Grovvth of California Red Fir Advance Regeneration ABter Overslory Removal and Thinning

WILLIAM W. OLIVER is in charge of the Station's silviculmnl research on California conifer types, wilh hcadquwcrs at Kcdding, Calif. He earned a bachelor's degree (1956) in forestry froin the University of New Hampshire. and a master of foreslry degree (1960) fmln the University of Michigan. He joined the Station in 1962. Advance regeneration is co~nmon under decadent, old-growth stands of California red fir (Abies magni$c~i A. Mum.). Intense competition for the site's resources can create sapling stands of poor vigor and advanced age. When competition is reduced by overstoiy removal and thinning, suppressed advance regenem-tion has been shown to respond with increased growth. But, to select leave trees, land managers need to know which tree characteristics we associated with growth after release and thinning. This paper reports those easily measured tree characteristics found to be most closely associated with growth after 8 years, on the Swain Mountain Experimental Forest in northeastern Cal-ifornia. About 400 saplings were monitored after removal of the over-story and thinning on 10 acres, at 6700 ft (2044 m) on the northeast face of Swain Mountain. At this elevation, most of the annual precipitation falls as snow, which usually accumulates to a depth of 6 ft (1.8 m). Site index is 45 ft (14 m) at 50 years. After trees were thinned to a 6-ft (1.8-m) spacing, about 200 were chosen randomly within 10 study plots to obtain at least nine trees each in nine live crown ratio classes from 10 to 90 percent. A variety of stem and crown characteristics expected to be related to growth was measured on the sample trees, which averaged 1 inch (2.5 cm) in diameter at breast height (d.b.h.), 6.8 ft (2. l m) tall, and 60 years old. Also, measured annually for d.b.h. only were 200 other saplings of similar size that were randomly selected from among well-fanned dominant and co-dominant trees. Rates of d.b.h. and height growth increased for most saplings during the 8 years of observation. According to the criteria used, variation in diameter growth was explained best by the easily measured characteristics: 3-year height growth before thinning (3-YHG), the product (PLC. CD) of percent live crown (PLC) and crown diameter (CD), and initial d.b.h. (ID). For height growth, the most effective variables by the same criteria were 3-YHG and PLC. CD. These variable sets were chosen for each of four response periods-0 to 2 , 0 …