pie ME a Milk ee 
Eos, Game 
- 1909] PHILLIPS--A STUDY OF PINON PINE 217 
sional specimens may be found even higher than this. The best 
stands are found on coarse gravel, gravelly loam, or a coarse sand, 
of 1.5™ (5 feet) or more in depth, on which humus and ground cover 
are almost entirely lacking. The species often occurs on rocky 
areas, where the soil is only 15 to 30°™ (6-12) in depth, and fre- 
quently it is found growing in rock crevices. It is one of the first 
trees to gain a foothold on the lava overflows which are known 
throughout the southwest as mal pais. This rock in its disintegrated 
form supports fair tree growth, but even before disintegration has 
progressed very far, the junipers and pifion may be found encroaching 
upon it. 
Another encroachment form of the pifion is to be found on small 
mounds which rise 0.6 to 3™ (2 to 10 feet) above the general level 
of the desert-like tableland at approximately 1500™ (5000 feet) 
elevation. On such islands as these, the pifion and one-seeded 
juniper take possession and maintain a limited growth. The same 
feature is noted at the bases of the hill and mountain slopes which 
bound these tablelands. This remarkably distinct tension line seems 
to be due to a greater soil porosity, less grass growth, and a smaller 
alkali content, which are manifest in slightly higher elevations. The 
distribution of these trees on such small mounds and limited in such 
a distinctive manner presents an ecological problem for future investi- 
gation. 
On slopes where site conditions are favorable for western yellow 
pine, the pifion usually occupies the south and west aspects. Where 
Conditions become less favorable, it occupies the north and east slopes, 
while the south and west slopes are bare or nearly so. This ability 
to stand poor conditions is also shown on a large number of mountain 
Slopes ranging from 2830 to 3135™ (6000 to 7000 feet) in elevation, 
where scattering Douglas fir, of scrubby growth and badly affected 
With witch’s broom, is found in the cafions; western yellow pine on 
the middle slopes; and pifion on the ridges and upper slopes, where 
the soil is scant and the soil moisture low. 
A distinctive peculiarity was observed between Servilleta and Taos, 
New Mexico, in an open stand of the species in which approximately 
two-thirds of the trees have constricted bases at the surface of the 
stound. This constriction amounted to an average of 197" (0.75") 
