Transcript Community measurement

Community Measurements
Indirect Gradient Analysis
o
Use Importance Values (Sum of Relative
Frequency, Rel. Dominance, Rel. Density)
Indirect Gradient Analysis
o
Develop
Climax
adaptation
number for
each species
(By
comparing the
stands with
different
leading
dominants)
Indirect Gradient Analysis
o
o
o
Those stands
the most
different are
placed at either
end
Those most like
the extremes
are placed close
to them
#’s are assigned
based on
similarity
Indirect Gradient Analysis
o
Use Importance Values (Sum of Relative
Frequency, Rel. Dominance, Rel. Density)
o
Develop Climax adaptation number for each
species (By comparing the stands with different
leading dominants)
o
Continuum Index for stand = ∑Imp. Val. x Climax
Adaptation # for each species found in stand
o
Plot the dominant species with point for each
stand (Imp. Value on Y axis; Cont. Index on X)
Distribution & Abundance
Direct Gradient Analysis
o
Some figure (usually density) plotted against an
environmental gradient (such as elevation)
Direct Gradient Analysis
o
If difficulty in measuring environmental factor:
• Classify species into ecological amplitude
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Trees: a)mesic b)submesic c)subxeric d)xeric
Values assigned (a=0, d=3)
For each stand count individuals in each group
Then multiply value X # of individuals in that group.
Sum products and divide by total # of individuals
One value for trees & tall shrubs, one for
herbaceous plants, then plot values
Continuum classes
Possible outcomes
Gradual vs. Steep (Whittaker)
Great Smoky Mtns.
Siskyou Mtns.
Ordination
o
Similar to Gradient Analysis
•
Stands ordered according to composition and
abundance, often with cluster analysis
o
Stands are plotted on a 2-dimensional grid
o
Values for each stand assigned to environmental
factors are then plotted
o
Look to see trends of factors that correlate with
the spread of the stands studied.
o
Stands may also be plotted geographically
Similarity Index
o
Coefficient of Community

CC = 2Sab/(Sa+Sb)
Where: Sa = # of species in sample A only
Sb = # of species in sample B only
Sab = # found in both samples
o
Same formulation as the Bray and Curtis
Similarity Index (simply different terms used)
Old Growth Forests - LS Index
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Northern Hardwood Index
200m X 10m plots (or transect taken)
Count trees over 16”dbh and trees with
lichen (Collema or Leptogium)
o
LS index then places the
stand in one of the
categories seen here