MIXED-CONIFER FOREST MORTALITY AND ESTABLISHMENT BEFORE AND AFTER PRESCRIBED FIRE IN SEQUOIA NATIONAL-PARK, CALIFORNIA

Pre- and post-burn tree mortality rates, size structure, bas at area, and ingrowth were determined for four 1.0 ha mixed conifer forest stan ds in the Log Creek and Tharp's Creek watersheds of Sequoia National P ark. Mean annual mortality between 1986 and 1990 was 0.8% for both wat ersheds. In the fall of 1990, the Tharp's Creek watershed was treated with a prescribed burn. Between 1991 and 1995, mean annual mortality w as 1.4% in the unburned Log Creek watershed and 17.2% in the burned Th arp's Creek watershed. A drought from 1987 to 1992 likely contributed to the mortality increase in the Log Creek watershed. The high mortali ty in the Tharp's Creek watershed was primarily related to crown scorc h from the 1990 fire and was modeled with logistic regression for whit e fir (Abies concolor [Gord. and Glend.]) and sugar pine (Pinus lamber tiana [Dougl.]). From 1989 to 1994, basal area declined an average of 5% per year in the burned Tharp's Creek watershed, compared to average annual increases of less than 1% per year in the unburned Log Creek w atershed and in the Tharp's watershed prior to burning. Postburn size structure was dramatically changed in the Tharp's Creek stands: 75% of trees less than or equal to 50 cm and 25% of trees >50 cm were killed by the fire.