Silvics Manual: http:www.na.fs.fed.usSpfopubssilvics_manualtable_of_contents.htm

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• Silvics Manual http//www.na.fs.fed.us/Spfo/pubs
  /silvics_manual/table_of_contents.htm

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Diameter Distributions Approach to describing a
stands tree size structure
Smith, D.M. 1986. The Practice of Silviculture.
John Wiley and Sons, Inc., New York, NY. 527 p.
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• Site Index A measure of actual or potential
  forest productivity expressed in terms of the
  average height of dominants and co-dominants in
  the stand at an index age (base age) for a
  particular species.
• Base age
• 50 years for hardwoods, 25 years for southern
  pine

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The Silvicultural System

• To meet landowner objectives and to create and
  maintain desired values
• Silviculturists alter the forest environment by
  manipulating stand structure
• Required environment is influenced by
• species composition
• silvical characteristics of desired species and
  competitors
• size structure (of existing stand)
• age structure
• density/spacing
• health and vigor
• potential damaging agents

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The Silvicultural System

• Primary categories of silvicultural activities
  control
• stand structure
• species composition
• stand density
• rotation length
• Restocking of unproductive or severely disturbed
  areas

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The Silvicultural System

• The silvicultural system encompasses everything
  that is done throughout a rotation.
• In theory, it is unique for each stand.
• The systems are named for their respective
  silvicultural methods.
• The method is how we regenerate the stand (e.g.
  clearcut, shelterwood, etc).
• These are not harvesting methods, they are
  methods of regeneration
• Naming convention identifies the structural
  character of a stand

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The Silvicultural System

• Each silvicultural system should (page 22)
• improve the quality
• optimize benefits
• shorten investment period
• contain costs
• sustain ecosystem health and productivity

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The Silvicultural System

• Even-aged (EA) and Uneven-aged systems (UEA)
• one age class vs. at least three age classes in
  a stand (an age class is defined at 20 of the
  rotation length)
• the three components of a silvicultural system
  tending, harvesting, and regenerating are applied
  at separate times during a rotation in an
  even-aged stand. They are applied simultaneously
  at each cutting cycle in an uneven-aged stand
• Mature trees are removed all at once in an EA
  system, periodically in an UEA system. An UEA
  system maintains continuous canopy cover.

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The Silvicultural System

• Two-aged systems
• a hybrid of EA and UEA. Uses EA methodology
  while maintaining some continual canopy cover.
• regeneration is accomplished (in general) two
  times over a standard rotation.
• referred to as irregular shelterwoods, reserve
  shelterwoods, or leave tree systems

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The Silvicultural System

• The system has three basic components Figures
  2-1
• Regeneration
• Tending
• Harvest

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The Silvicultural System

• Regeneration methods are classified into distinct
  categories
• clearcuting
• seed-tree
• shelterwood
• Selection (group and single-tree)
• Two-aged

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The Silvicultural System

• The choice of a method depends on
• landowners objective
• existing plant community and silvics
• range of treatments available for use

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The Silvicultural System

• Modifications of a silvicultural method
• Type apply different kinds of treatments
• e.g., burn vs. herbicide
• Intensity change the intensity of application
• e.g., headfire vs. backing fire)
• Timing alter timing of application
• e.g., winter vs. summer burn
• Sequence change the sequence of treatments over
  time
• e.g. control vines before or following harvest

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The Silvicultural System

• Modifications often implemented for non-timber
  considerations
• size of regeneration area
• rotation length
• kind, size and condition of residuals
• species left on site
• amount, kind, and frequency of mast production
• amount of light to forest floor
• kinds of reproduction
• coarse woody debris left on site (amount, size,
  and distribution)
• surface disturbance and effect on hydrology

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Biologic and economic factors that affect
silviculture
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Stand Development

• Four phases of stand development after Oliver and
  Larson (1996)
• stand initiation (reorganization phase
• stem exclusion (aggradation phase)
• understory reinitiation (transition phase)
• old growth (steady-state)

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Johnson, P.S., S.R. Shifley, and R. Rogers. 2002.
The Ecology and Silviculture of Oaks. CABI
Publishing, New York, NY. 503 p.
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Stand Development

• Each phase of stand development is accompanied by
  changes in stand structure and species
  composition.

