The form of tanoak varies greatly. In  closed stands, particularly in dense coniferous forests, tanoaks  develop one central axis, narrow crowns, ascending branches, and  long trunks that are clear for 9.1 to 24.4 in (30 to 80 ft). In  this form, tanoak is one of the most stately broadleaved trees in  the West. In open stands, however, especially in association with  Pacific madrone and California black oak, tanoaks are free  branching, the crowns are broad, the limbs horizontal and large,  and the trunks short and thick. The main trunk divides into  several large branches and forms a rounded crown.

   

Tanoak is usually classed as medium in size (15). Mature trees are  generally 15.2 to 27.4 in (50 to 90 ft) tall but frequently grow  to 45.7 in (150 ft) (26). The tallest tree reported was 63.4 in  (208 ft) high and 137 cm (54 in) in d.b.h. It was found on the  North Fork of the Little Sur River, Monterey County, CA.

   

Mature trees vary from 15 to 122 cm (6 to 48 in) in d.b.h. The  largest diameter of record is 277 cm (109 in), measured on a  tanoak near Kneeland, Humboldt County, CA. This tree was 30.5 in  (100 ft) tall and the crown had a spread of 23.2 in (76 ft) (1).  Tanoaks with the largest diameters generally grow in open stands  where tree heights are lower. Age-height-diameter relationships  in Sonoma County, CA, were as follows (24):

                                                                                                               

Age	Height		D.b.h.
yr	m	ft	cm	in
20 to 40	9.1 to 15.2	30 to 50	10 to 23	40 to 9
40 to 100	12.2 to 24.4	40 to 80	25 to 30	10 to 12
70 to 125	24.4 to 30.5	80 to 100	33 to 46	13 to 18
100 to 159	27.4 to 36.6	90 to 120	48 to 61	19 to 24
125 to 180	35.1 to 42.7	115 to 140	64 to 91	25 to 36
150 to 210	30.5 to 26.6	100 to 120	94 to 117	37 to 46
170 to 250	30.5 to 36.6	110 to 120	119 to 152	47 to 60

   

   

The growth of tanoak has been called slow, moderate, and fairly  rapid. Knowledge about growth rate is limited, for only a few  trees have been measured. Seven trees near Sherwood, Mendocino  County, CA, which varied from 36 to 69 cm (14 to 27 in) in  diameter at 0.61 in (2 ft) above the ground, had from 4 to 8  rings per centimeter (10 to 20/in). At another location, trees 48  years old averaged 25 cm (10 in) in d.b.h. and 10.7 in (35 ft)  tall. Trees 36 to 46 cm (14 to 18 in) in d.b.h. were from 80 to  128 years old, and trees 51 to 152 cm (20 to 60 in) were from 150  to 250 years old.

   

It is difficult to ascertain the age of tanoak. As noted earlier,  seedling sprouts in the understory were 50 to 60 years of age and  less than 2 in (6 ft) tall. A tanoak taller than 20 in (60+ ft)  had five stems ranging in size from 10 to 35 cm (4 to 12 in)  d.b.h. and in age from 29 to 94 years (29). It also had four  burls below ground 35 to 90 cm (1.5 to 2.5 ft) d.b.h. in  diameter, with scars of large stems 50 cm (1.5+ ft) which had  died, broken off, and decayed. This tree was likely older than  the 240-year-old conifers in the overstory. When the overstory is  removed, sprouting tanoak forms an even-aged stand above ground,  regardless of actual age.

   

Growth of tanoak stands 50 to 60 years old above ground thinned to  six different basal-area densities (19 to 32 m²/ha; 85 to  141 ft²/acre) grew about 6 m³/ha/yr (85 ft³/acre/yr)  for 8 years after thinning (16).