Tanoak is a heavy  seeder (3). In general, viable seeds are borne in abundance after  the 30th to 40th year (8), although 5-year-old sprouts also have  produced fairly heavy crops. A long dry period at pollination  time helps the setting of acorns. Trees are heavily laden almost  every alternate year, and complete seed crop failures are rare. "Jayhawking"-peeling  the bark from standing trees-has shown that girdling produces  excessively large acorn crops before the trees die. Scanty crops  generally are caused by frosts or by a dry year.

   

Mature trees produce the most acorns. One estimate places annual  acorn production of a veteran tanoak 76 cm (30 in) in d.b.h. at  about 454 kg (1,000 lb). Because about 110 acorns weigh 0.45 kg  (I lb), this production is more than 110,000 acorns. Other  estimates showed that trees between 46 and 61 cm (18 and 24 in)  d.b.h. produced 3,900 to 4,600 acorns.

   

Insects destroy a significant number of acorns. One study found  insect larvae infesting 51 percent of the acorns. The insects  identified were the filbert weevil (Curculio uniformis) and  the filbertworm. (Melissopus latiferreanus). Other insect  larvae that have been found in tanoak acorns are from the  families Gelechiidae and Pyralidae (5).

   

Many immature acorns have been seen on the ground as early as  August 25, but these were probably knocked down by heavy rains.  Mature tanoak acorns drop between September 20 and November 15.  The first acorns to fall are usually insect infested, whereas  those falling later are usually sound. Indians in California  placed a taboo on collecting acorns for food until their medicine  women held a ceremonial festival that celebrated the falling of  sound acorns.

   

Because the acorns are large-2.5 to 5.1 cm (1.0 to 2.0 in) long  and 15 to 18 min (0.6 to 0.7 in) in diameter-and heavy, most of  them fall straight to the ground and are found under the tree  crowns. Only a few bounce outward when dropping onto lower  branches or roll for short distances on steep slopes. In one  small study, acorns were counted under trees 46 to 61 cm (18 to  24 in) in diameter at ,rates of 194,000 to 226,000/ha (78,400 to  91,500/acre) (24).