All this food must be taken from storage. Hot streaks mean healthy trees must close leaves and wait out the heat. It's like running on internal batteries. Old, young and badly stressed trees are much more at risk of damage, decline and death because they have little storage. The little stored food they have is being used at two to three times normal rates.
Trees can starve to death during long hot, dry periods.
During the heat, watering can help if you don't overdo it. In heavy clay soils, it's easy to drown already starving tree roots. Don't apply nitrogen fertilizers when soil temperatures are high and there is little water. Prevent mechanical damage and injury from landscape chemicals. Thin layers of mulch around a tree help conserve water and keep the root area cooler, which reduces food demands.