Friedrich Casimir Gustav Heyer (11 March 1826 – 10 July 1883) was a German forestry professor and son of Carl Heyer who was also a famous forester.
Gustav was the first son of Carl Justus Heyer and was born in Giessen where his father taught forestry.
After school he went to study science under the guidance of his father.
In 1849 he joined Giessen University to teach forest science.
His body was found only on the 14th of July at Emmering in the river Amper downstream of Bruck (near Munich).