I've been searching around and it seems ACR installs 1.62 so that is a problem for me. But looking back at the screenshots initially released by BI the trees are bad in them too and also others on BI's forums are having the same problem with bad LOD.
See this screenshot and this is what I see but worse sometimes:
Look at the trees on the hill on the left and the tree that looks like a flat model is what happens also the trees in the distance appear really flat even with distance pushed right out to maximum.
This happens with ATOC on and off and doesn't appear to make any visible difference at all. I bought ACR for the units etc and didn't expect it to ruin ARMA 2 for me