Drainage basin morphometry, including the size, shape, and orientation of the drainage basin, influence the magnitude of channel change. Giant sequoias were much more widespread in the geologic past. Giant sequoias and the forests in which they grow have been manipulated, mostly in the form of fire management, by humans even before arrival of Europeans. Changes caused by human manipulation indluce density and composition of flora and fauna. Giant sequoias require fire in order to successfully reproduce in adequate numbers.
Fire also influences distribution of giant sequoias within groves.
Apparently the most important factor limiting extension of giant sequoias' range is the combination of poor seed dispersal and lack of adequate soil moisture outside current groves. However, recent work by Schaffer apparently emphasizes process geomorphology and field work and interpretation not driven by theory. Schaffer's work is hotly disputed. Several workers have proposed that the channel formed by overflow of Pleistocene Lake Manly. However, direct evidence of overflow is scant.