Cn.VI] COLD TEMPERATE WOODLAND AND GRASSLAND 547 



The question has often been asked — Why should this enormous fertile 

 steppe district be devoid of trees? Their absence has generally been 

 attributed to causes that are geological and geognostical rather than 

 climatic, although Woeikof had already correctly maintained that they are 

 climatic. The Russian steppe possesses not only a typical grassland climate, 

 bnt also includes cJiaracters that are hostile to trees l . 



Precipitations are moderate in the Russian steppes. Owing to their 

 distribution, as will be subsequently shown, they suffice for grassland, but 

 are insufficient for good forest growth. Their annual amount varies between 

 3J and 47 cm. : — for instance, Penza 46 cm., Simbirsk 44 cm., Samara 39 cm., 

 Orenburg 43 cm., Kursk 43 cm., Lugansk 37 cm., Margaritovka on the Sea of 

 Azov 47 cm., Odessa 40 cm., Nikolaiev 37 cm., Sevastopol 40 cm., Simpheropol 

 44 cm. In the adjoining districts, formerly clad with forests, but now 

 mainly given up to agriculture, the annual amount of precipitation is 

 always larger and usually considerably so : — for instance not far from the 

 northern border of the steppes at Kozmodemiyansk 57 cm., and at Pinsk 

 61 cm. The forest districts to the west of the steppes enjoy an even 

 more abundant rainfall, the mean annual amount of precipitation in 

 Austro-Hungary being 74 cm., according to Hann. Individual stations, 

 however, are not wanting in Central Europe where the rainfall only 

 slightly exceeds 40 cm. 



Such woodland, however, as occurs in the cold-winter belts is all 

 tropophilous, and appears to require for the normal growth of trees 

 a minimum precipitation of about 50 cm. With a scanty rainfall forest 

 growth becomes very stunted. Yet in the warm zones, in spite of the 

 much higher temperature, we have seen xerophilous forest growing with 

 still less precipitation ; but xerophilous forests have not been developed in 

 the cold-winter zones, for they require a climate specially suited to them, 

 namely, a markedly dry summer with a moist winter. 



Another feature which is even more unfavourable to tree-growth in the 

 climate of the steppe district is to be found in the strong dry cast zviuds. 

 The most striking climatic difference between South and North Russia, 

 according to Woeikof, consists in the fact that the steppe of South Russia, 

 during winter as well as in autumn and spring, experiences chiefly east 

 winds (NE., E.) ; whilst the forest district of North Russia, like Central 

 Europe, throughout the year is marked by the prevalence of westerly 

 winds. The east winds however are dry, and blow at a time when the 

 frozen ground cannot replace the water lost by plants. That dry winds 

 blowing at a time when the ground is frozen do much more injury to trees 

 than to dwarfer plants has been sufficiently explained in our earlier 

 remarks 2 . During the prevalence of southerly and westerly winds the 



1 See p. 173. a See p. 168. 



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