444 JOURNAL OF FORESTRY 



summits of flat-topped mesas, where the trees often grow to fair size. 

 Still another type of oak thicket is the so-called "shinnery"' of scrub 

 shin oak often covering the low divides and now rapidly spreading 

 over grassland areas. 



A remarkable transformation of grasslands into forest areas is now 

 taking place from isolated patches of original woodland on rough lands 

 to the rolling uplands in general and across intervening prairies. Cap- 

 ture by tree growth is still more remarkable in sections far removed, 

 from forest belts as in the western portion of the Edwards Plateau, 

 the denuded region and elsewhere. It is safe to say that fully 50 per 

 cent of the grassy uplands of the Edwards Plateau is now occupied by 

 some form of woody growth. The mountain cedar is not only main- 

 taining itself, but is spreading to new areas on steep slopes where no 

 other species except perhaps sumac has succeeded in gaining a foothold. 

 Sumac (Rhus viren^) seems to be a forerunner to the spread of cedar 

 and other important trees; at least under certain conditions where its 

 seed germinates and furnishes temporary protection to other species 

 which follow. Mountain oak thickets are spreading downward from 

 the ridges and mesa tops. Gradations in age of trees from the oldest 

 on mesa or ridge tops to the youngest marking the lower limit of tree 

 growth can be seen in many points of central Texas. The shinneries 

 now occupy many square miles in compact areas, crowding out the grass 

 over low divides an4 on uplands where the grass cover was formerly 

 complete. An open stand of mixed cedar, mesquite, mountain oak, and 

 live oak, with a ground cover of prickly pear, occupies vast areas of 

 rolling upland which, within the memory of men now living in the 

 region, was covered only with grass. Within the last 25 or 30 years 

 the change has been so marked as to become a matter of common 

 discussion and of considerable apprehension on the part of stockmen. 

 Every old resident can point out thickets of oak, mesquite areas or scat- 

 tered cedars, live oak, and mesquite growing on his ranch which in the 

 years gone by did not exist. 



The invasion of mesquite and other tree growth on level prairie 

 stretches in the regions surrounding the Edwards Plateau is a matter 

 of equal interest and importance. Mesquite has not only spread over 

 the entire Rio Grande Plain, and to a lesser extent over the Edwards 

 Plateau and the level lands of the denuded region north of it, but has 

 become a marked feature of the Black and Grand Prairies of east- 

 central Texas, and is actually invading portions of the lignitic belt of 



