702 XLVI. VERBENACEAE 



bearing forest in the province is on the Pegu Yoma, a range of hills composed 

 of tertiary sandstone and shale and forming for the greater part of its extent 

 the watershed between the Irrawaddy and Sittang rivers : these forests form 

 an unbroken stretch more than 200 miles in length and averaging about 

 30 miles in breadth. There are also extensive teak tracts in the drainages of 

 the Salween, particularly in the Southern Shan States, of the Thaungyin, the 

 Chindwin and its tributaries, and the upper Irrawaddy, including the Shweli, 

 Madaya, and other important drainages. Teak forests of varying extent occur 

 also on the eastern slopes of the Arakan Yoma, in the hills east of the Sittang 

 river, and in the Ataran drainage. The Myitnge river drainage contains several 

 teak areas, partly in the Northern Shan States and partly in the Yeyaman 

 tract of the Kyaukse district. 



Teak occurs normally in mixed deciduous forests, but occasionally teak 

 trees are found standing in dense evergreen forest (see Fig. 265). These trees 

 are often of very large size, testifying to the fertility of the soil. Such cases 

 are examples of progressive succession from a deciduous to a.n evergreen type, 

 for the teak is incapable of regenerating in dense evergreen forest, and must 

 have established itself when the forest was of a deciduous type. The gradual 

 encroachment of evergreen species in moist deciduous forest can often be 

 observed, particularly in areas where fire-protection has been introduced, and 

 in some cases teak trees may be found recently killed by the suppression of 

 faster-growing invasive species. 



The teak-bearing forests of Burma may be classified into numerous sub- 

 types, but the more important of these can be referred to one of two main 

 t;^^es which Kurz designated ' upper mixed ' and ' lower mixed ' respectively, 

 terms which have been adopted generally and are well understood. The 

 general distinction between these two main types is as follows : (1) upper 

 mixed forest (Fig. 266) as a rule occupies hilly or undulating country, and is 

 usually characterized by the prevalence of bamboos ; (2) lower mixed forest 

 (Fig. 267) occurs on lower ground, which is flat or nearly so, and is usually 

 alluvial, white bamboos are either absent or not well distributed. Both these 

 types are essentially deciduous, but in their moister parts they tend to merge 

 into evergreen, while the two types may merge imperceptibly into each other, 

 so that a sharp line cannot always be drawn between them. The upper mixed 

 forests are l)y far the more extensive, and may be regarded as the true home 

 of the teak ; some of the richest teak areas, however, are to be found in lower 

 mixed forest. 



The upper mixed forests may be divided into two chief sub-types, (a) dry 

 and (6) moist, according to the comparative dryness or moistness of the forest 

 growth, of which the best indicators are the bamboos, which are such an 

 important constituent of the crop. A sharp distinction cannot always be 

 drawn between these two sub-types, more especially since the majority of the 

 tree species associated with the teak occur in both. 



In dry upper mixed forest the typical bamboo is Dendrocalamus strictus, 

 but some of the bamboos of the moist forest, notably Cephalostacliyum per- 

 gracile, often in stunted form, extend into dry forest. Bambusa Tulda occurs 

 m both, and Thyrsostachys Oliver i is found in somewhat dry types as weU as 

 in fairly moist types in Upper Burma. Dry upper mixed forest may either 



