While photosynthesis has its optimum in cool days and decreases when the weather becomes too hot, respiration does not have such an optimum. The warmer it gets, the more intense is the respiration. Respiration is less sensitive to the lack of water than photosynthesis; that is why during droughts, when photosynthesis stops, respiration still continues and causes great harm to the tree. Inside temperatures of 120° to 130° F. are deadly.