A PROBLEM OF EROSION 



BY R. S. MADDOX 



lOHESTKR. TENNESSEK GEOLOGICAL SURVEY 



BECAUSE of the problems involved in forestry, .Mr. 

 Whittle's article in American Forestry of 

 August, on erosion, is of more than passing in- 

 terest. He shows pictures of and describes eroded lands 

 containing gulches 200 feet deep still eating back, under- 

 cutting and devastating both agricultural and forested 

 lands. Erosion is a big problem and in some sections, 

 particularly in the South, a serious one. On the debit 

 side of our nation's account are being written down \v 

 nature's book huge losses not only from our forests, but 

 also from our tilled lands. New fields are being con- 

 stantlv cleared to take the place of once cultivated fields 

 now turned out as waste. Much of this newly cleared 

 land is eroding in its turn and the cycle of destructirjn 

 goes on. Certainly there 

 must be a halt to this pro- 

 cess if both or either of 

 these natural resources of 

 land and timber are to be 

 maintained. 



But while the erosion 

 question is of most vital 

 miportance, the writing of 

 this article was called forth 

 because of the way in 

 which Mr. Whittle handled 

 his subject. Of the en- 

 croachment of eroded land> 

 discussed by Mr. Whittk-. 

 he said: "Only one stayin;; 

 hand has been lifted — th- 

 dark pine forests that grip 

 the earth with strong fin 

 gers and resolutely con- 

 front the dragons of the 

 caverns. Where the fores' 

 is weak the chasms have 

 pulled it down. Where the 

 forest is strong the caverns 

 give up the scruggle. Man 



has taken cognizance of the combat and given his only 

 aid to the struggle against erosion ; he has learned to lei 

 the forests alone where the gorges encroach. To plant 

 a forest athwart the line of approach has seemed futile to 

 the farmer landowner. He realizes how long it takes to 

 grow a forest and how formidable it has to be to with- 

 stand the undercutting of the persistent force. So that 

 once the gorge has invaded, the farmer abandons hope of 

 ever again bringing the land under agricultural subjec- 

 tion, so forbidding are the rough, steep slopes and so 

 narrow and tortuous the bottoms of the gorges." 



Whether Mr. Whittle expresses his own views or those 

 of the landowners, on that phase of erosion is uncertain 

 There is, however, room for open discussion of such a 



KI',CL.\.M,\TR).\ Ul' (.ULl.lLU L.\.\U 



The dam was built in September, 1916. 

 the black locusts shown were planted 

 Rraph was taken in July. 1917 



large subject. Wilhoui coiituiing his statements, it is 

 practically if not wholly impossible for such large 

 gulches to be held in check by forests at their heads. The 

 root system of the trees extends into the ground only a 

 short way compared to the depth of the steep, bare banks, 

 and the undercutting will eventually cause the forests to 

 topple over until by a catching u]3 and filling in of the 

 soil below there is an adjustment made between the 

 erosive forces and the declivity of the banks, thus stop- 

 [ling the running-off process. The steepness of the 

 banks is proof that the washing dirt has been carried 

 away practically as fast as it comes down. It is not 

 sufficient to depend upon the forested areas at the heads 

 of these eroded lands to check the waste. Mr. Whittle 



did not state whether llie 

 trees growing up from the 

 bottoms of the gulches 

 were now blocking the 

 passing out of the dirt con- 

 stantly washing in from 

 the sides. If this dirt is 

 caught and held by those 

 trees, eventually, even if 

 left alone to nature, a slope 

 between the bottoms of the 

 gulches and the top crests 

 will be established and cov- 

 ered with vegetation. If 

 the dirt jiasses out freelv 

 through the gulch so much 

 the longer will the slope be 

 in forming. P>ut in either 

 case, dirt must come from 

 the banks before this final, 

 fixed slo])e, as it might be 

 called, is obtained ; and 

 during this making process 

 it is necessary to sacrifice 

 more and more of the for- 

 ests and agricultural land 

 on the top of the banks until the adjusted slope is a re- 

 sult, unless man can come to the rescue. 



To hasten the ])rocess of adjustment, the washed down 

 liirt must be caught and held, that is, its running away 

 must be checked. This hel])S to raise the bottom level 

 of the drains and also provides stable soil on which to 

 start permanent growth. It is next to impossible to 

 get a growth started on a constantly shifting or moving 

 soil. If some of the trees growing in these gulches were 

 used in making temporary dams, then some permanent 

 growth could be set out on the dirt caught by them in 

 order to constitute a permanent dam. Black locust 

 bushes, Bermuda grass and honeysuckle vines are excel- 

 lent for this purpose and would no doubt be of 



in Weakley county. Tennessee, and 

 in the spring of 1917. The photo- 



714 



