Ron Fowler, in his nifty little book Making Perfect Landings, suggests turning onto final at about 400 feet agl. The advantage to this is that you are always starting the approach from the same altitude. If you are about a mile out, the visual approach slope indicator will show you to be on the proper glidepath. Day or night, this is good advice. But don't descend below pattern altitude prior to reaching the pattern.
Rough terrain is usually uninhabited and, therefore, unlit and difficult to see.
And if objects come between you and the runway lights during final approach, they are probably branches. Fowler suggests, as a touchdown target, a point on the runway at about the third set of runway lights. You should cross the threshold at a minimum of 100 feet. The FAA's Flight Training Handbook offers good advice on how to determine the roundout point. Fowler suggests having a go-around point in mind to avoid running off the end.