TREATMENT DURATION AND TIME SINCE DISTURBANCE AFFECT VEGETATION DEVELOPMENT IN A YOUNG CALIFORNIA RED FIR PLANTATION

The density and development of greenleaf manzanita, snowbrush, goldenb ush (rabbitbrush), and graminoids were evaluated in a young California red fir plantation in northern California from 1986 through 1995. Man ual grubbing and herbicides created treatment regimes that lasted for 3 to 6 years and vegetation recovery times of 4 to 10 years. The durat ion and timing of the grubbing and spraying operations constituted the treatments. Species response was mixed: greenleaf manzanita had highe r average values of density, foliar cover, and height when time since disturbance was longest, snowbrush density was lowest but cover and he ight were highest, and values for goldenbush and graminoids in general showed no trend. In the control at the end of the study, graminoids n umbered 82,350 per acre, greenleaf manzanita 10,850, goldenbush 10,800 , and snowbrush 1,850 plants per acre. Foliar cover of manzanita at 7, 300 ft(2) per acre was more than that of all other naturally establish ed species combined. Survival of red fir over all treatments after one growing season was 98 percent and after 10 seasons was 89 percent. Av erage height of red fir seedlings ranged from 3.2 feet with intensive release to 1.7 feet with no release. No release allowed greenleaf manz anita plants to be slightly taller than red fir seedlings and to place the seedlings in danger of being overtopped.