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 
