96 A Study of the Vegetation of 
equally certain that others buried in the moister duff escaped burn- 
ing. Hoffman (7) has shown that seeds of Thuja plicata may 
remain dormant in the soil for two years, while those of Pinus 
monticola and Pseudotsuga mucronata may be buried in the duff 
for six years and still remain viable. 
The distribution of the seedlings was very irregular. In some 
areas of a square meter or more none could be found, while in 
other more favored spots the seedlings would average as many 
as 8 per square meter. The ground occupied by these seedlings 
was well covered with a mulch of the dead leaves and stems of 
such herbaceous plants as have already been described for the 
region. 
On the denuded south slopes where the original forest growth 
consisted of an abundant stand of Pinus ponderosa with scattered 
individuals of Pseudotsuga mucronata, notwithstanding the pres- 
ence of a growth of Symphoricarpos, Pteridium, Epilobium, 
Cirsium, Achillea, and other plants in considerable abundance 
and so intermingled as to form a semi-shaded protected area, no 
coniferous seedlings were present. Their absence was no doubt 
due to insufficient soil moisture and excessive evaporation. 
These south mountain sides and their ravines and canyons will 
in the course of time be reclaimed by a new growth of yellow pine 
and Douglas fir unless ground fires occur and natural growth 
conditions are obliterated. 
Reforestation studies in areas swept by fires of all degrees of 
severity were made, especially in Thatuna Hills. In some cases 
only very local areas were concerned, while in others the fires 
covered considerable territory (Fig. 43). In practically all cases 
sufficient seed trees were either left standing in the burned area 
or on unburned ridges in close proximity to furnish the seed for 
reforestation. 
About twenty-nine years ago, many square miles of these hills 
were overrun by a fire which destroyed more or less completely 
much of the virgin timber, leaving here and there a few living 
trees representing the different species to serve as seed trees in 
subsequent years. These burns covered chiefly the north and 
northeast slopes of the mountains. In these mixed forests of 
96 