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• Stand Initiation rapid increase in the number of
  stems and biomass (establishment)
• Structure
• Begin vertical stratification of tree crowns
• brushy stage with herbaceous, shrub, small
  trees
• Invasion continues until all growing space is
  occupied
• Follows major disturbances (wind, fire,
  clearcuts)
• Regeneration of open space from seed, sprouts, or
  advance reproduction
• One cohort or age class
• Stage ends when canopy becomes continuous and
  trees begin to compete with each other for light
  and canopy space

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Stand Development

• Stem Exclusion begins at about crown closure,
  characterized by density dependent mortality and
  an accumulation of biomass. Phase ends when
  biomass peaks.
• Canopy continues to have one cohort and canopy
  too density to allow new trees to grow into
  canopy
• Competition is intense and density-dependant
  self-thinning occurs
• Crowns are small enough so that when a tree dies,
  others fill the vacant growing space by expanding
  their crowns

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Stem Exclusion

• Crown differentiation occurs the biggest trees
  tend to get bigger, the smaller ones tend to die.
  
• In stratified mixed species stands,
• Slower growing shade tolerant trees fall behind
  in height growth of faster growing shade
  intolerant species
• Because of their physiology, tolerant species are
  able to remain alive in the understory or
  midstory of the stand.
• Some species do not differentiate, stagnation
  occurs in species like slash or lodgepole pine.
• Mortality rates are high, especially in
  intermediate and suppressed crown classes (i.e.,
  the least competitive individuals die).

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• Crown classification
• Dominant - crown is larger than average and
  typically above the general upper level of the
  canopy receives full top light, considerable
  side light
• Codominant - top of crown is at upper canopy
  height receives full top light, little from
  sides medium-sized crown, usually somewhat
  crowded on its sides. Often wide range around
  average canopy tree.
• Intermediate - top of crown is below the top of
  the general canopy receives some top light from
  directly above, none from the side conspicuously
  narrower, smaller and shorter than the average
  crown.
• Overtopped (suppressed) - crown entirely below
  some foliage of the upper canopy receives no
  direct top light small, weak crown with low vigor

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• Understory Reinitiation
• Mortality of individuals cannot be closed by
  adjacent individuals
• Crowns of trees are now large enough so that when
  one overstory tree dies, the surrounding trees
  can not fill the gap
• Permanent canopy gaps form
• Permanent understory forms
• Tree reproduction becomes re-established beneath
  parent stand
• Factors that influence species composition
• Light Degree of shade tolerance
• Soil moisture

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• Old-Growth/Complex Stage
• Natural mortality of large overstory trees
  produces irregular canopy gaps
• Mortality and recruitment and are in
  balancebiomass is stable
• Stage marks the transition to an even-aged to an
  uneven-aged stand

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• Figure 9-6 on p204
• stand initiation (reorganization phase)-rapid
  increase in the number of stems
  (establishment)lots of stems, very little
  biomass.
• stem exclusion (aggradation phase)-begins at
  about crown closure at peak density (TPA),
  characterized by density dependent mortality and
  an accumulation of biomass. Phase ends when
  biomass peaks.
• understory reinitiation (transition
  phase)-permanent understory forms-permanent
  canopy gaps form-mortality of individuals cannot
  be closed by adjacent individuals. Biomass
  declines as smaller individuals replace canopy
  dominants.
• old growth (steady-state)-total biomass of system
  fluctuates around some mean. The structure of
  the forest is self sustaining.

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Stand and Tree Growth and Yield

• General growth and yield patterns of even-aged
  stands
• Net yield reflects the amount of yield (volume
  or biomass) available for removal at any given
  age,
• rises throughout stand initiation and stem
  exclusion phases, can decline during understory
  reinitiation phase (Nyland figure 9-6)
• Gross yield reflects total amount produced on a
  given site at a given age (volume of living trees
  volume of mortality), rises throughout stand
  development

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Stand and Tree Growth and Yield

• General growth and yield patterns of even-aged
  stands
• Density number of trees decrease continuously
  due to mortality as stand ages
• Height height of dominant and codominant trees
  increases through life of stand, can level off or
  flatten as stands become decadent
• Diameter diameter (dbh) of average tree
  increases throughout life of a stand as trees
  growth and as the smaller trees within the stand
  suffer a disproportionately higher mortality
  rate.

