to determine if you need to transform specific variables, you need to have a look on 2 things (Clarke and Gorley, 2006):

1) “are the samples roughly symmetrically distributed across the range of each variables” (i.e. are your samples skewed to one side)?

2) “if there are strong relationship between some pairs of variables, are these roughly linear rather than strongly curvilinear?”

Based on your draftsman plot, your samples are not really skewed on one side. So you do not necessarily need to transform your data, although you do have some outliers stuck to one side. So you could try a mild transformation (e.g. square root), and see if it improve or not the draftsman plot.

Sometimes if you have a doubt about transformation of your environmental variables, perform a mild (square root) or strong (log) transformation and run again the draftsman plots and see if you improve or not the plots. If not, do not bother with transformation. Sometimes just trying will help you to make your choice. Otherwise, as I mentioned, you mainly need to check if your samples are not skewed to one side or if you do not have outliers that skewed your data.

Hope that help,

Aimeric

Thank you very much Aimeric. Helpful indeed! Now I'm sure how to proceed.

Cheers.