The work performed by GexCon clearly shows that the trees surrounding the tankfarm played a major role in causing the high explosion overpressures that destroyed a majority of the tankfarm site and neighbouring buildings.

A presentation of the Buncefield accident investigation was given by Dr.Kees van Wingerden in Milan in 2009 on a FLACS industry seminar:

A copy of the presentation can be found here
The report from the experimental study showing the influence of trees on flame acceleration can be downloaded from here