20 BULLETIN 1176, U. S. DEPARTMENT OF AGRICULTURE. 
pened in less than 30 years. Apparently, for the present, we must 
depend on this process with fire protection f(fr control of brush al- 
ready present. 
Heaiw litter is definitely known to favor fir and cedar at the ex- 
pense of yellow pine. Heavier cutting in the yellow pine, the sugar 
pine-yellow pine, and the sugar pine-fir types with better distribution 
of reserved trees undoubtedly favors pine reproduction and is espe- 
cially necessary to release advance growth. 
In most cases the period required for natural regeneration will 
range from 10 years on the best to 20 years or more on the poorer 
sites. Bearing in mind the character of the virgin forests in which 
the best advance growth is found, an extensive application of the 
shelterwood system seems to offer the best chance of improving on 
conditions existing at the time of cutting. It is particularly adapted 
to the fir and sugar pine-fir types if an increasing proportion of fir 
is accepted as unavoidable. It was stated previously that most of 
the early cuttings inadvertently resembled shelterwood cuttings. 
How, then, are the unsatisfactory results explained? In the first 
place, sufficient time has not elapsed. Few good stands of reproduc- 
tion can be found in which all seedlings have been established in less 
than 10 years, except on the best sites or where a good seed crop has 
been followed by favorable seasons. 
In the second place, the system was not definitely in mind at the 
time of marking, and improper application of it resulted. Seed cut- 
tings Avere made where the presence of advance reproduction justified 
heavier removal cuttings. Even markings intended for seed cuttings 
were probably too light. On the other hand, some later very heavy 
cuttings, where advance growth is scanty, and which have left only 
three or four thrifty standards per acre for seed trees, will probably 
result in slow regeneration, as such trees bear little seed for a number 
of years after cutting. (PL VII.) In many cases in which the stands 
are essentially even-aged to start with, a heavy shelterwood cutting 
would be practically the same, as the present system of leaving a 
greater number of seed trees and at the same time a volume of 4,000 
to 10,000 feet board measure per acre for increased growth and im- 
proved quality of the second cut. (PI. IV.) The principal objection 
to this system is that even two cuttings within a reasonable period 
are not possible on most areas for economic reasons. Even to-day, 
however, it would be possible to cut over a second time several sale 
areas on the Plumas and other national forests. 
Fortunately, in nearly all cases considerable advance reproduction 
is already present and every effort should be made to preserve it and 
favor its growth. In the early markings not enough attention was 
given to such advance growth, especially if of small size or composed 
largely of fir and cedar. The aim was to secure a new crop. The ad- 
vance growth was given little protection in felling, yarding, and 
brush burning, with the result that in some cases much of it was de- 
stroyed. In others it remained suppressed by trees left for seed. An 
extreme case of this is represented by the Massack plots above, where 
the number of seedlings present now represents only 21.5 per cent of 
the 25,000 or more per acre before logging, and much of what remains 
is still suppressed. The present policy of heavier cutting and better 
distribution of reserves is again indicated. (PI. VIII.) 
