16 Bulletin of the University of Texas 



Texas, but far to the north, through Indian Territory, Kansas, 

 Nebraska and the Dakotas, the same thing may be seen. Like a 

 vast wave that has rolled in upon a level beach, the Atlantic for- 

 est breaks upon the dry plains halting, creeping forward, thin- 

 ning out, and finally disappearing, except where along a river 

 course it pushes far inland." Forest Resources of Texas. 



The trees of central Texas are made up of these last straggling 

 remnants of the mighty forests of the eastern states ; some species, 

 which have reached into it from Mexico and the Rocky Moun- 

 tains, together with others which are not found in any other part 

 of the world and may be regarded as its own peculiar product. 

 Central Texas is, therefore, the meeting ground for the outposts 

 of three great forest areas, and is peculiarly rich in the variety 

 of its tree flora. 



The trees of the Southwest and West are principally species 

 which have a wider distribution into Mexico and the Rocky 

 Mountains. 



INFLUENCE OF FORESTS ON CLIMATE, RUN-OFF 

 AND EROSION 



The chief value of forests is as a source of timber, but in many- 

 parts of the world they exert other influences which are of the 

 utmost importance. The chief subsidiary value of the forest 

 is in its relation to the climate, run-off, and erosion. 



The influence of forests on climate is chiefly to render the 

 atmosphere more humid, to modify the radiation of heat, and 

 check the winds. It is a popular belief that forests exert an in- 

 fluence on the amount of rainfall over a given area, but this 

 theory has not been substantiated by any experimental data. 

 It is very doubtful if forests influence in any way the actual 

 amount of precipitation. They do, however, exert a profound 

 influence on the retention of water, thus controlling run-off and 

 erosion. 



In the forest the heavy rain, as it falls, is checked by the 

 branches and leaves of the larger trees, particularly when they 

 are in full leaf. From these the water drips to the smaller trees 

 and undergrowth and then to the carpet of leaves below. Here 

 it is held in great quantities and slowly percolates into the humus 

 soil, which is also able to hold many times its own weight of 



