I was reading Cannabinoid Chemistry - 6.2 Extraction & pondered over the following:
Cannabis must be dried be(fore) it is extracted, because it is not possible to remove more than 50% of the cannabinoids from fresh material. THC-Acid is difficult to extract. If you plant(sic) to convert the THCA to THC, the plant material should be thoroughly decarboxylated by heating it under nitrogen at 105℃ for 1 hour before performing a solvent extraction.
Why is decarboxylation done 'under nitrogen'? My first guess would be that at 105℃ the plant begins to oxidize (but that is just my naive guess).
I've also sourced this graph:
Effect of heating time and temperature on the THC content of an n-hexane
after heating on the glass surface in an open reactor. Journal of Chromatography 520 (1990).
Which suggests that 122℃ for 27-30 minutes will be even more effective for decarboxylation, but if the sample begins to oxidize at 105℃ it seems even more important to get the right mixture of gases around it at 122℃.