Canonical Correspondence Analysis: how to interpret results

Hi, I am using Canonical Correspondence Analysis (CCA) to analyze phytolith abundances (similar to pollen) over environmental gradients. As I am new to CCA, I read some background info. The following section from explains how to look at the visualization of results (Buttigieg & Ramette, 2014):

How to relate samples and taxa to environmental gradients in a triplot

To assess the impact of the environmental gradients on samples or taxa, they should be projected orthogonally on the arrows representing the environmental gradients (samples: figure a, taxa: figure b ). Close to the arrowhead indicates strong representation, far away from the arrowhead (represented by dashed prolongations of the gradients in figures x a and b) indicates weak representation (Buttigieg & Ramette, 2014).

Figures a and b: how to relate samples (a) and taxa (b) to environmental gradients in a triplot? Samples (a) or taxa (b) are projected orthogonally on the arrows representing environmental gradients or their prolongations (dashed lines). Close to the arrowhead means strong representation, far from the arrowhead means weak representation **(****Buttigieg & Ramette, 2014) **.

My question relates to the dashed prolongation lines of the arrows (which represent environmental gradients): the direction of the arrow represents a stronger impact of that particular environmental gradient (Buttigieg & Ramette, 2014). But what when the orthogonal projection of a sample/ taxon ends up on the far end of a dashed prolongation line of such an arrow/ environmental gradient? Does that mean that this environmental gradient has a strong negative impact on the overall abundance of a sample/ abundance of an individual taxon?

Thank you in advance


This might not be the best place to ask this question, since I’m wondering if there are much people around here that will know the answer. You might want to try to find a site that suits your question in this community:

since usually there are more experts on those specific areas around.