Soils and Topography
Tanoak grows well on a variety of soils developed from igneous, metamorphic, or sedimentary rocks, or sedimentary rock alluvium. It grows best on soils that are deep, well-drained, and loamy, sandy, or gravelly. Tanoak also grows on soils derived from serpentine, which are intermediate between the moist and dry extremes, but is limited to a shrubby form. It is seldom found on heavy clayey soils.
High-site soils for redwood (Sequoia sempervirens) or Douglas-fir (Pseudotsuga menziesii), such as the Hugo, Sheetiron, Josephine, Empire, Larabee, Sites, and Melbourne (12) series, are also well suited for the growth of tanoak (28). These soils have been derived from either consolidated or soft sedimentary rocks. They are light grayish brown or light reddish brown to brown in color and are moderately to strongly acidic. Soil textures grade through gravelly loam, sand loam, fine sandy loam, loam, silt loam, to clay loam. Soil orders are mostly Inceptisols and Alfisols.
Besides growing well on deep soils, tanoak also thrives on stony and shallow soils that are less suitable for conifers. Yet tanoak requires more moisture than many other hardwoods. It will grow well on the shallow and stony soils of north slopes, for example, but will be supplanted by Pacific madrone (Arbutus menziesii), Oregon white oak Quercus garryana), or California black oak (Q. kelloggii) on the warmer, drier south slopes.
Throughout the Coast Ranges from the northern limit of tanoak's distribution (lat. 43° 42° N.) to the Santa Lucia Mountains (lat. 35° 40°N.) tanoak grows from sea level to elevations of 1220 or 1525 in (4,000 or 5,000 ft). The terrain is rough, steep, and extremely dissected by both major streams and smaller drainages. In the Santa Ynez Mountains, at the southern limit of its range (lat. 34° 34° N.), tanoak grows at 730 to 1435 in (2,400 to 4,700 ft). In the northern Sierra Nevada, it grows between elevations of 580 and 1220 in (1,900 and 4,000 ft) and in the central Sierra Nevada between 915 and 1525 m (3,000 and 5,000 ft). At its southern limit in the Sierra Nevada, tanoak is found between 1525 to 1980 in (5,000 and 6,500 ft) near Signal Peak (lat. 37° 32° N.) in the Sierra National Forest (24).
Tanoak is most abundant and, in general, attains its largest sizes in Humboldt and Mendocino Counties, CA, between elevations of 150 to 915 in (500 to 3,000 ft) on northerly and easterly slopes and toward the summits of the seaward exposures of the Coast Ranges. In the southern Coast Ranges, tanoak is common in the Santa Cruz and Santa Lucia Mountains, particularly on the westerly slopes. And in the central Sierra Nevada, where the climate is less humid, it grows in valleys, coves, ravines, along streams, and on north slopes.