Rii description needed

The Rii effect size estimate now becoming increasingly common in plant interaction studies needs description. Here is the citation to original paper: Armas, C., Ordiales, R. and Pugnaire, F. 2004. Measuring plant interactions: a new comparative index. – Ecology 85: 2682-2686 and link to the pdf online.

Idea (do a meta of the studies using it to date):

Rii description