A NATIONAL PLAN FOB AMERICAN FORESTRY 335 



report of the Chief of Engineers, U.S. Army, shows that in 1929 

 commercial tonnage on the principal rivers of this region was con- 

 siderably greater than that transported on the Mississippi River, 

 from Minneapolis to New Orleans. In order to maintain a ship 

 channel of proper depth in the Delaware River to the port of Philadel- 

 phia, the War Department between 1920 and 1931 spent $31,500,000, 

 chiefly in dredging, and from Philadelphia to Trenton, an additional 

 $800,000. Dredging the Schuylkill River at Philadelphia has cost 

 the Federal Government $1,300,000 in the same period. The main- 

 tenance of these and other ship channels of the Northeast in the face 

 of continued deposition of silt and similar material brought down by 

 the streams, is closely related to the fourth major stream flow and 

 watershed problem of the region. 



EROSION 



Soil erosion resulting from a rainfall of 35 or more inches a year, 

 at times concentrated in very brief periods, depends on three main 

 factors : Degree of slope, character of soil, and vegetative cover. Of 

 the forested area on the northeastern drainages, 10 percent has been 

 classified as very steep, 22 percent as steep, 15 percent as moderately 

 steep, 40 percent as gently rolling, and 13 percent as level. The 

 streams of northern New England are relatively free of silt and debris, 

 showing that erosion is not particularly serious. It is more than a 

 coincidence that even in the mountainous portions erosion is slight 

 and percentage of forest cover high. In southern New England, 

 Pennsylvania, and northern New Jersey erosion is prevalent. Here 

 the soils are heavier, and there is a greater proportion of agricultural 

 land. 



Erosion is unquestionably most severe on agricultural lands exposed 

 by plowing and clean cropping. Farm-land abandonment has been 

 general throughout the northeastern States; only a single small 

 county in one State New Jersey has escaped it. In Hamilton 

 County, N.Y., there has been since 1900 a decrease of 78 percent in 

 the area of cultivated land; in Cameron County, Pa., the decline is 

 63 percent; in Berkshire County, Mass., the decline is 60 percent. 

 For the northeastern drainages as a whole the acreage of crop land 

 abandoned in the past two decades amounts to over 10,000,000 acres. 

 Some of these lands have developed a sod which is holding the soil in 

 place. Many others lack cover, and are eroding seriously. 



How much of the present decline is due to decreased fertility of 

 farm land is not known, but the condition of some abandoned fields 

 shows that erosion was at least partly responsible. Although shoe- 

 string gullies in abandoned fields on steep slopes are not uncommon 

 in any State, sheet erosion is far more prevalent than gullying. ^ In 

 many parts of New England and New York, for example, the wide- 

 spread occurrence of gravel and stones on the surface of fields is 

 evidence that the finer soils have been removed by erosion following 

 clean cultivation. Several thousand acres of formerly excellent agri- 

 cultural land in northern New Jersey have gone entirely out of cul- 

 tivation as a result of such erosion. 



Clear cutting of the timber and burning of forest land exposed the 

 soil, at least temporarily, to erosion. The more complete the ex- 



