Vaporization of cannabis compounds begins first with the terpenoids at around 130 degrees F and continues up to 350 degrees F. The idea is to heat up the material enough to release the desired compounds (cannabinoids, terpenes) into a gas form, without causing combustion of the undesirable compounds. Excessive heat from combustion can also destroy some of the cannabinoids and terpenes.
MedicalJane has an excellent article on vaporizing here…
https://www.medicaljane.com/category/cannabis-classroom/consuming-cannabis/vaporization/#types-of-vaporizers
They note that a joint can burn as hot as 2,000 degrees F!
andrewvanmd