You will find that your figures will alter somewhat if the trees are predominantly faceing south.
The growth rings on one side of a tree will be broader where they are facing south , this will increase their polarity creating more pull.
All trees face south at some point of their trunk , so the only sure fire way to check their growth is to cut them down and look at their ring configuration .
When shooting over water cress you will note a downwards pull on your pellet , this will increase with the density of the cress coverage .
About as much use at field target , as a life guard at the Olympic swimming pool.