, in ft, shown in parentheses). Will provide value for commercial removal Recommended minimum number of seed trees for major southern pines, by DBH class. Number per acre. (Average distance between trees, in ft, shown in parentheses). Will provide value for commercial removal Recommended minimum number of seed trees for major southern pines, by DBH class. Number per acre. (Average distance between trees, in ft, shown in parentheses). Will provide value for commercial removal Recommended minimum number of seed trees for major southern pines, by DBH class. Number per acre. (Average distance between trees, in ft, shown in parentheses). Will provide value for commercial removal
Species Species Species Species
DBH (inches) Loblolly Shortleaf Slash Virginia
9 10 12 14 16 NA 12 (60) 9 (69) 6 (85) 4 (104) NA 20 (47) 14 (56) 12 (60) 12 (60) NA 12 (60) 9 (69) 6 (85) 4 (104) 6 (85) 5 (93) 4 (104) 4 (104) 4 (104)
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Characteristics of Quality Leave Trees

• Windfirmness
• Shallow rooted trees or species with weak wood
  are not desirable
• Wide, deep crowns, with high live crown ratio
• Indicators of vigorously growing trees
• Dominant or better codominant crown class
• Seed production is linked to crown area
• Height
• Height can influence distance of seed dispersion
• Age
• Must be old enough to produce seed

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Cutting Strategies Seed Tree System

• Prep Cut Optional initial treatment to increase
  tree vigor and seed production
• Seed Cut Treatment to establish seedling
  reproduction within the stand
• Removal Cut Removal of final overwood to release
  established seedlings
• Multiple cuttings can be used and are the same as
  for a shelterwood except for the density of the
  seed cut (i.e. can have a preparatory cut and a
  removal cut)
• Additional Management options
• Reserve Cutting retain seed trees to help make
  an early thinning of the next stand more
  economically feasible
• Not competing removal cut and retaining seed tree
  through next rotation to meet multiple-use
  objectives.

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Key Considerations for the Seed Tree Method

• Site Conditions An adequate seedbed and low
  level of competition are required
• Some well-distributed exposed soil is desirable,
  since seeds are small
• Best case thin, discontinuous litter, with some
  mineral soil exposed
• Dispersed skidding during logging may be
  sufficient, particularly if the stand has been
  burned regularly
• Consider a prescribed burn (for pines) if a heavy
  litter layer exists
• best if before harvest, and not between seedfall
  and a winter/early spring harvest
• Mechanical site preparation
• provides some density/distribution control

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Key considerations for the Seed Tree Method

• Reduce anticipated competition, if needed
• Logging operations can damage competition
  vegetation present at time of harvest
• Use a burning regime prior to harvest
• Involves planning many years ahead
• May be part of your silvicultural system for
  pines
• May need to include one or more summer burns just
  before the anticipated harvest
• Consider using herbicides or herbicide/burn
  combination

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Key considerations for the seed tree method

• Final removal of seed trees is an economic
  consideration as they do not modify the
  microenvironment
• You may consider increasing numbers of seed trees
  in order to make the final harvest merchantable
• Conversely, you may retain a few (but high
  quality) trees in order to make the first
  thinning more attractive financially

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Seed Tree Removal Consideration

• Do economic gains out-weight positives to
  retention?
• Damage to established reproduction
• Is area fully stock with reproduction?
• Additional site preparation may be necessary if
  reproduction does not develop
• If removal is chosen and growth of established
  reproduction is your 1 objective
• Implement removal cut when site is fully stocked
  with seedlings of desired height
• Level of stocking and seedling height required is
  species-specific

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• Advantages to Seed Tree Method
• Allows for the control of species and phenotypic
  characteristics of seed source
• Seed source abundant and uniformly spaced
• Provides full sun growth conditions
• Disadvantages
• Exposes seed source to increased risk of
  premature destruction.
• Does not provide protection to reproduction on
  harsh sites
• Application of Seed Tree Method
• Southern Pines slash, shortleaf, loblolly, sand
• Hardwoods yellow-poplar, cottonwood, willow, ash
• Western Conifers

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Ponderosa Pine
Shortleaf Pine
Slash Pine
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Shelterwood System

• Definition an even-aged silvicultural system
  where the reproduction method removes mature
  community in two or more successive cuttings,
  temporary leaving some old trees to serve as seed
  source and to protect the regeneration.
• Characteristics
• Relatively low density stand left of vigorous
  seed-bearing trees
• Residual overstory provides sufficient canopy to
  mitigate sensitive environmental conditions.
• Especially important on harsh or exposed sites.
• Residual trees are removed once new reproduction
  reaches adequate size (i.e. height) and density

