Questions for the Record for Dr

Intensive livestock grazing was an important cause of reduction in surface fire occurrence in many Western forests. This effect occurred primarily during the late 1800s and early decades of the 1900s. Very large herds of sheep, goats, cattle and horses removed the grass cover in under stories of ponderosa pine and mixed conifer forests. In 1890, for example, there were more than 5 million sheep and 1.5 million cattle in New Mexico! Prior to this intensive livestock grazing era, more-or-less continuous grass cover promoted fire ignitions by lightning and people, and extensive spread of these fires. Grazing and the creation of livestock trails and “driveways” effectively disrupted the fire ignition and spread process. The sheep industry declined after the First World War, and after 1910 the U.S. Forest Service also began to fight forest fires aggressively, and to reduce overgrazing on federal forest lands. During the subsequent century, lack of frequent surface fires in ponderosa pine and mixed conifer forests allowed many trees to establish and dead fuels (tree needles, branches, logs, and snags) to accumulate. This general history did not occur everywhere in the West, but it was fairly typical in the Southwest and in many pine-dominant and mixed conifer forests of the Sierra Nevada, and inter-mountain regions (Swetnam and Baisan 2003). This effect of livestock grazing, fire suppression, and subsequent fuel accumulation was generally not important in relatively higher elevation, wetter forests, such as spruce-fir and lodgepole pine forests. Grass cover was much less extensive in these forest types, and typically large fires only occurred at long intervals (>100 years), so fire suppression has had less or no effect here in lengthening the intervals between fires (Schoennagel et al. 2004).