SOUKCES OF HARM TO THE FOREST. 25 



the tree, or the sprouts, if they come up at all, will possess little 

 vigor. 



Some species, under the severest fires, show great hardiness. The 

 oaks resist tires better than the hickories, even when their bark is 

 burned through. Black Gum seems almost indestructible. (PI. V, 

 fig. 2.) 



FIRE BURNS AWAY THE FOREST FLOOR. 



The most serious result of the repeated fires at Scwanee is the one 

 that is most lightly regarded. The destruction of the humus and the 

 exposure of the bare soil has disastrous consequences. Humus, the 

 dead organic matter in the soil formed from decayed vegetation, is as 

 important to the forest as manure to the field. It not only enriches 

 the ground, but keeps it moist and prevents erosion. The sandy soil 

 of the plateau at Sewanee can not retain its moisture unless aided by 

 humus: when this is burned off the soil dries rapidly and, left unpro- 

 tected, is readily Avashed away. Fire renders the ground unfit for 

 termination. In burning off the humus it bakes the soil into a hard 

 crust which the tender rootlets of the few seeds that have survived the 

 flames can not penetrate. 



A fire can not burn in the forest without doing harm to the forest 

 floor. Either a part or all of the humus, or of the material which 

 would have made humus, must feed the flames. Repeated fires gradu- 

 ally consume all of the forest floor and render the chances of its form- 

 ing again less and less likely. 



PL VI, fig. 1, shows the present condition of a considerable part of 

 the southern end of the plateau. The forest has been burned more or 

 Less every year. Nothing is left to feed the flames except the last 

 crop of leaves that fell and the low growth less than a year old. In 

 such a forest the fire crawls along the ground until it dies from lack 

 of material, or is put out by rain, or by a wind that blows it backward. 

 Such small fires do not generate enough heat to injure trees larger 

 than small saplings, but they serve to keep the ground constant^ dry, 

 impoverished, and liable to erosion. 



EVILS OF OVERGRAZING. 



Cows, horses, and hogs have grazed the lands of The University of 

 the South from the time the country was settled. Since very little 

 grass grows in the woods, cattle are forced to live on weeds and small 

 trees. The grazing is good early in the season, and the cattle take 

 only those leaves the} 7 prefer; but later, when the choice food is ex- 

 hausted, they devour every leaf and stem in reach. 



PL VII, fig. 1, shows a bit of woods through which cows have just 

 ranged. The small saplings with bare stems are White Oaks, Yellow 

 Oaks, and Pignuts, propagated from the larger trees in the background., 



