Sampling Techniques THE SEQUEL

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Sampling TechniquesTHE SEQUEL
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Warning!

• This material (and last weeks lab lecture on
  sampling) will be included on Lecture Exam 1!

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Importance

• Often we want to know how important plant
  species are in a sampled area
• Measures of importance of a species (sp. A)
• Density of A No. inds. per unit area (reflects
  abundance of A)
• Frequency of A No. of times sp. A found in
  samples divided by total number of samples taken
  (reflects pattern of A)
• Cover of A Percent of area occupied by A in
  sampled area (reflects biomass of A)

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Methods

• 1) Quadrat
• 2) Belt transect
• 3) Line intercept
• 4) Plotless (distance) methods

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Plotless (distance) methods

• Based on points
• Points have no dimensions, so this 0 dimensional
  method
• Often used with trees, as one samples along a
  transect through the forest

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Plotless (distance) methods

• Information Collected
• 1) tree identity
• 2) tree size (reflects biomass or cover)
• 3) distance measurement (from something to
  something)

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Plotless (distance) methods

• Method 1 Nearest individual method

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Plotless (distance) methods

• Method 2 Nearest neighbor method

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Plotless (distance) methods

• Method 3 Random pairs method
• A) find nearest plant
• B) draw line from pt to plant
• C) make exclusion zone
• D) measure distance to nearest plant outside zone

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Plotless (distance) methods

• Method 4 Point centered quarter method

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Plotless (distance) methods

• Information Collected
• 1) tree identity
• 2) tree size (reflects biomass or cover)
• 3) distance measurement (from something to
  something)
• IV Rel. density Rel. frequency Rel. cover
• lt300 lt100 lt 100 lt 100
• How get rel. density, rel. frequency, rel. cover
  values from this information?

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Plotless (distance) methods

• Cover have DBH values for each tree
• Convert DBH to area of trunk for each species
• relative cover of species Y
• Cover of Y/Cover of all species X 100

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Plotless (distance) methods

• Frequency Have tree identities for each point
• frequency of species Y
• No. pts. with species Y/Total number pts. X 100
• rel. freq. of sp. Y
• Freq. of Y/freq. all species X 100
• IV Rel. density Rel. frequency Rel. cover

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Plotless (distance) methods

• Density ?? No areas were measured??
• Relies on geometric principle as density
  increases distances measured should decrease
• Note importance of random placement of points to
  this relationship!

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Plotless (distance) methods

• Steps
• 1) Calculate mean distance (D) for all trees
  sampled
• 2) Use magic formula
• Density (all species) A/(correction factor)(D)2
  
• To express results in metric units
• A10,000 m2/hectare (ha)
• D should be in meters (m)
• Correction factor?

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Plotless (distance) methods

• Steps
• Correction factor?
• 2 for nearest individual method
• 1.67 for nearest neighbor method
• 0.8 for random pairs method
• 1 for point centered quarter method
• 3) Calculate density of species Y
• No. Y/No. all species X Density all species
• 4) rel. density of Y
• Density of Y/Density all species X 100

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Plotless (distance) methods

• Can now calculate IV of species Y
• IV Rel. density Rel. frequency Rel. cover
• lt300 lt100 lt 100 lt 100
• Repeat calculations for all other species

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Plotless (distance) methods

• Note on Point Centered Quarter method
• 1) Get more data per point
• 2) Relatively simple method
• 3) No correction factor needed in density formula
  (correction factor 1)

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How place sample units?

• Generally, random is best
• How define?
• All potential sample units have equal chance of
  inclusion in sample
• Why best?
• Eliminates bias on part of sampler
• May be required to use statistics or other
  equations (e.g., density formula for plotless
  methods) on the data

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How place sample units?

• Note random not same as
• Arbitrary Choosing while attempting to eliminate
  conscious bias
• Systematic Choosing using numeric pattern (ex,
  every 5th tree along transect)
• Deliberate Choosing with list of criteria (ex,
  all trees gt 30 cm dbh)

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How place sample units?

• But, random may not always give representative
  sample
• Example

X
X
X
X
X
X
X
X
X
X
X
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How place sample units?

• Techniques
• Random
• vs.
• Stratified random (subdivide area and sample
  randomly in each division)

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How place sample units?

• Techniques
• Systematic

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How place sample units?

• Techniques
• Random-Systematic (select starting place
  randomly, place points on transect systematically
  or vice versa)

systematic
random
systematic
random
OR