This refers to the temperature from bed to bed.  It can refer to the wood-chip temperatures or the dryer gas-inlet temperatures. For wood chips the desired temperature-profile is to always keep the chips below about 150F to prevent “blue haze”, and usually to have the outlet chip temperature below 120F in preparation for further processing. The dryer gas temperature profile can begin at 500F is the chips are wet (they cool immediately on contact with chips due to water evaporation).  However, the dryer gas temperatures must be much lower at the back end of the dryer (under 200F) to prevent overheating the chips.