16,4 McGregor: Some Features of the Philippine Ornis 383 
as cooking and house and boat construction, play their parts in 
thinning the forest near large towns. 
A method of agriculture common to various tropical countries 
is also practiced in the Philippines, where it is known as the 
caingin system. The caiiTgin is merely a clearing in the forest, 
and if this were continuously cultivated no harm would result.®^ 
The caingin is seldom thoroughly cleared ; the smaller trees are 
cut and when dry are burned. Nearly all of the large trees in 
the field are killed in this process. A crop of corn, rice, sweet 
potatoes, or yams is now planted. For a few seasons good crops 
can be taken off a caingin without much labor, but grass soon 
becomes so well established that the farmer finds it easier to 
make a new caingin than to struggle with the grass. 
In the part of the Archipelago having distinct wet and dry 
seasons, that is, the western half, grass areas tend to remain in 
grass. The grass is frequently burned during the dry season, 
either by accident or intention, and this kills any forest-tree 
seedlings that have entered the grass, while the deep-seated 
perennial rhizomes of the grasses are uninjured. After the first 
rain the grass soon produces a luxuriant growth. On the east- 
ern side of the Islands there is a nearly continuous wet season. 
Here the more uniformly moist condition prevents grass fires 
and the grassland is soon invaded by tree species and gradually 
returns to forest.^® 
If the population of a thickly inhabited island decreases, which 
has undoubtedly happened as the result of war or epidemic 
disease, some of the rice fields will be abandoned. These, even 
when bordering forest, do not grow up to the old forest species 
of trees, but first with a rank grass and later with species of 
shrubs and second-growth trees. If this be in the region of 
marked wet and dry seasons, it will be very difficult for the 
forest species to regain a foothold in an area from which they 
have been removed.®® 
*"See Merrill, E. D., Philip. Journ. Sci. § C 7 (1912) 149. 
With regard to the soils and the climate of the Philippines see Cox, 
A. J., Philip. Journ. Sci. § A 6 (1911) 279-330; also Brown, W. H., and 
Matthews, D. M., ibid. § A 9 (1914) 417. 
With regard to revegetation in the Philippines see: Gates, F. C., 
The pioneer vegetation of Taal Volcano, Philip. Journ. Sci. § C 9 (1914) 
391-434, 8 pis.; Brown, W. H., and Matthews, D. M., Philippine diptero- 
carp forests, ibid. § A 9 (1914) 413-562, 13 pis., 1 map, 12 figs.; Merrill, 
E. D., Brown, W. H., and Yates, H. S., The revegetation of Volcano 
Island, Luzon, Philippine Islands, since the eruption of Taal Volcano in 
1911, ibid. § C 12 (1917) 177-248, 16 pis., 2 figs. 
