1st, I copied all of the terrain in the way of the model origin.
Then I used the clip tool to cut a path to the tree.
I pasted the terrain in again, clipping it the opposite way, so it would fill in the top, where the terrain was missing.
Lastly, I turned the top half of the melded triangles into one func_wall.
Ta-da !
Now ya still see it !
I did it just before I read that, actually.
Then, of course, I was all worried about it looking like crap !
lolz !!!
It looks normal though, thank goodness.
Cheers again !