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Uniform Shelterwood Components

• Preparatory Cut
• An optional initial treatment to
• Increase tree vigor and seed production in mature
  stand
• Remove undesirable seed sources
• Alter understory environment to promote
  development of advance reproduction

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Uniform Shelterwood Components (continued)

• 2. Establishment Cut
• Artificially moves stand into understory
  reinitiation phase of stand development
• Promotes seed germination and establishment by
  creating permanent openings in main canopy
• Opens the canopy for sufficient light
  availability to allow regeneration
• Maintains some control (shelter) of understory
  vegetation
• Generally, 25-60 ft2/ac residual basal area
• 30-40 ft2/ac southern pines, 50-60 ft2/ac for oak
• Should retain dominant, vigorous trees of
  favorable phenotypes

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Uniform Shelterwood Components (continued)

• 2. Establishment Cut
• Considerations for success
• Appreciably modify the understory environment
• Retain sufficient residual cover to create
  conditions that favor target species and seed
  supply
• Understory environment must promote seedling
  development

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Uniform Shelterwood Components (continued)

• 3. Removal Cut
• A harvest to take away the overwood, so the new
  reproduction can develop uninhibited.
• Conducted only after satisfactory establishment
  of reproduction based on density, height, and
  distribution of seedlings
• Will impact (i.e. damage) established
  reproduction
• Allow for losses of regeneration in logging
• Remove the overwood before suppression of
  regeneration becomes serious

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Shelterwood Method/System

• Applicability of the Shelterwood Method
• It is the most flexible even-aged method e.g.,
  you can delay the removal cutting in order to
• Obtain rapid increment of high quality wood
• Increase mast production
• Maintain aesthetics
• A good method for heavy-seeded species
• A good method where the seed supply is irregular

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Uniform Shelterwood Methods

• Three-cut Method Preparatory, Establishment, and
  removal cut are used
• Two-cut Method Establishment and Removal cut only

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Shelterwood Method/System

• How Much Overwood Do You Leave?
• Will crown closure of residuals occur
• What effect will the overwood have on the
  reproduction
• Consider the minimum volume to support
  merchantable overwood removal
• Consider the volume that will accumulate on the
  residual overwood stems
• Ease of logging (seed and removal cutting)
• Logging damage to reproduction
• Could be positive aspect and considered a no-cost
  thinning operation if density is too high
• Applicable to both seed tree and shelterwood
  methods

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Tradeoffs Between Overstory Retention, Light
Environment, and Understory Competition
Optimal level is dependant on species, site
productivity, and stand history
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Other Types of Shelterwood Systems

• Irregular or Reserve Shelterwood
• Leaves residual overstory for an extended period
  of time into new rotation creates two-aged
  stand
• Has ecological/aesthetic vs. economic/operational
  tradeoffs
• Characteristics of reserve trees are important

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Irregular Shelterwood
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Other Shelterwood Systems

• Group Shelterwood
• Takes advantage of existing patches of
  reproduction
• Removal cuttings done in patches containing
  reproduction
• Prep and seed cuts done in areas lacking
  favorable reproduction

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Group Shelterwood
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Other Types of Shelterwood Systems

• Strip Shelterwood
• Removal of mature age classes over a series of
  entries by cutting narrow strips not exceeding
  the height of adjacent standing trees
• Residual strips provide seed and partial shade to
  openings
• Strip Orientation
• Long axis of strips at right angles to prevailing
  winds to reduce blow-down
• Alignment in relation to suns path influences
  proportion of direct and diffuse radiation

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Strip Shelterwood
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Application of the Shelterwood System

• Upland and bottomland oak forests
• Eastern pines red pine, eastern white pine
• Southern pines longleaf pine
• Rocky mountain conifers western white pine,
  ponderosa pine, Douglas-fir (Rocky Mountain
  variety), western larch (on harsh sites).
• Cascade and coastal range regions western
  hemlock/Sitka spruce type and Douglas-fir

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Upland Oak Shelterwood
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Shelterwood in longleaf pine
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Brief Comparison Clearcut, Seed Tree, and
Shelterwood

• Clearcut
• Entire canopy removed in one operation
• Seedlings grow under open field conditions

• Seed Tree
• Canopy removed in 2 to 3 stand entries
• Residual trees retained to provide a seed source
  
• Seedlings grow under essentially open field
  conditions

• Shelterwood
• Residual trees retained to provide a seed source
  and modify understory microenvironment
• Canopy removed in 2 to 3 stand entries

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