Indirect gradient analysis - Alaska Geobotany Center

Summary
• Oridination is based on ordering vegetation types according to their
floristic similarity. It can also be used to examine the similarity of speicies
distribution within samples.
• The Bray and Curtis (polar ordination) method was the first indirect
ordination method. It was based on simple geometric principals that
showed plots in relation to each other based on their floristic similarity.
• There are several ways to relate ordinations to environmental gradients,
including isoline diagrams, biplot diagrams, and correlation of the axes
with environmental variables.
• Numerous more modern methods of ordination have been developed in
response to perceived weaknesses of the Bray and Curtis method. All of
these have specific assumptions and their own weaknesses that must be
recognized, and users of these methods should make sure they
understand these aspects before using the methods.
• PC-Ord is a good PC-based program that permits easy application of a
variety of ordination methods.