Fire is the principal enemy of individual  tanoak trees (3). Ground fires, as well as crown fires, are  sometimes fatal. More often, however, fires leave long vertical  wounds reaching from 1.2 to 3.0 in (4 to 10 ft) up the trunks.  Although the bark of mature trees is at least 3 to 8 cm (I to 3  in), and occasionally 10 or 13 cm (4 or 5 in) thick, some trees  are burned badly.

    Fire injuries to small trees often heal over, but fungi usually  enter the wounds on older trees. The exposed wood on these larger  trees rots and the wounds do not heal. If decayed wood catches  fire it burns readily and the original wound is enlarged.  Sometimes one-third to one-half the diameter of the tree is  destroyed as a result of repeated fires and decay.

    Until injured by fire, tanoak is relatively free from insect  attacks and fungal diseases and is windfirm (3). Injury to the  trunk, however, allows fungi to enter. Wind and heavy snows  eventually fell many trees originally injured by fire and  subsequently weakened by decay.

    Fire and fungi cause tanoak to be fairly defective. One study  based upon cubic volume in 90 trees showed that the amounts of  saw log cull were 39 percent in cull trees, 8 percent in noncull  trees, and 13 percent in all trees.

    Fungi found in living trees are the beefsteak fungus  (Fistulina hepatica), which causes a brown cubical rot; the  weeping conk (Inonotus dryadeus), a white root rot; and a  necrophyte (Schizophyllum commune), which causes a sap  rot on injured areas of standing trees. Tanoak is susceptible to  the shoestring root disease (Armillaria mellea). The  fungus Ceuthocarpum conflictum causes a commonly seen  leafspot on tanoak (10).

    Several insects have been found feeding on tanoak but, generally,  the damage is not economically significant. Two of these are  armored scales identified as the greedy scale (Hemiberlesia  rapax) and the oak scale (Quernaspis quercus). The  greedy scale chiefly infests the bark but also feeds on leaves.  The oak scale feeds on the undersides of leaves. Another insect,  the crown whitefly (Aleuroplatus coronatus), resembles  soft unarmored scales and feeds on the undersides of leaves,  sometimes causing the leaves to fall prematurely. Ehrhorn's oak  scale (Mycetococcus ehrhorni) is found on stems and the  white sage mealybug (Pseudococcus crawi) on stems and  leaves (5).

    In 1957, the California oakworm (Phryganidia californica) completely  destroyed that year's foliage of tanoaks growing on Hennessey  Ridge, near Salyer, Trinity County, CA. This damage was localized  and was not observed at other places nearby. Usually, the  California oakworm causes little damage but irregularly becomes  epidemic over large areas.

    Other insects work under the bark. Adults of the Pacific oak twig  girdler, Agrilus angelicus, feed on foliage, but its  larvae mine spiral galleries that girdle twigs, small limbs and  trunks, or sprouts. Adults of a false powderpost beetle (Mela1gus  confertus) prune twigs by boring at the fork of small  branches (5).

    Decline of tanoak sprout vigor was observed in mixed  conifer-hardwood forests in the central Sierra Nevada (18).  Affected clumps were wider and denser, but only one-fifth as tall  as unaffected clumps. Reason for the decline is not known.

    Tanoak is avoided by livestock if better feed is available. Mule  deer rarely browse it. The current year's growth of tanoak leaves  and twigs is protected by abundant stellate trichomes, which are  unpleasant to inhale.