The authors found that fire was frequent with median intervals of less than 15 years in the Jeffrey pine-mixed conifer forests. However, a period of reduced fire occurrence from the 1790s to 1830s coincided with a similar fire-free period across the Southwest and southern South America. The authors and others found a reduction in the amplitude of ENSO during this time that likely contributed to this reduction in fire occurrence. However, an increase in livestock grazing intensity and a reduction of fire use by native peoples occurred at the same time and likely also had strong influences on the fire regime during this period.