THE FLORA OF MANILA. 
149 
two-thirds per cent by second-growth forest, forty per cent is 
grass land, and ten per cent cultivated land.^ It is practically 
certain that before the advent of man in the Philippines, the 
entire country was covered with unbroken forest, of one kind 
or another, from sea-level to the tops of the highest mountains, 
except, perhaps, where the vegetation had been temporarily 
destroyed by natural causes, such as volcanic eruptions. Such 
types of vegetation as the extensive grass-covered hills, moun- 
tain sides, and plains, and the open cultivated areas, now such 
prominent features in the landscape, did not originally exist, 
so that the whole aspect of many localities must have been quite 
different from what it is to-day and from what has been its 
condition within historic times. When we consider that about 
two-thirds of the entire land surface of the Archipelago consists 
of cultivated areas, open grass lands, thickets, and second-growth 
forests, and that all these types of vegetation are due directly 
or indirectly to the presence of man, some idea can be obtained 
of the profound changes that have been wrought in the vegeta- 
tion of the country in past centuries. 
The first agricultural method employed in the Archipelago, 
whether by the supposedly aboriginal Negritos, or by later Malay 
invaders, was certainly the “caingin” system, still very exten- 
sively practiced. This primitive system of agriculture consists 
simply in clearing a selected area by felling the trees, burning the 
debris, and raising some simple crop on the area thus cleared. 
Such a clearing is, in general practice, utilized but one or two 
years, rarely longer ; and is abandoned as coarse grasses, weeds, 
shrubs, etc., commence to gain an ascendency over the cultivated 
plants. With only most primitive agricultural instruments, the 
average native to-day, as in centuries past, finds it much easier 
to fell and burn the trees, thus clearing a new area, than to 
combat the encroachment of weeds, and especially grasses such 
as the cogon (Imperata ctjlindrica Beauv.) with deep-seated 
perennial rhizomes. Moreover in each new clearing that he 
makes he has the advantage of virgin soil, although this last 
factor is in most cases doubtless a secondary consideration. A 
clearing once abandoned, may, depending on local conditions, 
revert to a forested condition through a succession of coarse 
annual weeds, shrubs, and various quick-growing trees, or it 
may become covered with coarse grasses, especially the cogon 
{Imperata cylindrica Beauv.), or sometimes other species, such 
^Whitford, H. N., Bull. Bureau Forest. (Philip.) 10' (1911) 12. 
