For the Acer, I would suggest: Keep the soil consistently moist, but not waterlogged. Give it a slow, deep watering around the root zone rather than repeatedly sprinkling a little water on the surface. Mulch around the base with a layer of organic mulch, keeping it a little away from the trunk. This helps retain moisture and keeps the roots cooler. Don't fertilise it yet. A severely stressed tree doesn't need encouragement to produce lots of new growth; it needs recovery time. Don't remove apparently dead branches immediately. Wait and see. A small scratch on the outer bark of a twig can sometimes reveal whether there is living green tissue underneath. If you're unsure, leave pruning until you're confident which wood is dead. Protect it from further heat and drying winds if possible. Temporary shade can help, particularly during extreme heat. Be patient. Some Japanese maples can look alarmingly bare after heat stress and subsequently produce another flush of leaves.