Effects of Fire and Browsing on Regeneration of Blue Oak 1

Blue oaks (Quercus douglasii) are not regenerating well over much of California. The roles of fire and browsing in regeneration are probably significant, but poorly understood. We burned two foothill blue oak woodland sites which contained significant numbers of small trees between 40 and 70 cm tall, then compared height growth over 14 years among 48 trees that were: a) unburned and unbrowsed, b) unburned but browsed, c) burned and browsed, and d) burned and unbrowsed. Fire completely killed and/or removed the tops, but all plants subsequently resprouted, creating an even-aged stem class. We found no evidence that fire stimulated regeneration. Protection from moderate browsing pressure by deer and cattle (approximately 75-80 percent of twigs to a height of 150 cm were browsed) favored regrowth and subsequent escape above the browse line, although some browsed plants also reached or exceeded browse height. Height growth differed significantly by site. On one site 11 of 12 unbrowsed plants had escaped to above the browse line, with several over 3 meters tall. On the other site growth was slower, but 9 of 11 surviving unbrowsed plants were above the browse line. Fourteen years after fire enough blue oaks were successfully recruited on both sites from the shrub into the sapling class to maintain or increase overall stand density.