Site Index

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Site Index
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Site Index (a)

• Site Index is a measure of the productive
  capability (biomass) of a forest stand, typically
  species and location specific.
• The higher the site index, the higher the
  productivity of a given stand.
• Mainly applies to even-aged stands, can be
  applied to specific species in uneven-aged stands.

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Site Index (b)

• Site index is the average height of dominant and
  codominant trees (Hd) at a certain age for a
  given stand
• Regardless of the current age of the stand, site
  index is always expressed as the height of
  dominants and codominants (Hd) at that certain
  age which is called the base age
• For fast growing plantations, the base age for
  site index is typically 25 years, for natural
  stands or slower growing plantations, the base
  age is typically 50 years.

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GROWTH AND YIELD
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Basic Terminology

• Growth change in an attribute over time (ideally
  positive number but does not have to be)
• Yield total amount of something available at a
  given point in time (present or future time)

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Basic Terminology

• Density (as applied to a forest as opposed to a
  sample of wood)
• How much is out there it is a quantitative
  measure
• Expressed in terms of trees per acre or basal
  area per acre

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Basic Terminology

• Stocking (as applied to a forest as opposed to a
  foot or a fireplace mantle on Christmas Eve)
• Relates how much is out there to a given
  management objective it is a qualitative measure

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Basic Terminology

• Over-stocked too much density to meet a given
  objective
• Fully-stocked (normal stocking) the correct
  (perfect) amount of density to meet an
  objective
• Average-stocking slightly less dense that the
  the previous, but still enough to meet the
  objective in general
• Under-stocked not enough density to meet the
  objective

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Types of Growth and Yield Models

• Stand-level models
• grow stands as a whole by focusing on stand level
  attributes (BA/acre, TPA, volume/ac, average
  height, QMD)
• Can back out individual tree data from them
• Commonly applied to (developed for) even-aged
  stands

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Types of Growth and Yield Models

• Size Class Distribution (Stand Table Projection)
  Models
• Focus on the trees per acre and volume per acre
  in diameter classes and project the classes over
  time
• Can back out individual tree data from them
• Can be applied to (developed for) even and
  uneven-aged stands

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Types of Growth and Yield Models

• Individual-Tree Models
• Focus on growing individual trees over time, and
  combining results to obtain stand-level
  information
• Primarily applied to (developed for) uneven-aged
  stands
• Tough to apply to larger acreages

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Measures of Growth

• Mean Annual Increment (MAI)
• MAI Size divided by Age
• Measures how much growth occurred per year over
  the life of a tree or stand
• The size attribute could be height, diameter,
  biomass, basal area, volume,

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Measures of Growth

• Periodic Annual Increment (PAI)
• PAI Change in Size divided by Years in a given
  time period
• Measures how much growth occurred per year over a
  set time frame (5 or 10 years common)
• The size attribute could be height, diameter,
  biomass, basal area, volume,

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Measures of Growth

• Current Annual Increment (CAI)
• CAI Change in Size over the most recent year
• Measures how much growth occurred over the last
  year
• The size attribute could be height, diameter,
  biomass, basal area, volume,

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Other Forest/Tree Measures
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Measures of Stand Density

• Basal Area per Acre
• Trees per Acre
• Stand Density Index
• Relative Spacing

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Stand Density Index

• A Standardized metric of relative density
  regardless of the size or age of an even aged
  stand

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Stand Density Index

• Stands with equal SDIs are equally dense,
  regardless of their respective stages of
  development
• If one stands SDI is larger than another, it is
  more dense, comparatively speaking, then the
  stand with a lower SDI value

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Stand Density Index

• Can compare densities of very different sized
  even aged stands!

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Relative Spacing

• Average distance (ft.) between trees divided by
  the average height (ft.) of the dominant and
  codominant trees (Hd)
• Is unitless (the units of feet cancel)
• Does sort of assume a square spacing so the
  metric is useful for plantations

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Relative Spacing

• RS

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Relative Spacing
Average growing space (sq.ft.) per tree
Length (ft.) of one side of one those squares
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Relative Spacing
Hd
As plantations become more dense, what happens,
numerically, to relative spacing ?
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Relative Spacing

• RS

If TPA increases and Hd stays the same, what
happens to relative spacing?
If Hd increases and TPA stays the same, what
happens to relative spacing?
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Relative Spacing

• Can compare how dense different sized stands
  are in relation to one another (like SDI, RS is a
  measure of relative density)

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Uses of Relative Spacing

• Might want to manage a plantation by thinning
  once a given relative spacing is reached
• Can assess potential for insect and disease based
  on relative spacing

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Stocking

• Stocking - adequacy of stand density to meet some
  management objective
• It is a relative term
• Understocked
• Fully-Stocked
• Overstocked

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Understocked

• Not enough density to meet a landowner objective
• If timber is your objective, having a stand in an
  understocked condition can lead to
• rough form (non-straight boles)
• excessive taper
• large live crown ratios (lack of lower
  branch mortality, possibility for
  epicormic branching)

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Overstocked

• Too much density to meet a landowner objective
• If timber is your objective, having a stand in an
  overstocked condition leads to
• stagnated growth
• excessive mortality
• trees in stressed condition
• small crown ratios

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Fully Stocked

• The correct amount of density to meet a landowner
  objective
• If timber is your objective, keeping a stand in a
  fully stocked condition leads to
• a closed canopy
• best growth

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Stocking Guides/Charts

• Charts that relate trees per acre and basal area
  per acre (and typically display quadratic mean
  diameter or average diameter) to different
  stocking levels with respect to a timber
  management objective
• Are species (or forest type) and regionally
  specific
• Can be developed for and applied to both even-
  and uneven aged stands

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Stocking Guides/Charts

• Lake States
• First developed by Gingrich (1967) so sometimes
  they are called Gingrich charts of Gingrich
  stocking charts
• Developed for upland hardwoods forests in the
  Central US
• Gingrich, S.F. 1967. Measuring and evaluating
  stocking and stand density in upland hardwood
  forests in the central states. Forest Science.
  1338-52.

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Upland hardwoods with QMDs in the 7 to 15 inch
diameter range
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Upland hardwoods with QMDs in the 3 to 7 inch
diameter range
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line A developed from stands at maximum density
line B developed from more open-grown trees
line C developed such that a stand could reach
line B within 10 years time (given a site index
base age 50 of 55 - 75)
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If below line C, consider regenerating the
stand, it will take too long to reach line B and
when it does, trees will have those understocked
issues
If at or near line A, it is time for a
selective harvest. As one marks a stand for
selective harvesting, make sure the residual
stand non-marked trees remain at or above the B
line Watchout for epicormic branching!
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If above line A, something needs to be done,
though the trees may not have enough crown or
vigor to react Be extremely cautious to watch
out for epicormic branching issues
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Useful Publication

• Dale, M.E. and D.E. Hilt. (year not known).
  Stocking chart for upland central hardwoods.
  North Central Forest Experiment Station Central
  Hardwoods Note 5.02. 3p.
• Available at
• http//www.ncrs.fs.fed.us/pubs/ch/ch_5_02.pdf

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What about Red Pine?