THE BIRDS OF NORTHERN THAILAND 25 



is a deciduous open forest of small or medium-sized trees (the domi- 

 nant species being Shorea obtusa and Pentacnie siamensis of the family 

 Dipterocarpaceae), with an abundant herbaceous undergrowth, 

 chiefly of grasses. It is usually found at elevations below 2,500 feet 

 on rather poor lateritic, sandy, or rocky soils. Its avifauna is limited ; 

 characteristic forms are Pieus erythropygius, Cyanops lineata, and 

 Garmlax monileger. 



2. Mixed-deciduous, an association highly developed at low eleva- 

 tions in the larger valleys of our provinces, replacing pa daeng where 

 the soil is richer and moister. It possesses many valuable timber 

 trees, for the most part deciduous in hot weather ; among them are the 

 teak (Tectona), redwood (Xylia), pradu {Pterocarpus) , and mango 

 {Mangifera). Characteristic species of the not extensive avifauna are 

 Dissemurus paradiseus and Garrulax leucolophus. 



3. Evergreen, a forest that fits the popular conception of a tropical 

 jungle. It contains an astonishing variety of lofty trees, often in- 

 terspersed with palms, and all are bound together with rattans and 

 other lianas. In certain parts of Nan and Chiang Rai Provinces such 

 growth occurs in extensive stands at the lowest elevations ; where water 

 is plentiful it is the normal forest on the mountains above 3,500 feet 

 in all the northern districts. Its avifauna is one of almost incredible 

 richness, and scarcely a nonaquatic family fails to be represented 

 therein. 



4. Open hill-forest, an association composed almost wholly of var- 

 ious species of chestnuts and oaks with an undergrowth of grasses, 

 mainly lalang (Imperata) . It is restricted to dry mountain slopes at 

 elevations above 3,500 feet. A characteristic bird of the limited fauna 

 is Prima atrogulavis. 



5. Pine forest, chiefly of Pinus merkusii but with some P. khasya; 

 it grows on the mountains of the Thanon Thong Chai and Khun Tan 

 ranges on dry slopes above 3,500 feet but, along the Daen Lao range, 

 at lower elevations. The trees are widely spaced and have an under- 

 growth of lalang. Characteristic forms of its avifauna are such 

 boreal types as Mycerobas melanozanthos and Parus major. 



6. Bamboo brakes, which, in one species or another, cover large 

 areas of all our provinces at any elevation. Between the dense clumps 

 there is heavy shade and, as a result, virtually no undergrowth. Char- 

 acteristic birds are Gecinulus viridis and Sasia ochracea. 



The writer has frequently used the word hai. This refers to a tract 

 cleared from the forest for cultivation and later, after a harvest or 

 two, to be abandoned ; in time it becomes a tangled mass of Eupator- 

 ium, Rub us, Imperata, and other weedy growth. 



In many districts it is customary for the people to facilitate travel 

 through the more arid types of forests by setting fire to the under- 



