Bark Beetles of the Southern California Forests

Bark Beetle and Fire Danger

The risk of fire is based on a number of factors including fuel loadings (the type and density of the fuels), fuel moisture (the moisture content of the fuels, primarily vegetation), and the fire weather outlook (air temperature, relative humidity, precipitation, wind conditions). The combination of these factors is used to determine the fire danger, which includes components for energy release (estimate of potential energy released in the active portion of the fire) and fire behavior (potential for surface fire, crown fire, or plume-dominated fire). During the summer and early fall of 2003 the risk of fire based upon all of the above factors was determined to be extremely high for the wildlands of Southern California with a high potential for large fires that would burn large tracts of land (Henson 2003).

The bark beetle killed trees reduce the overall fuel moisture in areas where large numbers of dead trees stand. The dead, dry trees burn faster and hotter than living trees within any given stand. Standing dead trees will burn to a crown fire. Whether or not the crown fire of a dead tree will be transferred to the surrounding living trees depends on the proximity of the live trees to the dead trees and the other conditions at the time of the fire.

The Old Fire in the San Bernardino National Forest was initiated by arson in two locations, Old Waterman Canyon and near the community of Crestline. The conditions were prime for the firestorm that consumed over 91,000 acres of land, 993 homes, and 10 commercial properties. The majority of the acreage consumed was chaparral. The areas of forest that burned had a high proportion of standing dead vegetation. Below are maps showing the type of fuels present in the San Bernardino National Forest and the extent of the Old Fire. Although the scales are different, one can see that the fire consumed more chaparral than forest. The efforts of the firefighters and the change in weather conditions allowed the containment of the fire before more acreage was lost.

Fuel Model Map
Fuel types of the San Bernardino National Forest
Source: Mountain Area Safety Taskforce

Extent of the Old Fire, San Bernardino County, CA
Source: Mountain Area Safety Taskforce

The photographs below show burned areas south of Highway 18. The photograph on the left shows that the fire consumed all of the chaparral of the foothills but left the majority of the forest intact. The photograph on the right shows the patchy nature of the burn where the fire approached the forest, and also again shows that the majority of the forest remains intact.

image of chaparral burned and forest intact image of fire from Hwy 18
Burned chaparral from the Old Fire, October 2003 Patchy burned forest from the Old Fire, October 2003
San Bernardino County Museum