Really nothing exceptional if you remember the section
on sampling. Most visited squares are sampled only once,
and not with harvestmen in mind.
The extremely rich (black) squares are easily explained.
They are (from left to right) where W. Slosse had pitfalls,
where I had pitfalls during the eighties and where
R. Kekenbosch
still continues his pitfall campaign.
Green squares stand mostly for campaigns where the
positioning
of the pitfalls did not cover the whole
diversity of the site.
Yellow squares are easy: use the umbrella, or visit a
second time.
My conclusion is that the species richness as we see it
today is a reflection of our sampling effort and nothing more.
Every species is probably present in every square.
I love numbers; show me the map with the numbers.