Echoing around the tree and animals will make the applique 'pop' so I would definitely do that. I would be careful about quilting through the back and the batting only because it can make them pull away from the front. An echo line of quilting right next to the applique will secure all three layers. Sometimes if an applique is large, people will 'simulate' the hand quilting look on he back and that doesn't go through to the front, but it is only for looks.