190 1 



AMERICAN FORESTRY ASSOCIATION. 



1S9 



is not a very important factor in tree 

 growth in this region. There are, how- 

 ever, other agencies of vital importance, 

 and these we study very closely. 



Fire, soil, moisture, wind, heat, and 

 animals are the natural agencies that influ- 

 ence most strongly the growth and distri- 

 bution of trees in this region. Fire has 

 been the most important agencv in deter- 

 mining the distribution of the forest. Dr. 

 Bessey argues with great force that fire 

 has been the sole cause of large areas of 

 the state being prairie instead of forest. 

 This much is certain : Since the settlement 

 of the country with the consequent pre- 

 vention of fires, many thousand acres of 

 prairie land along streams and ravines, 

 have naturally become covered by timber. 



Water is the limiting factor of mam- 

 species of forest trees in this region. The 

 eastern species extend westward to the 

 pomt where the moisture is not equal to 

 their requirements and there they stop. 

 The western species extend eastward to 

 the point where the moisture is too great, 

 and there find their limit. Moisture is, to 

 a great degree, the limiting agencv of I 

 eastern and western species. In "its influ- 

 ence upon trees, the moisture of the at- 

 mosphere is almost as important as the 

 moisture of the soil. Wind and heat are 

 important only because they intensify the 

 moisture conditions. While acting "indi- 

 rectly, their influence is often so powerful 

 as to cause trees to fail where they would 

 otherwise succeed. Many of the canons 



FIG. I. YOUNG TIMBER GROWING ON LAND THAT WAS IN CLOVER MEADOW TWENTY-FIVE 



YEARS AGO. THE DENSE GROWTH OF BOX ELDER, GREEN ASH, AND WHITE KLM 



HAS SINCE SPRUNG UP NATURALLY. TABLE ROCK, NEBRASKA. 



At the present time, fire is a matter of along the Loup Rivers have an excellent 



only local importance. growth of timber in spots protected Erom 



Soil is important, not on account of its wind and intense heat, while exposed spots 



chemical composition, but because of its are barren. 



physical condition. Trees thrive best on Animals keep young forest trees eaten 



porous soil where their roots can penetrate off, and the ground so tramped that seeds 



the ground deeply. The loess and sandy do not germinate. In the eastern part oi 



soils of Nebraska are very favorable to the state where the land is not pastured. 



trees for this reason. the forests are spreading; where it is pa-- 



