20 CALIFORNIA TANBARK OAK. 



to lay out accurately in felling. Even a slight injury to the trunk 

 permits the entrance of fungi which weaken the wood, and the loss of 

 such trees in heavy snowfalls is very large. 



Trees on slopes or canyon sides are the greatest sufferers; 95 per 

 cent of the tanbark oak trees in those positions are injured by fire 

 and 80 per cent fire hollowed. In the case of ridge trees, about 80 

 per cent are comparatively free from fire hollows, because a fire 

 traveling up a slope is either running high or going out when it 

 reaches the top. 



The most extensive destruction by fire in the tanbark oak belt 

 has probably been in Del Norte County, where in former days the 

 Indians regularly fired the woods to make better feed for the deer, 

 and the packers set fires to keep the trails open. Kidge after ridge 

 has been wholly or partly reduced to a low chaparral growth, although 

 there is evidence that a dense forest existed at a comparatively recent 

 date. A conservative estimate of the loss of tanbark by fire within 

 15 years in this region is 60,000 cords. 



In the second-growth districts the accumulation of debris inside 

 the circles of poles about the remains of the parent stumps furnishes 

 material for flames. Forty per cent of such poles show serious injury 

 at the bases. 



("^TANNIN EXTRACT PROCESSES. 



.The difficulty of transportation has prevented the exploitation of 

 some of the most productive tanbark oak regions in Humboldt and, 

 to a smaller extent, in Mendocino County. An attempt was made 

 to reduce this difficulty by grinding up the bark and shipping it in 

 sacks, but this did not help in the more remote districts where the 

 weight was the chief drawback. In the last few years attempts 

 have been made to solve this difficulty by extracting the tannin 

 from the bark and shipping the extract. 



Two methods have been tried in California, the open-pan process 

 and the vacuum-pan process. The open-pan process was tried in 

 southern Mendocino County hi 1900 and 1902, but was abandoned 

 because the heat necessary to secure rapid evaporation in concen- 

 trating the mixture of ground bark and liquid was said to scorch 

 the fluid and start fermentation, so that the barrels containing the 

 completed product often burst. 



The vacuum-pan process is used by an extract plant at Briceland, 

 Humboldt County. The liquid from the leaching vats is pumped 

 into settling tanks in the concentrator house, and thence fed as 

 needed into the "pan" or evaporator, which is a copper retort about 

 7 feet in diameter, heated by steam pipes coiled around the base. 

 By heating the pan under vacuum the temperature of the liquid 

 during evaporation is kept from exceeding* about 120 or 130 F. 



