The Science of Plant Ecology

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The Science ofPlant Ecology
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Warning!

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

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Research

• Secondary research Gathering data about facts
  already known
• Primary research Generates new knowledge

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Scientific Method
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Scientific Method

• Hypothesis Possible explanation for a
  phenomenon. Must be testable by experiment
• Experiment Test of an idea by observation or
  collection of data

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Experiments

• Manipulative experiment Compare a treated
  condition (manipulated) against a control
• Control Keeps other conditions the same

Fig. 1.2
Konza Prairie (KS)
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Experiments

• Natural experiment Manipulative experiment
  occurring due to natural process

1980 eruption
Mt. Saint Helens, OR
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Experiments

• Observational experiment Study of variation
  occurring under differing natural conditions

Fig. 19.12 Tree species richness (
species) across N. America (in standard area
plots)
AU!
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Theory

• Theory Broad, comprehensive explanation of large
  body of information. Essentially equivalent to
  scientific fact
• Examples Theory of gravity, Theory of
  relativity, Theory of evolution, Atomic theory

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Plant Sampling Techniques
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Sampling Why?

• Best way to find answer is to take 100 sample
  (count/measure everything)
• Usually not practical
• Ex, describe vegetation of Lee County AL

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Accuracy vs. Precision

• Accuracy how close to true value samples are
• Precision similarity of measurements to each
  other

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Accuracy vs. Precision

• Accuracy cant be known unless 100 sample taken
• Precision standard error of mean (S)

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Sampling

• Choosing a technique depends on
• 1) Desire for accuracy/precision
• 2) Objective of study
• 3) Time/money
• 4) Tradition!
• Solution Be reasonable! (compromise often needed)

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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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Focus on Cover

• Many ways to get cover (biomass) data
• 1) harvest and measure biomass
• 2) visual estimation
• Note how canopy edges filled in by observer

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Focus on Cover

• Many ways to get cover (biomass) data
• 1) harvest and measure biomass
• 2) visual estimation
• 3) point frame
• 4) moosehorn crown closure estimator

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Focus on Cover

• Many ways to get cover (biomass) data
• 5) Trees basal area (area of tree trunk per unit
  area of sampled location). Bitterlich method.

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Focus on Cover

• Many ways to get cover (biomass) data
• 6) Trees DBH (diameter at breast height 4.5
  feet or 1.3 m)

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Focus on Cover

• These methods have different speeds, accuracies,
  precisions, applicability to plant growth forms,
  etc.

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Other Challenges

• Clonal plants problem with density (how
  determine what an individual is?

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Other Challenges

• Canopy overlap hard to see where boundaries end

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Other Challenges

• Border calls is it in or out of the sample plot?
• Solution Be reasonable!

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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 ANo. inds. per unit area (reflects
  abundance of A)
• Frequency of ANo. of times sp. A found in
  samples divided by total number of samples taken
  (reflects pattern of A)
• Cover of APercent of area occupied by A in
  sampled area (reflects biomass of A)

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Importance

• Calculate Importance Value (IV)
• Defined as sum of Relative Density, Relative
  Frequency, and Relative Cover
• IV Rel. density Rel. frequency Rel. cover
• lt300 lt 100 lt 100 lt 100

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Sample Techniques

• 1) Quadrat methods
• 2 dimensional sample unit used quadrat

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Quadrat Method

• 1) Shape?
• Oblong better picks up more variation per sample
• But less perimeter means less in/out decisions
  (source of error)
• Compromise be reasonable!

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Quadrat Method

• 2) Size?
• Note this is VITAL for determining plant pattern
  (and important for density measurement as well)
• Can get idea of best size using species-area curve

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Quadrat Method

• 3) Number?
• Suggestions include
• A) Sample 1-20 of area being described
• B) Include 95 of species in area
• C) Use Running Mean Graph (Quadrat Sampling Lab
  4)

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Belt Transect Method

• Also a 2 dimensional method
• Useful in dense vegetation
• Useful for sampling along sharp environmental
  gradient

2m
2m
Environmental gradient
2m
2m
4 species of plants A red, B turquoise, etc.
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Belt Transect Method

• Example diagram and calculation of Importance
  Value of species A

2m
2m
Environmental gradient
2m
2m
4 species of plants A red, B turquoise, etc.
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Belt Transect Method

• Density of A 10/40m2 0.25/m2
• Frequency of A 9/10 0.9
• Frequency of A 0.9 X 100 90

2m
2m
4 species of plants A red, B turquoise, etc.
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Belt Transect Method

• Cover of A Assume we visually estimate covers of
  each species in each unit of transect
• Assume values for A are
• 10, 15, 15, 10, 0, 10, 5, 5, 10, 10
• Mean cover of A Sum of covers/10 9

2m
2m
4 species of plants A red, B turquoise, etc.
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Belt Transect Method

• Do density, frequency, cover calculations for all
  other species (B, C, D)
• IV Rel. density Rel. frequency Rel. cover
• For sp. A
• Rel. density density of A/density of all
  species X 100
• Rel. frequency frequency of A/frequency of all
  species X 100
• Rel. cover cover of A/cover of all species X
  100
• Can then calculate IV for other species (B, C, D)

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Belt Transect Method

• You will do IV calculations for species in lab 1
  (plotless sampling) and lab 4 (quadrat sampling)

Quadrat lab
Plotless lab
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Line Intercept Method

• 1 dimensional method (line has no width)
• Useful for dense vegetation scrub

Scrub in Australia
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Line Intercept Method

• Cover record distances along line covered by
  canopies of species
• Cover frequency Divide line into units.
  Determine frequency of species in those units
• Density?