Why does the 82℃ heat spike always happen in the rainforest?

AIDA64 showed 82℃ and 30 FPS in the rainforest, a hard floor. I tried disabling foliage, but GPU-Z still logged 1800MHz throttling. Using GamePP Fan Curve Configurator, I set 60℃ to 85% and 75℃ to 95% speed. Now AIDA64 reports 68-74℃ and RTSS tracks 11-12ms frame time. The visual detail is back.