Question
I have just recently bought a house with two HUGE magnolia trees on either side of the house. Pretty sure that they are sucking all the water away from smaller trees (walnuts, hickorys, oaks).  

Can I prune--even top--these trees to make them less hungry and thirsty?  I like the shade and the fragrance but they are behemoths!  Would a large-scale bonsai tactic work? One is single stem, roughly 18-20" in trunk diameter, the other is bifurcated but overall the same size.

Is the circular driveway the old owner put in around the one going to compact the soil to the tree's death?

Located in the piedmont in north carolina. Thanks for your response.  

Answer
Topping a tree this large is not recommend since it will more than likely kill the tree You can prune the lower limbs. The other trees you mentioned will compete well with the magnolia for water-they naturally occur together so do not worry about them as far as water is concerned. The drive will not effect the health of the tree but the tree root may effect the drive if the drive is too near the tree. The trees roots may push up the drive--this will maybe a long time effect and will not happen for many years. Since you just moved in I would suggest you contact the N.C State Forestry agency and ask one of their forester to come out to your house and advise you on how to care for your tree in your yard. This is a free service if most states. Check your local phone book for the number of the N. C. Forestry agency  or their web link to their contacts is http://www.dfr.state.nc.us/