106 JOURNAI, 01? FORESTRY 



in one pad of cow manure. When artificial!}' planted, both species of 

 catalpa grow from seed with great rapidity. Thus throughout their 

 whole life trees vegetate here most prosperously. Probably that is one 

 reason why they reach an early maturity and then decay. 



CONCLUSIONS 



Farmers have long recognized that timber originally was found in 

 central Iowa only on the poorer soils, or on those less suited to agri- 

 culture. Their work in planting groves, windbreaks, and orchards 

 shows, however, that the richer upland soils are very favorable for tree 

 growth. The time may come when it will pay to grow timber as a crop 

 on these soils. The increment is great enough ; the capital value has, 

 however, not yet made the timber crop the equal of corn. 



Just why the high prairie was originally free from trees does not 

 seem to the writer to be fully solved. From the climatic standpoint, 

 we are certainly near the western limit of forest conditions. The low 

 rainfall, the high altitude (about i,ooo feet above tide), and the parch- 

 ing southwest winds of summer are three prime factors in this general 

 limitation of forest. The dense prairie sod was undoubtedly hard to 

 make headway against. Early autumn frosts and late spring frosts 

 must have played a part in hampering the trees. Drought in winter is 

 another factor. At temperatures from zero to 20° Fahrenheit below 

 I have seen the dry, naked ground cracked to a depth of a foot or more, 

 with fissures wide enough to put one's finger in. But the exact bound- 

 aries of timber must have been largely determined by the regularly 

 recurring prairie fires, which licked up all surface vegetation, until 

 checked by moist foliage, wet litter, or lingering, protected snow. The 

 elimination of prairie fires is the one environmental change which has 

 been effected by civilization. And where fires still occur, as along 

 railways, trees do not come in. 



