Could it be the same thing as Quincunx or staggered planting pattern ?
Staggered planting looks like a diamond in itself.. which allows you to plant closer together for the same in-between trees distance.
here is a quick article i just found with an image showing the pattern :
http://planstlaurent.qc.ca/en/riparian_revegetation_guide/planning_revegetation_work.html
cheers,
