PHYTOGEOGRAPHY OF MANOA VALLEY, HAWAIIAN ISLANDS 589 
walls and head of the valley. It does not grow upon the exposed 
ridges which separate these alcoves from one another, nor upon the 
crests of the lateral ridges, but nestles in the alcoves. On the lateral 
walls it ascends to within 100 feet of the crest of the ridge. At the 
valley head the rain-forest rises 2,000 feet above the upper limits of 
the kukui zone. 
The chief botanical features of the Manoa lower forest are as 
follows : 
1. The lower forest presents a series of life conditions much less 
rigorous than those of the rain-forest. The slope, soil, protection 
from wind, and mean temperature, are all more favorable for plant 
development than are those same factors in the rain-forest region. 
2. The lower forest, in the days of the primitive Hawaiians, was 
an important zone for the raising of crop plants. Twelve species 
were cultivated in little clearings here and there along the skirts of 
the lower forest. This zone was subjected to the direct and indirect 
effects of human utilization to a much greater degree than was the 
rain-forest. In ancient Hawaii the rain-forest was not much fre- 
quented by the natives- — they made occasional visits for birds, canoe 
timbers, etc. 
3. The physiognomy of the lower forest zone has been strikingly 
modified by introduced Hawaiian crop plants, particularly Aleurites 
Moluccana, Cordyline terminalis, and Eugenia Malaccensis. The 
former has become the dominant tree, and in parts of Manoa and 
elsewhere in the islands forms pure stands of considerable magnitude. 
4. The lower boundary of this zone is undoubtedly at present at a 
much higher level than ever before in the history of the islands. In 
other words, the forested montane area is continuously diminishing; 
the forest margin is slowly creeping up the mountains. In geological 
time this movement was due to slow subsidence (according to the 
subsidence theory) ; in recent times it has been tremendously accel- 
erated by herbivorous animals. 
5. The undergrowth of herbaceous and herbaceous-perennial vege- 
tation is much richer in the lower forest than in the rain-forest. The 
pteridophyte representation is much greater, however, in the latter; 
the Manoa rain-forest possesses 93 species, the lower forest has 40 
species . 
6. The lower forest tends to be more or less open, whereas the rain- 
forest is a completely closed association. Epiphytic vegetation is 
much more abundant in the rain- than in the lower forest. 
