A NATIONAL PLAN FOR AMERICAN FORESTRY 415 



show that a single rain falling on a cornfield having a 10 percent slope 

 washed soil from a study plot at the rate of 23 tons per acre. Pre- 

 liminary results also show that under such conditions only 2 to 3 years 

 are required to wash away 1 inch of topsoil These data, substantiated 

 by observations, indicate that the cultivable life of these upland soils 

 ranges from 5 to 20 years. 



As a result of such conditions, wholesale abandonment of farm lands 

 has occurred. The surveys of the Southern Forest Experiment Sta- 

 tion indicate that on the upland watershed of the Yazoo River, totaling 

 roughly 3,487,000 acres, there are 813,000 acres of abandoned farm 

 lands and almost as large an area additional of land formerly aban- 

 doned but now used for pasture. More intensive surveys of five farms 

 also show that more than 50 percent of the total area of each farm 

 had been abandoned because of erosion. The abandonment of eroded 

 marginal lands is an important factor in the growth and spread of 

 gullies which usually proceed unchecked once the fields are taken out 

 of cultivation. Unless control measures are promptly taken, com- 

 plete destruction of the abandoned field results. 



RELATION OF FORESTS TO FLOOD AND EROSION PROBLEMS OF 

 THE DRAINAGE BASIN 



The original forest of the uplands was largely mixed pines and 

 hardwoods. In the southern portion of the region loblolly pine is pre- 

 dominant and seeds in abundantly on waste and abandoned areas. 

 In northern Mississippi shortleaf pine occurs in mixtures with the 

 mixed oak forest. Further north, the forest consists almost entirely 

 of oak, hickory, and other hardwoods. 



Clearing, primarily for agriculture, has been extensive. Less than 

 25 percent of the uplands area originally completely timbered is still 

 in forest. 



Lumbering is now of minor consequence in this region. In the past, 

 cutting as a rule was not heavy, and stands were culled of their large 

 white oak, yellow poplar, and other desirable species, rather than cut 

 clear. Later cuttings for ties and other minor products have seriously 

 depleted the stands. Logging seldom produced devastation conse- 

 quently, unless the logged-over area were put into cultivation, pro- 

 tection values were little changed. Within the range of the pines, cut- 

 over areas reseed within a few years as a rule and reproduction becomes 

 established in spite of fire and other mistreatment. Hardwood stands 

 are rarely cut clear and reproduction is usually complete. 



Fire is a much more serious factor than cutting, because fires, often 

 purposely set, burn over extensive areas of forest annually. Litter 

 accumulations, so necessary to good watershed conditions are thus 

 prevented, and in those areas where repeated fires occur at short 

 intervals, the forest often has greatly deteriorated. 



Grazing is typically a woodlot problem, although in some localities 

 the stock is turned loose in the woods. Most of the really serious 

 damage to the forest is done in cut-over hardwood stands where 

 repeated browsing of the new growth tends towards the formation of 

 brushy stands or in some places rather open woods. 



It is estimated that in the entire lower Mississippi Basin there are 

 approximately 17,854,000 acres of forest land, of which roughly 

 6,857,000 acres have a major influence on watershed values and 1,877,- 

 000 acres have a moderate influence. The relative influence ascribed 



