Fire Regime of the Lodgepole Pine (Pinus contorta var. murrayana) Forests of the Mt. San Jacinto State Park Wilderness, California

For the purpose of providing recommendations for the fire management plan of the Mt. San Jacinto State Park Wilderness, California, the natural fire regime of the lodgepole pine forests within the wilderness was determined. Fire-scarred lodgepole pine trees were cored, and their growth rings crossdated against a composite ring series, to obtain fire date estimates of fires that have burned within the forests during the last 300 years. U.S. Forest Service fire records and personal accounts were also used to determine recent fire history.Results indicate that the fires within the lodgepole pine forests of Mt. San Jacinto probably were quite small (< 0.4 ha). Because of this, the fire regime is probably one of low-intensity fires. Fires started principally by lightning and they generally did not spread far because of low woody fuel loading on the ground. These small fires, however, occurred quite frequently throughout the lodgepole pine forests. Fires probably burned every one to two years, and in many years, more than one fire burned. The average fire return interval for separate locations within the lodgepole pine forests was not determined exactly because most of the burned trees had only one fire-scar.The effects of this fire-regime on the forest vegetation composition was determined. This was accomplished with multiple regression analyses of vegetative and physiographic data collected from the area of each verified fire.In the 2500 to 2900 m elevation range, white fir generally increased in importance (relative basal area) over lodgepole pine as years since the fire increased. However, the relationships of lodgepole pine and white fir importances to the time since the fire were not statistically significant. Above 2800 m elevation, neither lodgepole pine nor limber pine importance was affected by the fire regime. Throughout the lodgepole pine forests of this wilderness area, the fire regime has not greatly affected the forest vegetation composition.To compare two methods of obtaining fire year estimates from living, fire-scarred trees, both wedging and coring was done on ten fire-scarred lodgepole pine trees. The rings of the wedges and cores were then crossdated against a composite ring series, and the respective fire year estimates of each method were compared for each tree. Seven pairs of wedges and cores were crossdated, and each pair gave the same fire year estimate for the respective tree. In the situation of single-scarred trees, the coring method, along with dendrochronology dating, should be attempted instead of wedging, which is more destructive to the tree than coring.Based on this study, I recommend that the fire management plan for the lodgepole pine forests of the Mt. San Jacinto State Park Wilderness contain two options for fire control. First, in areas that have heavy use by recreationists and cultural or historical benefits, fire suppression should begin immediately after a fire has been detected. Second, in all other areas, a “let burn” policy should be attempted, whereby the fire would be allowed to die out on its own. This would save the expense of fire suppression, which can be very costly in remote wilderness areas. These fires should be monitored in case they do burn near valuable areas. Prescribed burning is not recommended because of the weak relationship of the fire regime to the forest vegetation composition.

Please contact the Laboratory of Tree Ring Research to view this thesis.