I normally hunt fairly flat land, but am considering a tree stand. If I shoot instinctively, do I need to make a mental adjustment for shooting downward?

Practice from above and it will be fine.  You also need to correct your mind set on aiming points on the deer, since you have a new perspective.
ChuckC

thanks!

When shooting from a tree stand be sure you do not just lower your bow arm to get on target--bend at the waist so your arm/body angle remains the same as when shooting on the ground.

When shooting from a tree stand be sure you do not just lower your bow arm to get on target--bend at the waist so your arm/body angle remains the same as when shooting on the ground.

Sorry....double post.     Oops, I guess triple post. NEVER had that happen here before!

You can practice by shooting from a ladder, the garage roof or even shooting out of a window. And do what David said and said.  

Bend at the waist and you'll have to shoot a bit lower too.  This is going to turn into a long thread I predict.  Some folks will talk about gravity effect, some will talk about longer shooting distance , no difference in either.  

All you have to remember is shoot for the horizontal distance from the bottom of the tree to your target.  It always looks farther shooting from above and that's why I mentioned to shoot low.  It's the same for uphill shots.

thanks guys.  more responses than I figured.  obviously, the first thing to do is practice.  I'll be getting on my roof today.  thanks again.