Indirect gradient analysis - Alaska Geobotany Center

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Interpreting the ordination Bray and Curtis Wisconsin Upland Forest 100.0 80.0 60.0 40.0 20.0 0.0 -20.0 -40.0 3 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 1 4 2 7 6 5 10 8 9 y • We have formed an “ordination space” where the axes are <strong>gradient</strong>s of floristic similarity. Stands closest together are most similar. • The negative y values for several of the plots on the second axis can cause difficulties for interpretation. Selecting two other endpoints for the axis could improve this. However, this is a function of the decision regarding reference stands, and is really amounts to viewing the ordination from different angles. • The x and y axes of the Wisconsin upland forest ordination are obviously strongly correlated and there is little new information displayed on the 2nd axis. • At this point, we have no idea what the axes mean ecologically. • The x and y axes can be correlated with environmental data for each plot with the x and y coordinates using three primary methods: – (1) isloline diagram s (as shown earlier in this lesson), – (2) Spearman s rank correlation. The variable with highest correlation with the x values best represents the x axis. – (3) Biplot diagrams. A group of correlation arrows centrally located in the ordination space to show direction and strength of correlations between environmental variables and the ordination space.
Polar ordination weaknesses and advantages • Advantages – Easy to visualize and understand – Relatively easily taught • Weaknesses – Axes are not orthogonal. This can cause considerable distortion of the ordination space. – Distances in the ordination space are not metric. – Not completely objective because of choosing of the reference stands, but this really amounts to different viewing angles.
Page 1 and 2: Lesson 18 Ordination II: Indirect g
Page 3 and 4: Vegetation Ecosystem Environmental
Page 5 and 6: Indirect gradient analysis • “I
Page 7 and 8: Plot ordinations vs. species ordina
Page 9 and 10: 1-, 2-, and 3-dimensional plot ordi
Page 11 and 12: Species ordination Species ordinati
Page 13 and 14: Relating the plot ordination to env
Page 15 and 16: Polar ordination • Developed by B
Page 17 and 18: Steps in calculation of the ordinat
Page 19 and 20: Jaccard s and Sorenson s similarity
Page 21 and 22: Similarity and dissimilarity for pl
Page 23 and 24: Step 2. Matrices of similarities an
Page 25 and 26: Calculation of x values along the 1
Page 27 and 28: Geometric determination of plots al
Page 29 and 30: Step 4. Define the second axis and
Page 31: Plotting the ordination Bray and Cu
Page 35 and 36: Example of isoline diagrams from Ba
Page 37 and 38: Example of Biplot Diagram from Anja
Page 39 and 40: Relating the ordination to environm
Page 41 and 42: Other ordination methods • Princi
Page 43 and 44: Summary • Oridination is based on

Indirect gradient analysis - Alaska Geobotany Center

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