The Irrawaddy Plateau

AT the end of June 1937 I left railhead at Myitkyina in Burma on a third -^^journey to the sources of the Irrawaddy. Nowadays there is a cart road (passable for motors in the season) to Sumpra Bum, 139 miles from Myitkyina, and I was able to hire three bullock carts for the first half of the journey to Putao; a form of transport which, though very slow, has advantages in the moist heat of July. That part of Burma which extends north from Myitkyina and the Irrawaddy confluence to the Tibetan frontier is different from any other part of the country. lies entirely outside the tropics. is very mountainous and is traversed by tempestuous rivers. Rain falls at all seasons of the year, but mostly in the summer. The valleys and lower hill ranges are covered with tropical and sub-tropical evergreen rain forest instead of monsoon (deciduous) forest, as over a great part of Burma. This evergreen forest passes into subtropical pine forest at about 5000 feet, and that in turn into evergreen conifer forest above 8000 feet. Thus it is convenient to distinguish this large region as north Burma, distinct from Upper Burma, with which it has little in common. The distinction is more than academic. Upper Burma is essentially the valley of the middle Irrawaddy and lower Chindwin. lies within the dry zone and consists almost entirely of plains covered with thorn forest and tropical deciduous forest. The rainfall of north Burma varies greatly within a few miles, and from year to year. Actually in the hills it is probably never less than 100 inches, except in the extreme north; although Myitkyina itself, which is on the plain, has an average of about 75 inches. Temperatures are even more fluctuating, and in the north, where the valleys are deep and the mountains high and precipitous, exhibit violent contrasts. The one meteorological factor, and that the most important for plant life, which does not vary greatly is atmospheric humidity. This is always high, except locally, even in the winter. probably never falls below 75 per cent. of saturation, and for long periods is 90 per cent. or higher. Although surveyed, north Burma is, in the modern sense, almost unexplored. Mr. J. K. Stanford, who while Deputy Commissioner of the Myitkyina district from 1932 to 1936 made the most complete collection of birds yet obtained in north Burma (comprising 472 species), writes l: It can safely be said that naturalists have so far only guessed at the immense wealth of bird life in Myitkyina by recording what comes up to the surface, as it were, of an enormous sea of some of the densest and least-known jungle in the world.*' So much for the avifauna, and the same is at least equally true of the mammal life. Of the flora we have only scratched the surface sufhciently to prove that it is very large and, as might be expected both from the situation of north Burma and from the diversity of physical features and climate, extremely varied. So far as I can trace, the following appear to be the only comprehensive botanical collections made in the district

Geography · Plateau (mathematics · Asian Geopolitics and Ethnography · Mathematics