Indirect gradient analysis - Alaska Geobotany Center

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Step 3. Compute first axis of the ordination and position all plots along it 1. Sum all the similarities for each plot. 2. Select the plots at the ends of the first axis. These are the plots that are least similar to all the other plots and least similar to each other. The plot at the left end of the first axis has the lowest sum of similarities, i.e. is least similar to all other plots. Here Plot 3 is least similar to all the others. 3. The plot at the right end of the first axis is the one with the least similarity to the first. Here Plot 9 is most dissimilar to Plot 3. The maximum possible dissimilarity between these plots is 100%. The dissimilarity between the two stands defines the length of the first axis. 4. Locate all the other plots with respect to these two reference stands based on their geometric relationships.
Calculation of x values along the 1st axis A and B are the plots at the ends of the first axis. P is the plot to position with reference to the A and B. P has dissimilarity of dA with reference to Plot A and dissimilarity dB with respect to Plot B. Solving for x: x 2 + e 2 = (dA) 2 , e 2 = (dA) 2 - x 2 (L-x) 2 + e 2 = (dB) 2 (L-x) 2 + (dA) 2 - x 2 = (dB) 2 L 2 - 2Lx + x 2 + (dA) 2 - x 2 = (dB) 2 L 2 - 2Lx + (dA) 2 = (dB) 2 x =( L 2 + (dA) 2 - (dB) 2 )/2L Using a compass, P can be positioned with respect to A and B. The perpendicular from P to the first axis is e. x is the distance of P from A and is calculated by the Pythagorean theorem.
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: Step 2. Matrices of similarities an
Page 27 and 28: Geometric determination of plots al
Page 29 and 30: Step 4. Define the second axis and
Page 31 and 32: Plotting the ordination Bray and Cu
Page 33 and 34: Polar ordination weaknesses and adv
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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