CHANGE OF VEGETATION ON SOUTH TEXAS PEAIKIES. 6 



has the assistance of fire and is destroying the larger growth with 

 increasing rapidity. 



There are no springs or streams on the upper slopes of the volcano, 

 so that the grass is not pastured. Its long wiry stems and leaves 

 accumulate until there are quantities of fuel sufficient to kill large 

 trees and to drive back the forest for long distances at each confla- 

 gration.* The lower the grass comes the more luxuriant its growth 

 and the more destructive the next fire. This will continue as long 

 as the grass is ungrazed or care is not taken to burn it every year in 

 order to prevent the accumulation of dangerous quantities of fuel. 



Settlers in south Texas early adopted the practice of burning over 

 the prairies every year ; partly to protect their homes against the fires, 

 partly to give their cattle readier access to the fresh growth of grass. 

 The fires were often set near the coast, the strong breeze which blows 

 in from the Gulf spreading the flames over many square miles. 

 AYhile the grass was still abundant these annual burnings were able to 

 keep the woody vegetation well in check, though no longer able to 

 drive back the forest or even to prevent a slow advance. 



In spots where the grass is thin, seedling mesquites and oaks es- 

 cape the flames and in a year or two begin to shade the ground and 

 gain more protection against the dangerous proximity of the combus- 

 tible grass ; and even though the tops are killed by later fires the roots 

 may send up sprouts again and again to improve every chance of be- 

 coming established and joining branches with near neighbors to in- 

 crease the area of shade. The lessened quantity of grass also makes 

 it impracticable to burn the prairies over in the summer, as was cus- 

 tomary in former decades. Burning has now to be done in the winter 

 when the grass is dry, but the young trees are then in a dormant con- 

 dition and are much less injured by the fire than in the summer season 

 of vegetative activity.^ 



In the region between Houston and Victoria large tracts are being- 

 occupied by " oak runners." Farther south, the mesquite usually 

 held sway alone for a considerable period before the smaller and 

 less hardy types were able to advance against the gradually weaker 

 fires. With the building of barbed-wire fences and the provision of 



®The roots of tliis grass are well protected from tlie fire by masses of tlie 

 closely packed stems. These tufts remain wet while everything else is thor- 

 oughly dried. Except in rainy weather no water can be obtained from the 

 extremely coarse and loose volcanic ashes and rocks of which the upper parts 

 of the mountain are composed. Weldenia and other native plants show strik- 

 ing adaptations for drought resistance. Even the alder has a remarkably thick, 

 cheesy bark, which doubtless serves for the storage of additional supplies of 

 water. 



^ It is also pointed out by Mr. Frederick V. Coville that the young woody 

 plants must be able to make more rapid growth than formerly because of the 

 reduced competition of the grasses for the moisture of the soil. 

 [Cir. 14] 



