no no there is still air behind an object, therefore lift is maintained. what you're describing is turbulance. turbulance is different than lift. turbulance can and does have an adverse effect on flight. for example you were set up to fly a certain path based on the winds, perhaps a little left aileron. as you passed behind a tree the wind was blocked or perhaps swirled around the tree, suddenly you don't need that left aileron, now you're "over steering" to the left cause the force that required you to use left aileron has changed. however lift was maintained throughout.