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Upland Oak stand on average site (SI 70)
Schnur, G.L. 1937. Yield, stand, and volume
tables for even-aged upland oak forests. US
Department of Agriculture, Technical Bulletin No.
560. 87 p.
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Stand and Tree Growth and Yield

• Growth and yield patterns and rotation length
  Figure 9-5, p 203.
• Stage 1 rotation for maximum fiber production
  ends when mai pai
• Very little volume in small stems throughout
  stage 1, mass mortality, but little volume lost
  in any one stem
• Stage 2 rotation for sawtimber production, with
  exact length determined by economic criteria
• Stage 3 understory reinitiation phase
  (transition phase) where mortality exceeds
  production, and standing volume declines
  progressively
• As suggested by the production function, you can
  only economically manage into the understory
  reinitiation stage if a premium is paid for this
  material or if other byproducts that only occur
  here are of value (e.g. DDW, CWD, snags, an open
  canopy).

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Stand and Tree Growth and Yield

• Production, MAI, and PAI (notation 9-3)
• Production Net change in stand volume or basal
  area
• p A I M
• where, p production, A accretion, I
  ingrowth, M mortality

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Stand and Tree Growth and Yield

• Periodic Annual Increment (PAI) net change in
  production during a specific period
• PAI
• where,
• Y is the yield (volume, height, dbh, etc.) at
  times 1 and 2
• T1 represents the year starting the growth
  period, and
• T2 is the end year

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Stand and Tree Growth and Yield

• Mean Annual Increment Average growth per year a
  stand has exhibited/experienced to a specified
  age
• MAI

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Stand and Tree Growth and Yield

• Influence of Site Quality
• Height growth is primarily dependent on site
  quality (site index) except at extreme densities
• As site quality (SI) increases (page 431)
• Trees grow in height more quickly ? stand
  develops closed canopy more rapidly ? quickens
  time for the beginning competition induced
  mortality crown differentiation to begin ? this
  results in lower densities, larger average
  diameter, and more volume at a given age on high
  quality sites when compared to low quality sites.
• More rapid volume accumulates because of taller,
  larger trees present at a given age

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Schnur, G.L. 1937. Yield, stand, and volume
tables for even-aged upland oak forests. US
Department of Agriculture, Technical Bulletin No.
560. 87 p.
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Schnur, G.L. 1937. Yield, stand, and volume
tables for even-aged upland oak forests. US
Department of Agriculture, Technical Bulletin No.
560. 87 p.
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Schnur, G.L. 1937. Yield, stand, and volume
tables for even-aged upland oak forests. US
Department of Agriculture, Technical Bulletin No.
560. 87 p.
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Schnur, G.L. 1937. Yield, stand, and volume
tables for even-aged upland oak forests. US
Department of Agriculture, Technical Bulletin No.
560. 87 p.
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Stand and Tree Growth and Yield

• Influence of species on growth (Assmann 1970,
  Fig. 18) (Johnson et al 2002, Figure 10.2)

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Assmann, E. 1970. The principles of forest yield
study. Pergamon Press, Ltd., Elmsford, NY. 506 p.
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Johnson, P.S., S.R. Shifley, and R. Rogers. 2002.
The Ecology and Silviculture of Oaks. CABI
Publishing, New York, NY. 503 p.
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Stand and Tree Growth and Yield

• Influence of Density
• Height growth is only effected by extreme
  densities (open-grown trees and trees at
  extremely high densities)
• Relationship between density and mortality
  (Forest Regeneration Manual figure 15.3)
• Diameter growth
• Diameter increment is strongly influenced by
  stand density (i.e., available growing space)
  Clutter Figure 3.1
• At a given stand density, diameter growth is
  generally higher on better quality sites. Stand
  density is typically a much stronger driver of
  diameter growth than site quality.
• Relationship between density and tree/stand volume

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Clutter, J.L., J.C. Fortson, L.V. Pienaar, G.H.
Brister, and R.L. Bailey. 1983. Timber
management A quantitative approach. John Wiley
Sons, Inc. 333 p.
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Relationship Between Density and Tree/Stand
Volume Growth
Total Volume
Merchantable Volume or Total Volume in Species
Susceptible to Stagnation at High Densities
Patterns in volume per tree mirrors amount of
growing space available per tree.
Adapted from Daniel et al. 1979, Smith et al.
1997