Comparison of indirect ordination methods for analysis of the vegetation (Case study: Urmia airport plantation)

This study aimed at investigating a range of widely-used approaches for indirect ordination analysis of vegetation. To this aim, a black pine (Pinus nigra Arnold.) plantation (9.2 ha) located at Urmia airport was studied. Nine plots of 100 m2 each were randomly set up in 50×50 m sampling grid, in which vegetation was recorded. In addition, three plots of 100 m2 with 50 meters interval were set up along transect in an adjacent meadow site as control area. We evaluated three ordination techniques (Principal Component Analysis, Detrended Correspondence Analysis, Non-Metric Multidimensional Scaling) with varying values of gradient length, Kaiser-Guttman, Broken stick, 70% of variance, eigenvalues > 0.4, final stress in NMDS ordination and Procrustean analysis. Result showed that all three ordinations are able to illustrate length of environmental gradient, though Procrustean analysis of all three datasets revealed significant differences in correlation between ordination methods. DCA had eigenvalues > 4.0, and the covered Kaiser-Guttman criterion with an axis. Moreover, final stress was < 10 in NMDS ordination, yet PCA covered Kaiser-Guttman and broken stick criteria at three axes. In conclusion, the most appropriate ordination methods across our test site included DCA and NMDS