24 TIMBER OF THE EDWAEDS PLATEAU OF TEXAS. 



limited. But throughout the area of the Edwards Plateau it has 

 established itself upon pastures, often covering these with^ a thicket as 

 close as that of the scrub oak. More commonly, however, the mes- 

 quite forms an open, orchard-like growth, into which finally ent3r 

 various shrubs, or chaparral species, with verv commonly the prickh^ 

 pear and the slender round-stemmed Opuntia. The final result of 

 mesquite encroachment is a heav}^ covering of vegetation, which, 

 however well it might serve as a protector of water supply and soils, 

 is to be regarded as an incubus upon lands which would be vastly more 

 profitable under cultivation or under a good grass cover. ^' 



The capturing of pasture lands by mesquite is shown in PL IV. fig. 2. 



HOW THE TIMBER GETS STARTED OX STEEP, ROCKY HILLSIDES. 



The characteristic way in which some types of limestone formation 

 have been eroded leaves them so steep and bare of soil that timber 

 trees can find no anchorage. Even the cedar is for the most part 

 absent; but more likely because there is so little opportunity for seed- 

 ing than because of. lack of adaptabilit}^ to the location. The writer 

 has observed that certain shrubs, especially a southwestern sumach 

 (Rhus virens)^ find lodgment at the base of the low ledges of the 

 harder limestone strata, and, spreading thence, form a protection for 

 other species which slowly come to occupy the difficult location. 



INFLUENCE OF THE EDWARDS PLATEAU TIMBER UPON 

 CLIMATE, SOIL, AND WATER SUPPLY. 



The foregoing pages have described the importance and character 

 of the water supply derived from the Edwards Plateau, and the tim- 

 ber growth found upon it. It remains to consider the relation of this 

 timber growth to the water-yielding capacit}^ of the region, with a 

 view to discovering what practical conclusions can be drawn as to how 

 to secure the best usefulness of the forests. 



INFLUENXE OF THE TIMBER GROWTH UPOX CLIMATE. 



Although the general subject of the influence of forests upon cli- 

 mate has been for man}' years under careful investigation, final con- 

 clusions have not yet been reached. The widespread belief that forest 

 destruction on a large scale brings after it marked climatic changes 

 rests on no scientific proof, and is undoubtedh^ in part at least the 

 result of a misinterpretation of certain broad facts. That flourishing 

 forests and a moist climate go together, while the nearer the approach 

 to arid conditions the sparser and poorer does the tree growth become, 



«Oii many square miles of the Rio Grande Plain the mesquite has already become 

 a thicket, harboring the prickly pear and shrubby growth to the great detriment of 

 the cattle ranges. In spite of this the mesquite must be looked upon as a prolific 

 source of fuel, and to a less extent of construction material. 



