We have experienced the very hot (100 degrees and above during the day with nighttime lows of about 75 degrees) weather of our typical July/August days. Some of the trees are suffering and some are happy about the heat. Maples, Elms, Crabapples, Oaks, Beeches and some Boxwoods will have brown leaves or the leaf margins will be burnt. Not to worry. Look for the emergence of small green buds below the damaged tissue and you will see them coming out behind the ones that are dead. Some bonsai people call this process defoliation without scissors.
On the other hand Pines, Junipers, Holly, Ficus and Pyracantha are quite happy as the heat gets hotter. The hot days and nights seem to agree with their individual needs and they tend to grow most when our deciduous trees are basically stopped. Just remember to water well. Take off the crispy leaves and the bonsai will look niceras the new leaves emerge.