Why do our forests burn?
This website concerns itself with forest fires in the ponderosa pine forests of the American Southwest and southern Colorado Plateau uplands. Ponderosa is the most widespread forest type in western North America, with about 36 million acres from British Columbia down to Mexico.
Fire is a natural part of the ecology of western forests. Some forest types burn infrequently in high-intensity, stand-replacement fires, while still others experience a range of burning intensities and frequencies, or fire regimes. Ponderosa pine forests in the Southwest, with its semi-arid climate and abundant lightning, burn naturally in frequent, low-intensity fires. Today these small fires that once renewed the forest now risk quickly becoming stand-replacing crownfires.
Before Anglo settlement, early explorers described open ponderosa stands with an understory of native grasses and herbaceous plants. Research reveals that these forests experienced low-intensity ground fires at intervals ranging from 4 to 36 years, apparently related to short-term climate cycles. Lightning strikes could have been the source of ignition for all of these fires, but Indian burning may also have been a factor.
Land-use management and practices since settlement have led to dramatic changes in forest composition, structure and function. Intensive livestock grazing beginning in the 1880s and fire suppression policies in the early 1900s, coupled with widespread logging, led to forest conditions prone to catastrophic fire.
Tree densities in today's forests are far greater than they once were. Many areas are characterized by "dog-hair" thickets of young pines with heavy fuel loads of pine needles and other litter on the forest floor.
During periods of drought and other climatic stresses, bark beetles invade the forests, often killing entire stands of trees and increasing fire danger.
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Greville, F.: ”An Inquisition Upon Fame and Honour”, in Greville: Poems and Dramas. London 1939, 1633.
Last edited June 6, 2003