Thank you for a very useful post. I have now successfully used orditorp() to make a nice and tidy plot of my RDA. However, when I use text() to add biplot arrows to the plot, tick marks automatically appear on the top and right axes. Do you know how I can remove these?

It's hard coed in the vegan:::text.cca() function. The reason being I guess is that you need a scale of reference for the biplot arrows as the one used on the bottom and left is not appropriate for applying a quantitative scale to the biplot arrows. You'd need to study vegan:::text.cca() to see how it draws the arrows and then copy the essential bits into your own function that suppressed the two calls to axis() towards the end of the function.

Thank you. I'll give it a try.

It worked! I just had to delete the two lines of code calling the axes. Again, thank you so much! Looking forward to your next post.