Identical trees not reacting equally to wind

Hi, I have applied a tree model to the terrain, with all the trees being exactly the same height. I have added a wind zone to the scene and the trees are reacting to it. The problem is the trees are reacting with different strengths to the wind, even though they are identical. Some are bending really harshly, w$$anonymous$$le others are hardly affected at all. There also does not appear to be any pattern between those that are affected heavily and those that are not.

Does anyone know how to correct t$$anonymous$$s issue?

thanks