NORTH-WEST MONGOLIA AND CHINESE DZl!N(iAKIA. .'VJl 



B. NORTH-WEST IMONGOLIAN PLATEAU. 



General Notes on the Floral Zonen. 



The principal floral associations o£ North-West Alongolia can bo divided 

 into tliree groups consisting of the following : — 1. Plateau-Desert Association ; 

 2. Larch-Forest Association ; W. Alpine Association. Although many species 

 in these groups overlap, still, in general, each association can be said to 

 occur in definite zones, which vary according to the two principal factors, 

 altitude and latitude. Generally speakings at northern latitudes and at low 

 altitudes the same flora is found as in more southern latitudes at higher 

 altitudes, but the Larch-Forest Association tends to thin out in southern 

 latitudes, leaving the other two converging. Altitude and latitude are the 

 factors which cause temperature, rainfall, and snowfall, and the degree and 

 intensity of these natural conditions vary in almost exact relationship to the 

 altitude and latitude all over the North-West Mongolian Plateau. 



1. Tlie Plateau-Desert Association occurs in all the most low-lying parts 

 of the valley-bottoms, plains, and evaporating basins and all districts where 

 the distance from the mountains is great and consequently the rainfall small 

 or non-existent. Round some of the desert lakes a very thin zone of marsh 

 flora is to be found, growing \\here saline moisture has reached the surface. 

 With the exception of this and a few straggling patches of Larch forest, the 

 whole of North-West Mongolia between the altitudes of 2000 and 7.500 feet 

 is covered with the Plateau-desert association. At the last-named altitude 

 the colder climatic conditions and higbei rainfall generally enable either 

 the Larch-forest association or the Alpine assuciatiun to obtain the upper 

 hand. The Plateau-desert association, however, is broken in a few places 

 between 3000 and 7500 feet, for where special sheltered valleys shade the 

 vegetation from the fierce summer sun, there isolated and straggling patches 

 of the Larch-forest association can be seen. Plateau-desert association is 

 perhaps best studied in North-'West Mongolia at an altitude of about 

 6000 feet. It can be said to be sub-divided into two subordinate associations. 

 The first of these is found more on the shady side of the valleys and in 

 parts of the plains less exposed to cold or drying winds, and is characterised 

 by species of the genus Carat/ana. The second subdivision is found in the 

 driest, hottest, and most exposed plateau desert, and is the most widely 

 distributed. The most characteristic species of the latter are : — Potentilla 

 serkea, Arenaria capillaris, Chenopod'uim frutescens, var., Stijxi capiUata, 

 Artemisia argyrrcfoUa , Oxijtroins trutjaranthoiJes. 



2. The Larch-Forest Association is found scattered wherever conditions 

 are suitable between certain altitudes. Thus in the Kemchik valley on the 

 Upper Yenisei plateau, Larch forest is found on scattered areas between 

 3000 and 6000 feet. Some 80 miles to the south, in the Saklya valley on 



•2g2 



