EXTENSION OF TIMBER GROWTH. 23 



HOW SCRUB OAK TIMBER GAINS OX THE UPLAND PRAIRIES AND DIVIDES. 



Thoug-h the encroachment of timber on the prairie is gradual and 

 insidious, to those whose observation covers a- space of twent3^-five 

 years the change is truly startling. Where at the beginning of that 

 period the prairie held undisputed swa}', the observer now finds him- 

 self shut in by miles of oak scrub on every side. Men who drove cat- 

 tle in the earlier days say that they rode across an open country' from 

 above Georgetown to the Coloi-ado breaks, in Williamson County. 

 This same region is now all heavily timbered. A great deal of the 

 shinnery country undoubtedly represents a recent gain of timber 

 growth on prairie divides. 



This struggle of the timberlands to capture the grass lands is an 

 old warfare. For years the grass, unweakened b}' overgrazing of 

 stock, and with the fire for an ally, held victorious possession. Now the 

 timber has the advantage. It spreads like infection. From the edge 

 of the brush each year new sprouts or seedlings are pushed out a few 

 feet farther, or, under the protection of some isolated live oak or acci- 

 dental briar or shrub, a seedling gets its start, and presently offers 

 shelter for others. This has been going on all along, but in former 

 days these members of the vanguard and the scattered skirmishers 

 were killed by the prairie fires, and the timber front was held in check 

 or driven back into the hills. 



HOW CEDAR CAPTURES ADOBE SLOPES. 



It will be recalled that some of the limestones of this region break 

 up on exposure into a crumbly debris, ranging from cobblestone size 

 to adobe clay. Slopes occupied by this debris are long and gradual, 

 except where harder strata alternate. On account of the unstable and 

 arid nature of the formation, vegetation is commonly too scant}^ to 

 hide the white glare of the limestone. 



The mountain cedar has shown its capacit}^ to establish itself upon 

 such slopes in advance of ever}- other species of timber, and almost 

 of every other plant. PI. Ill, fig. 2, shows the cedar on a steep slope 

 where harder limestones intervene. This furnishes a particular!}^ 

 picturesque and parklike view, to which the photograph has b}' no 

 means done justice. There is a beautiful gradation in size of these 

 symmetrical young trees, from the youngest bushes toward the flats 

 to the old' trees which cap the summit of the buttes, from whence the 

 invasion began. 



THE SPREAD OF MESQUITE AND CHAPARRAL. 



B}^ no means the least striking phenomenon in this campaign of 

 encroachment of timber upon prairie land has been the spread of the 

 mesquite over the cattle countr}^ Mesquite is essentialh^ an occupant 

 of flat prairie lands; hence its extension in the hill country proper is 



