454 The Philippine Journal of Science wu 



ing grasslands until at the present time their extent is, according 

 to Whitfordj^" four times as great as that of cultivated lands. 



In regions without a pronounced dry season the grass does 

 not become so readily inflammable and the trees have a chance 

 to become established. This point has been discussed in connec- 

 tion with the distribution of forests in the Philippines. 



Imperata exaltata is rarely more than 1.5 meters in height, 

 while Saccharum spontaneum is frequently more than 3 meters. 

 The latter grass grows in more moist situations than does Im- 

 perata exaltata and forms denser stands. Growing along with 

 the grasses and particularly with Imperata are a few other 

 plants. Their total bulk is small, and they are usually char- 

 acterized by having large underground structures which are 

 not injured by fire. 



There are a few trees which are able to grow up through 

 the grass, even when this is burned over regularly, provided 

 the burnings do not occur at too frequent intervals. Notable 

 examples are Bauhinia malabarica (alibangbang) , Antidesma 

 ghaesembilla (binayuyu), and Acacia farnesiana (aroma). 

 These trees have well-developed roots, and sprout readily from 

 the base of the stem after the upper portion has been killed. 

 After each succeeding fire a larger stem is produced, until finally 

 the tree is able to shade out the grass around it to some extent 

 and may form the center of a small clump. These trees, how- 

 ever, occur in grass regions, which are regularly burned, only 

 as scattered individuals or small clumps, as they can make but 

 little headway against the grass when subjected to fire. 



Second-growth trees grow up and kill the grasses by shading 

 when the latter are not burned. This process generally requires 

 only a few years, as the trees to furnish seed are usually 

 scattered throughout the grass areas, especially in ravines and 

 along the banks of streams. The seeds are usually small and 

 are readily dispersed by birds or by the wind, and nearly all 

 of the second-growth species grow very rapidly. The first stages 

 in the invasion by tree species differ greatly from those on 

 cleared land. The first species present are naturally those fire- 

 resisting ones which are usually present in grass areas. How- 

 ever, many other species come in quickly, among which there are 

 usually individuals of the same species that invade cleared 

 areas. The chief difference between the first stages of second- 

 growth forest in grass areas and on cleared land is that on 



"Bull P. I. Bur. of Forestry (1911), No. 10. 



