32 BULLETIN 354, U. S. DEPARTMENT OF AGRICULTURE. 



moisture by the clouds, which leave the summits of these mountains 

 only intermittently during a considerable part of the year. Although 

 commercially of no value whatever, this scrub growth is tremendously 

 important in protecting the exposed slopes from erosion. 



Palma de sierra occurs throughout the uplands and in places in 

 sufficient numbers to dominate the stand, forming what may be 

 called the " sierra palm" type. This occurs alike on the exposed 

 easterly slope and in the protected basins, often where the land is 

 rough and stony and windfall most likely. Consequently it is quite 

 likely a temporary type brought about through windstorm or other 

 accident to the original stand. In the protected localities the 

 associated species comprising the more valuable hardwoods are 

 numerous and usually well developed, so that the growth is not 

 without commercial value and future possibilities. At present these 

 two types — the " hurricane hardwood " type, of no commercial value, 

 and the " sierra palm " type, only partially merchantable — aggregate 

 about half the forested area and dominate the mountain tops and 

 exposed uplands of the Luquillo. 



RAIN FORESTS OF THE EASTERN TROPICS. 



Many valuable species, including the great natural order of the Dipterocarpaceae, 

 find their homes in the luxuriant rain forests of the Philippines, the other East Indies, 

 and the neighboring mainland. The different trees of this order by the variety of 

 their woods, varying from those resembling our soft pine to the heaviest and hardest 

 cabinet woods, are suitable to almost every conceivable use. Several are gregarious 

 and form more or less pure forests, as for instance the eng (Dipterocarpus tuberculatus) 

 of Burma, the hora (D. zeylanicus) of Ceylon, also Vatica obscura and V. roxburghiana 

 of Ceylon. Other forests are dominated by members of this natural order. Thus, in 

 the moister forests of Ceylon there are portions composed almost entirely of different 

 species of Doona, freely mixed with Dipterocarpus, Shorea, Stemonoporus, Hopea, and 

 along rocky gullies Vateria. In the Philippines 70 per cent of the total stand of timber 

 is said to consist of trees of this family. Economically, therefore, this natural order 

 is a very important one, for besides its major timber products it yields many valuable 

 minor products, as camphor from Dryabalanops aromatica, gum resin and dammar 

 from several species of Shorea, Doona, and Dipterocarpus, and so on. The tribe of 

 the bamboos also finds in these wet tropical forests its greatest development. 



Besides the above there are many species of value both in the East Indies and on the 

 mainland, in Africa, and tropical Australia and Queensland. This region, not to 

 mention the resources of tropical America, affords opportunity for almost infinite 

 selection for introduction by which to repair any deficiencies in commercial qualities 

 of the Porto Rican tree flora. 



Dry Deciduous Forests. 



The dry deciduous formation known in others of the West Indies 

 and in Central America and Mexico as chaparral was in pre-Colum- 

 bian times the second most extensive. Typically a formation of the 

 semiarid region, it dominated the south coast lands, foothills, plains, 

 and lower slopes of the central mountains from Patillas to Hormin- 



