SYLVICULTURE. 



entirely different floras. Rain in summer stimulates growth much 

 more than rain in winter. De Candolle divides our globe according 

 to moisture and heat and on the basis of floral differences resulting 

 therefrom, into five regions in the fourth of which we are living. 



1. Hydromegathermal region (water great heat). Mean annual 

 temperature over 68 degrees Faht. (Amazon river region, wet tropi- 

 cal zone). 



2. Xerophilous (Dry loving) region. The region and borders of 

 arid deserts, prairies, sunny slopes, etc., exhibiting a flora very 

 modest in moisture requirements. 



3. Mesothermal (medium heat) region, having mean tempera- 

 ture of 59 to 68 degrees Faht. (northern Florida, etc.). 



4. Microthermal (little heat) region of 32 to 59 degrees Faht. 



5. Hecistothermal (least heat) region of less than 32 degrees 

 Faht. 



The most important representative of a Xerophilous character 

 is the Yellow Pine. The hecistothermal zone shows Spruces, Birches, 

 Cottonwoods. 



V. Wind. 



Wind brings moisture and drought, heat and cold; it covers 

 or uncovers vegetation with sand or snow drifts, tumbling, at 

 prior geographical eras, whole mountains into the valleys (Loess 

 formation). Severe wind d'^^•arfs tree growth and forces branches 

 to grow in leeward direction only. The influence of a slight obstruc- 

 tion, preventing the access of wind at high latitudes, is splendidly 

 illustrated by the growth of Spruce and Fir on Pisgah Ridge. On 

 high mountains tree growth is often entirely determined by wind 

 (slope of Little Ball). 



Species resisting wind best in. Pisgah Forest are Red Oak, 

 Chestnut, Locust. 



Pieea alba and dwarf pines like Pinus pungens and montana 

 show great strength in resisting Axind. In the west Tsuga merten- 

 siana, Pinus albicaulis, Pinus monticola, further western Juniper 

 rank flrst among the trees braving severe storms. 



Wind is essential for the breathing and for the perspiration of 

 leaves and bark; for driving pollen on stigma to fertilize the seed; 

 for trimming the branches, thus forming clear boles; for dis- 

 tributing seed. The investigations conducted by Fliohe (French 

 Forester) have, however, yielded the astonishing result that winged 

 seeds travel much slower than heavy seeds_ cbvetted by birds. Eliclie 

 gives the following number of years as required by trees traveling 

 from Nancy to Paris, a distance of 160 miles: 



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