With suitable conditions, tanoak reproduces well from seed. Acorns germinate in a wide range of environments from oldgrowth stands to recent clearcuts (31). However, survival of unprotected seed is low in clearcuts due to heavy predation. The dense shade of virgin forests, and the thick litter found under tanoaks, madrones, or other hardwoods, do not hinder germination. Seedlings are common in these conditions. Tanoak germination is hypogeous.
A limited number of tests show that germination rates vary from 19 to 80 percent (25). When acorns were planted with pointed end up, germination was significantly greater (13).
Almost all natural seedlings emerge in the spring; some germination may occur in the fall, but only if the weather is mild and moist. To preserve their viability, tanoak acorns must either be planted immediately in the nursery in light soil, or be stratified until spring at temperatures just above freezing. Seedlings appear about 3 weeks after planting.
Natural tanoak seedlings have been counted under parent trees left after the Douglas-fir overstory had been cut. Although 1 year's acorn crop produced 395 to 940 seedlings per hectare (160 to 380 seedlings/acre) under trees 51 to 66 cm (20 to 26 in) d.b.h., the efficiency of sound acorns in producing seedlings was only 0.64 percent. Only one seedling grew from 156 sound acorns.
Many natural seedlings are found in the understory of conifer stands, which appears to be an ideal environment for reproduction (29). In southwestern Oregon, seedling survival after 4 years ranged from 44 to 49 percent in conifer stands whose ages ranged from 50 to 100+ years (31). In the northern Sierra Nevada, from 17 to 347 new seedlings per acre were present annually during an 11-year period (13). The annual appearance of new seedlings along with modest rates of mortality resulted in relatively stable populations of 570 to 3000/ha (233 to 1,215/acre) during these 11 years. However, attempts to establish a plantation of tanoak by artificial seeding on an exposed site, which had been prepared by removing vegetation and exposing mineral soil, were unsuccessful (13).
Biotic factors contribute to low seed crop efficiency. Although the acorns have hard seedcoats-the generic name, Lithocarpus, from the Greek "lithos" meaning rock, and "karpos" meaning fruit, alludes to the hard acorn-at least 38 species of animals eat them (2). Principal consumers include 4 bird species, 11 rodent species, deer, bears, and raccoons. Goats, hogs, and cattle also prevent seedling reproduction by devouring acorns and browsing tender seedlings.
Heights of first-year, natural tanoak seedlings, measured from cotyledons to growing tip, in one study varied from 5 to 21 cm (1.9 to 8.3 in) and averaged 13 cm (5.2 in), greater than first-year heights of natural conifers on the same site (24). After the first year, the seedling growth rate is moderate, less than 5.0 cm (2 in) per year.
Tanoak seedlings begin to produce burls below ground at 1 to 2 years of age. Burls develop more quickly on good sites and, in one study, averaged 25 mm (1.0 in) in diameter in 10 to 12 years (29). After 6 to 12 years, the original stem dies (even without browsing or other damage) and a new top is produced that tends to be more vigorous than the original one. Tanoak seedlings thus become seedling-sprouts. Top replacement is common, and seedling-sprouts may support several live stems (29). The tallest stem ranged from 25 to 150 cm (10 to 60 in) on 20-year-old seedling- sprouts in southwestern Oregon interior sites. More rapid development is likely in the coast range and northern Sierra Nevada forests. Tanoak seedling-sprout ages can be estimated by counting xylem rings in the stem below the burl, but there is no reliable relation between top age and/or size and total seedling-sprout age (29). The growth potential of seedling-sprouts is low. Forty- to fifty-year-old tanoak seedling-sprouts, for example, had burls that were only 5.0 to 7.5 cm (2 to 3 in) in diameter. Three years after removal of the overstory by cutting and burning, they produced clumps of 4 to 6 stems that averaged only 51 cm (20 in) tall.
Records on the seasonal growth of tanoak are scanty. Some observations have been recorded in the vicinity of Salyer, CA. Here, in the Trinity River valley and on the low mountain slopes up to 610 m (2,000 ft) elevation, tanoak vegetative buds open in mid-April. From 610 to 1065 m (2,000 to 3,500 ft), buds burst in mid-May, and from 1065 to 1340 m (3,500 to 4,400 ft), foliage growth begins in late May. At its elevational. limit near Salyer, which is about 1370 m (4,500 ft), buds open in early June. Leaves persist for 3 to 4 years (24).
The growing season lasts 4 to 5 months in the mountains and somewhat longer at lower elevations and nearer the coast.
- Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp. http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm