Tanoak reproduces prolifically by vigorous sprouts that appear at practically any time under a wide variety of conditions (3). Sprouts may start to grow after a relatively minor basal injury, after bark has been stripped from the trees for tannin extraction, or when the aerial parts of the tree are destroyed by fire or logging (22). Even healthy trees sometimes sprout.
Sprouts develop from conical woody buds that lie under the bark at the base of the tree. Most of these buds are found on burls below the groundline. Because the number of buds varies from few to thousands, the number of sprouts also varies. As many as 1,400 have been counted on one large stump. The only mechanical damage that prevents sprouting is stripping the bark below the ground level to expose the buds.
Sprouts from burls grow rapidly in a wide range of environments. In clearcuts, they have reached 1.7 m (5.6 ft) the first year and 4.1 m (13.6 ft) after 5 years. The microclimate within sprout clumps is quite different from the microclimate immediately adjoining them (21). Sprout growth is reduced somewhat by a conifer overstory (13). The size of parent trees between 3 and 43 cm (1.3 and 16.8 in) in d.b.h. determined the height and diameter growth of sprout clumps, and the number of sprouts in a clump. The larger parent trees produced greater sprout development. Sprouts are reduced drastically in numbers early in their life and growth is concentrated on the dominant stems. In the first 15 or 20 years, sprouts grow an average of about 0.6 m (2 ft) in height a year. Often, a circle of four to eight slender 30-year-old poles grows around the stump of a parent tree. These poles may average 30 to 38 cm (12 to 15 in) in d.b.h. (24). Thinning all but 2 to 4 sprouts per clump of 3 to 10-year-old sprout clumps did not increase height or diameter growth of the remaining sprouts, largely because rapidly growing new sprouts quickly replaced those that had been cut (14).
Leaf area, total above-ground biomass, height, clump width and area, and number of stems 1 to 6 years after cutting were statistically correlated with parent tree diameter at 1.4 in (4.5 ft) before cutting or burning (9). Thus, sprout clump size and total stand cover can be predicted from stand stocking tables before harvesting or burning either conifer stands with a tanoak understory or pure tanoak stands (30).
Although not growing as fast as sprouts of some associated hardwoods, such as bigleaf maple and madrone, tanoak sprouts are significant competitors because they are usually abundant, especially in conifer stands. Tanoak sprouts often quickly dominate the vegetational cover after logging or fire. Although this ability helps reduce soil erosion, tanoak sprouts often provide severe competition to conifer reproduction and may suppress it. The thick, stiff, flat, leathery leaves often cover young conifer seedlings or cover the ground so thoroughly that conifer seedlings cannot emerge above them (20).
Propagation of tanoak by grafts or cuttings has not been reported.
Tanoak sprouts can be controlled by herbicides applied to frills on the stems, to stumps of freshly cut stems, or to foliage of young sprout clumps (32).