THE FLORA OF MOUNT PULOG. 295 
extends from the upper limits of .the pine region to an altitude varying 
from 2,500 m to 2,600 m. The fourth formation, the open, grass- 
covered summit, extends from the upper limits of the mossy forest to 
the top of the mountain. Mount Pulog is apparently the only peak in 
the entire region that has an area of grass land succeeding the mossy 
forest ; all the other peaks are forested to the summit. 
Probably moisture and temperature are the two factors which exercise 
the greatest influence on the formation of these vegetative types. The 
dry slopes of the lower parts of the Agno Valley seem to be too low in 
altitude, and too warm for the growth of the pine, although it is 
doubtful if the moisture conditions differ to any appreciable extent 
from those in the pine belt above. Both the grassy region and the pine 
forest belt are characterized by steep slopes and dry, well-drained soil 
of fair depth. 
At an altitude of about 2,000 m, which is above the general level 
of many of the mountain ranges of the region, there is a great increase 
in the humidity of the atmosphere. Observations made in January, 
May, and July, indicate that those portions of Mount Pulog and the 
other higher mountains of the Benguet-Lepanto region above an altitude 
of about 2,000 m are frequently enshrouded in damp misty clouds and 
that at the above altitude rains are frequent when at the same time 
the air in the valleys at lower altitudes is entirely clear. No doubt this 
condition is due to the condensation of moisture on contact of the upper 
strata of the air with the higher and cooler peaks after the air has 
passed over the warmer hills and mountains below. 
The moist condition of the air and consequently of the soil, com- 
bined with a somewhat lower temperature, favors the growth of hardwood 
trees, and while it is probably not unfavorable to the pine, for very 
scattered pine trees do occur both in the mossy forest and on the open 
grass-covered summit, the hardwoods crowd out the pines in the former 
habitat. The upper part of the mountain, above the present limits 
of the mossy forest, is higher than the neighboring mountain peaks 
and is subject to the full force of the wind; it may also be above the 
main cloud belt of the mountain, although this is uncertain, and can 
only be verified by continuous observation, for sometimes the summit 
is clouded when the mossy forest is clear, and vice versa. The exposed 
nature of the open peak, the unbroken sweep of the winds over its 
area, probably the lower average temperature, and probably some local 
differences in the distribution of moisture account for the absence of 
trees and shrubs on the upper parts of the mountain; it is possible, 
however, that the present limits of the summit grass lands may be 
due in part to fires that have been started from time to time by the 
natives. Mr. McGregor reports that a small area on the main peak 
had been burned over a short time before his visit to it in July, and 
te a 
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