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B. P. I. — 397. ^v^C?<?^5:^^^v^^^,r/^ 19, 1908, 



United States Department of Agriculture, 



BUREAU OF PLANT INDUSTRY— Circular No. 14. 



B. T. GALLOWAY, Chief of Bureau. 



CHANGE OF VEGETATION ON THE SOUTH TEXAS PRAIRIES. 



By O. F. Cook, 

 Bionomist in Charge of Bionomic Investigations of Tropical and SuMropical 



Plants. 



I 



It is a matter of popular knowledge in south Texas that extensive 

 regions which w^ere formerly grassy, open prairies are now covered 

 with a dense gTOwth of mesquite (Prosopis), prickly-pear cactus 

 (Opuntia), and many other shrubby plants of intermediate size. 

 Testimony to this effect is definite and unanimous. It differs locally 

 only in the number of years since the bushes began to grow — thirty 

 years, or twenty, or ten — subsequent to the establishment of the graz- 

 ing industry on a large scale, the annual burning of the grass by 

 the cattlemen, and finally the fencing of the land for still more 

 intensive grazing. 



Many localities are only now being invaded by the woody vegeta- 

 tion. Very often the old mesquite pioneers, the scattered trees Avhich 

 made the " open mesquite country " of other decades, are still con- 

 spicuous among their much smaller progeny and the crowds of 

 other camp-following species which now occupy the land to the 

 almost complete exclusion of the grasses upon which the herds of 

 former days were pastured. A new order of nature is at hand in 

 south Texas. The change has come so gradually that even those 

 who have the most intimate acquaintance with the facts have not 

 appreciated their significance, much less published them abroad. 



Before the prairies were grazed by cattle the luxuriant growths of 

 grass could accumulate for several years until conditions were favor- 

 able for accidental fires to spread. With these large supplies of fuel 

 the fires which swept over these prairies were very besoms of de- 

 struction not only for man and animals but for all shrubs and trees 

 54116— Cir. 14—08 



